Patent Publication Number: US-2019167883-A1

Title: Medical treatment system and methods using a plurality of fluid lines

Description:
This application is a division of U.S. patent application Ser. No. 13/667,696, filed Nov. 2, 2012 and issued as U.S. Pat. No. 9,078,971 on Jul. 14, 2015, which is a continuation in part of U.S. application Ser. No. 13/178,191, filed Jul. 7, 2011 and issued as U.S. Pat. No. 8,708,950 on Apr. 29, 2014, which claims the benefit of and U.S. Provisional application No. 61/362,259, filed Jul. 7, 2010. 
     This application is a continuation in part of U.S. application Ser. No. 12/864,357, filed Jul. 23, 2010, which was the National Stage of International Application No. PCT/US2009/000440, filed Jan. 23, 2009, which claims the benefit of U.S. Provisional application No. 61/011,967, filed Jan. 23, 2008 and U.S. Provisional application No. 61/058,469, filed Jun. 3, 2008. 
     This application is a continuation in part of U.S. application Ser. No. 12/864,378, filed Jul. 23, 2010, which was the National Stage of International Application No. PCT/US2009/000436, filed Jan. 23, 2009, which claims the benefit of U.S. Provisional application No. 61/011,967, filed Jan. 23, 2008 and U.S. Provisional application No. 61/058,469, filed Jun. 3, 2008. 
     This application is a continuation in part of U.S. application Ser. No. 12/864,391, filed Jul. 23, 2010 and issued as U.S. Pat. No. 8,197,439 on Jun. 12, 2012, which was the National Stage of International Application No. PCT/US2009/000439, filed Jan. 23, 2009, which claims the benefit of U.S. Provisional application No. 61/011,967, filed Jan. 23, 2008 and U.S. Provisional application No. 61/058,469, filed Jun. 3, 2008. 
     This application is a continuation in part of U.S. application Ser. No. 12/864,287, filed Jul. 23, 2010 and issued as U.S. Pat. No. 9,022,969 on May 5, 2015, which was the National Stage of International Application No. PCT/US2009/000437, filed Jan. 23, 2009, which claims the benefit of U.S. Provisional application No. 61/011,967, filed Jan. 23, 2008 and U.S. Provisional application No. 61/058,469, filed Jun. 3, 2008. 
     This application is a continuation in part of U.S. application Ser. No. 12/864,293, filed Jul. 23, 2010 and issued as U.S. Pat. No. 9,028,440 on May 12, 2015, which was the National Stage of International Application No. PCT/US2009/000433, filed Jan. 23, 2009, which claims the benefit of U.S. Provisional application No. 61/011,967, filed Jan. 23, 2008 and U.S. Provisional application No. 61/058,469, filed Jun. 3, 2008. 
     This application is a continuation in part of U.S. application Ser. No. 12/864,322, filed Jul. 23, 2010 and issued as U.S. Pat. No. 8,840,581 on Sep. 23, 2014, which was the National Stage of International Application No. PCT/US2009/000441, filed Jan. 23, 2009, which claims the benefit of U.S. Provisional application No. 61/011,967, filed Jan. 23, 2008 and U.S. Provisional application No. 61/058,469, filed Jun. 3, 2008. 
     This application claims the benefit of U.S. Provisional application No. 61/555,926, filed Nov. 4, 2011. 
    
    
     The above applications are hereby incorporated by reference in their entirety. 
     BACKGROUND 
     Peritoneal Dialysis (PD) involves the periodic infusion of sterile aqueous solution (called peritoneal dialysis solution, or dialysate) into the peritoneal cavity of a patient. Diffusion and osmosis exchanges take place between the solution and the bloodstream across the natural body membranes. These exchanges transfer waste products to the dialysate that the kidneys normally excrete. The waste products typically consist of solutes like sodium and chloride ions, and other compounds normally excreted through the kidneys like urea, creatinine, and water. The diffusion of water across the peritoneal membrane during dialysis is called ultrafiltration. 
     Conventional peritoneal dialysis solutions include dextrose in concentrations sufficient to generate the necessary osmotic pressure to remove water from the patient through ultrafiltration. 
     Continuous Ambulatory Peritoneal Dialysis (CAPD) is a popular form of PD. A patient performs CAPD manually about four times a day. During a drain/fill procedure for CAPD, the patient initially drains spent peritoneal dialysis solution from his/her peritoneal cavity, and then infuses fresh peritoneal dialysis solution into his/her peritoneal cavity. This drain and fill procedure usually takes about 1 hour. 
     Automated Peritoneal Dialysis (APD) is another popular form of PD. APD uses a machine, called a cycler, to automatically infuse, dwell, and drain peritoneal dialysis solution to and from the patient&#39;s peritoneal cavity. APD is particularly attractive to a PD patient, because it can be performed at night while the patient is asleep. This frees the patient from the day-to-day demands of CAPD during his/her waking and working hours. 
     The APD sequence typically lasts for several hours. It often begins with an initial drain phase to empty the peritoneal cavity of spent dialysate. The APD sequence then proceeds through a succession of fill, dwell, and drain phases that follow one after the other. Each fill/dwell/drain sequence is called a cycle. 
     During the fill phase, the cycler transfers a predetermined volume of fresh, warmed dialysate into the peritoneal cavity of the patient. The dialysate remains (or “dwells”) within the peritoneal cavity for a period of time. This is called the dwell phase. During the drain phase, the cycler removes the spent dialysate from the peritoneal cavity. 
     The number of fill/dwell/drain cycles that are required during a given APD session depends upon the total volume of dialysate prescribed for the patient&#39;s APD regimen, and is either entered as part of the treatment prescription or calculated by the cycler. 
     APD can be and is practiced in different ways. 
     Continuous Cycling Peritoneal Dialysis (CCPD) is one commonly used APD modality. During each fill/dwell/drain phase of CCPD, the cycler infuses a prescribed volume of dialysate. After a prescribed dwell period, the cycler completely drains this liquid volume from the patient, leaving the peritoneal cavity empty, or “dry.” Typically, CCPD employs 4-8 fill/dwell/drain cycles to achieve a prescribed therapy volume. 
     After the last prescribed fill/dwell/drain cycle in CCPD, the cycler infuses a final fill volume. The final fill volume dwells in the patient for an extended period of time. It is drained either at the onset of the next CCPD session in the evening, or during a mid-day exchange. The final fill volume can contain a different concentration of dextrose than the fill volume of the successive CCPD fill/dwell/drain fill cycles the cycler provides. 
     Intermittent Peritoneal Dialysis (IPD) is another APD modality. IPD is typically used in acute situations, when a patient suddenly enters dialysis therapy. IPD can also be used when a patient requires PD, but cannot undertake the responsibilities of CAPD or otherwise do it at home. 
     Like CCPD, IPD involves a series of fill/dwell/drain cycles. Unlike CCPD, IPD does not include a final fill phase. In IPD, the patient&#39;s peritoneal cavity is left free of dialysate (or “dry”) in between APD therapy sessions. 
     Tidal Peritoneal Dialysis (TPD) is another APD modality. Like CCPD, TPD includes a series of fill/dwell/drain cycles. Unlike CCPD, TPD does not completely drain dialysate from the peritoneal cavity during each drain phase. Instead, TPD establishes a base volume during the first fill phase and drains only a portion of this volume during the first drain phase. Subsequent fill/dwell/drain cycles infuse and then drain a replacement volume on top of the base volume. The last drain phase removes all dialysate from the peritoneal cavity. 
     There is a variation of TPD that includes cycles during which the patient is completely drained and infused with a new full base volume of dialysis. 
     TPD can include a final fill cycle, like CCPD. Alternatively, TPD can avoid the final fill cycle, like IPD. 
     APD offers flexibility and quality of life enhancements to a person requiring dialysis. APD can free the patient from the fatigue and inconvenience that the day to day practice of CAPD represents to some individuals. APD can give back to the patient his or her waking and working hours free of the need to conduct dialysis exchanges. 
     Still, the complexity and size of past machines and associated disposables for various APD modalities have dampened widespread patient acceptance of APD as an alternative to manual peritoneal dialysis methods. 
     SUMMARY OF INVENTION 
     Aspects of the invention relate to various components, systems and methods for use in medical applications, including medical infusion operations such as peritoneal dialysis. In some cases, aspects of the invention are limited to applications in peritoneal dialysis, while others to more general dialysis applications (e.g., hemodialysis) or infusion applications, while others to more general methods or processes. Thus, aspects of the invention are not necessarily limited to APD systems and methods, although many of the illustrative embodiments described relate to APD. 
     In one aspect of the invention, a tubing state detector may be included with a dialysis system for detecting the presence or absence of a tubing segment, such as a portion of a patient line to be connected to a patient access for delivering dialysate to the peritoneal cavity. The tubing state detector may include a first light emitter having a first optical axis directed toward a space in which a tubing segment is to be positioned, and a second light emitter, adjacent to the first light emitter and having a second optical axis directed toward the space. An optical sensor may be positioned on a side of the space opposite the first and second light emitters and arranged to receive light emitted by the first and second light emitters to determine a presence or absence of a tubing segment in the space. 
     In one embodiment, the first optical axis may be approximately collinear with a sensor optical axis of the optical sensor, and may pass approximately through a center of a tubing segment when the tubing segment is positioned in the space. In contrast, the second optical axis may be approximately parallel to the first optical axis, and thus, the second optical axis may be offset from the center of the tubing segment and sensor optical axis. 
     The optical sensor may be arranged to detect a range of light levels when a tubing segment is in the space, e.g., a light level that is higher and/or lower that a light level detected when the tubing segment is absent from the space. However, the optical sensor may detect a lower light level from the second light emitter when a tubing segment is in the space that is detected when the tubing segment it absent from the space. For example, with a tubing segment in the space, a detected light level for both the first and second light emitters may be within about 15-20% of a calibration light level for the first and second light emitters, where the calibration light level is a level detected when a tubing segment is known to be absent from the space. However, with a tubing segment not in the space, a detected light level for the second light emitter may be less than about 15-20% of the calibration light level for the second light emitter. This lower light level detection may be used to determine that a tubing segment is in the space. 
     In another embodiment, the tubing state detector may be arranged to detect whether there is liquid present in the tubing segment, e.g., whether the patient line is properly primed for use. For example, the detector may include a third light emitter having a third optical axis that is arranged at an oblique angle relative to the sensor optical axis. The oblique angle may be between 90 and 180 degrees, e.g., about 110-120 degrees. The optical sensor and third light emitter may be arranged such that with a tubing segment in the space and the tubing segment containing no liquid, a light level detected by the optical sensor may be over about 150% of a calibration light level detected with no tubing segment in the space. In addition, with a tubing segment in the space and containing liquid, the optical sensor may detect a light level from the third light emitter that is less than about 125% of the calibration light level. Thus, the optical sensor and third light emitter may be arranged such that with a tubing segment in the space and the tubing segment containing no liquid, a light level detected by the optical sensor may be over a threshold level, and with a tubing segment in the space and the tubing segment containing liquid, a light level detected by the optical sensor is less than the threshold level. This arrangement may allow the detector to determine whether liquid is contained in the patient line, e.g., whether the patient line is properly primed. In one embodiment, the third light emitter and the optical sensor may be arranged such that the optical sensor receives light from the third light emitter both when a tubing segment in the space is filled with liquid and when a tubing segment in the space is empty of liquid. Thus, the presence or absence of liquid in the tubing segment may be determined based on a detected light intensity rather than the presence or absence of light. This may help the system avoid false condition detection that might result if the detector were to use the absence of detected light to indicate a condition, such as the presence of liquid in the tubing segment. That is, since the optical sensor detects light from the third light emitter regardless of the presence of liquid, the optical sensor may be able to determine whether the third light emitter is operating properly (or at all). The space in which the tubing segment is held may be arranged to receive and hold the tubing segment, which may have a cylindrical outer surface, without substantially deforming the tubing segment. Thus, the detector may operate without deforming the tubing segment, thereby avoiding potential problems such as pinching, reduced flow in the tubing segment, etc. 
     In another aspect of the invention, a tubing state detector for detecting whether liquid is contained in a tubing segment may include a fill state light emitter having an optical axis that is arranged to pass through a space in which a tubing segment is to be positioned. The space may be arranged to receive a tubing segment having a cylindrical outer surface and to hold the tubing segment without substantially deforming the tubing segment. Thus, the detector may be useable with common tubing frequently used in dialysis systems and without requiring special purpose fittings or other components. An optical sensor may be positioned on a side of the space opposite the fill state light emitter and arranged to receive light emitted by the fill state light emitter to determine a presence or absence of liquid in the tubing segment. In one embodiment, the optical sensor may have a sensor optical axis that is arranged at an oblique angle to the optical axis of the fill state light emitter, and may be arranged to detect whether liquid is present in the tubing segment or not. The oblique angle may be between 90 and 180 degrees, e.g., about 110-120 degrees, and the optical sensor may be arranged to receive light from the fill state light emitter whether there is liquid present in the tubing segment or not. 
     The optical sensor and fill state light emitter may be arranged such that with a tubing segment in the space and the tubing segment containing no liquid, a light level detected by the optical sensor is over a threshold level, and such that with a tubing segment in the space and the tubing segment containing liquid, a light level detected by the optical sensor is less than the threshold level. Thus, if the optical sensor detects a light level below a threshold, e.g., below about 125-150% of a light level detected with no tubing segment in the space, a determination may be made that the tubing segment is filled with liquid. The fill state light emitter (as with other light emitters) may be a light emitting diode or other electromagnetic radiation emitting component, such as a device that emits infrared, UV, visible light, or other light in the visible and/or invisible spectrum. 
     In one embodiment, the tubing state detector may include a first light emitter having a first optical axis directed toward the space, and a second light emitter having a second optical axis directed toward the space. The second light emitter may be adjacent the first light emitter, and the second optical axis may be parallel to the first optical axis. The optical sensor may be positioned on a side of the space opposite the first and second light emitters and arranged to receive light emitted by the first and second light emitters to determine a presence or absence of a tubing segment in the space. For example, the first and second light emitters may be arranged with respect to each other and the optical sensor as described above, e.g., the first optical axis may pass through a center of a tubing segment in the space, the second optical axis may be offset from the tubing segment center, etc. 
     In another aspect of the invention, a peritoneal dialysis system may include at least one pump arranged to pump dialysate for delivery to a peritoneal cavity of a patient, and a patient line fluidly coupled to the at least one pump such that dialysate delivered from the pump is directed to the patient line. The patient line may have a distal end arranged for connection to a patient, e.g., for connection to a patient access to deliver dialysate to a peritoneal cavity of the patient. A patient line state detector may be arranged to be associated with the patient line and to detect both a presence of the patient line and a priming condition of the patient line. For example, the patient line state detector may be arranged to receive the distal end of the patient line to detect the presence of the distal end and whether the distal end of the patient line is filled with fluid. This arrangement may be useful to allow the system and a patient to confirm that the patient line is sufficiently full of dialysate before connecting the patient line to the patient access connection. 
     The patient line state detector may include a cavity to receive the distal end of the patient line, one or more light emitters associated with the cavity arranged to direct light into the cavity, and one or more light detectors arranged to detect light emitted by the one or more light emitters. In one embodiment, a single light detector may be used to determine both the presence or absence of the patient line, as well as whether liquid is present in the patient line. The patient line state detector may be arranged in any of the ways that the tubing state detectors described above may be arranged. For example, first and second light emitters may be arranged adjacent each other and on a side of a cavity to receive the patient line that is opposite an optical sensor. A third light emitter may be arranged to have its optical axis arranged at an oblique angle to a sensor axis of the optical sensor, and thereby enable detection of liquid in the patient line. Other features of the tubing state detectors described above may be incorporated into the patient line state detector, including the detection and use of relative light levels to indicate a presence of the patient line and/or liquid in the patient line, and so on. 
     In another aspect of the invention, a method for detecting a presence of a tubing segment includes emitting first light along a first optical axis toward a space in which a tubing segment is to be optionally positioned, and emitting second light along a second optical axis toward the space, wherein the first and second light are emitted from a first side of the space. At least portions of the first and second light may be sensed on a second side of the space opposite the first side, and a presence or absence of a tubing segment in the space may be determined based on the sensed portions of the first and second light. The second optical axis may be approximately parallel to the first optical axis, and the first optical axis may pass through a center of the tubing segment. In one embodiment, a first calibration level of the first light may be detected with no tubing segment in the space, and a first light level may be detected of the first light when a tubing segment is in the space. The first light level may be higher, or lower, than the first calibration level. However, a second calibration level of the second light may be detected with no tubing segment in the space, and a second light level may be detected of the second light when a tubing segment is in the space, where the second light level is lower than the second calibration level. Thus, the detection of a second light level that is lower than the second calibration level may indicate the presence of a tubing segment in the space. In one embodiment, a detected second light level for the second light may be less than about 15-20% of the second calibration level with a tubing segment in the space. 
     In another aspect of the invention, a method for detecting a presence of liquid in a tubing segment may include emitting light along an optical axis toward a space in which a tubing segment is positioned, where the tubing segment has a cylindrical outer surface, and sensing light along a sensor optical axis that extends into the space, where the sensor optical axis is arranged at an oblique angle (e.g., about 110-120 degrees) relative to the optical axis. A presence or absence of liquid in the tubing segment in the space may be determined based on a sensed light level sensed along the sensor optical axis. For example, a determination may be made that fluid is not present in the tubing segment if a light level detected along the sensor optical axis is over a threshold level, and a determination may be made that fluid is present in the tubing segment if a light level detected along the sensor optical axis is below a threshold level. The threshold level may be approximately equal to about 125-150% of a light level detected along the sensor optical axis with no tubing segment in the space. 
     In one aspect of the invention, a disposable fluid handling cassette, such as that useable with an APD cycler device or other infusion apparatus, includes a generally planar body having at least one pump chamber formed as a depression in a first side of the body and a plurality of flowpaths for fluid that includes a channel. A patient line port may be arranged for connection to a patient line and be in fluid communication with the at least one pump chamber via at least one flowpath, and a membrane may be attached to the first side of the body over the at least one pump chamber. In one embodiment, the membrane may have a pump chamber portion with an unstressed shape that generally conforms to the pump chamber depression in the body and is arranged to be movable for movement of fluid in the useable space of the pump chamber. If the cassette body include two or more pump chamber depressions, the membrane may likewise include two or more pre-shaped pump portions. In other embodiments, the membrane need not be included with the cassette, e.g., where a control surface of the cycler interacts with the cassette to control pumping and/or valve functions. 
     In another embodiment, the pump chamber may include one or more spacer elements that extend from an inner wall of the depression, e.g., to help prevent the membrane from contacting the inner wall, thereby preventing blocking of an inlet/outlet of the pump chamber, helping remove or trap air in the pump chamber, and/or preventing sticking of the membrane to the inner wall. The spacer elements may be arranged to minimize deformation of the membrane at edges of the spacer elements when the membrane is forced against the spacer elements. 
     In another embodiment, a patient line port and a drain line port may be located at a first end of the body and be in fluid communication with the at least one pump chamber via at least one flowpath. A plurality of solution line spikes may, on the other hand, be located at a second end of the body opposite the first end, with each of the solution line spikes being in fluid communication with the at least one pump chamber via at least one flowpath. This arrangement may enable automated connection of solution lines to the cassette, and/or separate occlusion of the patient and/or drain lines relative to the solution lines. In one embodiment, a heater bag line port may also be located at the first end of the body and be in fluid communication with the at least one pump chamber via at least one flowpath. Flexible patient, drain and heater bag lines may be respectively connected to the patient line port, drain line port and heater bag line port. 
     In another embodiment, the body may include a vacuum vent clearance depression formed adjacent the at least one pump chamber. This depression may aid in the removal of fluid (gas and/or liquid) between the membrane and a corresponding control surface of the cycler, e.g., by way of a vacuum port in the control surface. That is, the depression may help ensure that the membrane is not forced against the vacuum port, leaving the port open to draw fluid into a collection chamber as necessary. 
     In one embodiment, one or more ports, such as a drain line port and heater bag line port, and/or one or more solution line spikes may communicate with a common flowpath channel of the cassette base. As needed, a plurality of valves may each be arranged to control flow in a respective flowpath between the at least one pump chamber and the patient line port, the drain line port, and the plurality of solution line spikes. In one embodiment, portions of the membrane may be positioned over respective valves and be movable to open and close the respective valve. Similarly, flow through openings into the pump chamber(s) may be controlled by corresponding valves that are opened and closed by movement of one or more portions of the membrane. 
     In some embodiments, the membrane may close at least some of the flowpaths of the body. That is, the body may be formed with open flow channels that are closed on at least one side by the membrane. In one embodiment, the body may include flowpaths formed on opposite planar sides, and at least some of the flowpaths on a first side may communicate with flowpaths on the second side. 
     In one embodiment, one or more spikes on the cassette (e.g., for receiving dialysate solution) may be covered by a spike cap that seals the spike closed and is removable. 
     In another aspect of the invention, a disposable fluid handling cassette, for use with a reusable automated peritoneal dialysis cycler device, includes a generally planar body having at least one pump chamber formed as a depression in a first side of the body and a plurality of flowpaths for fluid that includes a channel, a patient line port arranged for connection to a patient line, the patient line port being in fluid communication with the at least one pump chamber via at least one flowpath, and a flexible membrane attached to the first side of the body over the at least one pump chamber. A pump chamber portion of the membrane over the at least one pump chamber may have an unstressed shape that generally conforms to usable area of the pump chamber depression in the body and be arranged to be movable for movement of fluid in the pump chamber. In one embodiment, the cassette is configured for operative engagement with a reusable automated peritoneal dialysis cycler device. 
     The cassette may include a drain line port arranged for connection to a drain line, the drain line port being in fluid communication with the at least one pump chamber via at least one flowpath, and/or a plurality of solution line spikes that are in fluid communication with the at least one pump chamber via at least one flowpath. The pump chamber portion of the membrane may be generally dome shaped, and may include two pump chamber portions that have a shape that generally conforms to usable area of a corresponding pump chamber depression. In one embodiment, a volume of the pump chamber portion may be between 85-110% of the useable volume of the pump chamber depression. In another embodiment, the pump chamber portion may be arranged to be 85-110% of the depth of the useable area of the pump chamber depression. In another embodiment, the pump chamber portion may be arranged to have a size that is between 85-100% of the circumference of the useable area of the pump chamber depression. The useable area of the pump chamber may be defined at least in part by one or more spacer elements that extend from an inner wall of the depression. In one embodiment, a plurality of spacer elements may be of graduated lengths or varying height that define a generally dome-shaped region or other shape. The spacer elements may be arranged in a concentric elliptical pattern or other shape when viewed in plan. One or more breaks in the pattern may be provided, e.g., to allow communication between voids. In one embodiment, the spacer elements may be arranged to minimize deformation of the membrane at edges of the spacer elements when the membrane is forced against the spacer elements. In another embodiment, one or more spacers may be configured to inhibit the membrane from covering the fluid inlet and/or outlet of the pump chamber. 
     In another aspect of the invention, a fluid handling cassette for use with a fluid handling system of a medical infusion device includes a generally planar body having at least one pump chamber formed as a depression in a first side of the body and a plurality of flowpaths for fluid that includes a channel, the at least one pump chamber including one or more spacer elements that extend from an inner wall of the depression, a patient line port arranged for connection to a patient line, the patient line port being in fluid communication with the at least one pump chamber via at least one flowpath, a drain line port arranged for connection to a drain line, the drain line port being in fluid communication with the at least one pump chamber via at least one flowpath, and a plurality of solution line spikes being in fluid communication with the at least one pump chamber via at least one flowpath. 
     In one aspect of the invention, a disposable component system for use with a fluid line connection system of a peritoneal dialysis system includes a fluid handling cassette having a generally planar body with at least one pump chamber formed as a depression in a first side of the body and a plurality of flowpaths for fluid, a solution line spike located at a first end of the body, the solution line spike being in fluid communication with the at least one pump chamber via at least one flowpath, and a spike cap configured to removably cover the solution line spike, wherein the cap includes at least one raised feature (e.g., an asymmetrical or symmetrical flange) to aid in removal of the cap for connection to a solution line prior to the commencement of a peritoneal dialysis therapy. 
     In one embodiment, the cassette includes a skirt arranged around the spike to receive the end of the spike cap, and there may be a recess between the skirt and the spike that are arranged to aid in forming a seal between the spike cap and skirt. 
     In another embodiment, a solution line cap may be removably connected to a solution line, and the solution line cap may include a recessed feature (such as a symmetrical or asymmetrical groove). At least a portion of the solution line cap may include a flexible material, such as silicone rubber. The recessed feature may aid in the removal of a spike cap from the cassette. 
     In another embodiment, the spike cap includes a second raised feature that may function as a stop for the solution line cap. 
     In another embodiment, a main axis of one or more spikes is in substantially a same plane as the generally planar body of the fluid handling cassette. 
     In another aspect of the invention, a fluid handling cassette for use with a peritoneal dialysis system includes a generally planar body with at least one pump chamber formed as a depression in a first side of the body and a plurality of flowpaths for fluid, and a spike located at a first end of the body for engagement with a dialysate solution line. The spike may be in fluid communication with the at least one pump chamber via at least one flowpath and include a distal tip and a lumen arranged so that the distal tip of the spike is positioned substantially near the longitudinal axis of the spike. In one embodiment, the lumen may be positioned substantially off the longitudinal axis. 
     In another aspect of the invention, a disposable component system for use with a fluid line connection system of a peritoneal dialysis system includes a spike cap configured to removably cover a spike of a fluid handling cassette. The cap may include at least one feature to aid in removal of the cap for connection to a solution line prior to the commencement of a peritoneal dialysis therapy. The feature may be a raised feature, or a recessed feature, and may be configured for engagement with a solution line cap. 
     In another aspect of the invention, a disposable component system for use with a fluid line connection system of a peritoneal dialysis system includes a solution line cap for removable attachment to a solution line, wherein the solution line cap includes at least one feature to aid in removal of a spike cap to enable connection between a solution line and a spike prior to the commencement of a peritoneal dialysis therapy. The feature may be a raised feature, or a recessed feature, and may be configured for engagement with a spike cap. Indicia may e associated with a solution line, e.g., so that a solution associated with the line may be identified and affect at least one function of the peritoneal dialysis system. 
     In another aspect of the invention, a medical infusion fluid handling system, such as an APD system, may be arranged to de-cap and connect one or more lines (such as solution lines) with one or more spikes or other connection ports on a fluid handling cassette. This feature may provide advantages, such as a reduced likelihood of contamination since no human interaction is required to de-cap and connect the lines and spikes. For example, an APD system may include a carriage arranged to receive a plurality of solution lines each having a connector end and a cap. The carriage may be arranged to move along a first direction so as to move the connector ends of the solution lines along the first direction, and a cap stripper may be arranged to engage with caps on the solution lines on the carriage. The cap stripper may be arranged to move in a second direction transverse to the first direction, as well as to move with the carriage along the first direction. For example, the carriage may move toward a cassette in an APD cycler in a first direction so as to engage caps on the solution lines with caps on spikes of the cassette. The cap stripper may engage the caps (e.g., by moving in a direction transverse to the motion of the carriage) and then move with the carriage as the carriage pulls away from the cassette to remove the caps from the spikes. The carriage may then pull the connector ends of the solution lines from the caps on the cap stripper, which may retract to allow the carriage to engage the now exposed solution line connector ends with the exposed spikes on the cassette. 
     In one embodiment, the carriage may include a plurality of grooves that each receive a corresponding solution line. By positioning solution lines in corresponding grooves, each of the lines may be more easily individually identified, e.g., by reading a barcode or other identifier on the line, and controlling the system accordingly. The carriage may be mounted to a door of a cycler housing, and a carriage drive may move the carriage along the first direction. In one embodiment, the carriage drive may engage the carriage when the door is moved to a closed position, and disengage from the carriage when the door is moved to an open position. 
     In one embodiment, the cap stripper may include a plurality of fork-shaped elements arranged to engage with a corresponding cap on a solution line carried by the carriage. The fork-shaped elements may hold the caps when they are removed from the solution lines, and each of the solution line caps may itself hold a spike cap. In another embodiment, the cap stripper may include a plurality of rocker arms each associated with a fork-shaped element. Each of the rocker arms may be arranged to move to engage a spike cap, e.g., to assist in removing the spike cap from the corresponding spike. Each of the rocker arms may be arranged to engage with a corresponding spike cap only when the associated fork-shaped element engages with a cap on a solution line. Thus, the cap stripper may not engage or remove spike caps from the cassette in locations where there is no corresponding solution line to connect with the spike. 
     In another aspect of the invention, a method for connecting fluid lines in a medical infusion fluid handling system, such as an APD cycler, may involve locating solution lines and spikes of a cassette in an enclosed space away from human touch. The solution lines and/or spikes may have caps removed and the lines connected to spikes while in the enclosed space, thus providing the connection while minimizing potential contamination at the connection, e.g., by fingers carrying pathogens or other potentially harmful substances. For example, one method in accordance with this aspect of the invention includes providing a plurality of solution lines each having a connector end and a cap, providing a fluid handling cassette having a plurality of spikes each covered by a spike cap, enclosing the connector ends of the plurality of solution lines with caps covering the connector ends and the plurality of spikes with spike caps covering the spikes in a space that prevents human touch of the caps or spike caps, removing the caps from the connector ends of the plurality of solution lines without removing the caps or connector ends from the space, removing the spike caps from the spikes without removing the spike caps or spikes from the space, engaging the caps with respective ones of the spike caps, and fluidly connecting the plurality of connector ends to corresponding spikes while maintaining the connector ends and spikes in the space and protected from human touch. 
     In one embodiment, the solution line caps and spike caps may be engaged with each other before their removal from the lines or spikes, and then may be removed from both the lines and the spikes while engaged with each other. This technique may simplify the de-capping/capping process, as well as allow for easier storage of the caps. 
     In another embodiment, the solution lines may be disconnected from the spikes, and the connector ends of the lines and the spikes may be re-capped, e.g., after a treatment is completed. 
     In another aspect of the invention, a dialysis machine may include a fluid handling cassette having a plurality of spikes and a plurality of spike caps covering a respective spike, a plurality of solution lines each having a cap covering a connector end of the respective line, and a cap stripper arranged to remove one or more caps from a connector end of a solution line, and remove one or more spike caps from a spike on the cassette while the one or more caps are secured to a corresponding one of the spike caps. As discussed above, the machine may be arranged to automatically fluidly connect a connector end of a solution line with a corresponding spike after the caps are removed. 
     In another aspect of the invention, a dialysis machine, such as an APD system, may include a cassette having a plurality of fluid spikes and a plurality of spike caps covering a respective spike, a carriage arranged to receive a plurality of solution lines each having a cap covering a connector end of the respective line, and a cap stripper arranged to engage one or more caps covering a connector end of a line. The carriage and cap stripper may be configured to engage one or more caps on a connector end of a line while the one or more caps are engaged with a corresponding spike cap covering a spike on the cassette, and to remove the spike cap from the spike and the cap from the connector end of the solution line, and to fluidly connect the spike and the connector end of the solution line after the caps are removed. 
     In another aspect of the invention, a dialysis machine may include a cap stripper that is arranged to remove one or more caps on a connector end of a solution line, remove one or more spike caps from spikes on a fluid handling cassette, and to retain and reattach the caps to the solution lines and the spike caps to the spikes on the cassette. 
     In another aspect of the invention, a fluid line connection system for a peritoneal dialysis system includes a fluid handling cassette having a generally planar body with at least one pump chamber formed as a depression in a first side of the body and a plurality of flowpaths for fluid, a plurality of dialysate solution line spikes located at a first end of the body, the solution line spikes being in fluid communication with the at least one pump chamber via at least one flowpath and arranged so that the spikes are generally co-planar with the generally planar body of the fluid handing cassette, and a carriage arranged to receive a plurality of solution lines, where each solution line has a connector end. The carriage may be arranged to automatically fluidly connect a connector end of a solution line with a corresponding spike. 
     In one embodiment, the carriage is arranged to move the solution lines and respective caps along a first direction substantially parallel to the generally planar body of the fluid handling cassette. A carriage drive that moves the carriage only the first direction may include a drive element and a pneumatic bladder or screw drive to move the drive element along the first direction. A cap stripper may be provided that is arranged to remove one or more caps from a connector end of a solution line, and remove one or more spike caps from a spike on the cassette while the one or more caps are secured to a corresponding one of the spike caps. In one embodiment, the cap stripper may be arranged to r retain and reattach the caps to the solution lines and the spike caps to the spikes on the cassette. 
     In another aspect of the invention, a peritoneal dialysis system may include a cycler device with components suitable for controlling delivery of dialysate to the peritoneal cavity of a patient. The cycler device may have a housing that encloses at least some of the components and have a heater bag receiving section. (The term “heater bag” is used herein to refer to any suitable container to heat dialysate, such as a flexible or rigid container, whether made of polymer, metal or other suitable material.) A lid may be mounted to the housing and be movable between an open position in which a heater bag is placeable in the heater bag receiving section and a closed position in which the lid covers the heater bag receiving section. Such an arrangement may allow for faster or more efficient heating of dialysate in the heater bag, e.g., because heat may be retained by the lid. Also, the lid may help prevent human touch of potentially hot surfaces. 
     In one embodiment, the dialysis system may include a fluid handling cassette with a heater bag port attached to a heater bag line, a patient port attached to a patient line, and at least one pump chamber to move fluid in the patient line and the heater bag line. A heater bag may be attached to the heater bag line and be arranged for placement in the heater bag receiving section. 
     In another embodiment, the system may include an interface (such as a visual display with a touch screen component) that is movably mounted to the housing and is movable between a first position in which the interface is received in the heater bag receiving section, and a second position in which the interface is located out of the heater bag receiving section (e.g., a position in which a user may interact with the interface). Thus, the interface may be hidden from view when the system is idle, allowing the interface to be protected. Also, storing the interface in the heater bag receiving section may make the system more compact, at least in an “as stored” condition. 
     In another aspect of the invention, a dialysis system includes a supply of pneumatic pressure and/or vacuum suitable for controlling pneumatically-operated components of the system, a pneumatically-operated component that is fluidly connected to the supply of pneumatic pressure and/or vacuum, and a control system that provides pneumatic pressure or vacuum to the pneumatically-operated component and subsequently isolates the pneumatically-operated component from the supply of pneumatic pressure or vacuum for a substantial period of time before again providing pneumatic pressure or vacuum to the pneumatically-operated component. Such an arrangement may be useful for components that are actuated relatively infrequently, such as the occluder arrangement described herein. Small motions of some components may cause the component to emit noise that may be found bothersome by a patient. By isolating the component from the pneumatic pressure/vacuum, the component may avoid slight movement caused by variations in the supply pressure/vacuum, e.g., resulting from draws on the pressure/vacuum by other system components. In one embodiment, the substantial period of time may be 5 minutes or more, 1 hour or more, 50% or more of a time period required to deliver or remove a volume of dialysate suitable for a dialysis treatment with respect to a patient&#39;s peritoneal cavity, or other suitable periods. 
     In another aspect of the invention, a dialysis system includes a supply of pneumatic pressure and/or vacuum suitable for controlling pneumatically-operated components of the system, a pneumatically-operated component that is fluidly connected to the supply of pneumatic pressure and/or vacuum, and a control system that provides pneumatic pressure or vacuum to the pneumatically-operated component and controls the pneumatic pressure or vacuum so as to reduce noise generated by the pneumatically-operated component. For example, the pneumatically-operated component may include at least one moving part (such as a pump diaphragm), and the control system may reduce the pneumatic pressure or vacuum provided to the pneumatically-operated component so as to slow movement of the moving part as the moving part stops and/or changes direction (e.g., the pressure/vacuum may be controlled to slow movement of the diaphragm before the diaphragm changes direction). In another embodiment, a pulse width modulation control of a pressure/vacuum supply valve may be used, e.g., to reduce noise emitted by moving parts of the valve. 
     In another aspect of the invention, a dialysis system includes a supply of pneumatic pressure and vacuum suitable for controlling pneumatically-operated components of the system. A first pneumatically-operated component may be fluidly connected to the supply of pneumatic pressure and/or vacuum, and have a first output line to release pneumatic pressure. A second pneumatically-operated component may be fluidly connected to the supply of pneumatic pressure and/or vacuum, and have a second output line to release pneumatic vacuum. A space, such as that defined by an accumulator, manifold or sound-insulated chamber, may be fluidly connected to both the first and second output lines. A control system may provide pneumatic pressure or vacuum to the pneumatically-operated components so that when the first and second components release pressure/vacuum during operation, the released pressure/vacuum may be received into the common space (e.g., a manifold). In some circumstances, gas under positive pressure released by components may be balanced by negative pressure released by other components, thus reducing noise generated. 
     In another aspect of the invention, a peritoneal dialysis system may include a fluid handling cassette having a patient line fluidly connected to and leading from the peritoneal cavity of a patient, and which includes at least one pump chamber to move dialysate solution in the patient line. A cycler device may be arranged to receive and interact with the fluid handling cassette and cause the at least one pump chamber to move dialysate solution in the patient line. The cycler may include a control system arranged to control the at least one pump chamber to operate in a priming operation to force dialysate solution into the patient line so as to remove any air in the patient line, and may be adapted to interact with two types of fluid handling cassettes that differ with respect to a volume of the patient line connected to the cassette body. A first type of cassette may have a relatively low volume patient line (e.g., for pediatric applications), and a second type of cassette may have a relatively high volume patient line (e.g., for adult applications), and the control system may detect whether a cassette received by the cycler is a first type or a second type and to adjust cycler operation accordingly. 
     In one embodiment, the control system may detect whether a cassette received by the cycler is a first type or a second type by determining the volume of the patient line during priming, and to adjust the amount of fluid moved through the cassette during operation of the system. In another embodiment, indicia, such as a barcode, on the cassette may be detected by the cycler and cause the cycler to adjust a pumping operation based on the type of cassette. 
     In another aspect of the invention, a dialysis machine includes a fluid handling cassette having a plurality of spikes and at least one pump chamber to move fluid in the spikes, a plurality of solution lines each engaged with a respective spike on the cassette, and a control system that reads indicia on each of the solution lines to determine a type for each of the solution lines. The control system may adjust a pumping operation or other cycler operation based in the identity of one or more of the solution lines. For example, a solution line may be identified as being an effluent sampling line and the pumping operation may be adjusted to direct used dialysate from a patient to the effluent sampling line during a drain cycle. 
     In another aspect of the invention, a method of automatically recovering from a tilt condition in a dialysis system may include (A) detecting an angle of tilt of at least a portion of a dialysis system, the portion of the dialysis system including machinery for performing a dialysis therapy, (B) determining that a tilt condition exists in which the angle of tilt exceeds a predetermined threshold, (C) in response to (B), pausing the dialysis therapy, (D) monitoring the angle of tilt while the dialysis therapy is paused, (E) determining that the tilt condition no longer exists, and (F) in response to (E), automatically resuming the dialysis therapy. 
     In another aspect of the invention, a patient data interface for a dialysis system includes a device port comprising a recess in a chassis of at least a portion of the dialysis system and a first connector disposed within the recess. A patient data storage device may include a housing and a second connector coupled to the housing, where the second connector is adapted to be selectively coupled to the first connector. The recess may have a first shape and the housing may have a second shape corresponding to the first shape such that when the first and second connectors are coupled, the housing of the patient data storage device is received at least partially within the recess. The first and second shapes may be irregular and the patient data storage device may have a verification code that is readable by the dialysis system to verify that the patient data storage device is of an expected type and/or origin. 
     In another aspect of the invention, a method for providing peritoneal dialysis includes delivering or withdrawing dialysate with respect to the patient&#39;s peritoneal cavity at a first pressure, and adjusting a pressure at which dialysate is delivered or withdrawn to minimize patient sensation of dialysate movement. In one embodiment, the pressure may be adjusted during a same fill or empty cycle of a peritoneal dialysis therapy, and/or within different fill or empty cycles of a peritoneal dialysis therapy. For example, when withdrawing dialysate from a patient, the pressure at which dialysate is withdrawn may be reduced when an amount of dialysate remaining in the peritoneal cavity drops below a threshold volume. Reducing the pressure (negative pressure or vacuum) near the end of a drain cycle may reduce the sensation the patient may have of the dialysate withdrawal. 
     In another aspect of the invention, a method for providing peritoneal dialysis includes providing a first solution to a patient&#39;s peritoneal cavity using a reusable cycler device during a first treatment of peritoneal dialysis, and providing a second solution to the patient&#39;s peritoneal cavity using the reusable cycler device during a second treatment of peritoneal dialysis immediately subsequent to the first treatment, where the second solution has a different chemical makeup relative to the first solution. The different solutions may be created by mixing liquid material from two or more solution containers that are connected to the cycler (e.g., via a cassette mounted to the cycler). The solution containers may be automatically identified by the cycler, e.g., by reading a barcode, RFID tag, or other indicia. 
     In another aspect of the invention, a medical infusion system includes a housing that encloses at least some of the components of the system, and a control surface attached to the housing and constructed and arranged to control the operation of a fluid handling cassette that may be removably mounted to the housing. The control surface may have a plurality of movable portions arranged to control fluid pumping and valve operations of the cassette, and at least one of the movable portions may have an associated vacuum port arranged to draw fluid from a region near the movable portion. 
     In one embodiment, the control surface includes a sheet of resilient polymer material, and each of the movable portions may have an associated vacuum port. In another embodiment, the cassette includes a membrane that is positionable adjacent the control surface, and the vacuum port is arranged to remove fluid from a space between the membrane and the control surface. A liquid sensor may be arranged to detect liquid drawn into the vacuum port, e.g., in case the membrane ruptures, allowing liquid to leak from the cassette. 
     In another aspect of the invention, a volume of fluid moved by a pump, such as a pump in an APD system, may be determined based on pressure measurement and certain known chamber and/or line volumes, but without direct measurement of the fluid, such as by flow meter, weight, etc. In one embodiment, a volume of a pump chamber having a movable element that varies the volume of the pump chamber may be determined by measuring pressure in the pump chamber, and a reference chamber both while isolated from each other, and after the two chambers are fluidly connected so that pressures in the chambers may equalize. In one embodiment, equalization of the pressures may be assumed to occur in an adiabatic way, e.g., a mathematical model of the system that is based on an adiabatic pressure equalization process may be used to determine the pump chamber volume. In another embodiment, pressures measured after the chambers are fluidly connected may be measured at a time before complete equalization has occurred, and thus the pressures for the pump and reference chambers measured after the chambers are fluidly connected may be unequal, yet still be used to determine the pump chamber volume. This approach may reduce a time between measurement of initial and final pressures, thus reducing a time during which heat transfer may take place and reducing error that may be introduced given the adiabatic model used to determine the pump chamber volume. 
     In one aspect of the invention, a method for determining a volume of fluid moved by a pump includes measuring a first pressure for a pump control chamber when the pump control chamber is isolated from a reference chamber. The pump control chamber may have a volume that varies at least in part based on movement of a portion of the pump, such as a pump membrane or diaphragm. A second pressure may be measured for the reference chamber when the reference chamber is isolated from the pump control chamber. The reference chamber may have a known volume. A third pressure associated with the pump control chamber after fluidly connecting the reference chamber and the pump control chamber may be measured, but the measurement may occur before substantial equalization of pressures between the pump control and reference chambers has occurred. Similarly, a fourth pressure associated with the reference chamber after fluidly connecting the reference chamber and the pump control chamber may be measured, but before substantial equalization of pressures between the pump control and reference chambers has occurred. A volume for the pump control chamber may be determined based on the first, second, third and fourth measured pressures. 
     In one embodiment, the third and fourth pressures are measured at approximately a same time and the third and fourth pressures are substantially unequal to each other. For example, equalization of the pressures in the pump control and reference chambers may occur after an equalization time period once the pump control and reference chambers are fluidly connected, but the third and fourth pressures may be measured at a time after the pump control and reference chambers are fluidly connected that is approximately 10% to 50% of the equalization time period. Thus, the third and fourth pressures may be measured long before (in time sense) the pressures in the chambers have fully equalized. In another embodiment, the third and fourth pressures may be measured at a time when the pressures in the chambers has reached approximately 50-70% equalization, e.g., the pressures in the chambers have changed from an initial value that is within about 50-70% of an equalized pressure value. Thus, a time period between measurement of the first and second pressures and measurement of the third and fourth pressures may be minimized. 
     In another embodiment, a model for determining the volume of the pump control chamber may incorporate an assumption that an adiabatic system exists from a point in time when the first and second pressures are measured for the isolated pump control chamber and the reference chamber until a point in time when the third and fourth pressures are measured. 
     To determine a volume of fluid moved by the pump, the steps of measuring the first, second, third and fourth pressures and the step of determining may be performed for two different positions of a pump membrane to determine two different volumes for the pump control chamber. A difference between the two different volumes may represent a volume of fluid delivered by the pump. 
     As mentioned above, this aspect of the invention may be used in any suitable system, such as a system in which the pump is part of a disposable cassette and the pump control chamber is part of a dialysis machine used in a dialysis procedure. 
     In one embodiment, the first and/or second pressure may be selected from a plurality of pressure measurements as coinciding with a point in time at which a pressure in the pump control chamber or reference chamber (as appropriate) first begins to change from a previously stable value. For example, the point in time may be identified based on a determination of when a best fit line for a plurality of consecutive sets of measured pressures first deviates from a constant slope. This approach may help identify initial pressures for the pump control and reference chambers that are as late in time as possible, while reducing error in the pump volume determination. 
     In another embodiment, a technique may be used to identify an optimal point in time at which the third and fourth pressures are measured. For example, a plurality of pressure values for the pump control chamber may be measured after the pump control and reference chambers are fluidly connected, and a plurality of change in volume values may be determined for the pump control chamber based on the plurality of pressure values for the pump control chamber. Each of the plurality of change in volume values may corresponding to a unique point in time and a measured pressure value for the pump chamber. In this case, the change in volume values are due to movement of an imaginary piston that is present at the valve or other component that initially isolates the pump control and reference chambers, but moves upon opening of the valve or other component. Thus, the pump chamber does not actually change size or volume, but rather the change in volume is an imaginary condition due to the pressures in the pump chamber and reference chamber being different from each other initially. Similarly, a plurality of pressure values for the reference chamber may be measured after the pump control and reference chambers are fluidly connected, and a plurality of change in volume values for the reference chamber may be determined based on the plurality of pressure values for the reference chamber. Each of the plurality of change in volume values may correspond to a unique point in time and a measured pressure value for the reference chamber, and like the change in volume values for the pump chamber, are a result of movement of an imaginary piston. A plurality of difference values between change in volume values for the pump control chamber and for the reference chamber may be determined, with each difference value being determined for corresponding change in volume values for the pump control chamber and change in volume values for the reference chamber, i.e., the pairs of change in volume values for which a difference value is determined correspond to a same or substantially same point in time. The difference values may be analyzed, and a minimum difference value (or a difference value that is below a desired threshold) may indicate a point in time for which the third and fourth pressures should be measured. Thus, the third and fourth pressure values may be identified as being equal to the pump control chamber pressure value and the reference chamber pressure value, respectively, that correspond to a difference value that is a minimum or below a threshold. 
     In another embodiment, the pressures measured are pressures of a gas within the pump control chamber and the reference chamber, the equalization of pressures within the pump control chamber and reference chamber is assumed to occur adiabatically, the equalization of pressures between the pump control chamber and reference chamber is assumed to include a change in the volume of a gas in the pump control chamber and reference chamber in equal but opposite directions, and the volume of gas in the reference chamber at the time of the fourth pressure measurement is calculated from the known volume of the reference chamber, and the second and fourth pressures. The change in volume of gas in the reference chamber may be assumed to be the difference between the known volume of the reference chamber and the calculated value of the volume of gas in the reference chamber at the time of the fourth pressure measurement. Also, the change in volume of gas in the pump control chamber may be assumed to be the difference between the initial volume of the pump control chamber and the volume of gas in the pump control chamber at the time of the third pressure measurement, wherein the change in volume of gas in the pump control chamber is equal to but opposite the change in volume of gas in the reference chamber. 
     In another aspect of the invention, a method for determining a volume of fluid moved by a pump includes providing a fluid pump apparatus having a pump chamber separated from a pump control chamber by a movable membrane, and a reference chamber that is fluidly connectable to the pump control chamber, adjusting a first pressure in the pump control chamber to cause the membrane to move and thereby move fluid in the pump chamber, isolating the reference chamber from the pump control chamber and establishing a second pressure in the reference chamber that is different from a pressure in the pump control chamber, fluidly connecting the reference chamber and the pump control chamber to initiate equalization of pressures in the pump control chamber and the reference chamber, and determining a volume for the pump control chamber based on the first and second pressures, and an assumption that the pressures in the pump control and reference chambers initiate equalization in an adiabatic way. 
     In one embodiment, third and fourth pressures for the pump control and reference chambers, respectively, may be measured after fluidly connecting the reference chamber and the pump control chamber, and the third and fourth pressures may be used to determine the volume for the pump control chamber. The third and fourth pressures may be substantially unequal to each other. Similar to that mentioned above, the adjusting, isolating, fluidly connecting and determining steps may be repeated, and a difference between the two determined volumes for the pump control chamber may be determined, where the difference represents a volume of fluid delivered by the pump. 
     In another embodiment, the pump is part of a disposable cassette and the pump control chamber is part of a dialysis machine used in a dialysis procedure. 
     In another aspect of the invention, a medical infusion system includes a pump control chamber, a control surface associated with the pump control chamber so that at least a portion of the control surface is movable in response to a pressure change in the pump control chamber, a fluid handling cassette having at least one pump chamber positioned adjacent the control surface and arranged so that fluid in the at least one pump chamber moves in response to movement of the portion of the control surface, a reference chamber that is fluidly connectable to the pump control chamber, and a control system arranged to adjust a pressure in the pump control chamber and thus control movement of fluid in the pump chamber of the fluid handling cassette. The control system may be arranged to measure a first pressure for the pump control chamber when the pump control chamber is isolated from the reference chamber, measure a second pressure for the reference chamber when the reference chamber is isolated from the pump control chamber, fluidly connect the pump control chamber and the reference chamber, measure third and fourth pressures associated with the pump control chamber and the reference chamber, respectively, after fluidly connecting the reference chamber and the pump control chamber, and determine a volume for the pump control chamber based on the first, second, third and fourth measured pressures and a mathematical model that defines equalization of pressure in the pump control and reference chambers as occurring adiabatically when the pump control and reference chambers are fluidly connected. 
     In one embodiment, the third and fourth pressures are substantially unequal to each other, e.g., the third and fourth pressures may be measured prior to substantial equalization of pressures in the pump control and reference chambers. 
     In another aspect of the invention, a method for determining a volume of fluid moved by a pump includes measuring a first pressure for a pump control chamber when the pump control chamber is isolated from a reference chamber, the pump control chamber having a volume that varies at least in part based on movement of a portion of the pump, measuring a second pressure for the reference chamber when the reference chamber is isolated from the pump control chamber, measuring a third pressure associated with both the pump control chamber and the reference chamber after fluidly connecting the reference chamber and the pump control chamber, and determining a volume for the pump control chamber based on the first, second and third measured pressures. 
     In one embodiment, the third pressure may be measured after complete equalization of pressures in the pump control and reference chambers is complete. In one embodiment, a model used to determine the pump chamber volume may assume an adiabatic system in equalization of pressure between the pump chamber and the reference chamber. 
     In one aspect of the invention, a method for determining a presence of air in a pump chamber includes measuring a pressure for a pump control chamber when the pump control chamber is isolated from a reference chamber, the pump control chamber having a known volume and being separated from a pump chamber, that is at least partially filled with liquid, by a membrane, measuring a pressure for the reference chamber when the reference chamber is isolated from the pump control chamber, the reference chamber having a known volume, measuring a pressure after fluidly connecting the reference chamber and the pump control chamber and prior to a time when the pressure in the chambers has equalized, and determining a presence or absence of an air bubble in the pump chamber based on the measured pressures and known volumes. 
     In one embodiment, a model used to determine the presence or absence of an air bubble assumes an adiabatic system from a point in time when the pressures are measured for the isolated pump control chamber and the reference chamber until a point in time after the chambers are fluidly connected. In another embodiment, the pressure for the pump control chamber is measured with the membrane drawn toward a wall of the pump control chamber. 
     In another aspect of the invention, an automated peritoneal dialysis system includes a reusable cycler that is constructed and arranged for coupling to a disposable fluid handling cassette containing at least one pumping chamber. The disposable fluid handling cassette may be configured to be connected in fluid communication with the peritoneum of a patient via a first collapsible tube and with a second source and/or destination (such as a solution container line) via a second collapsible tube. An occluder may be configured and positioned within the cycler to selectively occlude the first collapsible tube while not occluding the second collapsible tube. In one embodiment, the occluder can occlude a plurality of collapsible tubes, such as a patient line, a drain line and/or a heater bag line. The cassette may have a generally planar body with at least one pump chamber formed as a depression in a first side of the body and a plurality of flowpaths for fluid, a patient line port located at a first end of the body arranged for connection to the first collapsible tube, and a solution line port located at a second end of the body opposite the first end, and arranged for connection to the second collapsible tube. The occluder may be configured and positioned within the cycler to selectively occlude the first tube and a third collapsible tube (e.g., for a drain) while not occluding the second collapsible tube. 
     In another embodiment, the occluder includes first and second opposed occluding members pivotally connected to each other, a tube contacting member connected to, or comprising at least a portion of, at least one of the first and second occluding members, and a force actuator constructed and positioned to apply a force to at least one of the first and second occluding members. Application of the force by the force actuator may cause the tube contacting members to move between a tube occluding and an open position. The occluder may include a release member configured and positioned to enable an operator to manually move the tube contacting member from the tube occluding position to the open position even with no force applied to the occluding member by the force actuator. The force actuator may apply a force sufficient to bend both the first and second occluding members, so that upon application of the force by the force actuator to bend the first and second occluding members, the tube contacting member may move between a tube occluding and an open position. The occluding members may be spring plates pivotally connected together at opposite first and second ends, and the tube contacting member may be a pinch head connected to the spring plates at the first ends, while the second ends of the spring plates may be affixed directly or indirectly to a housing to which the occluder is connected. In one embodiment, the force actuator comprises an inflatable bladder positioned between the first and second occluding members. The force actuator may increase a distance between the first and second occluding members in a region where the first and second occluding members are in opposition so as to move the tube contacting member between a tube occluding and an open position. In one embodiment, the force actuator may bend one or both of the occluding members to move the tube contacting member from a tube occluding position to an open position. 
     Various aspects of the invention are described above and below with reference to illustrative embodiments. It should be understood that the various aspects of the invention may be used alone and/or in any suitable combination with other aspects of the invention. For example, the pump volume determination features described herein may be used with a liquid handling cassette having the specific features described, or with any other suitable pump configuration. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Aspects of the invention are described below with reference to illustrative embodiments that are shown, at least in part, in the following figures, in which like numerals reference like elements, and wherein: 
         FIG. 1  shows a schematic view of an automated peritoneal dialysis (APD) system that incorporates one or more aspects of the invention; 
         FIG. 1A  shows an alternative arrangement for a dialysate delivery set shown in  FIG. 1 ; 
         FIG. 2  is a schematic view of an illustrative set for use with the APD system of  FIG. 1 ; 
         FIG. 3  is an exploded perspective view of a cassette in a first embodiment; 
         FIG. 4  is a cross sectional view of the cassette along the line  4 - 4  in  FIG. 3 ; 
         FIG. 5  is a perspective view of a vacuum mold that may be used to form a membrane having pre-formed pump chamber portions in an illustrative embodiment; 
         FIG. 6  shows a front view of the cassette body of  FIG. 3 ; 
         FIG. 7  is a front view of a cassette body including two different spacer arrangements in an illustrative embodiment; 
         FIG. 8  is a rear perspective view of the cassette body of  FIG. 3 ; 
         FIG. 9  is a rear view of the cassette body of  FIG. 3 ; 
         FIG. 9-1A  is a front perspective view of an exemplary configuration of a patient line state detector or liquid level detector; 
         FIG. 9-1B  is a rear perspective view of a patient line state detector or liquid level detector; 
         FIG. 9-2  is a perspective layout view of three LEDs and an optical detector surface-mounted on a printed circuit board; 
         FIG. 9-3  is a plan view of three LEDs and an optical detector mounted on a detector circuit board; 
         FIG. 9-4  is an exploded perspective view of the detector of  FIG. 9-1  showing the printed circuit board and transparent or translucent plastic insert. 
         FIG. 9-5  is a perspective view of an alternative configuration of a liquid level detector; 
         FIG. 9-6  is a perspective view of the front of an unloaded organizer (absent any solution lines); 
         FIG. 9-7  is a back view of the organizer of  FIG. 9-6 ; 
         FIG. 9-8  is a perspective view of an organizer including a plurality of solution lines, a patient line, and a drain line; 
         FIG. 9-9  is a perspective view of an organizer clip; 
         FIG. 9-10  is a perspective view of an organizer clip receiver; 
         FIG. 9-11  is a perspective view of a door latch sensor assembly associated with a cycler; 
         FIG. 9-11   a  is a cross-sectional view of the door latch sensor assembly of  FIG. 9-11 ; 
         FIG. 9-12  is a graph showing the ability of the liquid level detector of  FIG. 9-1  to distinguish between a primed and a non-primed patient line; 
         FIG. 9-12   a  is a graph showing the range of signals corresponding to a primed and a non-primed patient line for different cyclers using the liquid detector of  FIG. 9.1 ; 
         FIG. 9-13  is a graph showing measurements collected by an optical sensor comparing liquid detection using an orthogonally oriented LED vs. an angled LED; 
         FIG. 9-14  is a graph showing the ability of the liquid level detector of  FIG. 9-1  to distinguish between the presence and absence of a tubing segment within the detector; 
         FIG. 10  is a perspective view of the APD system of  FIG. 1  with the door of the cycler in an open position; 
         FIG. 11  is a perspective view of the inner side of the door of the cycler show in  FIG. 10 ; 
         FIG. 11-1  is a perspective view of a carriage in a first embodiment; 
         FIG. 11-2  is an enlarged perspective view of a solution line loaded into the carriage of  FIG. 11-1 ; 
         FIG. 11-3  is a perspective view of an open identification tag; 
         FIG. 11-4  is a perspective view of a carriage drive assembly including an AutoID camera mounted to an AutoID camera board; 
         FIG. 11-5  is a perspective view of an embodiment for a stripper element of a cap stripper; 
         FIG. 11-6  is a front perspective view of the carriage drive assembly of  FIG. 11-4  showing the position of the stripper element of  FIG. 11-5  within the carriage drive assembly; 
         FIG. 11-7   a  shows a perspective view of a portion of the stripper element of  FIG. 11-5 , in which a spike cap is positioned; 
         FIG. 11-7   b  shows a perspective view of a portion of the stripper element of  FIG. 11-5 , in which a solution line cap is positioned over a spike cap; 
         FIG. 11-7   c  shows a perspective view of a portion of the stripper element of  FIG. 11-5 , showing a sensor element and rocker arm in the absence of a spike cap; 
         FIG. 12  is a right front perspective view of a carriage drive assembly and cap stripper in a first embodiment; 
         FIG. 13  a left front perspective view of the carriage drive assembly and cap stripper of  FIG. 12 ; 
         FIG. 14  is a partial rear view of the carriage drive assembly of  FIG. 12 ; 
         FIG. 15  is a rear perspective view of a carriage drive assembly in a second illustrative embodiment; 
         FIG. 16  is a left rear perspective view of the carriage drive assembly and cap stripper of  FIG. 15 ; 
         FIG. 17  is a left front perspective view of a cap stripper element in an illustrative embodiment; 
         FIG. 18  is a right front perspective view of the cap stripper element of  FIG. 17 ; 
         FIG. 19  is a front view of the cap stripper element of  FIG. 17 ; 
         FIG. 20  is a cross sectional view along the line  20 - 20  in  FIG. 19 ; 
         FIG. 21  is a cross sectional view along the line  21 - 21  in  FIG. 19 ; 
         FIG. 22  is a cross sectional view along the line  22 - 22  in  FIG. 19 ; 
         FIG. 23  is a close-up exploded view of the connector end of a solution line in an illustrative embodiment; 
         FIG. 24  is a schematic view of a cassette and solution lines being loaded into the cycler of  FIG. 10 ; 
         FIG. 25  is a schematic view of the cassette and solution lines after placement in respective locations of the door of the cycler of  FIG. 10 ; 
         FIG. 26  is a schematic view of the cassette and solution lines after the door of the cycler is closed; 
         FIG. 27  is a schematic view of the solution lines being engaged with spike caps; 
         FIG. 28  is a schematic view of the cap stripper engaging with spike caps and solution line caps; 
         FIG. 29  is a schematic view of the solution lines with attached caps and spike caps after movement away from the cassette; 
         FIG. 30  is a schematic view of the solution lines after movement away from the solution line caps and spike caps; 
         FIG. 31  is a schematic view of the cap stripper retracting with the solution line caps and spike caps; 
         FIG. 32  is a schematic view of the solution lines being engaged with the spikes of the cassette; 
         FIG. 33  is a cross sectional view of a cassette with five stages of a solution line connection operation shown with respect to corresponding spikes of the cassette; 
         FIG. 34  shows a rear view of a cassette in another illustrative embodiment including different arrangements for a rear side of the cassette adjacent the pump chambers; 
         FIG. 35  shows an end view of a spike of a cassette in an illustrative embodiment; 
         FIG. 35A  shows a perspective view of an alternative embodiment of the spikes of a cassette; 
         FIG. 35B  shows an embodiment of a spike cap configured to fit over the spikes shown in  FIG. 35A ; 
         FIG. 35C  shows a cross-sectional view of a spike cap shown in  FIG. 35B ; 
         FIG. 36  shows a front view of a control surface of the cycler for interaction with a cassette in the  FIG. 10  embodiment; 
         FIG. 36A  shows a front view and selected cross-sectional views of an embodiment of a control surface of the cycler; 
         FIG. 37  shows an exploded view of an assembly for the interface surface of  FIG. 36 , with the mating pressure delivery block and pressure distribution module; 
         FIG. 37A  shows an exploded view of the integrated manifold; 
         FIG. 37B  shows two isometric views of the integrated manifold; 
         FIG. 37C  shows an schematic of the pneumatic system that controls fluid flow through the cycler; 
         FIG. 38  shows an exploded perspective view of an occluder in an illustrative embodiment; 
         FIG. 39  shows a partially exploded perspective view of the occluder of  FIG. 38 ; 
         FIG. 40  shows a top view of the occluder of  FIG. 38  with the bladder in a deflated state; 
         FIG. 41  shows a top view of the occluder of  FIG. 38  with the bladder in an inflated state; 
         FIG. 42  is a schematic view of a pump chamber of a cassette and associated control components and inflow/outflow paths in an illustrative embodiment; 
         FIG. 43  is a plot of illustrative pressure values for the control chamber and the reference chamber from a point in time before opening of the valve X 2  until some time after the valve X 2  is opened for the embodiment of  FIG. 42 ; 
         FIG. 44  is a perspective view of an interior section of the cycler of  FIG. 10  with the upper portion of the housing removed; 
         FIG. 45  is a schematic block diagram illustrating an exemplary implementation of control system for an APD system; 
         FIG. 45A  is a schematic block diagram illustrating an exemplary arrangement of the multiple processors controlling the cycler and the safe line; 
         FIG. 45B  is a schematic block diagram illustrating exemplary connections between the hardware interface processor and the sensors, the actuators and the automation computer; 
         FIG. 46  is a schematic block diagram of illustrative software subsystems of a user interface computer and the automation computer for the control system of  FIG. 45 ; 
         FIG. 47  shows a flow of information between various subsystems and processes of the APD system in an illustrative embodiment; 
         FIG. 48  illustrates an operation of the therapy subsystem of  FIG. 46 ; 
         FIG. 49  shows a sequence diagram depicting exemplary interactions of therapy module processes during initial replenish and dialyze portions of the therapy; 
         FIG. 49-1  shows a schematic cross section of the cycler illustrating the components of the heater system for the heater bag; 
         FIG. 49-2  shows the software processes interacting with the heater controller process; 
         FIG. 49-3  shows the block diagram of a nested feedback loop to control the heater bag temperature; 
         FIG. 49-4  shows the block diagram of an alternative nested feedback loop to control the heater bag temperature; 
         FIG. 49-5  shows the block diagram of another alternative nested feedback loop to control the heater bag temperature; 
         FIG. 49-6  shows the block diagram of the thermal model of the heater bag and heater tray; 
         FIG. 49-7  shows the temperature response of the heater bag and heater tray for nominal conditions; 
         FIG. 49-8  shows the temperature response of the heater bag and heater tray for warm conditions; 
         FIG. 49-9  shows the temperature response of the heater bag and heater tray for cold conditions; 
         FIG. 49-10  is a schematic block diagram of one embodiment of a heater control system; 
         FIG. 49-11  is a is a schematic block diagram illustrating a heater circuit configured with a pair of heating elements; 
         FIG. 49-12  is a is a schematic block diagram illustrating a heater circuit configured with a pair of heating elements with reduced potential for current leakage; 
         FIG. 49-13  is a circuit diagram of a heater circuit configured with a pair of heating elements; 
         FIG. 49-14  shows a flow chart diagram illustrating a method to select the heater configuration in an APD cycler, according to one embodiment of the present invention; and 
         FIG. 49-15  shows a flow chart diagram illustrating a method to select the heater configuration in an APD cycler where a stored value of the AC mains voltage is queried during selection of the heater configuration, according to one embodiment of the present invention. 
         FIGS. 50-55  show exemplary screen views relating to alerts and alarms that may be displayed on a touch screen user interface for the APD system; 
         FIG. 56  illustrates component states and operations for error condition detection and recovery in an illustrative embodiment; 
         FIG. 57  shows exemplary modules of a UI view subsystem for the APD system; 
         FIGS. 58-64  shows illustrative user interface screens for providing user information and receiving user input in illustrative embodiments regarding system setup, therapy status, display settings, remote assistance, and parameter settings; 
         FIG. 65  shows an exemplary patient data key and associated port for transferring patient data to and from the APD system; 
         FIG. 65A  shows a patient data key with an alternative housing configuration. 
         FIG. 66  shows an exemplary pressure tracing from a control or actuation chamber of a pumping cassette during a liquid delivery stroke; 
         FIG. 67  shows an illustration of an adaptive tidal therapy mode during CCPD; 
         FIG. 68  shows an illustration of the implementation of a revised-cycle mode during CCPD; 
         FIG. 69  shows an illustration of the implementation of a revised-cycle mode during a tidal therapy; and 
         FIG. 70  shows an illustration of the implementation of an adaptive tidal mode during a tidal therapy. 
     
    
    
     DETAILED DESCRIPTION 
     Although aspects of the invention are described in relation to a peritoneal dialysis system, certain aspects of the invention can be used in other medical applications, including infusion systems such as intravenous infusion systems or extracorporeal blood flow systems, and irrigation and/or fluid exchange systems for the stomach, intestinal tract, urinary bladder, pleural space or other body or organ cavity. Thus, aspects of the invention are not limited to use in peritoneal dialysis in particular, or dialysis in general. 
     APD System 
       FIG. 1  shows an automated peritoneal dialysis (APD) system  10  that may incorporate one or more aspects of the invention. As shown in  FIG. 1 , for example, the system  10  in this illustrative embodiment includes a dialysate delivery set  12  (which, in certain embodiments, can be a disposable set), a cycler  14  that interacts with the delivery set  12  to pump liquid provided by a solution container  20  (e.g., a bag), and a control system  16  (e.g., including a programmed computer or other data processor, computer memory, an interface to provide information to and receive input from a user or other device, one or more sensors, actuators, relays, pneumatic pumps, tanks, a power supply, and/or other suitable components—only a few buttons for receiving user control input are shown in  FIG. 1 , but further details regarding the control system components are provided below) that governs the process to perform an APD procedure. In this illustrative embodiment, the cycler  14  and the control system  16  are associated with a common housing  82 , but may be associated with two or more housings and/or may be separate from each other. The cycler  14  may have a compact footprint, suited for operation upon a table top or other relatively small surface normally found in the home. The cycler  14  may be lightweight and portable, e.g., carried by hand via handles at opposite sides of the housing  82 . 
     The set  12  in this embodiment is intended to be a single use, disposable item, but instead may have one or more reusable components, or may be reusable in its entirety. The user associates the set  12  with the cycler  14  before beginning each APD therapy session, e.g., by mounting a cassette  24  within a front door  141  of the cycler  14 , which interacts with the cassette  24  to pump and control fluid flow in the various lines of the set  12 . For example, dialysate may be pumped both to and from the patient to effect APD. Post therapy, the user may remove all or part of the components of the set  12  from the cycler  14 . 
     As is known in the art, prior to use, the user may connect a patient line  34  of the set  12  to his/her indwelling peritoneal catheter (not shown) at a connection  36 . In one embodiment, the cycler  14  may be configured to operate with one or more different types of cassettes  24 , such as those having differently sized patient lines  34 . For example, the cycler  14  may be arranged to operate with a first type of cassette with a patient line  34  sized for use with an adult patient, and a second type of cassette with a patient line  34  sized for an infant or pediatric use. The pediatric patient line  34  may be shorter and have a smaller inner diameter than the adult line so as to minimize the volume of the line, allowing for more controlled delivery of dialysate and helping to avoid returning a relatively large volume of used dialysate to the pediatric patient when the set  12  is used for consecutive drain and fill cycles. A heater bag  22 , which is connected to the cassette  24  by a line  26 , may be placed on a heater container receiving portion (in this case, a tray)  142  of the cycler  14 . The cycler  14  may pump fresh dialysate (via the cassette  24 ) into the heater bag  22  so that the dialysate may be heated by the heater tray  142 , e.g., by electric resistance heating elements associated with the tray  142  to a temperature of about 37 degrees C. Heated dialysate may be provided from the heater bag  22  to the patient via the cassette  24  and the patient line  34 . In an alternative embodiment, the dialysate can be heated on its way to the patient as it enters, or after it exits, the cassette  24  by passing the dialysate through tubing in contact with the heater tray  142 , or through an in-line fluid heater (which may be provided in the cassette  24 ). Used dialysate may be pumped from the patient via the patient line  34  to the cassette  24  and into a drain line  28 , which may include one or more clamps to control flow through one or more branches of the drain line  28 . In this illustrative embodiment, the drain line  28  may include a connector  39  for connecting the drain line  28  to a dedicated drain receptacle, and an effluent sample port  282  for taking a sample of used dialysate for testing or other analysis. The user may also mount the lines  30  of one or more containers  20  within the door  141 . The lines  30  may also be connected to a continuous or real-time dialysate preparation system. (The lines  26 ,  28 ,  30 ,  34  may include a flexible tubing and/or suitable connectors and other components (such as pinch valves, etc.) as desired.) The containers  20  may contain sterile peritoneal dialysis solution for infusion, or other materials (e.g., materials used by the cycler  14  to formulate dialysate by mixing with water, or admixing different types of dialysate solutions). The lines  30  may be connected to spikes  160  of the cassette  24 , which are shown in  FIG. 1  covered by removable caps. In one aspect of the invention described in more detail below, the cycler  14  may automatically remove caps from one or more spikes  160  of the cassette  24  and connect lines  30  of solution containers  20  to respective spikes  160 . This feature may help reduce the possibility of infection or contamination by reducing the chance of contact of non-sterile items with the spikes  160 . 
     In another aspect, a dialysate delivery set  12   a  may not have cassette spikes  160 . Instead, one or more solution lines  30  may be permanently affixed to the inlet ports of cassette  24 , as shown in  FIG. 1A . In this case, each solution line  30  may have a (capped) spike connector  35  for manual connection to a solution container or dialysate bag  20 . 
     With various connections made, the control system  16  may pace the cycler  14  through a series of fill, dwell, and/or drain cycles typical of an APD procedure. For example, during a fill phase, the cycler  14  may pump dialysate (by way of the cassette  24 ) from one or more containers  20  (or other source of dialysate supply) into the heater bag  22  for heating. Thereafter, the cycler  14  may infuse heated dialysate from the heater bag  22  through the cassette  24  and into the patient&#39;s peritoneal cavity via the patient line  34 . Following a dwell phase, the cycler  14  may institute a drain phase, during which the cycler  14  pumps used dialysate from the patient via the line  34  (again by way of the cassette  24 ), and discharges spent dialysis solution into a nearby drain (not shown) via the drain line  28 . 
     The cycler  14  does not necessarily require the solution containers  20  and/or the heater bag  22  to be positioned at a prescribed head height above the cycler  14 , e.g., because the cycler  14  is not necessarily a gravity flow system. Instead, the cycler  14  may emulate gravity flow, or otherwise suitably control flow of dialysate solution, even with the source solution containers  20  above, below or at a same height as the cycler  14 , with the patient above or below the cycler, etc. For example, the cycler  14  can emulate a fixed head height during a given procedure, or the cycler  14  can change the effective head height to either increase or decrease pressure applied to the dialysate during a procedure. The cycler  14  may also adjust the rate of flow of dialysate. In one aspect of the invention, the cycler  14  may adjust the pressure and/or flow rate of dialysate when provided to the patient or drawn from the patient so as to reduce the patient&#39;s sensation of the fill or drain operation. Such adjustment may occur during a single fill and/or drain cycle, or may be adjusted across different fill and/or drain cycles. In one embodiment, the cycler  14  may taper the pressure used to draw used dialysate from the patient near the end of a drain operation. Because the cycler  14  may establish an artificial head height, it may have the flexibility to interact with and adapt to the particular physiology or changes in the relative elevation of the patient. 
     Cassette 
     In one aspect of the invention, a cassette  24  may include patient and drain lines that are separately occludable with respect to solution supply lines. That is, safety critical flow to and from patient line may be controlled, e.g., by pinching the lines to stop flow, without the need to occlude flow through one or more solution supply lines. This feature may allow for a simplified occluder device since occlusion may be performed with respect to only two lines as opposed to occluding other lines that have little or no effect on patient safety. For example, in a circumstance where a patient or drain connection becomes disconnected, the patient and drain lines may be occluded. However, the solution supply and/or heater bag lines may remain open for flow, allowing the cycler  14  to prepare for a next dialysis cycle; e.g., separate occlusion of patient and drain lines may help ensure patient safety while permitting the cycler  14  to continue to pump dialysate from one or more containers  20  to the heater bag  22  or to other solution containers  20 . 
     In another aspect of the invention, the cassette may have patient, drain and heater bag lines at one side or portion of the cassette and one or more solution supply lines at another side or portion of the cassette, e.g., an opposite side of the cassette. Such an arrangement may allow for separate occlusion of patient, drain or heater bag lines with respect to solution lines as discussed above. Physically separating the lines attached to the cassette by type or function allows for more efficient control of interaction with lines of a certain type or function. For example, such an arrangement may allow for a simplified occluder design because less force is required to occlude one, two or three of these lines than all lines leading to or away from the cassette. Alternately, this arrangement may allow for more effective automated connection of solution supply lines to the cassette, as discussed in more detail below. That is, with solution supply lines and their respective connections located apart from patient, drain and/or heater bag lines, an automated de-capping and connection device may remove caps from spikes on the cassette as well as caps on solution supply lines, and connect the lines to respective spikes without interference by the patient, drain or heater bag lines. 
       FIG. 2  shows an illustrative embodiment of a cassette  24  that incorporates aspects of the invention described above. In this embodiment, the cassette  24  has a generally planar body and the heater bag line  26 , the drain line  28  and the patient line  34  are connected at respective ports on the left end of the cassette body, while the right end of the cassette body may include five spikes  160  to which solution supply lines  30  may be connected. In the arrangement shown in  FIG. 2 , each of the spikes  160  is covered by a spike cap  63 , which may be removed, exposing the respective spike and allowing connection to a respective line  30 . As described above, the lines  30  may be attached to one or more solution containers or other sources of material, e.g., for use in dialysis and/or the formulation of dialysate, or connected to one or more collection bags for sampling purposes or for peritoneal equilibration testing (PET test). 
       FIGS. 3 and 4  show exploded views (perspective and top views, respectively) of the cassette  24  in this illustrative embodiment. The cassette  24  is formed as a relatively thin and flat member having a generally planar shape, e.g., may include components that are molded, extruded or otherwise formed from a suitable plastic. In this embodiment, the cassette  24  includes a base member  18  that functions as a frame or structural member for the cassette  24  as well as forming, at least in part, various flow channels, ports, valve portions, etc. The base member  18  may be molded or otherwise formed from a suitable plastic or other material, such as a polymethyl methacrylate (PMMA) acrylic, or a cyclic olefin copolymer/ultra low density polyethylene (COC/ULDPE), and may be relatively rigid. In an embodiment, the ratio of COC to ULDPE can be approximately 85%/15%.  FIG. 3  also shows the ports for the heater bag (port  150 ), drain (port  152 ) and the patient (port  154 ) that are formed in the base member  18 . Each of these ports may be arranged in any suitable way, such as, for example, a central tube  156  extending from an outer ring or skirt  158 , or a central tube alone. Flexible tubing for each of the heater bag, drain and patient lines  26 ,  28 ,  34  may be connected to the central tube  156  and engaged by the outer ring  158 , if present. 
     Both sides of the base member  18  may be covered, at least in part, by a membrane  15  and  16 , e.g., a flexible polymer film made from, for example, polyvinyl chloride (PVC), that is cast, extruded or otherwise formed. Alternatively, the sheet may be formed as a laminate of two or more layers of poly-cyclohexylene dimethylene cyclohexanedicarboxylate (PCCE) and/or ULDPE, held together, for example, by a coextrudable adhesive (CXA). In some embodiments, the membrane thickness may be in the range of approximately 0.002 to 0.020 inches thick. In a preferred embodiment, the thickness of a PVC—based membrane may be in the range of approximately 0.012 to 0.016 inches thick, and more preferably approximately 0.014 inches thick. In another preferred embodiment, such as, for example, for laminate sheets, the thickness of the laminate may be in the range of approximately 0.006 to 0.010 inches thick, and more preferably approximately 0.008 inches thick. 
     Both membranes  15  and  16  may function not only to close or otherwise form a part of flowpaths of the cassette  24 , but also may be moved or otherwise manipulated to open/close valve ports and/or to function as part of a pump diaphragm, septum or wall that moves fluid in the cassette  24 . For example, the membranes  15  and  16  may be positioned on the base member  18  and sealed (e.g., by heat, adhesive, ultrasonic welding or other means) to a rim around the periphery of the base member  18  to prevent fluid from leaking from the cassette  24 . The membrane  15  may also be bonded to other, inner walls of the base member  18 , e.g., those that form various channels, or may be pressed into sealing contact with the walls and other features of the base member  18  when the cassette  24  suitably mounted in the cycler  14 . Thus, both of the membranes  15  and  16  may be sealed to a peripheral rim of the base member  18 , e.g., to help prevent leaking of fluid from the cassette  24  upon its removal from the cycler  14  after use, yet be arranged to lie, unattached, over other portions of the base member  18 . Once placed in the cycler  14 , the cassette  24  may be squeezed between opposed gaskets or other members so that the membranes  15  and  16  are pressed into sealing contact with the base member  18  at regions inside of the periphery, thereby suitably sealing channels, valve ports, etc., from each other. 
     Other arrangements for the membranes  15  and  16  are possible. For example, the membrane  16  may be formed by a rigid sheet of material that is bonded or otherwise made integral with the body  18 . Thus, the membrane  16  need not necessarily be, or include, a flexible member. Similarly, the membrane  15  need not be flexible over its entire surface, but instead may include one or more flexible portions to permit pump and/or valve operation, and one or more rigid portions, e.g., to close flowpaths of the cassette  24 . It is also possible that the cassette  24  may not include the membrane  16  or the membrane  15 , e.g., where the cycler  14  includes a suitable member to seal pathways of the cassette, control valve and pump function, etc. 
     In accordance with another aspect of the invention, the membrane  15  may include a pump chamber portion  151  (“pump membrane”) that is formed to have a shape that closely conforms to the shape of a corresponding pump chamber  181  depression in the base  18 . For example, the membrane  15  may be generally formed as a flat member with thermoformed (or otherwise formed) dome-like shapes  151  that conform to the pump chamber depressions of the base member  18 . The dome-like shape of the pre-formed pump chamber portions  151  may be constructed, for example, by heating and forming the membrane over a vacuum form mold of the type shown in  FIG. 5 . As shown in  FIG. 5 , the vacuum may be applied through a collection of holes along the wall of the mold. Alternatively, the wall of the mold can be constructed of a porous gas-permeable material, which may result in a more uniformly smooth surface of the molded membrane. In one example, the molded membrane sheet  15  is trimmed while attached to the vacuum form mold. The vacuum form mold then presses the trimmed membrane sheet  15  against the cassette body  18  and bonds them together. In one embodiment the membrane sheets  15 , 16  are heat-welded to the cassette body  18 . In this way, the membrane  15  may move relative to the pump chambers  181  to effect pumping action without requiring stretching of the membrane  15  (or at least minimal stretching of the membrane  15 ), both when the membrane  15  is moved maximally into the pump chambers  181  and (potentially) into contact with spacer elements  50  (e.g., as shown in solid line in  FIG. 4  while pumping fluid out of the pump chamber  181 ), and when the membrane  15  is maximally withdrawn from the pump chamber  181  (e.g., as shown in dashed line in  FIG. 4  when drawing fluid into the pump chamber  181 ). Avoiding stretching of the membrane  15  may help prevent pressure surges or other changes in fluid delivery pressure due to sheet stretch and/or help simplify control of the pump when seeking to minimize pressure variation during pump operation. Other benefits may be found, including reduced likelihood of membrane  15  failure (e.g., due to tears in the membrane  15  resulting from stresses place on the membrane  15  during stretching), and/or improved accuracy in pump delivery volume measurement, as described in more detail below. In one embodiment, the pump chamber portions  151  may be formed to have a size (e.g., a define a volume) that is about 85-110% of the pump chamber  181 , e.g., if the pump chamber portions  151  define a volume that is about 100% of the pump chamber volume, the pump chamber portion  151  may lie in the pump chamber  181  and in contact with the spacers  50  while at rest and without being stressed. 
     Providing greater control of the pressure used to generate a fill and delivery stroke of liquid into and out of a pump chamber may have several advantages. For example, it may be desirable to apply the minimum negative pressure possible when the pump chamber draws fluid from the patient&#39;s peritoneal cavity during a drain cycle. A patient may experience discomfort during the drain cycle of a treatment in part because of the negative pressure being applied by the pumps during a fill stroke. The added control that a pre-formed membrane can provide to the negative pressure being applied during a fill stroke may help to reduce the patient&#39;s discomfort. 
     A number of other benefits may be realized by using pump membranes pre-formed to the contour of the cassette pump chamber. For example, the flow rate of liquid through the pump chamber can be made more uniform, because a constant pressure or vacuum can be applied throughout the pump stroke, which in turn may simplify the process of regulating the heating of the liquid. Moreover, temperature changes in the cassette pump may have a smaller effect on the dynamics of displacing the membrane, as well as the accuracy of measuring pressures within the pump chambers. In addition, pressure spikes within the fluid lines can be minimized. Also, correlating the pressures measured by pressure transducers on the control (e.g. pneumatic) side of the membrane with the actual pressure of the liquid on the pump chamber side of the membrane may be simpler. This in turn may permit more accurate head height measurements of the patient and fluid source bags prior to therapy, improve the sensitivity of detecting air in the pump chamber, and improve the accuracy of volumetric measurements. Furthermore, eliminating the need to stretch the membrane may allow for the construction and use of pump chambers having greater volumes. 
     In this embodiment, the cassette  24  includes a pair of pump chambers  181  that are formed in the base member  18 , although one pump chamber or more than two pump chambers are possible. In accordance with an aspect of the invention, the inner wall of pump chambers  181  includes spacer elements  50  that are spaced from each other and extend from the inner wall of pump chamber  18  to help prevent portions of the membrane  15  from contacting the inner wall of pump chamber  181 . (As shown on the right-side pump chamber  181  in  FIG. 4 , the inner wall is defined by side portions  181   a  and a bottom portion  181   b . The spacers  50  extend upwardly from the bottom portion  181   b  in this embodiment, but could extend from the side portions  181   a  or be formed in other ways.) By preventing contact of the membrane  15  with the pump chamber inner wall, the spacer elements  50  may provide a dead space (or trap volume) which may help trap air or other gas in the pump chamber  181  and inhibit the gas from being pumped out of the pump chamber  181  in some circumstances. In other cases, the spacers  50  may help the gas move to an outlet of the pump chamber  181  so that the gas may be removed from the pump chamber  181 , e.g., during priming. Also, the spacers  50  may help prevent the membrane  15  from sticking to the pump chamber inner wall and/or allow flow to continue through the pump chamber  181 , even if the membrane  15  is pressed into contact with the spacer elements  50 . In addition, the spacers  50  help to prevent premature closure of the outlet port of the pump chamber (openings  187  and/or  191 ) if the sheet happens to contact the pump chamber inner wall in a non-uniform manner. Further details regarding the arrangement and/or function of spacers  50  are provided in U.S. Pat. Nos. 6,302,653 and 6,382,923, both of which are incorporated herein by reference. 
     In this embodiment, the spacer elements  50  are arranged in a kind of “stadium seating” arrangement such that the spacer elements  50  are arranged in a concentric elliptical pattern with ends of the spacer elements  50  increasing in height from the bottom portion  181   b  of the inner wall with distance away from the center of the pump chamber  181  to form a semi-elliptical domed shaped region (shown by dotted line in  FIG. 4 ). Positioning spacer elements  50  such that the ends of the spacer elements  50  form a semi-elliptical region that defines the domed region intended to be swept by the pump chamber portion  151  of the membrane  15  may allow for a desired volume of dead space that minimizes any reduction to the intended stroke capacity of pump chambers  181 . As can be seen in  FIG. 3  (and  FIG. 6 ), the “stadium seating” arrangement in which spacer elements  50  are arranged may include “aisles” or breaks  50   a  in the elliptical pattern. Breaks (or aisles)  50   a  help to maintain an equal gas level throughout the rows (voids or dead space)  50   b  between spacer elements  50  as fluid is delivered from the pump chamber  181 . For example, if the spacer elements  50  were arranged in the stadium seating arrangement shown in  FIG. 6  without breaks (or aisles)  50   a  or other means of allowing liquid and air to flow between spacer elements  50 , the membrane  15  might bottom out on the spacer element  50  located at the outermost periphery of the pump chamber  181 , trapping whatever gas or liquid is present in the void between this outermost spacer element  50  and the side portions  181   a  of the pump chamber wall. Similarly, if the membrane  15  bottomed out on any two adjacent spacer elements  50 , any gas and liquid in the void between the elements  50  may become trapped. In such an arrangement, at the end of the pump stroke, air or other gas at the center of pump chamber  181  could be delivered while liquid remains in the outer rows. Supplying breaks (or aisles)  50   a  or other means of fluidic communication between the voids between spacer elements  50  helps to maintain an equal gas level throughout the voids during the pump stroke, such that air or other gas may be inhibited from leaving the pump chamber  181  unless the liquid volume has been substantially delivered. 
     In certain embodiments, spacer elements  50  and/or the membrane  15  may be arranged so that the membrane  15  generally does not wrap or otherwise deform around individual spacers  50  when pressed into contact with them, or otherwise extend significantly into the voids between spacers  50 . Such an arrangement may lessen any stretching or damage to membrane  15  caused by wrapping or otherwise deforming around one or more individual spacer elements  50 . For example, it has also been found to be advantageous in this embodiment to make the size of the voids between spacers  50  approximately equal in width to the width of the spacers  50 . This feature has shown to help prevent deformation of the membrane  15 , e.g., sagging of the membrane into the voids between spacers  50 , when the membrane  15  is forced into contact with the spacers  50  during a pumping operation. 
     In accordance with another aspect of the invention, the inner wall of pump chambers  181  may define a depression that is larger than the space, for example a semi-elliptical or domed space, intended to be swept by the pump chamber portion  151  of the membrane  15 . In such instances, one or more spacer elements  50  may be positioned below the domed region intended to be swept by the membrane portion  151  rather than extending into that domed region. In certain instances, the ends of spacer elements  50  may define the periphery of the domed region intended to be swept by the membrane  15 . Positioning spacer elements  50  outside of, or adjacent to, the periphery of the domed region intended to be swept by the membrane portion  151  may have a number of advantages. For example, positioning one or more spacer elements  50  such that the spacer elements are outside of, or adjacent to, the domed region intended to be swept by the flexible membrane provides a dead space between the spacers and the membrane, such as described above, while minimizing any reduction to the intended stroke capacity of pump chambers  181 . 
     It should be understood that the spacer elements  50 , if present, in a pump chamber may be arranged in any other suitable way, such as for example, shown in  FIG. 7 . The left side pump chamber  181  in  FIG. 7  includes spacers  50  arranged similarly to that in  FIG. 6 , but there is only one break or aisle  50   a  that runs vertically through the approximate center of the pump chamber  181 . The spacers  50  may be arranged to define a concave shape similar to that in  FIG. 6  (i.e., the tops of the spacers  50  may form the semi-elliptical shape shown in  FIGS. 3 and 4 ), or may be arranged in other suitable ways, such as to form a spherical shape, a box-like shape, and so on. The right-side pump chamber  181  in  FIG. 7  shows an embodiment in which the spacers  50  are arranged vertically with voids  50   b  between spacers  50  also arranged vertically. As with the left-side pump chamber, the spacers  50  in the right-side pump chamber  181  may define a semi-elliptical, spherical, box-like or any other suitably shaped depression. It should be understood, however, that the spacer elements  50  may have a fixed height, a different spatial pattern that those shown, and so on. 
     Also, the membrane  15  may itself have spacer elements or other features, such as ribs, bumps, tabs, grooves, channels, etc., in addition to, or in place of the spacer elements  50 . Such features on the membrane  15  may help prevent sticking of the membrane  15 , etc., and/or provide other features, such as helping to control how the sheet folds or otherwise deforms when moving during pumping action. For example, bumps or other features on the membrane  15  may help the sheet to deform consistently and avoid folding at the same area(s) during repeated cycles. Folding of a same area of the membrane  15  at repeated cycles may cause the membrane  15  to prematurely fail at the fold area, and thus features on the membrane  15  may help control the way in which folds occur and where. 
     In this illustrative embodiment, the base member  18  of the cassette  24  defines a plurality of controllable valve features, fluid pathways and other structures to guide the movement of fluid in the cassette  24 .  FIG. 6  shows a plan view of the pump chamber side of the base member  18 , which is also seen in perspective view in  FIG. 3 .  FIG. 8  shows a perspective view of a back side of the base member  18 , and  FIG. 9  shows a plan view of the back side of the base member  18 . The tube  156  for each of the ports  150 ,  152  and  154  fluidly communicates with a respective valve well  183  that is formed in the base member  18 . The valve wells  183  are fluidly isolated from each other by walls surrounding each valve well  183  and by sealing engagement of the membrane  15  with the walls around the wells  183 . As mentioned above, the membrane  15  may sealingly engage the walls around each valve well  183  (and other walls of the base member  18 ) by being pressed into contact with the walls, e.g., when loaded into the cycler  14 . Fluid in the valve wells  183  may flow into a respective valve port  184 , if the membrane  15  is not pressed into sealing engagement with the valve port  184 . Thus, each valve port  184  defines a valve (e.g., a “volcano valve”) that can be opened and closed by selectively moving a portion of the membrane  15  associated with the valve port  184 . As will be described in more detail below, the cycler  14  may selectively control the position of portions of the membrane  15  so that valve ports (such as ports  184 ) may be opened or closed so as to control flow through the various fluid channels and other pathways in the cassette  24 . Flow through the valve ports  184  leads to the back side of the base member  18 . For the valve ports  184  associated with the heater bag and the drain (ports  150  and  152 ), the valve ports  184  lead to a common channel  200  formed at the back side of the base member  18 . As with the valve wells  183 , the channel  200  is isolated from other channels and pathways of the cassette  24  by the sheet  16  making sealing contact with the walls of the base member  18  that form the channel  200 . For the valve port  184  associated with the patient line port  154 , flow through the port  184  leads to a common channel  202  on the back side of the base member  18 . 
     Returning to  FIG. 6 , each of the spikes  160  (shown uncapped in  FIG. 6 ) fluidly communicates with a respective valve well  185 , which are isolated from each other by walls and sealing engagement of the membrane  15  with the walls that form the wells  185 . Fluid in the valve wells  185  may flow into a respective valve port  186 , if the membrane  15  is not in sealing engagement with the port  186 . (Again, the position of portions of the membrane  15  over each valve port  186  can be controlled by the cycler  14  to open and close the valve ports  186 .) Flow through the valve ports  186  leads to the back side of the base member  18  and into the common channel  202 . Thus, in accordance with one aspect of the invention, a cassette may have a plurality of solution supply lines (or other lines that provide materials for providing dialysate) that are connected to a common manifold or channel of the cassette, and each line may have a corresponding valve to control flow from/to the line with respect to the common manifold or channel. Fluid in the channel  202  may flow into lower openings  187  of the pump chambers  181  by way of openings  188  that lead to lower pump valve wells  189  (see  FIG. 6 ). Flow from the lower pump valve wells  189  may pass through a respective lower pump valve port  190  if a respective portion of the membrane  15  is not pressed in sealing engagement with the port  190 . As can be seen in  FIG. 9 , the lower pump valve ports  190  lead to a channel that communicates with the lower openings  187  of the pump chambers  181 . Flow out of the pump chambers  181  may pass through the upper openings  191  and into a channel that communicates with an upper valve port  192 . Flow from the upper valve port  192  (if the membrane  15  is not in sealing engagement with the port  192 ) may pass into a respective upper valve well  194  and into an opening  193  that communicates with the common channel  200  on the back side of the base member  18 . 
     As will be appreciated, the cassette  24  may be controlled so that the pump chambers  181  can pump fluid from and/or into any of the ports  150 ,  152  and  154  and/or any of the spikes  160 . For example, fresh dialysate provided by one of the containers  20  that is connected by a line  30  to one of the spikes  160  may be drawn into the common channel  202  by opening the appropriate valve port  186  for the proper spike  160  (and possibly closing other valve ports  186  for other spikes). Also, the lower pump valve ports  190  may be opened and the upper pump valve ports  192  may be closed. Thereafter, the portion of the membrane  15  associated with the pump chambers  181  (i.e., pump membranes  151 ) may be moved (e.g., away from the base member  18  and the pump chamber inner wall) so as to lower the pressure in the pump chambers  181 , thereby drawing fluid in through the selected spike  160  through the corresponding valve port  186 , into the common channel  202 , through the openings  188  and into the lower pump valve wells  189 , through the (open) lower pump valve ports  190  and into the pump chambers  181  through the lower openings  187 . The valve ports  186  are independently operable, allowing for the option to draw fluid through any one or a combination of spikes  160  and associated source containers  20 , in any desired sequence, or simultaneously. (Of course, only one pump chamber  181  need be operable to draw fluid into itself. The other pump chamber may be left inoperable and closed off to flow by closing the appropriate lower pump valve port  190 .) 
     With fluid in the pump chambers  181 , the lower pump valve ports  190  may be closed, and the upper pump valve ports  192  opened. When the membrane  15  is moved toward the base member  18 , the pressure in the pump chambers  181  may rise, causing fluid in the pump chambers  181  to pass through the upper openings  191 , through the (open) upper pump valve ports  192  and into the upper pump valve wells  194 , through the openings  193  and into the common channel  200 . Fluid in the channel  200  may be routed to the heater bag port  150  and/or the drain port  152  (and into the corresponding heater bag line or drain line) by opening the appropriate valve port  184 . In this way, for example, fluid in one or more of the containers  20  may be drawn into the cassette  24 , and pumped out to the heater bag  22  and/or the drain. 
     Fluid in the heater bag  22  (e.g., after having been suitably heated on the heater tray for introduction into the patient) may be drawn into the cassette  24  by opening the valve port  184  for the heater bag port  150 , closing the lower pump valve ports  190 , and opening the upper pump valve ports  192 . By moving the portions of the membrane  15  associated with the pump chambers  181  away from the base member  18 , the pressure in the pump chambers  181  may be lowered, causing fluid flow from the heater bag  22  and into the pump chambers  181 . With the pump chambers  181  filled with heated fluid from the heater bag  22 , the upper pump valve ports  192  may be closed and the lower pump valve ports  190  opened. To route the heated dialysate to the patient, the valve port  184  for the patient port  154  may be opened and valve ports  186  for the spikes  160  closed. Movement of the membrane  15  in the pump chambers  181  toward the base member  18  may raise the pressure in the pump chambers  181  causing fluid to flow through the lower pump valve ports  190 , through the openings  188  and into the common channel  202  to, and through, the (open) valve port  184  for the patient port  154 . This operation may be repeated a suitable number of times to transfer a desired volume of heated dialysate to the patient. 
     When draining the patient, the valve port  184  for the patient port  154  may be opened, the upper pump valve ports  192  closed, and the lower pump valve ports  190  opened (with the spike valve ports  186  closed). The membrane  15  may be moved to draw fluid from the patient port  154  and into the pump chambers  181 . Thereafter, the lower pump valve ports  190  may be closed, the upper valve ports  192  opened, and the valve port  184  for the drain port  152  opened. Fluid from the pump chambers  181  may then be pumped into the drain line for disposal or for sampling into a drain or collection container. (Alternatively, fluid may also be routed to one or more spikes  160 /lines  30  for sampling or drain purposes). This operation may be repeated until sufficient dialysate is removed from the patient and pumped to the drain. 
     The heater bag  22  may also serve as a mixing container. Depending on the specific treatment requirements for an individual patient, dialysate or other solutions having different compositions can be connected to the cassette  24  via suitable solution lines  30  and spikes  160 . Measured quantities of each solution can be added to heater bag  22  using cassette  24 , and admixed according to one or more pre-determined formulae stored in microprocessor memory and accessible by control system  16 . Alternatively, specific treatment parameters can be entered by the user via user interface  144 . The control system  16  can be programmed to compute the proper admixture requirements based on the type of dialysate or solution containers connected to spikes  160 , and can then control the admixture and delivery of the prescribed mixture to the patient. 
     In accordance with an aspect of the invention, the pressure applied by the pumps to dialysate that is infused into the patient or removed from the patient may be controlled so that patient sensations of “tugging” or “pulling” resulting from pressure variations during drain and fill operations may be minimized. For example, when draining dialysate, the suction pressure (or vacuum/negative pressure) may be reduced near the end of the drain process, thereby minimizing patient sensation of dialysate removal. A similar approach may be used when nearing the end of a fill operation, i.e., the delivery pressure (or positive pressure) may be reduced near the end of fill. Different pressure profiles may be used for different fill and/or drain cycles in case the patient is found to be more or less sensitive to fluid movement during different cycles of the therapy. For example, a relatively higher (or lower) pressure may be used during fill and/or drain cycles when a patient is asleep, as compared to when the patient is awake. The cycler  14  may detect the patient&#39;s sleep/awake state, e.g., using an infrared motion detector and inferring sleep if patient motion is reduced, or using a detected change in blood pressure, brain waves, or other parameter that is indicative of sleep, and so on. Alternately, the cycler  14  may simply “ask” the patient—“are you asleep?” and control system operation based on the patient&#39;s response (or lack of response). 
     Patient Line State Detection Apparatus 
     In one aspect, a patient line state detector detects when a fluid line to a patient, such as patient line  34 , is adequately primed with fluid before it is connected to the patient. (It should be understood that although a patient line state detector is described in connection with a patient line, aspects of the invention include the detection of the presence any suitable tubing segment or other conduit and/or a fill state of the tubing segment or other conduit. Thus, aspects of the invention are not limited to use with a patient line, as a tubing state detector may be used with any suitable conduit.) In some embodiments, a patient line state detector can be used to detect adequate priming of a tubing segment of the patient-connecting end of a fluid line. The patient line  34  may be connected to an indwelling catheter in a patient&#39;s blood vessel, in a body cavity, subcutaneously, or in another organ. In one embodiment, the patient line  34  may be a component of a peritoneal dialysis system  10 , delivering dialysate to and receiving fluid from a patient&#39;s peritoneal cavity. A tubing segment near the distal end of the line may be placed in an upright position in a cradle within which the sensor elements of the detector are located.  FIG. 9-1A  shows a front perspective view of an exemplary configuration of a patient line state detector  1000 , which may be mounted on, or otherwise exposed at, the left side exterior of the housing  82 , e.g., to the left of the front door  141 . The patient line  34  should preferably be primed prior to being connected to the patient, because air could otherwise be delivered into the patient, raising the risk of complications. It may be permissible in some settings to allow up to 1 mL of air to be present in the patient line  34  prior to being connected to a patient&#39;s peritoneal dialysis catheter. The exemplary configurations of the patient line state detector  1000  described below will generally meet or exceed this standard, as they are capable of detecting a liquid level in a properly positioned tubing segment of line  34  so that at most about 0.2 mL of air remains in the distal end of line  34  after priming. 
     In one aspect, a first configuration patient line state detector  1000  may include a base member  1002 . There may also be a patient line state detector housing  1006  affixed to (or co-molded with) the base member  1002 , such that the detector housing  1006  may extend outwardly from the base member  1002 . The detector housing  1006  defines a tube or connector holding channel  1012  within which a tubing segment  34   a  near the distal end of a patient line  34 , or its associated connector  36  may be positioned. The portion of the detector housing  1006  facing the base member  1002  may be substantially hollow, and as a result an open cavity  1008  (shown in  FIG. 9-3 ) may be created behind the detector housing  1006 . The open cavity  1008  may accommodate the placement and positioning of sensor elements ( 1026 ,  1028 ,  1030  and  1032  shown in  FIG. 9-3 ) next to the channel  1012  within which tubing segment  34   a  may be positioned. In an alternative embodiment, there may also optionally be a stabilizing tab  1010  extending outwardly from the base member  1002 . The stabilizing tab  1010  may have a concave outer shape, so that it may substantially conform to the curvature of the patient line connector  36  when the patient line  34  is placed in the patient line state detector housing  1006 . The stabilizing tab  1010  may help to prevent the connector  36  from moving during priming of the patient line  34 , increasing the accuracy and efficiency of the priming process. The detector housing  1006  may have a shape that generally helps to define the tube or connector holding channel  1012 , which in turn may have dimensions that vary to accommodate the transition from tubing segment  34   a  to tube connector  36 . 
     In this illustrative embodiment, the channel  1012  may substantially conform to the shape of the patient line connector  36 . As a result the channel  1012  may be “U-shaped” so as to encompass a portion of the connector  36  when it is placed into the channel  1012 . The channel  1012  may be made up of two distinct features; a tube portion  1014  and a cradle  1016 . In another aspect, the tube portion  1014  may be positioned below the cradle  1016 . Additionally, the cradle  1016  may be formed by a pair of side walls  1018  and a back wall  1020 . Both of the side walls  1018  may be slightly convex in shape, while the back wall  1020  may be generally flat or otherwise may have a contour generally matching the shape of the adjacent portion of connector  36 . A generally convex shape of the side walls  1018  helps to lock the patient line connector  36  into place when positioned in the cradle  1016 . 
     In an illustrative embodiment for a first configuration of patient line state detector  1000 , a region  36   a  of the patient line connector  36  may have a generally planar surface that can rest securely against the opposing back wall  1020  of channel  1012 . Additionally, this region  36   a  of the connector  36  may have recesses  37  on opposing sides, which can be positioned adjacent to the opposing side walls  1018  of channel  1012  when the connector  36  is positioned within the detector housing  1006 . The recesses  37  can be defined by flanking raised elements  37   a  of connector  36 . One of these recesses  37  is partially visible in  FIG. 9-1 . The two side walls  1018  may have a generally mating shape (such as, e.g. a convex shape) to engage recesses  37  and to help lock connector  36  into place within cradle  1016 . This helps to prevent the connector  36  and tubing segment  34   a  from being inadvertently removed from the detector housing  1006  during priming of the patient line  34 . If the raised elements  37   a  of connector  36  are made of sufficiently flexible material (such as, e.g., polypropylene, polyethylene, or other similar polymer-based material) a threshold pulling force against connector  36  will be capable of disengaging connector  36  and tubing segment  34   a  from the detector housing  1006 . 
     In another aspect, the tube portion  1014  of the cavity  1012  may surround a majority of tubing segment  34   a  at a point just before tubing segment  34   a  attaches to the connector  36 . The tube portion  1014  may contain a majority of tubing segment  34   a  using three structures: the two side walls  1018  and the back wall  1020 . In an embodiment, the two side walls  1018  and back wall  1020  may be transparent or sufficiently translucent (constructed from, e.g. plexiglass) so as to allow the light from a plurality of LED&#39;s (such as, e.g., LED&#39;s  1028 ,  1030 , and  1032  in  FIG. 9-3 ) to be directed through the walls without being significantly blocked or diffused. An optical sensor  1026  (shown in  FIG. 9-2 ), may also be positioned along one of the walls  1018 , and can detect the light being emitted by the LED&#39;s. In the illustrated embodiment, a transparent or translucent plastic insert  1019  may be constructed to snap into the main detector housing  1006  in the region where the LED&#39;s have been positioned in the housing. 
       FIG. 9-2  shows a perspective layout view with LED&#39;s  1028 ,  1030 , and  1032  and optical sensor  1026  surface-mounted on a patient line state detector printed circuit board  1022 .  FIG. 9-3  shows a plan view of LED&#39;s  1028 ,  1030 , and  1032  and optical sensor  1026  mounted on detector circuit board  1022 , where the detector circuit board  1022  can be positioned adjacent the back wall  1020  and side walls  1018  of detector housing  1006 .  FIG. 9-4  is an exploded perspective view of detection assembly  1000  showing the relative positions of the printed circuit board  1022  and the translucent or transparent plastic insert  1019  with respect to the housing  1006 . 
     Referring also to the illustrative embodiment of  FIG. 9-1B , the detector circuit board  1022  may be positioned on a support structure  1004  and inside open cavity  1008 , which was formed from detector housing  1006  extending outwardly from base member  1002 . The base member  1002  and support structure  1004  may be affixed to one another, or may be co-molded, so that the base member  1002  is generally perpendicular to the support structure  1004 . This orientation generally permits the plane of the detector circuit board  1022  to be generally perpendicular to the long axis of tubing segment  34   a  when secured within channel  1012 . The detector circuit board  1022  may conform generally to the cross-sectional shape of open cavity  1008 , and it may also include a cutout  1024  ( FIG. 9-2, 9-3 ) generally matching the cross-sectional shape of channel  1012  formed by back wall  1020  and side walls  1018  ( FIG. 9-1A ). The detector circuit board  1022  may then be positioned within open cavity  1008  with cutout  1024  nearly adjacent to side walls  1018  and back wall  1020  of detector housing  1006  in order to ensure proper alignment of the detector circuit board  1022  with tubing segment  34   a  or connector  36 . 
     The detector circuit board  1022  may include a plurality of LED&#39;s and at least one optical sensor, which may be attached to circuit board  1022 , and in one embodiment, the LED&#39;s and optical sensor may be surface-mounted to circuit board  1022 . In one aspect, the detector circuit board  1022  may include a first LED  1028 , a second LED  1030 , a third LED  1032 , and an optical sensor  1026 . A first LED  1028  and a second LED  1030  may be positioned so as to direct light through the same side wall  1018   a  of channel  1012 . The light emitted by the first LED  1028  and the second LED  1030  may be directed in a generally parallel direction, generally perpendicular to the side wall  1018   a  to which they are nearest. An optical sensor  1026  may be positioned along the opposite side wall  1018   b  of channel  1012 . Furthermore, a third LED  1032  may be positioned along the back wall  1020  of channel  1012 . In this illustrative embodiment, such a configuration of the LED&#39;s and the optical sensor  1026  allows the patient line state detector  1000  to detect three different states during the course of priming the patient line  34 ; a tubing segment  34   a  or connector  36  nearly completely filled with fluid (primed state), an incompletely filled tubing segment  34   a  or connector  36  (non-primed state), or the absence of a tubing segment  34   a  and/or connector  36  from channel  1012  (line-absent state). 
     When used in a peritoneal dialysis system such as, for example peritoneal dialysis system  10 , configuring the detector circuit board  1022  in this fashion allows the appropriate control signal to be sent to the PD cycler controller system  16 . Controller system  16  may then inform the user, via user interface  144 , to position the distal end of line  34  in the patient line state detector  1000  prior to making a connection to the peritoneal dialysis catheter. The controller may then monitor for placement of tubing segment  34   a  within patient line state detector  1000 . The controller may then proceed to direct the priming of line  34 , to direct termination of priming once line  34  is primed, and then to instruct the user to disengage the distal end of line  34  from the patient line state detector  1000  and connect it to the user&#39;s peritoneal dialysis catheter. 
     Surface mounting the LED&#39;s  1028 ,  1030 , and  1032  and the optical sensor  1026  to the circuit board  1022  can simplify manufacturing processes for the device, can allow the patient line state detector  1000  and circuit board  1022  to occupy a relatively small amount of space, and can help eliminate errors that may arise from movement of the LED&#39;s or the optical sensor relative to each other or to the channel  1012 . Were it not for surface mounting of the sensor components, misalignment of the components could occur either during assembly of the device, or during its use. 
     In one aspect, the optical axis (or central optical axis) of LED  1032  may form an oblique angle with the optical axis of optical sensor  1026 . In the illustrated embodiment, the optical axis of a first LED  1028 , a second LED  1030 , and an optical sensor  1026  are each generally parallel to each other and to back wall  1020  of channel  1012 . Thus, the amount of light directed toward optical sensor  1026  from the LED&#39;s may vary depending on the presence or absence of (a) a translucent or transparent conduit within channel  1012  and/or (b) the presence of liquid within the conduit (which, for example, may be tubing segment  34   a ). Preferably, LED  1032  may be positioned near the side wall (e.g.,  1018   a ) that is farthest from optical sensor  1026  in order for some of the light emitted by LED  1032  to be refracted by the presence of a translucent or transparent tubing segment  34   a  within channel  1012 . The degree of refraction away from or toward optical sensor  1026  may depend on the presence or absence of fluid in tubing segment  34   a.    
     In various embodiments, the oblique angle of LED  1032  with respect to optical sensor  1026  creates a more robust system for determining the presence or absence of liquid with a translucent or transparent conduit in channel  1012 . LED  1032  may be positioned so that its optical axis can form any angle between 91° and 179° with respect to the optical axis of optical sensor  1026 . Preferably the angle may be set within the range of about 95° to about 135° with respect to the optical sensor&#39;s optical axis. More preferably, LED  1032  may be set to have an optical axis of about 115°+/−5° with respect to the optical axis of optical sensor  1026 . In an illustrative embodiment shown in  FIG. 9-3 , the angle θ of the optical axis of LED  1032  with respect to the optical axis of optical sensor  1026  was set to approximately 115°, +/−5°. (The optical axis of optical sensor  1026  in this particular embodiment is roughly parallel to back wall  1020 , and roughly perpendicular to side wall  1018   b ). The advantage of angling LED  1032  with respect to the optical axis of optical sensor  1026  was confirmed in a series of tests comparing the performance of the optical sensor  1026  in distinguishing a fluid filled tube segment (wet tube) from an air filled tube segment (dry tube) using an LED  1032  oriented at about a 115° angle vs. an LED whose optical axis was directed either perpendicularly or parallel to the optical axis of optical sensor  1026 . The results showed that an angled LED-based system was more robust in distinguishing the presence or absence of liquid in tubing segment  34   a . Using an angled LED  1032 , it was possible to select an optical sensor signal strength threshold above which an empty tubing segment  34   a  could reliably be detected. It was also possible to select an optical sensor signal strength threshold below which a liquid-filled tubing segment  34   a  could reliably be detected. 
       FIG. 9-12  shows a graph of test results demonstrating the ability of patient line state detector  1000  to distinguish between a liquid-filled tubing segment  34   a  (primed state) and an empty tubing segment  34   a  (non-primed state). The results were recorded with LED  1032  (third LED) oriented at an angle of about 115° with respect to the optical axis of optical sensor  1026 , and LED  1030  (second LED) oriented roughly parallel to the optical axis of optical sensor  1026 . The results plotted in  FIG. 9-12  demonstrate that patient line state detector  1000  can reliably discriminate between a primed state and a non-primed state. When the relative signal strength associated with light received from LED  1030  was approximately 0.4 or above, it was possible to resolve an upper signal detection threshold  1027  and a lower signal detection threshold  1029  for a non-primed vs. primed state using only the light signal received from LED  1032 . The upper threshold  1027  can be used to identify the non-primed state, and the lower threshold  1029  can be used to identify the primed state. The data points located above the upper-threshold  1027  are associated with an empty tubing segment  34   a  (non-primed state), and the data points located below the lower-threshold  1029  are associated with a liquid-filled tubing segment  34   a  (primed state). A relatively narrow region  1031  between these two threshold values defines a band of relative signal strength associated with light received from LED  1032  in which an assessment of the priming state of tubing segment  34   a  may be indeterminate. A controller (such as, e.g., control system  16 ) may be programmed to send the user an appropriate message whenever a signal strength associated with light received from LED  1032  falls within this indeterminate range. For example, the user may be instructed to assess whether tubing segment  34   a  and/or connector  36  are properly mounted in patient line state detector  1000 . In the context of a peritoneal dialysis system, if optical sensor  1026  generates a signal corresponding with an empty tubing segment  34   a , the controller can direct the cycler to continue to prime patient line  34  with dialysate. A signal corresponding to a liquid-filled tubing segment  34   a  can be used by the controller to stop further priming and instruct the user that the fluid line  34  is ready to be connected to a dialysis catheter. 
     In an embodiment, the cycler controller may continuously monitor the received signal from one of the LED&#39;s at the initiation of the priming procedure. Upon detection of a change in the received signal, the controller may halt further fluid pumping to carry out a full measurement using all of the LED&#39;s. If the received signals are well within the range indicating a wet tube, then further priming may be halted. However, if the received signals are within the indeterminate region  1031  or within the ‘dry’ region, then the cycler may command a series of small incremental pulses of fluid into the patient line by the pumping cassette, with a repeat reading of the LED signal strengths after each pulse of fluid. The priming can then be halted as soon as a reading is achieved that indicates a fluid-filled line at the level of the sensor. Incremental pulses of fluid may be accomplished by commanding brief pulses of the valve connecting the pressure reservoir to the pump actuation or control chamber. Alternatively, the controller may command the application of continuous pressure to the pump actuation or control chamber, and command the pump&#39;s outlet valve to open briefly and close to generate the series of fluid pulses. 
       FIG. 9-13  shows a graph of test results demonstrating the superiority of an angled LED  1032  (LEDc) when compared with an LED (LEDd) whose optical axis is roughly perpendicular to the optical axis of optical sensor  1026 . In this case, the relative signal strength generated by optical sensor  1026  in response to light from LEDc was plotted against the signal strength associated with light from LEDd. Although some separation between a liquid-filled (‘primed’) and empty (‘non-primed’) tubing segment  34   a  was apparent at an LEDd relative signal strength of about 0.015, there remained a substantial number of ‘non-primed’ data points  1035  that cannot be distinguished from ‘primed’ data points based on this threshold value. On the other hand, a relative signal strength  1033  associated with light from LEDc of 0.028-0.03 can effectively discriminate between ‘primed’ tubing segment  34   a  (primed state) and ‘non-primed’ tubing segment  34   a  (non-primed state). Thus an angled LED ( 1032 ) can generate more reliable data than an orthogonally oriented LED. 
     In another embodiment, a patient line state detector  1000  can also determine whether a tubing segment  34   a  is present in channel  1012 . In one aspect, a first LED  1028  and a second LED  1030  may be positioned next to one another. One LED (e.g., LED  1028 ) may be positioned so that its optical axis passes through approximately the center of a properly positioned translucent or transparent conduit or tubing segment  34   a  in channel  1012 . The second LED (e.g. LED  1030 ) may be positioned so that its optical axis is shifted slightly off center with respect to conduit or tubing segment  34   a  in channel  1012 . Such an on-center/off-center pairing of LED&#39;s on one side of channel  1012 , with an optical sensor  1026  on the opposing side of channel  1012 , has been shown to increase the reliability of determining whether a liquid conduit or tubing segment  34   a  is present or absent within channel  1012 . In a series of tests in which a tubing segment  34   a  was alternately absent, present but improperly positioned, or present and properly positioned within channel  1012 , signal measurements were taken by the optical sensor  1026  from the first LED and the second LED  1030 . The signals received from each LED were plotted against each other, and the results are shown in  FIG. 9-14 . 
     As shown in  FIG. 9-14 , in the majority of cases in which tubing segment  34   a  was absent from channel  1012  (region  1039 ), the signal strength received by optical sensor  1026  attributable to LEDa (LEDa reception strength) was found not to be significantly different from the signal strength received from LEDa during a calibration step in which LEDa was illuminated in a known absence of any tubing in channel  1012 . Similarly, the signal strength associated with LEDb (LEDb reception strength), was found not to be significantly different from LEDb during a calibration step in which LEDb was illuminated in a known absence of any tubing in channel  1012 . Patient line state detector  1000  can reliably determine that no tube is present within channel  1012  if the ratio of LEDa to its calibration value, and the ratio of LEDb to its calibration value are each approximately 1±20%. In a preferred embodiment, the threshold ratio can be set at 1±15%. In an embodiment in which patient line state detector  1000  is used in conjunction with a peritoneal dialysis cycler, LEDa and LEDb values within region  1039  of  FIG. 9-14 , for example, can be used to indicate the absence of tube segment  34   a  from channel  1012 . The cycler controller can be programmed to pause further pumping actions and inform the user via user interface  144  of the need to properly position the distal end of patient line  34  within patient line state detector  1000 . 
     The configuration and alignment of the three LED&#39;s and the optical sensor  1026  described above is capable of generating the required data using translucent or transparent fluid conduits (e.g. tubing segment  34   a ) having a wide range of translucence. In additional testing, patient line state detector  1000  was found to be capable of providing reliable data to distinguish liquid from air in a fluid conduit, or the presence or absence of a fluid conduit, using samples of tubing having significantly different degrees of translucence. It was also capable of providing reliable data regardless of whether the PVC tubing being used was unsterilized, or sterilized (e.g., EtOx-sterilized). 
     The measurements taken by the optical sensor  1026  from the LED&#39;s can be used as inputs to a patient line state detector algorithm in order to detect the state of tubing segment  34   a . Besides detecting a full, empty, or absent tubing segment  34   a , the result of the algorithm may be indeterminate, possibly indicating movement or improper positioning of the tubing segment  34   a  within the patient line state detector  1000 , or possibly the presence of a foreign object in channel  1012  of patient line state detector  1000 . Manufacturing variations may cause the output from the LED&#39;s and the sensitivity of optical sensor  1026  to vary among different assemblies. Therefore, it may be advantageous to perform an initial calibration of the patient line state detector  1000 . For example, the following procedure may be used to obtain calibration values of the LED&#39;s and sensor:
         (1) Ensure that no tubing segment  34   a  is loaded in the patient line state detector  1000 .   (2) Poll the optical sensor  1026  in four different states:
           (a) no LED illuminated   (b) first LED  1028  (LEDa) illuminated   (c) second LED  1030  (LEDb) illuminated   (d) third LED  1032  (LEDc) illuminated   
           (3) Subtract the ‘no LED illuminated’ signal value from each of the other signal values to determine their ambient corrected values, and store these three readings as ‘no-tube’ calibration values.       

     Once calibration values for the LED&#39;s and sensor are obtained, the state of tubing segment  34   a  may then be detected. In this illustrative embodiment, the patient line state detector algorithm performs a state detection in a test as follows:
         (1) Poll the optical sensor  1026  in four different states:
           (a) no LED illuminated   (b) first LED  1028  (LEDa) illuminated   (c) second LED  1030  (LEDb) illuminated   (d) third LED  1032  (LEDc) illuminated   
           (2) Subtract the ‘no LED illuminated’ value from each of the other values to determine their ambient corrected values.   (3) Calculate the relative LED values by dividing the test values associated with each LED by their corresponding calibration (‘no-tube’) values.       

     Results:
         If the ambient corrected LEDa value is less than 0.10, then there may be a foreign object in the detector, or an indeterminate result can be reported to the user.   If the ambient corrected LEDa and LEDb values fall within ±15% of their respective stored calibration (no-tube) values, then report to the user that no tubing segment is present in the detector.   If the ambient corrected LEDb value is equal to or greater than about 40% of its stored calibration (‘no-tube’) value,
           (a) check the signal associated with LEDc
               (i) if the ambient corrected signal associated with LEDc is equal or greater than about 150% of its calibration (‘no-tube’) value, then report to the user that the tubing segment is empty.   (ii) If the ambient corrected signal associated with LEDc is equal to or less than about 125% of its calibration (‘no-tube’) value, then report to the user that the tubing segment is filled with liquid.   (iii) Otherwise, the result is indeterminate, and either repeat the measurement (e.g., the tubing segment may be moving, may be indented, or otherwise obscured), or report to the user that the tubing segment should be checked to ensure that it is properly inserted in the detector.   
               
           If the ambient corrected LEDb value is less than about 40% of its stored calibration (‘no-tube’) value, then the LEDc threshold for determining the presence of a dry tube may be greater. In an embodiment, for example, the LEDc empty tube threshold was found empirically to follow the relationship: [LEDc empty tube threshold]=−3.75×[LEDb value]+3.       

     Once it is determined that the tubing segment  34   a  has been loaded in the patient line state detector  1000 , the patient line state detector algorithm can perform the following:
         a) Poll the optical sensor  1026  with no LED illuminated and store this as the no LED value.   b) Illuminate LEDc   c) Poll the optical sensor  1026 , subtract the no LED value from the LEDc value, and store this as the initial value.   d) Begin pumping   e) Poll the optical sensor  1026  and subtract the no LED value from the subsequent LEDc value.   f) If this value is less than 75% of the initial value, then conclude that tubing segment  34   a  is filled with liquid, stop pumping, confirm the detector state using the above procedure, and when indicated, report to the user that priming is complete. Otherwise, keep repeating the poll, calculation, and comparison. In an embodiment, the system controller can be programmed to perform the polling protocol as frequently as desired, such as, for example, every 0.005 to 0.01 seconds. In an embodiment, the entire polling cycle can conveniently be performed every 0.5 seconds.       

       FIG. 9-12A  shows the results of sample calibration procedures for six cyclers. The signal strength range that distinguishes a dry tube from a wet tube (‘wet/dry threshold’ ranges) is noted to vary among the different cyclers. (The variations in these ranges may be due to minor variations in manufacturing, assembly and positioning of the various components). Thus at calibration, each cycler may be assigned a wet/dry threshold signal strength range that optimally separates the data points generated with a dry tube from the data points generated with a wet tube. 
       FIG. 9-5  shows a perspective view of a second configuration of a patient line state detector  1000 . Two or more different patient line state detector configurations may necessary to accommodate varying types of patient connectors. In this illustrative embodiment, the second configuration patient line state detector  1000  may include most of the same components as in the first configuration patient line state detector  1000 . However, in order to accommodate a different type of connector, the second configuration may include a raised element  1036  above housing  1006 , rather than the stabilizing tab  1010  found in the first configuration patient line state detector  1000 . The raised element  1036  may generally conform to the shape of a standard patient line connector cap or connector flange. 
     In accordance with an aspect of the disclosure, detector housing  1006  may not include a tube portion  1014 . Therefore, open cavity  1008  may be arranged to allow placement of detector circuit board  1022  so that the LED&#39;s and optical sensor may be positioned next to a translucent or transparent patient line connector  36  rather than a section of tubing. Channel  1012  consequently may be shaped differently to accommodate the transmission of LED light through connector  36 . 
     Solution Line Organizer 
       FIG. 9-6 ,  FIG. 9-7 , and  FIG. 9-8 , show a perspective view of the front of an unloaded organizer  1038 , a perspective view of the back of an unloaded organizer  1038 , and a perspective view of a loaded organizer  1038  respectively. In this embodiment, the organizer  1038  may be substantially formed from a moderately flexible material (such as, e.g., PAXON AL55-003 HDPE resin). Forming the organizer  1038  from this or another relatively flexible polymer material increases the organizer&#39;s  1038  durability when attaching and removing solution lines or solution line connectors. 
     The organizer  1038  may conveniently be mounted or attached to an outer wall of the cycler housing  82 . The organizer  1038  may include a tube holder section  1040 , a base  1042 , and a tab  1044 . The tube holder section  1040 , the base  1042 , and the tab  1044  may all be flexibly connected, and may be substantially formed from the same HDPE-based material. The tube holder section  1040  may have a generally rectangular shape, and may include a generally flat top edge and a bottom edge that may be slightly curved in an outwardly direction. The tube holder section  1040  may include a series of recessed segments  1046  that extend horizontally along the bottom edge of the tube holder section  1040 . Each of the recessed segments  1046  may be separated by a series of support columns  1048 , which may also define the shape and size of the segments  1046 . The tube holder section  1040  may also include a raised area that extends horizontally along the top edge of the tube holder section  1040 . The raised area may include a plurality of slots  1050 . The slots  1050  may be defined in a vertical orientation, and may extend from the top edge of the tube holder section  1040  to the top of the recessed segments  1046 . The slots  1050  may have a generally cylindrical shape so as to conform to the shape of a drain line  28 , solution line  30 , or patient line  34 . The depth of the slots  1050  may be such that the opening of the slot  1050  is narrower then the inner region of the slot  1050 . Therefore, once a line is placed into the slot  1050  it becomes locked or snap-fit into place. The line may then require a pre-determined minimum amount of force to be removed from the slot  1050 . This ensures that the lines are not unintentionally removed from the organizer  1050 . 
     In one aspect, the tab  1044  may be flexibly connected to the top edge of the tube holder section  1040 . The tab  1044  may have a generally rectangular shape. In another embodiment, the tab  1044  may also include two slightly larger radius corners. The tab  1044  may also include two vertically extending support columns  1048 . The support columns  1048  may be connected to the top edge of the tube holder section  1040 , and may extend in an upward direction into the tab  1044 . In alternative embodiment, the length and number of the support columns  1048  may vary depending on the desired degree of flexibility of the tab  1044 . In another aspect, the tab  1044  may include a ribbed area  1052 . The purpose of the tab  1044  and the ribbed area  1052  is to allow the organizer  1038  to be easily grasped by a user so that the user can easily install, transport, or remove the solution lines  30  from the organizer  1038 . Also, the tab  1044  provides an additional area of support when removing and loading the lines into the organizer  1038 . 
     In another aspect, the base  1042  may be flexibly connected to the bottom edge of the tube holder section  1040 . The base  1042  may have a generally rectangular shape. In another embodiment, the base  1042  may also include two slightly larger radius corners. The base  1042  may include an elongated recessed segment  1046 , which may be defined by a support ring  1054  that surrounds the recessed segment  1046 . The support columns  1050 , the support ring  1054 , and the raised area may all create a series of voids  1056  along the back of the organizer  1038  (shown, e.g., in  FIG. 9-7 ). 
       FIG. 9-9  and  FIG. 9-10  show a perspective view of an organizer clip  1058 , and a perspective view of an organizer clip receiver  1060  respectively. In these illustrative embodiments, the clip  1058  may be made from a relatively high durometer polyurethane elastomer, such as, for example, 80 Shore A durometer urethane. In an alternative embodiment, the clip  1058  may be made from any type of flexible and durable material that would allow the organizer  1038  to flex and pivot along the base  1042  when positioned in the clip  1058 . The clip  1058  may be “U-shaped”, and may include a back portion that extends slightly higher than a front portion. Additionally, there may be a lip  1062  that extends along the top edge of the front portion of the clip  1058 . The lip  1062  extends slightly into the cavity of the clip  1058 . The back portion of the clip  1058  may also include a plurality of elastomeric pegs  1064  connected to (or formed from) and extending away from the back portion of the clip  1058 . The pegs  1064  may include both a cylindrical section  1066  and a cone  1068 . The cylindrical section  1066  may connect to the back portion of the clip  1058 , and the cone  1068  may be attached to an open end of the cylindrical section  1066 . The pegs  1064  allow the clip  1058  to be permanently connected to the organizer clip receiver  1060 , by engaging the pegs  1064  within a plurality of holes  1070  in the organizer clip receiver  1060 . 
     The organizer clip receiver  1060  may include a plurality of chamfered tabs  1072 . The chamfered tabs  1072  may mate with corresponding slots on the back portion of the clip  1058  when the pegs  1064  are engaged with the organizer clip receiver  1060 . Once the chamfered tabs  1072  engage the slots, they can extend through the back portion of the clip  1058 , and act as locking mechanisms to hold the organizer  1038  in place when positioned into the clip  1058 . When the organizer  1038  is positioned within the clip  1058 , the chamfers  1072  fit into the void  1056  on the back of the base  1042 , which was created by the raised support ring  1054 . Referring again to  FIG. 9-7 , and in accordance with another aspect of the present disclosure, there may be a plurality of ramps  1074  extending outwardly from the back of the organizer  1038 . The ramps  1074  may be generally shaped as inclined planes. This allows the organizer  1038  to angle away from the cycler  14  when placed into the clip  1058 , which provides numerous advantages over previous designs. For example, in this illustrative embodiment, the angle of the organizer  1038  ensures that neither the tab  1044 , nor any of the lines (or line caps) connected to the organizer  1038  are allowed to interfere with the heater lid  143  when the lid  143  is being opened and closed. Additionally, the angle of the organizer  1038  in relation to the cycler  14 , coupled with the flexibility of the organizer  1038 , both encourage the user to remove the solution lines  30  from the bottom instead of from the connector end  30   a  of the solution lines. Preferably, the user should not remove the solution lines  30  by grasping the connector ends  30   a , because in doing so the user could inadvertently remove one or more caps  31 , which could cause contamination and spills. Another advantage of the organizer  1038  is that it aids the user in connecting color coded solution lines  30  to the correct containers  20  by helping to separate the color coded lines  30 . 
     Door Latch Sensor 
       FIG. 9-11 , shows a perspective view of a door latch sensor assembly  1076 . In this illustrative embodiment, the door latch sensor assembly  1076  may include a magnet  1078  that is attached or connected to door latch  1080 , and can pivot with door latch  1080  as it pivots into and our of a latching position with its mating base unit catch  1082 . A sensor (not shown in  FIG. 9-11 ) may be positioned behind the front panel  1084  of cycler  14 , near base unit catch  1082 , to detect the presence of magnet  1078  as door latch  1080  engages with base unit catch  1082 . In one embodiment, the sensor may be an analog Hall effect sensor. The purpose of the door latch sensor assembly  1076  is to confirm both that the door  141  is closed and that the door latch  1080  is sufficiently engaged with catch  1082  to ensure a structurally sound connection.  FIG. 9-11   a  shows a cross-sectional view of the door latch sensor assembly  1076 . Sensor  1079  is positioned on a circuit board  1077  behind front panel  1084 . Sensor  1079  is preferably oriented off-axis from the line of motion of magnet  1078 , because in this orientation, sensor  1079  is better able to resolve a variety of positions of magnet  1078  as it approaches front panel  1084  as door  141  is closed. 
     In one example, the door  141  may be considered to be sufficiently engaged when the door latch  1080  has at least a 50% engagement with the catch  1082 . In one embodiment, the door latch  1080  may engage to a degree of approximately 0.120 inch nominally. Additionally, the sensor  1079  may only sense a closed door  141  when the door latch  1080  is sufficiently engaged with the catch  1082 . Therefore, the sensor  1082  may only sense a closed door  141  when the door latch  1080  is engaged to a degree of approximately 0.060 inch. These engagement thresholds for the door latch  1080  may be set approximately at the middle range for acceptable engagement between the door latch  1080  and the catch  1082 . This can help to ensure a robust design by accounting for sensor drift due to time, temperature, and other variations. Testing was conducted to determine the robustness of the sensor  1082  by collecting numerous measurements both at room temperature (approximately 24° C.) and at an abnormally cold temperature (approximately −2° C. to 9° C.). The room temperature readings were repeatedly higher than the cold readings, but only by a small percentage of the 0 inch to 0.060 inch range. In one aspect, the output of the sensor  1079  may be ratiometric to the voltage supplied. 
     Therefore, both the supply voltage and the output of the sensor  1079  may be measured (see formulas below, where the supply voltage and the output of the sensor  1079  are represented by Door_Latch and Monitor_5V0 respectively). Both the output of the sensor  1079  as well as the voltage supplied may then pass through ¼ resistor dividers. Dividing the output of the sensor  1079  and the voltage supplied may allow for a stable output to be produced. This procedure may ensure that the output remains stable even if the supply voltage fluctuates. 
     In another aspect, the sensor  1079  may respond to both positive and negative magnetic fields. Consequently, if there is no magnetic field, the sensor  1079  may output half the supply voltage. Additionally, a positive magnetic field may cause the output of the sensor  1079  to increase, while a negative magnetic field may result in a decrease of the output of the sensor  1079 . In order to obtain an accurate measurement of the output from the sensor  1079 , the magnet polarity can be ignored, and the supply voltage can simultaneously be compensated for. The following formula may be used to calculate the latch sensor ratio: 
       Latch Sensor Ratio=absolute value(( V Door_Latch/ V Monitor_5 V 0)−noFieldRatio)  (1)
 
     Where the noFieldRatio is calculated by (VDoor_Latch/VMonitor_5V0) with the door  141  fully open. 
     Using this formula: 
       Ratio=0.0 indicates no magnetic field 
       Ratio&gt;0.0 indicates some magnetic field; direction indeterminate. 
     Shims of various thicknesses may be used between the inside of door  141  and front panel  1084  to vary the degree of engagement between latch  1080  and catch  1082 , in order to calibrate the strength of the magnetic field detected by sensor  1079  with various positions of engagement of the door latch assembly  1076 . In one embodiment, this data can be used to develop field strength ratios with and without a shim, or in other embodiments with several shims of varying thicknesses. In one example, the door latch sensor assembly  1076  may complete the procedure for determining if the door latch  1080  is sufficiently engaged with the catch  1082  by performing the following: 
     Calculate the nearRatio and the farRatio: 
       nearRatio=noShimRatio−(0.025/0.060)×(noShimRatio−withShimRatio)  (2)
 
       farRatio=noShimRatio−(0.035/0.060)×(noShimRatio−withShimRatio)  (3)
 
     In an embodiment, the door latch sensor assembly  1076  may save the noFieldRatio, nearRatio, and farRatio to a calibration file. The door latch sensor assembly  1076  may then load the noFieldRatio, nearRatio, and farRatio from the calibration file, and the sensor assembly  1076  may then use the nearRatio and farRatio as the hysteresis limits for the sensor  1079 . The door latch sensor assembly  1076  may then begin with the initial condition that the door  141  is open, and then repeatedly calculate the Latch Sensor Ratio. If the Latch Sensor Ratio is greater than the nearRatio, the door latch sensor assembly  1076  will change the latch state to closed, and if the Latch Sensor Ratio is less than the farRatio, the door latch sensor assembly  1076  will change the latch state to open. In an alternative embodiment for the door latch sensor assembly  1076 , a middleRatio can be calculated from the calibration data by averaging the noShimRatio and the withShimRatio. In this case, measurements greater than the middleRatio indicate that the door latch  1080  is engaged, and measurements less than the middleRatio indicate that the door latch  1080  is not engaged. 
     Set Loading and Operation 
       FIG. 10  shows a perspective view of the APD system  10  of  FIG. 1  with the door  141  of the cycler  14  lowered into an open position, exposing a mounting location  145  for the cassette  24  and a carriage  146  for the solution lines  30 . (In this embodiment, the door  141  is mounted by a hinge at a lower part of the door  141  to the cycler housing  82 .) When loading the set  12 , the cassette  24  is placed in the mounting location  145  with the membrane  15  and the pump chamber side of the cassette  24  facing upwardly, allowing the portions of the membrane  15  associated with the pump chambers and the valve ports to interact with a control surface  148  of the cycler  14  when the door  141  is closed. The mounting location  145  may be shaped so as to match the shape of the base member  18 , thereby ensuring proper orientation of the cassette  24  in the mounting location  145 . In this illustrative embodiment, the cassette  24  and mounting location  145  have a generally rectangular shape with a single larger radius corner which requires the user to place the cassette  24  in a proper orientation into the mounting location  145  or the door  141  will not close. It should be understood, however, that other shapes or orientation features for the cassette  24  and/or the mounting location  145  are possible. 
     In accordance with an aspect of the invention, when the cassette  24  is placed in the mounting location  145 , the patient, drain and heater bag lines  34 ,  28  and  26  are routed through a channel  40  in the door  141  to the left as shown in  FIG. 10 . The channel  40 , which may include guides  41  or other features, may hold the patient, drain and heater bag lines  34 ,  28  and  26  so that an occluder  147  may selectively close/open the lines for flow. Upon closing of door  141 , occluder  147  can compress one or more of patient, drain and heater bag lines  34 ,  28  and  26  against occluder stop  29 . Generally, the occluder  147  may allow flow through the lines  34 ,  28  and  26  when the cycler  14  is operating (and operating properly), yet occlude the lines when the cycler  14  is powered down (and/or not operating properly). (Occlusion of the lines may be performed by pressing on the lines, or otherwise pinching the lines to close off the flow path in the lines.) Preferably, the occluder  147  may selectively occlude at least the patient and drain lines  34  and  28 . 
     When the cassette  24  is mounted and the door  141  is closed, the pump chamber side of the cassette  24  and the membrane  15  may be pressed into contact with the control surface  148 , e.g., by an air bladder, spring or other suitable arrangement in the door  141  behind the mounting location  145  that squeezes the cassette  24  between the mounting location  145  and the control surface  148 . This containment of the cassette  24  may press the membranes  15  and  16  into contact with walls and other features of the base member  18 , thereby isolating channels and other flow paths of the cassette  24  as desired. The control surface  148  may include a flexible gasket or membrane, e.g., a sheet of silicone rubber or other material, that is associated with the membrane  15  and can selectively move portions of the membrane  15  to cause pumping action in the pump chambers  181  and opening/closing of valve ports of the cassette  24 . The control surface  148  may be associated with the various portions of the membrane  15 , e.g., placed into intimate contact with each other, so that portions of the membrane  15  move in response to movement of corresponding portions of the control surface  148 . For example, the membrane  15  and control surface  148  may be positioned close together, and a suitable vacuum (or pressure that is lower relative to ambient) may be introduced through vacuum ports suitably located in the control surface  148 , and maintained, between the membrane  15  and the control surface  148  so that the membrane  15  and the control surface  148  are essentially stuck together, at least in regions of the membrane  15  that require movement to open/close valve ports and/or to cause pumping action. In another embodiment, the membrane  15  and control surface  148  may be adhered together, or otherwise suitably associated. 
     In some embodiments, the surface of the control surface  148  or gasket facing the corresponding cassette membrane overlying the pump chambers and/or valves is textured or roughened. The texturing creates a plurality of small passages horizontally or tangentially along the surface of the gasket when the gasket is pulled against the surface of the corresponding cassette membrane. This may improve evacuation of air between the gasket surface and the cassette membrane surface in the textured locations. It may also improve the accuracy of pump chamber volume determinations using pressure-volume relationships (such as, for example, in the FMS procedures described elsewhere), by minimizing trapped pockets of air between the gasket and the membrane. It may also improve the detection of any liquid that may leak into the potential space between the gasket and the cassette membrane. In an embodiment, the texturing may be accomplished by masking the portions of the gasket mold that do not form the portions of the gasket corresponding to the pump membrane and valve membrane locations. A chemical engraving process such as the Mold-Tech® texturing and chemical engraving process may then be applied to the unmasked portions of the gasket mold. Texturing may also be accomplished by any of a number of other processes, such as, for example, sand blasting, laser etching, or utilizing a mold manufacturing process using electrical discharge machining. 
     Before closing the door  141  with the cassette  24  loaded, one or more solution lines  30  may be loaded into the carriage  146 . The end of each solution line  30  may include a cap  31  and a region  33  for labeling or attaching an indicator or identifier. The indicator, for example, can be an identification tag that snaps onto the tubing at indicator region  33 . In accordance with an aspect of the invention and as will be discussed in more detail below, the carriage  146  and other components of the cycler  14  may be operated to remove the cap(s)  31  from lines  30 , recognize the indicator for each line  30  (which may provide an indication as to the type of solution associated with the line, an amount of solution, etc.) and fluidly engage the lines  30  with a respective spike  160  of the cassette  24 . This process may be done in an automated way, e.g., after the door  141  is closed and the caps  31  and spikes  160  are enclosed in a space protected from human touch, potentially reducing the risk of contamination of the lines  30  and/or the spikes  160  when connecting the two together. For example, upon closing of the door  141 , the indicator regions  33  may be assessed (e.g., visually by a suitable imaging device and software-based image recognition, by RFID techniques, etc.) to identify what solutions are associated with which lines  30 . The aspect of the invention regarding the ability to detect features of a line  30  by way of an indicator at indicator region  33  may provide benefits such as allowing a user to position lines  30  in any location of the carriage  146  without having an affect on system operation. That is, since the cycler  14  can automatically detect solution line features, there is no need to ensure that specific lines are positioned in particular locations on the carriage  146  for the system to function properly. Instead, the cycler  14  may identify which lines  30  are where, and control the cassette  24  and other system features appropriately. For example, one line  30  and connected container may be intended to receive used dialysate, e.g., for later testing. Since the cycler  14  can identify the presence of the sample supply line  30 , the cycler  14  can route used dialysate to the appropriate spike  160  and line  30 . As discussed above, since the spikes  160  of the cassette  24  all feed into a common channel, the input from any particular spike  160  can be routed in the cassette  24  in any desired way by controlling valves and other cassette features. 
     With lines  30  mounted, the carriage  146  may be moved to the left as shown in  FIG. 10  (again, while the door  141  is closed), positioning the caps  31  over a respective spike cap  63  on a spike  160  of the cassette  24  and adjacent a cap stripper  149 . The cap stripper  149  may extend outwardly (toward the door  141  from within a recess in the cycler  14  housing) to engage the caps  31 . (For example, the cap stripper  149  may include five fork-shaped elements that engage with a corresponding groove in the caps  31 , allowing the cap stripper  149  to resist left/right movement of the cap  31  relative to the cap stripper  149 .) By engaging the caps  31  with the cap stripper  149 , the caps  31  may also grip the corresponding spike cap  63 . Thereafter, with the caps  31  engaged with corresponding spike caps  63 , the carriage  146  and cap stripper  149  may move to the right, removing the spike caps  63  from the spikes  160  that are engaged with a corresponding cap  31 . (One possible advantage of this arrangement is that spike caps  63  are not removed in locations where no solution line  30  is loaded because engagement of the cap  31  from a solution line  30  is required to remove a spike cap  63 . Thus, if a solution line will not be connected to a spike  160 , the cap on the spike  160  is left in place.) The cap stripper  149  may then stop rightward movement (e.g., by contacting a stop), while the carriage  146  continues movement to the right. As a result, the carriage  146  may pull the terminal ends of the lines  30  from the caps  31 , which remain attached to the cap stripper  149 . With the caps  31  removed from the lines  30  (and the spike caps  63  still attached to the caps  31 ), the cap stripper  149  may again retract with the caps  31  into the recess in the cycler  14  housing, clearing a path for movement of the carriage  146  and the uncapped ends of the lines  30  toward the spikes  160 . The carriage  146  then moves left again, attaching the terminal ends of the lines  30  with a respective spike  160  of the cassette  24 . This connection may be made by the spikes  160  piercing an otherwise closed end of the lines  30  (e.g., the spikes may pierce a closed septum or wall in the terminal end), permitting fluid flow from the respective containers  20  to the cassette  24 . In an embodiment, the wall or septum may be constructed of a flexible and/or self-sealing material such as, for example, PVC, polypropylene, or silicone rubber. 
     In accordance with an aspect of the invention, the heater bag  22  may be placed in the heater bag receiving section (e.g., a tray)  142 , which is exposed by lifting a lid  143 . (In this embodiment, the cycler  14  includes a user or operator interface  144  that is pivotally mounted to the housing  82 , as discussed below. To allow the heater bag  22  to be placed into the tray  142 , the interface  144  may be pivoted upwardly out of the tray  142 .) As is known in the art, the heater tray  142  may heat the dialysate in the heater bag  22  to a suitable temperature, e.g., a temperature appropriate for introduction into the patient. In accordance with an aspect of the invention, the lid  143  may be closed after placement of the heater bag  22  in the tray  142 , e.g., to help trap heat to speed the heating process, and/or help prevent touching or other contact with a relatively warm portion of the heater tray  142 , such as its heating surfaces. In one embodiment, the lid  143  may be locked in a closed position to prevent touching of heated portions of the tray  142 , e.g., in the circumstance that portions of the tray  142  are heated to temperatures that may cause burning of the skin. Opening of the lid  143  may be prevented, e.g., by a lock, until temperatures under the lid  143  are suitably low. 
     In accordance with another aspect of the invention, the cycler  14  includes a user or operator interface  144  that is pivotally mounted to the cycler  14  housing and may be folded down into the heater tray  142 . With the interface  144  folded down, the lid  143  may be closed to conceal the interface  144  and/or prevent contact with the interface  144 . The interface  144  may be arranged to display information, e.g., in graphical form, to a user, and receive input from the user, e.g., by using a touch screen and graphical user interface. The interface  144  may include other input devices, such as buttons, dials, knobs, pointing devices, etc. With the set  12  connected, and containers  20  appropriately placed, the user may interact with the interface  144  and cause the cycler  14  to start a treatment and/or perform other functions. 
     However, prior to initiating a dialysis treatment cycle, the cycler  14  must at least prime the cassette  24 , the patient line  34 , heater bag  22 , etc., unless the set  12  is provided in a pre-primed condition (e.g., at the manufacturing facility or otherwise before being put into use with the cycler  14 ). Priming may be performed in a variety of ways, such as controlling the cassette  24  (namely the pumps and valves) to draw liquid from one or more solution containers  20  via a line  30  and pump the liquid through the various pathways of the cassette  24  so as to remove air from the cassette  24 . Dialysate may be pumped into the heater bag  22 , e.g., for heating prior to delivery to the patient. Once the cassette  24  and heater bag line  26  are primed, the cycler  14  may next prime the patient line  34 . In one embodiment, the patient line  34  may be primed by connecting the line  34  (e.g., by the connector  36 ) to a suitable port or other connection point on the cycler  14  and causing the cassette  24  to pump liquid into the patient line  34 . The port or connection point on the cycler  14  may be arranged to detect the arrival of liquid at the end of the patient line (e.g., optically, by conductive sensor, or other), thus detecting that the patient line is primed. As discussed above, different types of sets  12  may have differently sized patient lines  34 , e.g., adult or pediatric size. In accordance with an aspect of the invention, the cycler  14  may detect the type of cassette  24  (or at least the type of patient line  34 ) and control the cycler  14  and cassette  24  accordingly. For example, the cycler  14  may determine a volume of liquid delivered by a pump in the cassette needed to prime the patient line  34 , and based on the volume, determine the size of the patient line  34 . Other techniques may be used, such as recognizing a barcode or other indicator on the cassette  24 , patient line  34  or other component that indicates the patient line type. 
       FIG. 11  shows a perspective view of the inner side of the door  141  disconnected from the housing  82  of the cycler  14 . This view more clearly shows how the lines  30  are received in corresponding grooves in the door  141  and the carriage  146  such that the indicator region  33  is captured in a specific slot of the carriage  146 . With the indicator at indicator region  33  positioned appropriately when the tubing is mounted to the carriage  146 , a reader or other device can identify indicia of the indicator, e.g., representing a type of solution in the container  20  connected to the line  30 , an amount of solution, a date of manufacture, an identity of the manufacturer, and so on. The carriage  146  is mounted on a pair of guides  130  at top and bottom ends of the carriage  146  (only the lower guide  130  is shown in  FIG. 11 ). Thus, the carriage  146  can move left to right on the door  141  along the guides  130 . When moving toward the cassette mounting location  145  (to the right in  FIG. 11 ), the carriage  146  can move until it contacts stops  131 . 
       FIG. 11-1  and  FIG. 11-2  show a perspective view of a carriage  146 , and an enlarged perspective view of a solution line  30  loaded into the carriage  146 . In these illustrative embodiments, the carriage  146  may have the ability to move on the door  141  along the guide  130 . The carriage  146  may include five slots  1086 , and therefore may have the ability to support up to five solution lines  30 . Each slot  1086  may include three different sections; a solution line section  1088 , an ID section  1090 , and a clip  1092 . The solution line section  1088  may have a generally cylindrical shaped cavity that allows the solution lines  30  to remain organized and untangled when loaded into the carriage  146 . The clip  1092  may be located at the opposite end of each of the slots  1086 , relative to the solution line section  1088 . The purpose of the clip  1092  is to provide a secure housing for a membrane port  1094  located at the connector end  30   a  of the solution line  30 , and to prevent the solution line  30  from moving during treatment. 
     In one embodiment of the present disclosure, the clip  1092  may have a semicircular shape, and may include a middle region that extends slightly deeper than the two surrounding edge regions. The purpose of including the deeper middle region is to accommodate a membrane port flange  1096 . The flange  1096  may have a substantially greater radius than the rest of the membrane port. Therefore, the deeper middle region is designed to fit the wider flange  1096 , while the two edge regions provide support so that the membrane port  1094  is immobilized. Additionally, the deep middle region may have two cutouts  1098  positioned on opposite sides of the semicircle. The cutouts  1098  may have a generally rectangular shape so as to allow a small portion of the flange  1096  to extend into each of the cutouts  1098  when positioned in the clip  1092 . The cutouts  1098  may be formed so that the distance between the top edges of each cutout  1098  is slightly less than the radius of the flange  1096 . Therefore, a sufficient amount of force is required to snap the flange  1096  into the clip  1092 . Also, allowing for the distance between the top edges of the two cutouts  1098  to be less than the radius of the flange  1096  helps to keep the solution line  30  from inadvertently becoming dislodged during treatment. 
     In this illustrative embodiment, the carriage  146  may provide superior performance over previous designs because of its ability to counteract any deformation of the membrane ports  1094 . The carriage  146  is designed to stretch the membrane ports  1094  between the front of the flange  1096  and the back of the sleeve. If the membrane port  1094  is further stretched at any point during treatment, a wall in the carriage  146  may support the flange  1096 . 
     In accordance with another aspect of the present disclosure, the ID section  1090  may be positioned between the solution line section  1088  and the clip  1092 . The ID section  1090  may have a generally rectangular shape, thus having the ability to house an identification tag  1100  that may snap onto the solution line  30  at the indicator region  33 . The indicator region  33  may have an annular shape that is sized and configured to fit within the ID section  1090  when mounted in the carriage  146 . The identification tag  1100  may provide an indication as to the type of solution associated with each line  30 , the amount of solution, a date of manufacture, and an identity of the manufacturer. As shown in  FIG. 11-1 , the ID section  1090  may include a two dimensional (2-D) barcode  1102 , which may be imprinted on the bottom of the ID section  1090 . The barcode  1102  may be a Data Matrix symbol with 10 blocks per side, and may include an “empty” Data Matrix code. The barcode  1102  may be positioned on the carriage  146  underneath the identification tag  1100 , when the solution lines  30  are loaded into the carriage  146 . However, in an alternative embodiment, the barcode  1102  may be added to the ID section  1090  of the carriage  146  by way of a sticker or laser engraving. Also, in another embodiment, the barcode  1102  may include a Data Matrix that consists of varying dimensions of length and width, as well as varying numbers of blocks per side. 
     In this illustrative embodiment, however, the specific number of block per side, and the specific length and width of each barcode  1102  was specifically chosen in order to provide the most robust design under a variety of conditions. Using only 10 blocks per side may result in the barcode  1102  having larger blocks, which therefore ensures that the barcode  1102  is easily readable, even under the dark conditions that exist inside of the cycler housing  82 . 
       FIG. 11-3  and  FIG. 11-4  show a perspective view of a folded identification tag  1100 , and a perspective view of a carriage drive assembly  132  including an AutoID camera  1104  mounted to an AutoID camera board  1106  respectively. In accordance with an aspect of the present disclosure, the identification tag  1100  may be formed from an injection mold, and it may then fold to snap around the indicator region  33 . The identification tag  1100  may include edges that are rounded, which may prevent damage to the solution containers  20  during shipping. The identification tag  1100  may also include an 8×8 mm two dimensional (2-D) Data Matrix symbol  1103  with 18 blocks per side plus a quiet zone, which may be added by way of a sticker. The information contained in these Data Matrix symbols  1103  may be provided from the camera  1104  to the control system  16 , which may then obtain indicia, through various processes such as by way of image analysis. Therefore, the AutoID camera  1104  will have the ability to detect slots  1086  that contain a solution line  30  that is correctly installed, a line  30  that is incorrectly installed, or the absence of a line  30 . A solution line  30  that is correctly installed will allow the camera  1104  to detect the Data Matrix symbol  1103  located on the identification tag  1100 , the absence of a solution line  30  will allow the camera  1104  to detect an “empty” Data Matrix barcode  1102  located on the carriage  146  underneath the membrane port  1094 , and a solution line  30  that is incorrectly loaded will occlude the “empty” Data Matrix barcode  1102 , resulting in no Data Matrix being decoded by the camera  1104  for that slot. Thus, the camera  1104  should always decode a Data Matrix in every slot  1086  on the carriage  146 , baring an incorrectly loaded solution line  30 . 
     In this illustrative embodiment, ability to detect features of a solution line  30  by way of an identification tag  1100  located at indicator region  33  may provide benefits such as allowing a user to position lines  30  in any location of the carriage  146  without having an effect on system operation. Additionally, since the cycler  14  can automatically detect solution line features, there is no need to ensure that specific lines  30  are positioned in particular locations on the carriage  146  for the system to function properly. Instead, the cycler  14  may identify which lines  30  are where, and control the cassette  24  and other system features appropriately. 
     In accordance with another aspect of the disclosure, the identification tag  1100  must face into the carriage drive assembly  132  in order to be decoded by the camera  1104 . To ensure this, the carriage  146  and identification tag  1100  may have complementary alignment features. Additionally, the solution lines  30  with identification tags  1100  should also fit within the Cleanflash machine, thus, the solution line  30  with identification tag  1100  may be constructed to fit within a 0.53 inch diameter cylinder. In an embodiment, the alignment feature may be a simple flat bottomed bill on the identification tag  1100  and matching rib in the carriage  146 . In one embodiment of the present disclosure, the bill and rib may slightly interfere, forcing the back of the identification tag  1100  in an upward direction. While this configuration may create a small amount of misalignment, it reduces misalignment in the other axis. Finally, to ensure that the identification tag  1100  is properly seated, the front of the carriage drive assembly  132  can be designed with only about 0.02 inch of clearance over the present carriage  146  and identification tag  1100  alignment. 
     In accordance with another aspect of the disclosure, the AutoID camera board  1106  may be mounted to the back of the carriage drive assembly  132 . Additionally, the AutoID camera  1104  may be mounted to the camera board  1106 . The camera board  1106  may be placed approximately 4.19 inches from the identification tag  1100 . However, in an alternative embodiment, the camera board  1106  may be moved backward without any serious consequences. A plastic window  1108  may also be attached to the front of the carriage drive assembly  132 , which may allow the identification tags  1100  to be imaged while also preventing fluid and finger ingress. The AutoID camera  1104  may include a camera lens, which may be any type of lens, such as those used for security applications, or lenses intended for camera phones with the IR filter removed. In accordance with an aspect of the present disclosure, the camera lens may consist of a small size, light weight, low cost, and high image quality. 
     Additionally, a single SMD IR LED  1110  may be attached to the camera board  1106 . The LED  1110  may then illuminate the identification tags  1100  so that the camera  1104  may easily decode the Data Matrices. It is important that the identification tags  1100  be illuminated because the environment inside of the cycler housing  82  is mostly absent of light. Therefore, without the LED  1110  to illuminate the identification tags  1100  the camera  1104  would be unable to decode the Data Matrixes. Furthermore, to avoid creating glare in front of the identification tags  1100 , the LED  1110  may be mounted 0.75 inch away from the camera  1104 . An FPGA may also be mounted to the camera board  1106 , and may act as an intermediary between the OV3640 image sensor and Voyager&#39;s UI processor. In addition to making the processor&#39;s job easier, this architecture may allow for a different image sensor to be used without a change to any other Voyager hardware or software. Finally, image decoding is handled by the open source package libdmtx, which is addressable from a number of programming languages and can run from a command line for testing. 
       FIG. 12  shows a perspective view of a carriage drive assembly  132  in a first embodiment that functions to move the carriage  146  to remove the caps from spikes  160  on the cassette, remove caps  31  on the solution lines  30  and connect lines  30  to the spikes  160 . A drive element  133  is arranged to move left to right along rods  134 . In this illustrative embodiment, an air bladder powers the movement of the drive element  133  along the rods  134 , but any suitable drive mechanism may be used, including motors, hydraulic systems, etc. The drive element  133  has forwardly extending tabs  135  that engage with corresponding slots  146   a  on the carriage  146  (see  FIG. 11 , which shows a top slot  146   a  on the carriage  146 ). Engagement of the tabs  135  with the slots  146   a  allow the drive element  133  to move the carriage  146  along the guides  130 . The drive element  133  also includes a window  136 , through which an imaging device, such as a CCD or CMOS imager, may capture image information of the indicators at indicator regions  33  on the lines  30  mounted to the carriage  146 . Image information regarding the indicators at indicator regions  33  may be provided from the imaging device to the control system  16 , which may obtain indicia, e.g., by image analysis. The drive element  133  can selectively move the cap stripper  149  both to the left and right along the rods  134 . The cap stripper  149  extends forward and back using a separate drive mechanism, such as a pneumatic bladder. 
       FIG. 13  shows a left side perspective view of the carriage drive assembly  132 , which more clearly shows how a stripper element of the cap stripper  149  is arranged to move in and out (a direction generally perpendicular to the rods  134 ) along grooves  149   a  in the housing of the cap stripper  149 . Each of the semicircular cut outs of the stripper element may engage a corresponding groove of a cap  31  on a line  30  by extending forwardly when the cap  31  is appropriately positioned in front of the stripper  149  by the drive element  133  and the carriage  146 . With the stripper element engaged with the caps  31 , the cap stripper  149  may move with the carriage  146  as the drive element  133  moves.  FIG. 14  shows a partial rear view of the carriage drive assembly  132 . In this embodiment, the drive element  133  is moved toward the cassette  24  mounting location  145  by a first air bladder  137  which expands to force the drive element  133  to move to the right in  FIG. 14 . The drive element can be moved to the left by a second air bladder  138 . Alternatively, drive element  133  can be moved back and forth by means of one or more motors coupled to a linear drive gear assembly, such as a ball screw assembly (in which the carriage drive assembly is attached to a ball nut), or a rack and pinion assembly, for example. The stripper element  1491  of the cap stripper  149  can be moved in and out of the cap stripper housing by a third bladder, or alternatively, by a motor coupled to a linear drive assembly, as described previously. 
       FIGS. 15-18  show another embodiment of a carriage drive assembly  132  and cap stripper  149 . As can be seen in the rear view of the carriage drive assembly  132  in  FIG. 15 , in this embodiment the drive element  133  is moved right and left by a screw drive mechanism  1321 . As can be seen in the right rear perspective view of the carriage drive assembly  132  in  FIG. 16 , the stripper element is moved outwardly and inwardly by an air bladder  139 , although other arrangements are possible as described above. 
       FIGS. 17 and 18  show left and right front perspective views of another embodiment for the stripper element  1491  of the cap stripper  149 . The stripper element  1491  in the embodiment shown in  FIG. 13  included only fork-shaped elements arranged to engage with a cap  31  of a solution line  30 . In the  FIGS. 17 and 18  embodiment, the stripper element  1491  not only includes the fork-shaped elements  60 , but also rocker arms  61  that are pivotally mounted to the stripper element  1491 . As will be explained in more detail below, the rocker arms  61  assist in removing spike caps  63  from the cassette  24 . Each of the rocker arms  61  includes a solution line cap engagement portion  61   a  and a spike cap engagement portion  61   b . The rocker arms  61  are normally biased to move so that the spike cap engagement portions  61   b  are positioned near the stripper element  1491 , as shown in the rocker arms  61  in  FIG. 18 . However, when a cap  31  is received by a corresponding fork-shaped element  60 , the solution line cap engagement portion  61   a  contacts the cap  31 , which causes the rocker arm  61  to pivot so that the spike cap engagement portion  61   b  moves away from the stripper element  1491 , as shown in  FIG. 17 . This position enables the spike cap engagement portion  61   b  to contact a spike cap  63 , specifically a flange on the spike cap  63 . 
       FIG. 19  shows a front view of the stripper element  1491  and the location of several cross-sectional views shown in  FIGS. 20-22 .  FIG. 20  shows the rocker arm  61  with no spike cap  63  or solution line cap  31  positioned near the stripper element  1491 . The rocker arm  61  is pivotally mounted to the stripper element  1491  at a point approximately midway between the spike cap engagement portion  61   b  and the solution cap engagement portion  61   a . As mentioned above, the rocker arm  61  is normally biased to rotate in a counterclockwise direction as shown in  FIG. 20  so that the spike cap engagement portion  61   b  is positioned near the stripper element  1491 .  FIG. 21  shows that the rocker arm  61  maintains this position (i.e., with the spike cap engagement portion  61   b  located near the stripper element  1491 ) even when the stripper element  1491  advances toward a spike cap  63  in the absence of a solution line cap  31  engaging with the fork-shaped element  60 . As a result, the rocker arm  61  will not rotate clockwise or engage the spike cap  63  unless a solution line cap  31  is present. Thus, a spike cap  63  that does not engage with a solution line cap  31  will not be removed from the cassette  24 . 
       FIG. 22  shows an example in which a solution line cap  31  is engaged with the fork-shaped element  60  and contacts the solution line cap engagement portion  61   a  of the rocker arm  61 . This causes the rocker arm  61  to rotate in a clockwise direction (as shown in the figure) and the spike cap engagement portion  61   b  to engage with the spike cap  63 . In this embodiment, engagement of the portion  61   b  includes positioning the portion  61   b  adjacent a second flange  63   a  on the spike cap  63  so that when the stripper element  1491  moves to the right (as shown in  FIG. 22 ), the spike cap engagement portion  61   b  will contact the second flange  63   a  and help pull the spike cap  63  from the corresponding spike  160 . Note that the solution line cap  31  is made of a flexible material, such as silicone rubber, to allow a barb  63   c  of the spike cap  63  to stretch the hole  31   b  of cap  31  (see  FIG. 23 ) and be captured by a circumferential inner groove or recess within cap  31 . A first flange  63   b  on the spike cap  63  acts as a stop for the end of solution line cap  31 . In another example, the spike cap  63  does not include a first flange  63   b . The walls defining the groove or recess in the cap  31  hole  31   b  may be symmetrical, or preferably asymmetrically arranged to conform to the shape of the barb  63   c . (See  FIG. 33  for a cross sectional view of the cap  31  and the groove or recess.) The second flange  63   a  on spike cap  63  acts as a tooth with which the spike cap engagement portion  61   b  of the rocker arm  61  engages in order to provide an additional pulling force to disengage the spike cap  63  from the spike  160 , if necessary. 
       FIG. 11-5  and  FIG. 11-6  show two different perspective views of another embodiment for the stripper element  1491  of the cap stripper  149 . The stripper element  1491  in the embodiment shown in  FIG. 13  uses fork-shaped elements  60  arranged to engage with a cap  31  of a solution line  30 . In the embodiment shown in  FIG. 11-5 , the stripper element  1491  not only includes the fork-shaped elements  60 , but may also include a plurality of sensing elements  1112 , and a plurality of rocker arms  1114 . The sensing elements  1112  and rocker arms  1114  may be arranged in two parallel columns that run vertically along the stripper element  1491 . In an embodiment, each vertical column may contain five individual sensing elements  1112  and rocker arms  1114 , each being positioned to generally align in a row corresponding with each of the fork-shaped elements  60 . Each sensing element  1112  may be mechanically connected or linked to one of the corresponding rocker arms  1114 . In addition, the assembly comprising each sensing element  1112  and rocker arm  1114  may include a biasing spring (not shown) that keeps each rocker arm  1114  biased toward a non-engagement position and sensing element  1112  in a position to be contacted and moved by the presence of a solution line cap  31  in fork-shaped element  60 . Each sensing element  1112  can be displaced and tilted toward the back of the stripper element  1491  by contact with a corresponding solution line cap  31  in forked-shaped element  60 . Through the mechanical connection between sensing element  1112  and rocker arm  1114 , rocker arm  1114  can pivotally rotate or tilt laterally toward spike cap  63  upon contact between solution line cap  31  and sensing element  1112 . As rocker arm  1114  rotates or tilts toward spike cap  63 , it can engage second flange  63   a  on spike cap  63 , allowing the stripper assembly to remove spike cap  63  from its corresponding spike. 
       FIGS. 11-7   a - c  illustrate the relationship between sensing element  1112  and a solution line cap  31 , and between rocker arm  1114  and spike cap  63 .  FIG. 11-7   c  shows the sensing element  1112  and rocker arm  1114  in the absence of a spike cap  63  and solution line cap  31 . As shown in  FIG. 11-7   b , an outer flange  31   c  of solution line cap  31  has a diameter sufficiently large to make contact with sensing element  1112 . As shown in  FIG. 11-7   a , in the absence of a solution line cap  31 , the mere presence of spike cap  63  alone does not contact sensing element  1112  sufficiently enough to displace it and cause it to rotate away from spike cap  63 . As shown in  FIG. 11-7   b , the displacement of sensing element  1112  causes rotation or tilting of rocker arm  1114  toward spike cap  63 , ultimately to the point of being positioned adjacent flange  63   a  of spike cap  63 . As shown in  FIG. 11-7   a , when rocker arm  1114  is in a non-deployed position, it can clear the outer circumference of second flange  63   a  of spike cap  63  by a pre-determined amount (e.g., 0.040 inch). Upon movement of rocker arm  1114  into a deployed position, its range of travel may be configured so as to provide a slight compression force against its corresponding spike cap  63  to ensure a secure engagement. 
     Once a rocker arm  1114  is positioned adjacent flange  63   a  of a spike cap  63 , movement of stripper element  1491  to the right will engage spike cap  63  via flange  63   a  and help to pull spike cap  63  from its corresponding spike  160 . In the absence of a solution line and its associated solution line cap  31 , stripper element  1491  will not remove the corresponding spike cap  63 , keeping its associated spike  160  sealed. Thus, fewer than the maximum number of cassette spikes  161  may be accessed when fewer than the maximum number of solution lines need to be used. 
       FIG. 23  shows a close-up exploded view of the connector end  30   a  of a solution line  30  with the cap  31  removed. (In  FIG. 23 , the caps  31  are shown without a finger pull ring like that shown in  FIG. 24  for clarity. A pull ring need not be present for operation of the cap  31  with the cycler  14 . It may be useful, however, in allowing an operator to manually remove the cap  31  from the terminal end of solution line  30 , if necessary). In this illustrative embodiment, the indicator at indicator region  33  has an annular shape that is sized and configured to fit within a corresponding slot of the carriage  146  when mounted as shown in  FIGS. 10 and 11 . Of course, the indicator may take any suitable form. The cap  31  is arranged to fit over the extreme distal end of the connector end  30   a , which has an internal bore, seals, and/or other features to enable a leak-free connection with a spike  160  on a cassette  24 . The connector end  30   a  may include a pierceable wall or septum (not shown—see  FIG. 33  item  30   b ) that prevents leakage of solution in the line  30  from the connector end  30   a , even if the cap  31  is removed. The wall or septum may be pierced by the spike  160  when the connector end  30   a  is attached to the cassette  24 , allowing flow from the line  30  to the cassette  24 . As discussed above, the cap  31  may include a groove  31   a  that is engaged by a fork-shaped element  60  of the cap stripper  149 . The cap  31  may also include a hole  31   b  that is arranged to receive a spike cap  63 . The hole  31   b  and the cap  31  may be arranged so that, with the cap stripper  149  engaged with the groove  31   a  and the spike cap  63  of a spike  160  received in the hole  31   b , the cap  31  may grip the spike cap  63  suitably so that when the carriage  146 /cap stripper  149  pulls the cap  31  away from the cassette  24 , the spike cap  63  is removed from the spike  160  and is carried by the cap  31 . This removal may be assisted by the rocker arm  61  engaging with the second flange  63   a  or other feature on the spike cap  63 , as described above. Thereafter, the cap  31  and spike cap  63  may be removed from the connector end  30   a  and the line  30  attached to the spike  160  by the carriage  146 . 
     Solution Line Connector Heater 
     In one embodiment, a connector heater may be provided near the indicator region  33  of the solution lines  30 . The connector heater may control the temperature of the connector end  30   a  and in particular the pierceable wall or septum  30   b  in order to limit the carriage force required attach the solution lines to the spikes  160  on the cassette  24 . There may be enough variation in ambient (room) temperature to affect the hardness of the pierceable wall or septum  30   b  of the connector end  30   a  of the solution line, which may in turn affect the performance of the carriage  146  in joining the spike  160  to the connector end  30   a  of the solution line  30 . For example, at lower ambient temperatures, the increased hardness of the pierceable wall or septum  30   b  may require a greater force for spike  160  to penetrate it. On the other hand, at higher ambient temperatures, the pierceable wall or septum may be so soft as to deform rather than separate when contacted by the spike  160 . 
     The temperature of the connector ends  30   a  may be controlled in a number of ways, which may include placing a heating element in an appropriate location (e.g., at or near location  2807  on the door  141 ), installing a temperature sensor to monitor the temperature of connector ends  30   a , and using a controller to receive temperature data and modulate the operation of the heating element. The temperature may be measured by a temperature sensor element mounted on the stripper element  1491  or on the carriage  146 . Alternatively, the temperature of the connector end  30   a  may be determined using an infra-red (IR) sensor tuned to measure surface temperature of the connector end  30   a.    
     The controller may be a software process in the automation computer  300 . Alternatively, the controller may be implemented in the hardware interface  310 . The controller may modulate the power sent to a resistance heater, for example, in one of a number of ways. For example, the controller may send a PWM signal to a MOSFET that can modulate the flow of electrical power to the resistance heater. The controller may control the measured temperature to the desired temperature through a number of algorithms. One exemplary algorithm includes a proportional-integral (PI) feedback loop on the measured temperature to set the heater power. Alternatively, the heater power can be modulated in an open loop algorithm that sets the heater power based on the measured ambient temperature. 
     In another embodiment, the temperature of the connector end  30   a  may be controlled by mounting a radiant heater in the door  141  at location  2807 , for example, and aimed at the connector ends. Alternatively, the temperature of the connector ends may be controlled by mounting a thermo-electric element at location  2807 , for example, on the door  141 . The thermo-electric element may provide either heating or cooling to the area surrounding the connector ends when mounted on the carriage  146 . The radiant heater or thermo-electric element may be modulated by a controller to maintain the temperature within a given range. The preferred temperature range for the connector end  30   a  depends on the material comprising the pierceable wall or septum, and may be determined empirically. In one embodiment, the piercable wall is PVC and the preferred temperature range is set at about 10° C. to 30° C., or more preferably to a temperature range of about 20° C. to 30° C. 
     In an embodiment, the connector heater near the indicator region  33  may be used after the door is closed and before the solution lines  30  are attached to the cassette  24 . The automation computer  300  or a controller enables the connector heater if the measured temperature near the connector  30   a  is outside a preferred range. The automation computer  300  or a controller may delay the auto-connection process until the measured temperature is within the preferred range. The connector heater may be disabled after the auto-connection process is completed. 
     Once treatment is complete, or the line  30  and/or the cassette  24  are ready for removal from cycler  14 , the cap  31  and attached spike cap  63  may be re-mounted on the spike  160  and the line  30  before the door  141  is permitted to be opened and the cassette  24  and line  30  removed from the cycler  14 . Alternatively, the cassette  24  and solution containers with lines  30  can be removed en bloc from cycler  14  without re-mounting cap  31  and the attached spike cap  63 . An advantage of this approach includes a simplified removal process, and avoidance of any possible fluid leaks onto the cycler or surrounding area from improperly re-mounted or inadequately sealing caps. 
       FIGS. 24-32  show a perspective view of the carriage  146 , cap stripper  149  and cassette  24  during a line mounting and automatic connection operation. The door  141  and other cycler components are not shown for clarity. In  FIG. 24 , the carriage  146  is shown in a folded down position, as if the door  141  is open in the position shown in  FIG. 0.8 . The lines  30  and cassette  24  are positioned to be lowered onto the door  141 . In  FIG. 25 , the lines  30  are loaded into the carriage  146  and the cassette  24  is loaded into the mounting location  145 . At this point the door  141  can be closed to ready the cycler for operation. In  FIG. 26 , the door  141  is closed. Identifiers or indicators located at indicator region  33  on the lines  30  may be read to identify various line characteristics so that the cycler  14  can determine what solutions, how much solution, etc., are loaded. In  FIG. 27 , the carriage  146  has moved to the left, engaging the caps  31  on the lines  30  with corresponding spike caps  63  on the cassette  24 . During the motion, the drive element  133  engages the cap tripper  149  and moves the cap stripper  149  to the left as well. However, the cap stripper  149  remains in a retracted position. In  FIG. 28 , the cap stripper  149  moves forward to engage the fork-shaped elements  60  with the caps  31 , thereby engaging the caps  31  that have been coupled to the spike caps  63 . If present, the rocker arms  61  may move to an engagement position with respect to the spike caps  63 . Next, as shown in  FIG. 29 , the carriage  146  and the cap stripper  149  move to the right, away from the cassette  24  so as to pull the caps  31  and spike caps  63  from the corresponding spikes  160  on the cassette  24 . It is during this motion that the rocker arms  61 , if present, may assist in pulling spike caps  63  from the cassette  24 . In  FIG. 30 , the cap stripper  149  has stopped its movement to the right, while the carriage  146  continues to move away from the cassette  24 . This causes the connector ends  30   a  of the lines  30  to be pulled from the caps  31 , leaving the caps  31  and spike caps  63  mounted on the cap stripper  149  by way of the fork-shaped elements  60 . In  FIG. 31 , the cap stripper  149  retracts, clearing a path for the carriage  146  to move again toward the cassette  24 . In  FIG. 32 , the carriage  146  moves toward the cassette  24  to engage the connector ends  30   a  of the lines  30  with the corresponding spikes  160  of the cassette  24 . The carriage  146  may remain in this position during cycler operation. Once treatment is complete, the movements shown in  FIGS. 24-32  may be reversed to recap the spikes  160  and the solution lines  30  and remove the cassette  24  and/or lines  30  from the cycler  14 . 
     To further illustrate the removal of caps  31  and spike caps  63 ,  FIG. 33  shows a cross-sectional view of the cassette  24  at five different stages of line  30  connection. At the top spike  160 , the spike cap  63  is still in place on the spike  160  and the solution line  30  is positioned away from the cassette  24 , as in  FIG. 26 . At the second spike  160  down from the top, the solution line  30  and cap  31  are engaged over the spike cap  63 , as in  FIGS. 27 and 28 . At this point, the cap stripper  149  may engage the cap  31  and spike cap  63 . At the third spike  160  from the top, the solution line  30 , cap  31  and spike cap  63  have moved away from the cassette  24 , as in  FIG. 29 . At this point, the cap stripper  149  may stop movement to the right. At the fourth spike  160  from the top, the solution line  30  continues movement to the right, removing the cap  31  from the line  30 , as in  FIG. 30 . Once the caps  31  and  63  are retracted, the solution line  30  moves to the left to fluidly connect the connector end  30   a  of the line  30  to the spike  160 , as in  FIG. 32 . 
     Various sensors can be used to help verify that the carriage  146  and cap stripper  149  move fully to their expected positions. In an embodiment, the carriage drive assembly  132  can be equipped with six Hall effect sensors (not shown): four for the carriage  146  and two for the cap stripper  149 . A first cap stripper sensor may be located to detect when the cap stripper  149  is fully retracted. A second cap stripper sensor may be located to detect when the cap stripper  149  is fully extended. A first carriage sensor may be located to detect when the carriage  146  is in the “home” position, i.e. in position to permit loading the cassette  24  and lines  30 . A second carriage sensor may be located to detect when the carriage  146  is in position to have engaged the spike caps  63 . A third carriage sensor may be located to detect when the carriage  146  has reached a position to have removed the caps  31  from the lines  30 . A fourth carriage sensor may be located to detect when the carriage  146  has moved to a position to have engaged the connector ends  30   a  of the lines  30  with the corresponding spikes  160  of the cassette  24 . In other embodiments, a single sensor can be used to detect more than one of the carriage positions described above. The cap stripper and carriage sensors can provide input signals to an electronic control board (“autoconnect board”), which in turn can communicate specific confirmation or error codes to the user via the user interface  144 . 
       FIG. 11-6  shows a perspective view of an alternative embodiment of the carriage drive assembly  132 . The carriage drive assembly  132  in the embodiment shown in  FIG. 12  included only the drive element  133 , the rods  134 , the tabs  136 , and the window  136 . In the  FIG. 11-6  embodiment, the carriage drive assembly  132  not only includes the drive element  133 , the rods  134 , the tabs  136 , and the window  136 , but may also include a vertical column of AutoID view boxes  1116 . The view boxes  1116  may be positioned directly adjacent to the window  136 . Also, the view boxes  1116  may be positioned and shaped so that the horizontal axis of each of the five slots  1086  located on the carriage  146  run through the center of a corresponding view box  1116 , when the carriage  146  moves either right or left along the guides  130 . The view boxes  1116  may allow for the AutoID camera  1104 , which is attached to the camera board  1106 , to detect if the solution line caps  31  are positioned on the lines  30  prior to the engaging of the solution lines with the spike cap  63 . This may allow for confirmation that the user hasn&#39;t removed the caps  31  prematurely. Once the presence or absence of the caps  31  is determined, the camera  1104  can provide a corresponding input signal to an electronic control board (referred to as the autoconnect board later in the specification), which in turn can communicate specific confirmation or error codes, relating to the presence of the caps  31  on the lines  30 , to the user via the user interface  144 . 
     In accordance with another aspect of the disclosure, the carriage drive assembly  132  may include an autoconnect board  1118 . The autoconnect board  1118  may be attached to the top of the carriage drive assembly  132 , and may extend the entire length of the assembly  132 . In this illustrative embodiment, there may also be an LED  1120  mounted to the autoconnect board  1118 . The LED  1120  may be located in a fixed position directly above the fork-shaped elements  60 . Also, the LED  1120  may be directed is a fashion so that the light being emitted from the LED  1120  travels downward across the stripper element  1491 . In accordance with another aspect of the present disclosure, the carriage drive assembly  132  may also include a fluid board  1122 . The fluid board  1122  may be attached to the bottom of the carriage drive assembly  132 , and may also extent the length of the assembly  132 . In this illustrative embodiment, there may be a receiver  1124  (not pictured) mounted to the fluid board  1122  at a location directly below the LED  1120 , which is mounted to the autoconnect board  1118 . Therefore, the LED  1120  can emit light across the fork-shaped elements  60 , and if the light it detected by the receiver  1124  then there are no solution line caps  31  left in the stripper element  1491 , however, if the light is interrupted on its way towards the receiver  1124  then there may be a cap  31  left in the stripper element  1491 . This LED  1120  and receiver  1124  combination allows for the detection of caps  31  that may have been inadvertently left in the stripper element  1491  either by the user or by the cycler  14 . In accordance with an aspect of the disclosure, the fluid board  1122  may also have the ability to detect humidity, moisture, or any other liquid that may be present inside of the carriage drive assembly  132 , which could potentially cause the cycler  14  to fail. 
     There may be an advantage in adjusting the force with which the carriage  146  engages the spike caps  63 , depending on how many lines  30  are being installed. The force required to complete a connection to the cassette  24  increases with the number of caps  31  that must be coupled to spike caps  63 . The sensing device for detecting and reading information from the line indicators at indicator regions  33  can also be used to provide the data required to adjust the force applied to drive element  133 . The force can be generated by a number of devices, including, for example, the first air bladder  137 , or a linear actuator such as a motor/ball screw. An electronic control board (such as, for example, the autoconnect board) can be programmed to receive input from the line detection sensor(s), and send an appropriate control signal either to the motor of a linear actuator, or to the pneumatic valve that controls inflation of air bladder  137 . The controller  16  can control the degree or rate of movement of drive element  133 , for example by modulating the voltage applied to the motor of a linear actuator, or by modulating the pneumatic valve controlling the inflation of bladder  137 . 
     In accordance with an aspect of the present disclosure, it may be necessary for the carriage drive assembly  132  to be capable of generating a force of at least 550 N (124 lbf) on carriage  146 , in order to engage the membrane ports with spikes  160 . This force is to be measured in the carriage direction of the membrane port spiking onto the cassette  24 . The maximum force required to spike a sterilized PVC membrane port onto the spike  160  may be 110 N. Additionally, the maximum force required to spike a sterilized JPOC membrane port onto the spike  160  may be 110 N. These force requirements ensure carriage drive assembly  132  is able to spike five JPOC ports. In an alternative embodiment, the PVC port force requirement may be lowered further based on current insertion forces. 
     The aspect of the invention by which caps  31  on lines  30  are removed together with caps  63  on spikes  160  of the cassette  24  may provide other advantages aside from simplicity of operation. For example, since spike caps  63  are removed by way of their engagement with a cap  31  on a line  30 , if there is no line  30  mounted at a particular slot on the carriage  146 , the spike cap  63  at that position will not be removed. For example, although the cassette  24  includes five spikes  160  and corresponding spike caps  63 , the cycler  14  can operate with four or less (even no) lines  30  associated with the cycler  14 . For those slots on the carriage  146  where no line  30  is present, there will be no cap  31 , and thus no mechanism by which a spike cap  63  at that position can be removed. Thus, if no line  30  will be connected to a particular spike  160 , the cap  63  on that spike  160  may remain in place during use of the cassette  24 . This may help prevent leakage at the spike  160  and/or contamination at the spike  160 . 
     The cassette  24  in  FIG. 33  includes a few features that are different from those shown, for example, in the embodiment shown in  FIGS. 3, 4 and 6 . In the  FIGS. 3, 4 and 6  embodiment, the heater bag port  150 , drain line port  152  and patient line port  154  are arranged to have a central tube  156  and a skirt  158 . However, as mentioned above and shown in  FIG. 33 , the ports  150 ,  152 ,  154  may include only the central tube  156  and no skirt  158 . This is also shown in  FIG. 34 . The embodiment depicted in  FIG. 34  includes raised ribs formed on the outside surface of the left-side pump chamber  181 . The raised ribs may also be provided on the right-side pump chamber  181 , and may provide additional contact points of the outside walls of pump chambers  181  with the mechanism in the door  141  at the cassette mounting location  145 , which presses the cassette against the control surface  148  when the door  141  is closed. The raised ribs are not required, and instead the pump chambers  181  may have no rib or other features, as shown for the right-side pump chamber  181  in  FIG. 34 . Similarly, the spikes  160  in the  FIGS. 3, 4 and 6  embodiment include no skirt or similar feature at the base of the spike  160 , whereas the embodiment in  FIG. 33  includes a skirt  160   a . This is also shown in  FIG. 34 . The skirt  160   a  may be arranged to receive the end of the spike cap  63  in a recess between the skirt  160   a  and the spike  160 , helping to form a seal between the spike  160  and the spike cap  63 . 
     Another inventive feature shown in  FIG. 33  relates to the arrangement of the distal tip of the spike  163  and the lumen  159  through the spike  160 . In this aspect, the distal tip of the spike  160  is positioned at or near the longitudinal axis of the spike  160 , which runs generally along the geometric center of the spike  160 . Positioning the distal tip of the spike  160  at or near the longitudinal axis may help ease alignment tolerances when engaging the spike  160  with a corresponding solution line  30  and help the spike  160  puncture a septum or membrane  30   b  in the connector end  30   a  of the line  30 . As a result, the lumen  159  of the spike  160  is located generally off of the longitudinal axis of the spike  160 , e.g., near a bottom of the spike  160  as shown in  FIG. 33  and as shown in an end view of a spike  160  in  FIG. 35 . Also, the distal end of the spike  160  has a somewhat reduced diameter as compared to more proximal portions of the spike  160  (in this embodiment, the spike  160  actually has a step change in diameter at about ⅔ of the length of the spike  160  from the body  18 ). The reduced diameter of the spike  160  at the distal end may provide clearance between the spike  160  and the inner wall of the line  30 , thus allowing the septum  30   b  a space to fold back to be positioned between the spike  160  and the line  30  when pierced by the spike  160 . The stepped feature  160   b  on the spike  160  (shown, e.g., in  FIG. 35A ) may also be arranged to engage the line  30  at the location where the septum  30   b  is connected to the inner wall of the line  30 , thus enhancing a seal formed between the line  30  and the spike  160 . 
     In another embodiment, as shown in  FIG. 35A , the length of the base  160   c  of spike  160  may be shortened to reduce the force required to remove the spike cap  63  from spike  160 , or to reduce the force required to spike the connector end  30   a  of solution line  30 . Shortening the base  160   c  reduces the area of frictional contact between spike  160  and its cap  63 , or between spike  160  and the internal surface of connector end  30   a . In addition, the skirt  160   a  at the base of spike  160  may be replaced by individual posts  160   d . The posts  160   d  allow the spike cap  63  to be properly seated onto spike  160  while also allowing for more thorough circulation of sterilization fluid or gas around spike  160  during the sterilization process prior to or after packaging of the dialysate delivery set  12 . 
     To more fully take advantage of the embodiment shown in  FIG. 35A , a spike cap  64 , as shown in  FIG. 35B  may be used. A skirt  65  on the base of spike cap  64  is constructed to fit snugly over the posts  160   d  of the base of spike  160  shown in  FIG. 35A . In addition, interrupted ribs  66 ,  67  within the inner circumference of the base of spike  160  may provide a snug fit between spike cap  64  and the base  160   c  of spike  160 , while also permitting sterilizing gas or fluid to penetrate more distally over the base of a capped spike  160 . As shown in  FIG. 35C , in a cross-sectional view of spike cap  64 , a set of three inner ribs  66 ,  67 ,  68  may be used to provide a snug fit between spike cap  64  and the base  160   c  of spike  160 . In an embodiment, rib  66  and rib  67  have interruptions or gaps  66   a  and  67   a  along their circumference to permit gas or fluid external to the cassette to flow over the base  160   c  of spike  160 . A third rib  68  may be circumferentially intact in order to make a sealing engagement between spike cap  64  and the base  160   c  of spike  160 , sealing off the base  160   c  from rest of the external surface of spike  160 . In other embodiments, ribs within spike cap  64  may be oriented longitudinally rather than circumferentially, or in any other orientation to provide a snug fit between spike cap  64  and spike  160 , while also permitting an external gas or fluid to make contact with the outside of the base  160   c  of spike  160 . In the embodiment shown, for example, the outer surface of the cassette, spike cap and most of the base  160   c  of spike  160  can be sterilized by exposing the cassette externally to ethylene oxide gas. Because the diameter of the stepped feature  160   b  and the distal end of spike  160  are smaller than the inner diameter of the overlying portion of spike cap  64 , any gas or fluid entering the spike lumen from within the cassette can reach the outer surface of spike  160  up to the sealing rib  68 . Thus any sterilizing gas such as ethylene oxide entering the fluid passages of the cassette may reach the remainder of the external surface of spike  160 . In an embodiment, the gas may enter the cassette through a vented cap, for example, on the end of patient line  34  or drain line  28 . 
     The spike cap  34  may include 3 or more centering ribs  64 D that contact the end of the spike  160 . The ribs  64 D are oriented along the major access of spike cap  34  and located near the closed end of the spike cap  34 . Preferably there are at least three ribs  63 D to center the closed end of the cap on the spike without over constraining the cap/spike orientation. The spike cap  64  includes a tapered end with a blunt tip to facilitate the penetration of the spike cap  34  into the hole  31   b  of the solution cap  31 . The tapered end will guide the spike cap  34  if it misaligned with the hole  31   b . The blunt tip avoids snagging the solution cap  31  unlike a sharp tip that might catch the inside edge of the hole  31   b  and dig into the solution cap material. In contrast a blunt tip can slide past the edges of the hole  31   b.    
     Once the cassette  24  and lines  30  are loaded into the cycler  14 , the cycler  14  must control the operation of the cassette  24  to move fluid from the solution lines  30  to the heater bag  22  and to the patient.  FIG. 36  shows a plan view of the control surface  148  of the cycler  14  that interacts with the pump chamber side of the cassette  24  (e.g., shown in  FIG. 6 ) to cause fluid pumping and flowpath control in the cassette  24 . When at rest, the control surface  148 , which may be described as a type of gasket, and comprise a sheet of silicone rubber, may be generally flat. Valve control regions  1481  may (or may not) be defined in the control surface  148 , e.g., by a scoring, groove, rib or other feature in or on the sheet surface, and be arranged to be movable in a direction generally transverse to the plane of the sheet. By moving inwardly/outwardly, the valve control regions  1481  can move associated portions of the membrane  15  on the cassette  24  so as to open and close respective valve ports  184 ,  186 ,  190  and  192  of the cassette  24 , and thus control flow in the cassette  24 . Two larger regions, pump control regions  1482 , may likewise be movable so as to move associated shaped portions  151  of the membrane  15  that cooperate with the pump chambers  181 . Like the shaped portions  151  of the membrane  15 , the pump control regions  1482  may be shaped in a way to correspond to the shape of the pump chambers  181  when the control regions  1482  are extended into the pump chambers  181 . In this way, the portion of the control sheet  148  at the pump control regions  1482  need not necessarily be stretched or otherwise resiliently deformed during pumping operation. 
     Each of the regions  1481  and  1482  may have an associated vacuum or evacuation port  1483  that may be used to remove all or substantially all of any air or other fluid that may be present between the membrane  15  of cassette  24 , and the control surface  148  of cycler  14 , e.g., after the cassette  24  is loaded into the cycler  14  and the door  141  closed. This may help ensure close contact of the membrane  15  with the control regions  1481  and  1482 , and help control the delivery of desired volumes with pump operation and/or the open/closed state of the various valve ports. Note that the vacuum ports  1482  are formed in locations where the control surface  148  will not be pressed into contact with a wall or other relatively rigid feature of the cassette  24 . For example, in accordance with one aspect of the invention, one or both of the pump chambers of the cassette may include a vacuum vent clearance region formed adjacent the pump chamber. In this illustrative embodiment as shown in  FIGS. 3 and 6 , the base member  18  may include vacuum vent port clearance or extension features  182  (e.g., recessed areas that are fluidly connected to the pump chambers) adjacent and outside the oval-shaped depressions forming the pump chambers  181  to allow the vacuum vent port  1483  for the pump control region  1482  to remove any air or fluid from between membrane  15  and control surface  148  (e.g., due to rupture of the membrane  15 ) without obstruction. The extension feature may also be located within the perimeter of pump chamber  181 . However, locating vent port feature  182  outside the perimeter of pump chamber  181  may preserve more of the pumping chamber volume for pumping liquids, e.g., allows for the full footprint of pump chamber  181  to be used for pumping dialysate. Preferably, extension feature  182  is located in a vertically lower position in relation to pump chamber  181 , so that any liquid that leaks between membrane  15  and control surface  148  is drawn out through vacuum port  1483  at the earliest opportunity. Similarly, vacuum ports  1483  associated with valves  1481  are preferably located in a vertically inferior position with respect to valves  1481 . 
       FIG. 36A  shows that control surface  148  may be constructed or molded to have a rounded transition between the base element  1480  of control surface  148  and its valve and pump control regions  1481 ,  1482 . The junctions  1491  and  1492  may be molded with a small radius to transition from base element  1480  to valve control region  1481  and pump control region  1482 , respectively. A rounded or smooth transition helps to prevent premature fatigue and fracture of the material comprising control surface  148 , and may improve its longevity. In this embodiment, channels  1484  leading from vacuum ports  1483  to the pump control regions  1482  and valve control regions  1481  may need to be lengthened somewhat to accommodate the transition feature. 
     The control regions  1481  and  1482  may be moved by controlling a pneumatic pressure and/or volume on a side of the control surface  148  opposite the cassette  24 , e.g., on a back side of the rubber sheet that forms the control surface  148 . For example, as shown in  FIG. 37 , the control surface  148  may be backed by a mating or pressure delivery block  170  that includes control chambers or depressions  171 A located in association with each control region  1481 , and control chambers or depressions  171 B, located in association with each control region  1482 , and that are isolated from each other (or at least can be controlled independently of each other if desired). The surface of mating or pressure delivery block  170  forms a mating interface with cassette  24  when cassette  24  is pressed into operative association with control surface  148  backed by mating block  170 . The control chambers or depressions of mating block  170  are thus coupled to complementary valve or pumping chambers of cassette  24 , sandwiching control regions  1481  and  1482  of control surface  148  adjacent to mating block  170 , and the associated regions of membrane  15  (such as shaped portion  151 ) adjacent to cassette  24 . Air or other control fluid may be moved into or out of the control chambers or depressions  171 A,  171 B of mating block  170  for the regions  1481 ,  1482 , thereby moving the control regions  1481 ,  1482  as desired to open/close valve ports of the cassette  24  and/or effect pumping action at the pump chambers  181 . In one illustrative embodiment shown in  FIG. 37 , the control chambers  171 A may be arranged as cylindrically-shaped regions backing each of the valve control regions  1481 . The control chambers or depressions  171 B may comprise ellipsoid, ovoid or hemi-spheroid voids or depressions backing the pump control regions  1482 . Fluid control ports  173 A may be provided for each control chamber  171 A so that the cycler  14  can control the volume of fluid and/or the pressure of fluid in each of the valve control chambers  1481 . Fluid control ports  173 C may be provided for each control chamber  171 B so that the cycler  14  can control the volume of fluid and/or the pressure of fluid in each of the volume control chambers  1482 . For example, the mating block  170  may be mated with a manifold  172  that includes various ports, channels, openings, voids and/or other features that communicate with the control chambers  171  and allow suitable pneumatic pressure/vacuum to be applied to the control chambers  171 . Although not shown, control of the pneumatic pressure/vacuum may be performed in any suitable way, such as through the use of controllable valves, pumps, pressure sensors, accumulators, and so on. Of course, it should be understood that the control regions  1481 ,  1482  may be moved in other ways, such as by gravity-based systems, hydraulic systems, and/or mechanical systems (such as by linear motors, etc.), or by a combination of systems including pneumatic, hydraulic, gravity-based and mechanical systems. 
       FIG. 37A  shows an exploded view of an integrated pressure distribution module or assembly  2700  for use in a fluid flow control apparatus for operating a pumping cassette, and suitable for use as pressure distribution manifold  172  and mating block  170  of cycler  14 .  FIG. 37B  shows a view of an integrated module  2700  comprising a pneumatic manifold or block, ports for supply pressures, pneumatic control valves, pressure sensors, a pressure delivery or mating block and a control surface or actuator that includes regions comprising flexible membranes for actuating pumps and valves on a pumping cassette. The integrated module  2700  may also include reference chambers within the pneumatic manifold for an FMS volume measurement process for determining the volume of fluid present in a pumping chamber of a pumping cassette. The integrated module may also comprise a vacuum port, and a set of pathways or channels from interfaces between the actuator and flexible pump and valve membranes of a pumping cassette to a fluid trap and liquid detection system. In some embodiments, the pneumatic manifold may be formed as a single block. In other embodiments, the pneumatic manifold may be formed from two or more manifold blocks mated together with gaskets positioned between the manifold blocks. The integrated module  2700  occupies a relatively small space in a fluid flow control apparatus, and eliminates the use of tubes or flexible conduits connecting the manifold ports with corresponding ports of a pressure delivery module or block mated to a pumping cassette. Among other possible advantages, the integrated module  2700  reduces the size and assembly cost of the pneumatic actuation assembly of a peritoneal dialysis cycler, which may result in a smaller and less expensive cycler. Additionally, the short distances between pressure or vacuum distribution ports on the pressure distribution manifold block and corresponding pressure or vacuum delivery ports on a mating pressure delivery block, together with the rigidity of the conduits connecting the ports, may improve the responsiveness of an attached pumping cassette and the accuracy of cassette pump volume measurement processes. When used in a peritoneal dialysis cycler  14 , in an embodiment, an integrated module comprising a metallic pressure distribution manifold mated directly to a metallic pressure delivery block may also reduce any temperature differences between the control volume  171 B and the reference chamber  174  of the cycler  14 , which may improve the accuracy of the pump volume measurement process. 
     An exploded view of the integrated module  2700  is presented in  FIG. 37A . The actuator surface, mounted on a mating block or pressure delivery block, is analogous or equivalent to the gasket or control surface  148 , that includes flexible regions arranged to move back and forth to pump fluid and/or open and close valves by pushing or pulling on a membrane  15  of a pump cassette  24 . With respect to cycler  14 , the control surface  148  is actuated by the positive and negative pneumatic pressure supplied to the control volumes  171 A,  171 B behind the control regions  1481 ,  1482 . The control surface  148  attaches to the pressure delivery block or mating block  170  by fitting tightly on a raised surface  2744  on the front surface of the mating block  170  with a lip  2742 . The mating block  170  may include one or more surface depressions  2746  to align with and support the oval curved shape of one or more corresponding pump control surfaces  1482 , forming a pump control chamber. A similar arrangement, with or without a surface depression, may be included in forming a valve control region  171 A to align with a corresponding control surface  1481  for controlling one or more valves of a pumping cassette. The mating block  170  may further include grooves  2748  on the surface of depression  2746  of mating block  170  behind the pump control surface  1482  to facilitate the flow of control fluid or gas from the port  173 C to the entire back surface the pump control surface  1482 . Alternatively, rather than having grooves  2748 , the depression  2746  may be formed with a roughened surface or a tangentially porous surface. 
     The mating block  170  connects the pressure distribution manifold  172  to the control surface  148 , and delivers pressure or vacuum to various control regions on control surface  148 . The mating block  170  may also be referred to as a pressure delivery block in that it provides pneumatic conduits to supply pressure and vacuum to the valve control regions  1481  and the pump control regions  1482 , vacuum to the vacuum ports  1483  and connections from the pump control volumes  171 B to the pressure sensors. The ports  173 A connect the valve control volumes  171 A to the pressure distribution manifold  172 . The ports  173 C connect the pump control volume  171 B to the pressure distribution manifold  172 . The vacuum ports  1483  are connected to the pressure distribution manifold  172  via ports  173 B. In one embodiment, the ports  173 B extend above the surface of the pressure delivery block  170  to pass through the control surface  148  to provide vacuum at port  1483  without pulling the control surface  148  onto the port  173 B and blocking flow. 
     The pressure delivery block  170  is attached to the front face of the pressure distribution manifold  172 . The ports  173 A,  173 B,  173 C line up with pneumatic circuits on the pressure distribution manifold  172  that connect to valve ports  2714 . In one example, the pressure delivery block  170  is mated to the pressure distribution manifold  172  with a front flat gasket  2703  clamped between them. The block  170  and manifold  172  are held together mechanically, which in an embodiment is through the use of bolts  2736  or other types of fasteners. In another example, rather than a flat gasket  2703 , compliant elements are placed in or molded in either the pressure delivery block  170  or the pressure distribution manifold  172 . Alternatively, the pressure delivery block  170  may be bonded to the pressure distribution manifold  172  by an adhesive, double sided tape, friction welding, laser welding, or other bonding method. The block  170  and manifold  172  may be formed of metal or plastic and the bonding methods will vary depending on the material. 
     The pressure distribution manifold  172  contains ports for the pneumatic valves  2710 , reference chambers  174 , a fluid trap  1722  and pneumatic circuitry or of the integrated module  2700 . connections provides pneumatic connections between the pressure reservoirs, valves, and contains ports  2714  that receive multiple cartridge valves  2710 . The cartridge valves  2710  includes but is not limited to the binary valves  2660  controlling flow to valve control volumes  171 A, the binary valves X 1 A, X 1 B, X 2 , X 3  controlling flow to pump control volumes  171 B, and the binary valves  2661 - 2667  controlling flow to the bladders  2630 ,  2640 ,  2650  and pressure reservoirs  2610 ,  2620 . The cartridge valves  2710  are pressed into the valve ports  2714  and electrically connected to the hardware interface  310  via circuit board  2712 . 
     The pneumatic circuitry in the pressure distribution manifold  172  may be formed with a combination of grooves or slots  1721  on the front and back faces and approximately perpendicular holes that connect the grooves  1721  on one face to valve ports  2714 , the fluid trap  1722  and to grooves and ports on the opposite face. Some grooves  1721  may connect directly to the reference chambers  174 . A single perpendicular hole may connect a groove  1721  to multiple valve ports  174  that are closely spaced and staggered. Sealed pneumatic conduits are formed when the grooves  1721  are isolated from one another by in one example the front flat gasket  2703  as shown in  FIG. 37A . 
     The presence of liquid in the fluid trap  1722  may be detected by a pair of conductivity probes  2732 . The conductivity probes  2732  slide through a back gasket  2704 , a back plate  2730  and holes  2750  before entering the fluid trap  1722  in the pressure distribution manifold  172 . 
     The back plate  2730  seals the reference volumes  174 , the grooves  1721  on the back face of the pressure distribution manifold  172  and provides ports for the pressure sensors  2740  and ports for pressure and vacuum lines  2734  and vents to the atmosphere  2732 . In one example, the pressure sensors may be IC chips soldered to a single board  2740  and pressed as a group against the back gasket  2704  on the back plate  2730 . In one example, bolts  2736  clamp the back plate  2730 , pressure distribution manifold  172  and pressure delivery block  170  together with gaskets  2703 ,  2702  between them. In another example, the back plate  2730  may be bonded to the pressure delivery manifold  172  as described above. The assembled integrated module  2700  is presented in  FIG. 37C . 
       FIG. 37C  presents a schematic of the pneumatic circuit in the integrated manifold  2700  and pneumatic elements outside the manifold. The pump  2600  produces vacuum and pressure. The pump  2600  is connected via 3 way valves  2664  and  2665  to a vent  2680  and the negative or vacuum reservoir  2610  and the positive reservoir  2620 . The pressure in the positive and negative reservoirs  2620 ,  2610  are measure respectively by pressure sensors  2678 ,  2676 . The hardware interface  310  controls the speed of the pump  2600  and the position of 3-way valves  2664 ,  2665 ,  2666  to control the pressure in each reservoir. The autoconnect stripper element bladder  2630  is connected via 3-way valve  2661  to either the positive pressure line  2622  or the negative or vacuum line  2612 . The automation computer  300  commands the position of valve  2661  to control the location of the stripper element  1461 . The occluder bladder  2640  and piston bladder  2650  are connected via 3-way valves  2662  and  2663  to either the pressure line  2622  or vent  2680 . The automation computer  300  commands valve  2663  to connect the piston bladder to the pressure line  2622  after the door  141  is closed to securely engage the cassette  24  against the control surface  148 . The occluder bladder  2640  is connected to the pressure line  2622  via valve  2662  and restriction  2682 . The occluder bladder  2640  is connected to the vent  2680  via valve  2662 . The orifice  2682  advantageously slows the filling of the occluder bladder  2640  that retracts the occluder  147  in order to maintain the pressure in the pressure line  2622 . The high pressure in the pressure line  2622  keeps the various valve control surfaces  171 A and the piston bladder actuated against the cassette  24 , which prevents flow to or from the patient as the occluder  147  opens. Conversely the connection from the occluder bladder  2640  to the vent  2680  is unrestricted, so that occluder  147  can quickly close. 
     The valve control surfaces  1481  are controlled by the pressure in the valve control volume  171 A, which in turn is controlled by the position of the 3-way valves  2660 . The valves  2660  can be controlled individually via commands from the automation computer  300  passed to the hardware interface  310 . The valves controlling the pumping pressures in the pump control volumes  171 B are controlled with 2-way valves X 1 A, X 1 B. The valves X 1 A, X 1 B in one example may be controlled by the hardware interface  310  to achieve a pressure commanded by the automation computer  300 . The pressure in each pump control chamber  171 B is measured by sensors  2672 . The pressure in the reference chambers is measured by sensors  2670 . The 2-way valves X 2 , X 3  respectively connect the reference chamber  174  to the pump control chamber  171 B and the vent  2680 . 
     The fluid trap  2622  is to the vacuum line  2612  during operation as explained elsewhere in this application. The fluid trap is connected by several lines to the ports  173 B in the pressure delivery block  170 . The pressure in the fluid trap is monitored by pressure sensor  2674  that is mounted on the back plate  2730 . 
     The vacuum ports  1483  may be employed to separate the membrane  15  from the control surface  148  at the end of therapy before or during the opening the door. The vacuum provided by the negative pressure source to the vacuum ports  1483  sealingly engages the membrane  15  to the control surface  148  during therapy. In some instances a substantial amount of force may be needed to separate the control surface from the cassette membrane  15 , preventing the door  141  from freely rotating into the open position, even when the application of vacuum is discontinued. Thus, in an embodiment, the pressure distribution module  2700  is configured to provide a valved channel between the positive pressure source and the vacuum ports  1483 . Supplying positive pressure at the vacuum ports may aid in separating the membrane  15  from the control surface  148 , thereby allowing the cassette  24  to separate more easily from the control surface  148  and allow the door  141  to open freely. The pneumatic valves in the cycler may be controlled by the automation computer  300  to provide a positive pressure to the vacuum ports  1483 . The manifold  172  may include a separately valved channel dedicated for this purpose, or alternatively it may employ the existing channel configurations and valves, operated in a particular sequence. 
     In one example the vacuum ports  1483  may be supplied with positive pressure by temporarily connecting the vacuum ports  1483  to the positive pressure reservoir  2620 . The vacuum ports  1483  are normally connected to the vacuum reservoir  2610  via a common fluid collection chamber or Fluid Trap  1722  in the manifold  172  during therapy. In one example, the controller or automation computer may open valve X 1 B between the positive pressure reservoir and the volume control chamber  171 B and the valve X 1 A between the negative pressure reservoir and the same volume control chamber  171 B simultaneously, which will pressurize the air in the Fluid Trap  1722  and the vacuum ports  1483 . The pressurized air will flow through the vacuum ports  1483  and between the membrane  15  and the control surface  148 , breaking any vacuum bond between the membrane and control surface. However, in the illustrated manifold, the stripper element  1491  of the cap stripper  149  may extend while the positive pressure is supplied to common fluid collection chamber  1722  fluid, because the stripper bladder  2630  is connected to a the vacuum supply line  2612 . In this example, in a subsequent step, the fluid trap  1722  may be valved off from the now-pressurized vacuum line and the two valves X 1 A, X 1 B connecting the positive and vacuum reservoirs to the volume control chamber  171 B may be closed. The vacuum pump  2600  is then operated to reduce the pressure in the vacuum reservoir  2610  and the vacuum supply line  2612 , which in turn allows the stripper element  1491  to be withdrawn. The door  141  may then be opened after detaching the cassette  24  from the control surface  148  and retracting the stripper element  1491 . 
     In accordance with an aspect of the invention, the vacuum ports  1483  may be used to detect leaks in the membrane  15 , e.g., a liquid sensor in a conduit or chamber connected to a vacuum port  1483  may detect liquid if the membrane  15  is perforated or liquid otherwise is introduced between the membrane  15  and the control surface  148 . For example, vacuum ports  1483  may align with and be sealingly associated with complementary vacuum ports  173 B in mating block  170 , which in turn may be sealingly associated with fluid passages  1721  leading to a common fluid collection chamber  1722  in manifold  172 . The fluid collection chamber  1722  may contain an inlet through which vacuum can be applied and distributed to all vacuum ports  1483  of control surface  148 . By applying vacuum to the fluid collection chamber  1722 , fluid may be drawn from each of the vacuum ports  173 B and  1483 , thus removing fluid from any space between the membrane  15  and the control surface  148  at the various control regions. However, if there is liquid present at one or more of the regions, the associated vacuum port  1483  may draw the liquid into the vacuum ports  173 B and into the lines  1721  leading to the fluid collection chamber  1722 . Any such liquid may collect in the fluid collection chamber  1722 , and be detected by one or more suitable sensors, e.g., a pair of conductivity sensors that detect a change in conductivity in the chamber  1722  indicating the presence of liquid. In this embodiment, the sensors may be located at a bottom side of the fluid collection chamber  1722 , while a vacuum source connects to the chamber  1722  at an upper end of the chamber  1722 . Therefore, if liquid is drawn into the fluid collection chamber  1722 , the liquid may be detected before the liquid level reaches the vacuum source. Optionally, a hydrophobic filter, valve or other component may be place at the vacuum source connection point into the chamber  1722  to help further resist the entry of liquid into the vacuum source. In this way, a liquid leak may be detected and acted upon by controller  16  (e.g., generating an alert, closing liquid inlet valves and ceasing pumping operations) before the vacuum source valve is placed at risk of being contaminated by the liquid. 
     In one embodiment, the inner wall of the control chambers  171 B can include raised elements somewhat analogous to the spacer elements  50  of the pump chamber, e.g., as shown in  FIG. 37  for the control chambers  171 B associated with the pump control regions  1482 . These raised elements can take the form of plateau features, ribs, or other protrusions that keep the control ports recessed away from the fully retracted control regions  1482 . This arrangement may allow for a more uniform distribution of pressure or vacuum in the control chamber  171 B, and prevent premature blocking of any control port by the control surface  148 . A pre-formed control surface  148  (at least in the pump control regions) may not be under a significant stretching force when fully extended against either the inner wall of the pump chamber of the cassette  24  during a delivery stroke, or the inner wall of the control chamber  171  during a fill stroke. It may therefore be possible for the control region  1482  to extend asymmetrically into the control chamber  171 B, causing the control region  1482  to prematurely close off one or more ports of the control chamber before the chamber is fully evacuated. Having features on the inner surface of the control chamber  171 B that prevent contact between the control region  1482  and the control ports may help to assure that the control region  1482  can make uniform contact with the control chamber inner wall during a fill stroke. 
     As suggested above, the cycler  14  may include a control system  16  with a data processor in electrical communication with the various valves, pressure sensors, motors, etc., of the system and is preferably configured to control such components according to a desired operating sequence or protocol. The control system  16  may include appropriate circuitry, programming, computer memory, electrical connections, and/or other components to perform a specified task. The system may include pumps, tanks, manifolds, valves or other components to generate desired air or other fluid pressure (whether positive pressure—above atmospheric pressure or some other reference—or negative pressure or vacuum—below atmospheric pressure or some other reference) to control operation of the regions of the control surface  148 , and other pneumatically-operated components. Further details regarding the control system  16  (or at least portions of it) are provided below. 
     In one illustrative embodiment, the pressure in the pump control chambers  171 B may be controlled by a binary valve, e.g., which opens to expose the control chamber  171  to a suitable pressure/vacuum and closes to cut off the pressure/vacuum source. The binary valve may be controlled using a saw tooth-shaped control signal which may be modulated to control pressure in the pump control chamber  171 B. For example, during a pump delivery stroke (i.e., in which positive pressure is introduced into the pump control chamber  171 B to move the membrane  15 /control surface  148  and force liquid out of the pump chamber  181 ), the binary valve may be driven by the saw tooth signal so as to open and close at a relatively rapid rate to establish a suitable pressure in the control chamber  171 B (e.g., a pressure between about 70-90 mmHg). If the pressure in the control chamber  171 B rises above about 90 mmHg, the saw tooth signal may be adjusted to close the binary valve for a more extended period. If the pressure drops below about 70 mmHg in the control chamber  171 B, the saw tooth control signal may again be applied to the binary valve to raise the pressure in the control chamber  171 . Thus, during a typical pump operation, the binary valve will be opened and closed multiple times, and may be closed for one or more extended periods, so that the pressure at which the liquid is forced from the pump chamber  181  is maintained at a desired level or range (e.g., about 70-90 mmHg). 
     In some embodiments and in accordance with an aspect of the invention, it may be useful to detect an “end of stroke” of the membrane  15 /pump control region  1482 , e.g., when the membrane  15  contacts the spacers  50  in the pump chamber  181  or the pump control region  1482  contacts the wall of the pump control chamber  171 B. For example, during a pumping operation, detection of the “end of stroke” may indicate that the membrane  15 /pump control region  1482  movement should be reversed to initiate a new pump cycle (to fill the pump chamber  181  or drive fluid from the pump chamber  181 ). In one illustrative embodiment in which the pressure in the control chamber  171 B for a pump is controlled by a binary valve driven by a saw tooth control signal, the pressure in the pump chamber  181  will fluctuate at a relatively high frequency, e.g., a frequency at or near the frequency at which the binary valve is opened and closed. A pressure sensor in the control chamber  171 B may detect this fluctuation, which generally has a higher amplitude when the membrane  15 /pump control region  1482  are not in contact with the inner wall of the pump chamber  181  or the wall of the pump control chamber  171 B. However, once the membrane  15 /pump control region  1482  contacts the inner wall of the pump chamber  181  or the wall of the pump control chamber  171 B (i.e., the “end of stroke”), the pressure fluctuation is generally damped or otherwise changes in a way that is detectable by the pressure sensor in the pump control chamber  171 B. This change in pressure fluctuation can be used to identify the end of stroke, and the pump and other components of the cassette  24  and/or cycler  14  may be controlled accordingly. 
     In one embodiment, the pneumatic pressure applied to the control chamber  171 B is actively controlled by a processor receiving a signal from a pressure transducer  2672  ( FIG. 37C ) connected to the control chamber  171 B and a fast acting binary valve X 1 A, X 1 B between a pressure reservoir  2620 ,  2610  and the control chamber  171 B. The processor may control the pressure with a variety of control algorithms including closed loop proportional or proportional-integrator feedback control that varies the valve duty cycle to achieve the desired pressure in the control volume  171 B. In a one embodiment, the processor controls the pressure in the control chamber with an on-off controller often called a bang-bang controller. The on-off controller monitors the pressure in the control volume  171 B during a deliver stroke and open the binary valve X 1 B (connecting the control volume  171 B to the positive reservoir  2620 ) when the pressure is less than a lower first limit and closes the binary valve X 1 B when the pressure is above a higher second limit. During a fill stroke, the on-off controller opens the binary valve X 1 A (connecting the control volume  171 B to the negative reservoir  2610 ) when the pressure is greater than a third limit and closes the binary valve X 1 A when the pressure is less than a forth limit, where the forth limit is lower than the third limit and both the third and forth limits are less than the first limit. A plot of the pressure over time as during a deliver stroke and the subsequent FMS measurement is shown in  FIG. 66 . The control chamber pressure  2300  oscillates between the lower first limit  2312  and the higher second limit  2310  as the membrane  15  moves across the control chamber  171 B. The pressure stops oscillating between the limits when the membrane  15  stops moving. The membrane  15  typically stops moving when it contacts either the stadium steps  50  of the cassette or it contacts the control chamber surface  171 B. The membrane  15  may also stop moving if the outlet fluid line is occluded. 
     The automation computer  300  detects the end of stroke by evaluating the pressure signals. There are many possible algorithms to detect the end of pressure oscillation that indicate the end-of-stroke (EOS). The algorithms and methods to detect EOS in the section labeled “Detailed Description of the system and Method of Measuring Change Fluid Flow Rate” in U.S. Pat. No. 6,520,747 and the section describing the filtering to detect end of stroke in U.S. Pat. No. 8,292,594 are herein incorporated by reference. 
     One example of an algorithm to detect EOS, the AC  300  evaluates the time between the pressure crossing the first and second limits during a deliver stroke or third and fourth limits during a fill stroke. The on-off controller opens and closes the valves X 1 A, X 1 B in response to the pressure oscillating between the two limits as the control chamber volume changes during the fill or deliver stroke. When the membrane  15  stops moving at the end-of-stroke, the pressure changes will significantly diminish so that the pressure no longer exceeds one or both limits. The AC  300  may detect EOS by measuring the time between the pressure exceeding alternating limits. If the time since pressure cross the last limit exceeds a predefined threshold, then the AC  300  may declare an EOS. The algorithm may further include an initial period during which the AC  300  does not measure the time between limit crossings. 
     In another example algorithm, the AC  300  evaluates the derivative of the pressure signal with respect to time. The AC  300  may declare an EOS, if the derivative remains below a minimum threshold for a minimum length of time. In a further example, the minimum threshold is the average of the absolute value of the average pressure derivative during the stroke. The algorithm calculates the slope (derivative wrt time) of a curve fit to a set of data points, where the data points are taken from a moving window. The absolute value of each slope is then averaged over the stroke to calculate the absolute avalue of the average pressure derivative. In another example of an EOS algorithm, the AC  300  may not include the pressure data until after an initial delay. The AC  300  ignores the initial pressure data to avoid false EOS detections due to irregular pressure traces that occasionally occur during the early part of the stroke. In another example, the AC  300  declares an EOS only after the second derivative of the pressure in the later part of the stroke has remained below a threshold for a minimum time and a wait period of time has past. 
     The criteria to declare an EOS may be optimized for different pumping conditions. The optimized EOS detection conditions include the second pressure derivative threshold, the minimum time to remain below the second derivative threshold, the duration of the initial delay and a length of the wait period. These EOS detection criteria may be optimized differently, for example, the fill stroke from the bags  20 , 22 , the deliver stroke to the patient, the fill stroke from the patient, and the deliver stroke to the bags  20 , 22 . Alternatively each EOS detection criteria may be a function of the pumping pressure in the control chamber  171 B. 
     Occluder 
     In one aspect of the invention, an occluder for opening/closing one or more flexible lines may include a pair of opposed occluding members, which may be configured as resilient elements, such as flat plates made of a spring steel (e.g., leaf springs), having a force actuator configured to apply a force to one or both of the occluding members to operate the occluder. In certain embodiments, the force actuator may comprise an expandable or enlargable member positioned between the resilient elements. With the expandable member in a reduced size condition, the resilient elements may be in a flat or nearly flat condition and urge a pinch head to engage with one or more lines so as to pinch the lines closed. However, when the expandable member urges the resilient elements apart, the resilient elements may bend and withdraw the pinch head, releasing the lines and allowing flow through the lines. In other embodiments, the occluding members could be essentially rigid with respect to the levels of force applied by the force actuator. In certain embodiments, the force actuator may apply a force to one or both opposed occluding members to increase the distance between the occluding members in at least a portion of the region where they are opposed to effect opening or closing of the flexible tubing. 
       FIG. 38  shows an exploded view and  FIG. 39  shows a partially assembled view of an illustrative embodiment of an occluder  147  that may be used to close, or occlude, the patient and drain lines  34  and  28 , and/or other lines in the cycler  14  or the set  12  (such as, for example, the heater bag line  26 ). The occluder  147  includes an optional pinch head  161 , e.g., a generally flat blade-like element that contacts the tubes to press the tubes against the door  141  and pinch the tubes closed. In other embodiments, the function of the pinch head could be replaced by an extending edge of one or both of occluding members  165 . The pinch head  161  includes a gasket  162 , such as an O-ring or other member, that cooperates with the pinch head  161  to help resist entry of fluid (air or liquid for example) into the cycler  14  housing, e.g., in case of leakage in one of the occluded lines. The bellows gasket  162  is mounted to, and pinch head  161  passes through, a pinch head guide  163  that is mounted to the front panel of the cycler housing, i.e., the panel exposed by opening the door  141 . The pinch head guide  163  allows the pinch head  161  to move in and out of the pinch head guide  163  without binding and/or substantial resistance to sliding motion of the pinch head  161 . A pivot shaft  164  attaches a pair of opposed occluder members, comprising in the illustrated embodiment spring plates  165 , that each include a hook-shaped pivot shaft bearing, e.g., like that found on standard door hinges, to the pinch head  161 . That is, the openings of shaft guides on the pinch head  161 , and the openings formed by the hook-shaped bearings on the spring plates  165  are aligned with each other and the pivot shaft  164  is inserted through the openings so the pinch head  161  and the spring plates  165  are pivotally connected together. The spring plates  165  may be made of any suitable material, such as steel, and may be arranged to be generally flat when unstressed. The opposite end of the spring plates  165  includes similar hook-shaped bearings, which are pivotally connected to a linear adjustor  167  by a second pivot shaft  164 . In this embodiment, the force actuator comprises a bladder  166  is positioned between the spring plates  165  and arranged so that when fluid (e.g., air under pressure) is introduced into the bladder, the bladder may expand and push the spring plates  165  away from each other in a region between the pivot shafts  164 . The bladder  166  may be attached to one or both spring plates  165  by pressure sensitive adhesive (PSA) tape. A linear adjustor  167  is fixed to the cycler housing  82  while the pinch head  161  is allowed to float, although its movement is guided by the pinch head guide  163 . The linear adjustor  167  includes slot holes at its lower end, allowing the entire assembly to be adjusted in position and thus permitting the pinch head to be appropriately positioned when the occluder  147  is installed in the cycler  14 . A turnbuckle  168  or other arrangement may be used to help adjust the position of the linear adjustor  167  relative to the housing  82 . That is, the pinch head  161  generally needs to be properly positioned so that with the spring plates  165  located near each other and the bladder  166  substantially emptied or at ambient pressure, the pinch head  161  suitably presses on the patient and drain lines so as to pinch the tubes closed to flow without cutting, kinking or otherwise damaging the tubes. The slot openings in the linear adjustor  167  allows for this fine positioning and fixing of the occluder  147  in place. An override release device, such as provided by release blade  169  is optionally positioned between the spring plates  165 , and as is discussed in more detail below, may be rotated so as to push the spring plates  165  apart, thereby withdrawing the pinch head  161  into the pinch head guide  163 . The release blade  169  may be manually operated, e.g., to disable the occluder  147  in case of power loss, bladder  166  failure or other circumstance. 
     Additional configurations and descriptions of certain components that may be instructive in constructing certain embodiments of the occluder are provided in U.S. Pat. No. 6,302,653. The spring plates  165  may be constructed from any material that is elastically resistant to bending forces and which has sufficient longitudinal stiffness (resistance to bending) to provide sufficient restoring force, in response to a bending displacement, to occlude a desired number of collapsible tubes. In the illustrated embodiment, each spring plate is essentially flat when unstressed and in the shape of a sheet or plate. In alternative embodiments utilizing one or more resilient occluding members (spring members), any occluding member(s) that is elastically resistant to bending forces and which has sufficient longitudinal stiffness (resistance to bending) to provide sufficient restoring force, in response to a bending displacement to occlude a desired number of collapsible tubes may be utilized. Potentially suitable spring members can have a wide variety of shapes as apparent to those of ordinary skill in the art, including, but not limited to cylindrical, prism-shaped, trapezoidal, square, or rectangular bars or beams, I-beams, elliptical beams, bowl-shaped surfaces, and others. Those of ordinary skill in the art can readily select proper materials and dimensions for spring plates  165  based on the present teachings and the requirements of a particular application. 
       FIG. 40  shows a top view of the occluder  147  with the bladder  166  deflated and the spring plates  165  located near each other and in a flat or nearly flat condition. In this position, the pinch head  161  is fully extended from the pinch head guide and the front panel of the cycler  14  (i.e., the panel inside of the door  141 ) and enabled to occlude the patient and drain lines.  FIG. 41 , on the other hand, shows the bladder  166  in an inflated state in which the spring plates  165  are pushed apart, thereby retracting the pinch head  161  into the pinch head guide  163 . (Note that the linear adjustor  167  is fixed in place relative to the cycler housing  82  and thus fixed relative to the front panel of the housing  82 . As the spring plates  165  are moved apart, the pinch head  161  moves rearwardly relative to the front panel since the pinch head  161  is arranged to move freely in and out of the pinch head guide  163 .) This condition prevents the pinch head  161  from occluding the patient and drain lines and is the condition in which the occluder  147  remains during normal operation of the cycler  14 . That is, as discussed above, various components of the cycler  14  may operate using air pressure/vacuum, e.g., the control surface  148  may operate under the drive of suitable air pressure/vacuum to cause fluid pumping and valve operation for the cassette  24 . Thus, when the cycler  14  is operating normally, the cycler  14  may produce sufficient air pressure to not only control system operation, but also to inflate the bladder  166  to retract the pinch head  161  and prevent occlusion of the patient and drain lines. However, in the case of system shut down, failure, fault or other condition, air pressure to the bladder  166  may be terminated, causing the bladder  166  to deflate and the spring plates  165  to straighten and extend the pinch head  161  to occlude the lines. One possible advantage of the arrangement shown is that the return force of the spring plates  165  is balanced such that the pinch head  161  generally will not bind in the pinch head guide  163  when moving relative to the pinch head guide  163 . In addition, the opposing forces of the spring plates  165  will tend to reduce the amount of asymmetrical frictional wear of the pivot shafts and bushings of the assembly. Also, once the spring plates  165  are in an approximately straight position, the spring plates  165  can exert a force in a direction generally along the length of the pinch head  161  that is several times larger than the force exerted by the bladder  166  on the spring plates  165  to separate the spring plates  165  from each other and retract the pinch head  161 . Further, with the spring plates  165  in a flat or nearly flat condition, the force needed to be exerted by fluid in the collapsed tubing to overcome the pinching force exerted by the pinch head  161  approaches a relatively high force required, when applied to the spring plates at their ends and essentially parallel to the plane of the flattened spring plates, to buckle the spring plates by breaking the column stability of the flattened spring plates. As a result, the occluder  147  can be very effective in occluding the lines with a reduced chance of failure while also requiring a relatively small force be applied by the bladder  166  to retract the pinch head  161 . The dual spring plate arrangement of the illustrative embodiment may have the additional advantage of significantly increasing the pinching force provided by the pinch head, for any given force needed to bend the spring plate, and/or for any given size and thickness of spring plate. 
     In some circumstances, the force of the occluder  147  on the lines may be relatively large and may cause the door  141  to be difficult to open. That is, the door  141  must oppose the force of the occluder  147  when the pinch head  161  is in contact with and occluding lines, and in some cases this may cause the latch that maintains the door  141  in a closed state to be difficult or impossible to operate by hand. Of course, if the cycler  14  is started and produces air pressure to operate, the occluder bladder  166  can be inflated and the occluder pinch head  161  retracted. However, in some cases, such as with a pump failure in the cycler  14 , inflation of the bladder  166  may be impossible or difficult. To allow opening of the door, the occluder  147  may include a manual release. In this illustrative embodiment, the occluder  147  may include a release blade  169  as shown in  FIGS. 38 and 39  which includes a pair of wings pivotally mounted for rotary movement between the spring plates  165 . When at rest, the release blade wings may be aligned with the springs as shown in  FIG. 39 , allowing the occluder to operate normally. However, if the spring plates  165  are in a flat condition and the pinch head  161  needs to be retracted manually, the release blade  169  may be rotated, e.g., by engaging a hex key or other tool with the release blade  169  and turning the release blade  169 , so that the wings push the spring plates  165  apart. The hex key or other tool may be inserted through an opening in the housing  82  of the cycler  14 , e.g., an opening near the left side handle depression in the cycler housing  82 , and operated to disengage the occluder  147  and allow the door  141  to be opened. 
     Pump Volume Delivery Measurement 
     In another aspect of the invention, the cycler  14  may determine a volume of fluid delivered in various lines of the system  10  without the use of a flowmeter, weight scale or other direct measurement of fluid volume or weight. For example, in one embodiment, a volume of fluid moved by a pump, such as a pump in the cassette  24 , may be determined based on pressure measurements of a gas used to drive the pump. In one embodiment, a volume determination can be made by isolating two chambers from each other, measuring the respective pressures in the isolated chambers, allowing the pressures in the chambers to partially or substantially equalize (by fluidly connecting the two chambers) and measuring the pressures. Using the measured pressures, the known volume of one of the chambers, and an assumption that the equalization occurs in an adiabatic way, the volume of the other chamber (e.g., a pump chamber) can be calculated. In one embodiment, the pressures measured after the chambers are fluidly connected may be substantially unequal to each other, i.e., the pressures in the chambers may not have yet completely equalized. However, these substantially unequal pressures may be used to determine a volume of the pump control chamber, as explained below. 
     For example,  FIG. 42  shows a schematic view of a pump chamber  181  of the cassette  24  and associated control components and inflow/outflow paths. In this illustrative example, a liquid supply, which may include the heater bag  22 , heater bag line  26  and a flow path through the cassette  24 , is shown providing a liquid input at the upper opening  191  of the pump chamber. The liquid outlet is shown in this example as receiving liquid from the lower opening  187  of the pump chamber  181 , and may include a flow path of the cassette  24  and the patient line  34 , for example. The liquid supply may include a valve, e.g., including the valve port  192 , that can be opened and closed to permit/impede flow to or from the pump chamber  181 . Similarly, the liquid outlet may include a valve, e.g., including the valve port  190 , that can be opened and closed to permit/impede flow to or from the pump chamber  181 . Of course, the liquid supply could include any suitable arrangement, such as one or more solution containers, the patient line, one or more flow paths in the cassette  24  or other liquid source, and the liquid outlet could likewise include any suitable arrangement, such as the drain line, the heater bag and heater bag line, one or more flow paths in the cassette  24  or other liquid outlet. Generally speaking, the pump chamber  181  (i.e., on the left side of the membrane  14  in  FIG. 42 ) will be filled with an incompressible liquid, such as water or dialysate, during operation. However, air or other gas may be present in the pump chamber  181  in some circumstances, such as during initial operation, priming, or other situations as discussed below. Also, it should be understood that although aspects of the invention relating to volume and/or pressure detection for a pump are described with reference to the pump arrangement of the cassette  24 , aspects of the invention may be used with any suitable pump or fluid movement system. 
       FIG. 42  also shows schematically to the right of the membrane  15  and the control surface  1482  (which are adjacent each other) a control chamber  171 B, which may be formed as a void or other space in the mating block  170 A associated with the pump control region  1482  of the control surface  1482  for the pump chamber  181 , as discussed above. It is in the control chamber  171 B that suitable air pressure is introduced to cause the membrane  15 /control region  1482  to move and effect pumping of liquid in the pump chamber  181 . The control chamber  171 B may communicate with a line L 0  that branches to another line L 1  and a first valve X 1  that communicates with a pressure source  84  (e.g., a source of air pressure or vacuum). The pressure source  84  may include a piston pump in which the piston is moved in a chamber to control a pressure delivered to the control chamber  171 B, or may include a different type of pressure pump and/or tank(s) to deliver suitable gas pressure to move the membrane  15 /control region  1482  and perform pumping action. The line L 0  also leads to a second valve X 2  that communicates with another line L 2  and a reference chamber  174  (e.g., a space suitably configured for performing the measurements described below). The reference chamber  174  also communicates with a line L 3  having a valve X 3  that leads to a vent or other reference pressure (e.g., a source of atmospheric pressure or other reference pressure). Each of the valves X 1 , X 2  and X 3  may be independently controlled. Pressure sensors may be arranged, e.g., one sensor at the control chamber  171 B and another sensor at the reference chamber  174 , to measure pressure associated with the control chamber and the reference chamber. These pressure sensors may be positioned and may operate to detect pressure in any suitable way. The pressure sensors may communicate with the control system  16  for the cycler  14  or other suitable processor for determining a volume delivered by the pump or other features. 
     As mentioned above, the valves and other components of the pump system shown in  FIG. 42  can be controlled so as to measure pressures in the pump chamber  181 , the liquid supply and/or liquid outlet, and/or to measure a volume of fluid delivered from the pump chamber  181  to the liquid supply or liquid outlet. Regarding volume measurement, one technique used to determine a volume of fluid delivered from the pump chamber  181  is to compare the relative pressures at the control chamber  171 B to that of the reference chamber  174  in two different pump states. By comparing the relative pressures, a change in volume at the control chamber  171 B can be determined, which corresponds to a change in volume in the pump chamber  181  and reflects a volume delivered from/received into the pump chamber  181 . For example, after the pressure is reduced in the control chamber  171 B during a pump chamber fill cycle (e.g., by applying negative pressure from the pressure source through open valve X 1 ) so as to draw the membrane  15  and pump control region  1482  into contact with at least a portion of the control chamber wall (or to another suitable position for the membrane  15 /region  1482 ), valve X 1  may be closed to isolate the control chamber from the pressure source, and valve X 2  may be closed, thereby isolating the reference chamber  174  from the control chamber  171 B. Valve X 3  may be opened to vent the reference chamber to ambient pressure, then closed to isolate the reference chamber. With valve X 1  closed and the pressures in the control chamber and reference chamber measured, valve X 2  is then opened to allow the pressure in the control chamber and the reference chamber to start to equalize. The initial pressures of the reference chamber and the control chamber, together with the known volume of the reference chamber and pressures measured after equalization has been initiated (but not yet necessarily completed) can be used to determine a volume for the control chamber. This process may be repeated at the end of the pump delivery cycle when the sheet  15 /control region  1482  are pushed into contact with the spacer elements  50  of the pump chamber  181 . By comparing the control chamber volume at the end of the fill cycle to the volume at the end of the delivery cycle, a volume of liquid delivered from the pump can be determined. 
     Conceptually, the pressure equalization process (e.g., at opening of the valve X 2 ) is viewed as happening in an adiabatic way, i.e., without heat transfer occurring between air in the control and reference chambers and its environment. The conceptual notion is that there is an imaginary piston located initially at the valve X 2  when the valve X 2  is closed, and that the imaginary piston moves in the line L 0  or L 2  when the valve X 2  is opened to equalize the pressure in the control and reference chambers. Since (a) the pressure equalization process happens relatively quickly, (b) the air in the control chamber and the reference chamber has approximately the same concentrations of elements, and (c) the temperatures are similar, the assumption that the pressure equalization happens in an adiabatic way may introduce only small error into the volume measurements. Also, in one embodiment, the pressures taken after equalization has been initiated may be measured before substantial equalization has occurred—further reducing the time between measuring the initial pressures and the final pressures used to determine the pump chamber volume. Error can be further reduced, for example, by using low thermal conductivity materials for the membrane  15 /control surface  1482 , the cassette  24 , the control chamber  171 B, the lines, the reference chamber  174 , etc., so as to reduce heat transfer. 
     Given the assumption that an adiabatic system exists between the state when the valve X 2  is closed until after the valve X 2  is opened and the pressures equalize, the following applies: 
         PV   γ =Constant  (1)
 
     where P is pressure, V is volume and γ is equal to a constant (e.g., about 1.4 where the gas is diatomic, such as air). Thus, the following equation can be written to relate the pressures and volumes in the control chamber and the reference chamber before and after the opening of valve X 2  and pressure equalization occurs: 
         PrVr   γ   +PdVd   γ =Constant= PfVf   γ   (2)
 
     where Pr is the pressure in the reference chamber and lines L 2  and L 3  prior to the valve X 2  opening, Vr is the volume of the reference chamber and lines L 2  and L 3  prior to the valve X 2  opening, Pd is the pressure in the control chamber and the lines L 0  and L 1  prior to the valve X 2  opening, Vd is the volume of the control chamber and the lines L 0  and L 1  prior to the valve X 2  opening, Pf is the equalized pressure in the reference chamber and the control chamber after opening of the valve X 2 , and Vf is the volume of the entire system including the control chamber, the reference chamber and the lines L 0 , L 1 , L 2 , and L 3 , i.e., Vf=Vd+Vr. Since Pr, Vr, Pd, Pf and γ are known, and Vf=Vr+Vd, this equation can be used to solve for Vd. (Although reference is made herein, including in the claims, to use of a “measured pressure” in determining volume values, etc., it should be understood that such a measured pressure value need not necessarily be any particular form, such as in psi units. Instead, a “measured pressure” or “determined pressure” may include any value that is representative of a pressure, such as a voltage level, a resistance value, a multibit digital number, etc. For example, a pressure transducer used to measure pressure in the pump control chamber may output an analog voltage level, resistance or other indication that is representative of the pressure in the pump control chamber. The raw output from the transducer may be used as a measured pressure, and/or some modified form of the output, such as a digital number generated using an analog output from the transducer, a psi or other value that is generated based on the transducer output, and so on. The same is true of other values, such as a determined volume, which need not necessarily be in a particular form such as cubic centimeters. Instead, a determined volume may include any value that is representative of the volume, e.g., could be used to generate an actual volume in, say, cubic centimeters.) 
     In an embodiment of a fluid management system (“FMS”) technique to determine a volume delivered by the pump, it is assumed that pressure equalization upon opening of the valve X 2  occurs in an adiabatic system. Thus, Equation 3 below gives the relationship of the volume of the reference chamber system before and after pressure equalization: 
         Vrf=Vri ( Pf/Patm ) −(1/γ)   (3)
 
     where Vrf is the final (post-equalization) volume of the reference chamber system including the volume of the reference chamber, the volume of the lines L 2  and L 3  and the volume adjustment resulting from movement of the “piston”, which may move to the left or right of the valve X 2  after opening, Vri is the initial (pre-equalization) volume of the reference chamber and the lines L 2  and L 3  with the “piston” located at the valve X 2 , Pf is the final equalized pressure after the valve X 2  is opened, and Patm is the initial pressure of the reference chamber before valve X 2  opening (in this example, atmospheric pressure). Similarly, Equation 4 gives the relationship of the volume of the control chamber system before and after pressure equalization: 
         Vdf=Vdi ( Pf/Pdi ) −(1/γ)   (4)
 
     where Vdf is the final volume of the control chamber system including the volume of the control chamber, the volume of the lines L 0  and L 1 , and the volume adjustment resulting from movement of the “piston”, which may move to the left or right of the valve X 2  after opening, Vdi is the initial volume of the control chamber and the lines L 0  and L 1  with the “piston” located at the valve X 2 , Pf is the final pressure after the valve X 2  is opened, and Pdi is the initial pressure of the control chamber before valve X 2  opening. 
     The volumes of the reference chamber system and the control chamber system will change by the same absolute amount after the valve X 2  is opened and the pressure equalizes, but will differ in sign (e.g., because the change in volume is caused by movement of the “piston” left or right when the valve X 2  opens), as shown in Equation 5: 
       Δ Vr =(−1)Δ Vd   (5)
 
     (Note that this change in volume for the reference chamber and the control chamber is due only to movement of the imaginary piston. The reference chamber and control chamber will not actually change in volume during the equalization process under normal conditions.) Also, using the relationship from Equation 3, the change in volume of the reference chamber system is given by: 
       Δ Vr=Vrf−Vri=Vri (−1+( Pf/Patm ) −(1/γ) )  (6)
 
     Similarly, using Equation 4, the change in volume of the control chamber system is given by: 
       Δ Vd=Vdf−Vdi=Vdi (−1+( Pf/Pdi ) −(1/γ) )  (7)
 
     Because Vri is known, and Pf and Patm are measured or known, ΔVr can be calculated, which according to Equation 5 is assumed to be equal to (−)ΔVd. Therefore, Vdi (the volume of the control chamber system before pressure equalization with the reference chamber) can be calculated using Equation 7. In this embodiment, Vdi represents the volume of the control chamber plus lines L 0  and L 1 , of which L 0  and L 1  are fixed and known quantities. Subtracting L 0  and L 1  from Vdi yields the volume of the control chamber alone. By using Equation 7 above, for example, both before (Vdi 1 ) and after (Vdi 2 ) a pump operation (e.g., at the end of a fill cycle and at the end of a discharge cycle), the change in volume of the control chamber can be determined, thus providing a measurement of the volume of fluid delivered by (or taken in by) the pump. For example, if Vdi 1  is the volume of the control chamber at the end of a fill stroke, and Vdi 2  is the volume of the control chamber at the end of the subsequent delivery stroke, the volume of fluid delivered by the pump may be estimated by subtracting Vdi 1  from Vdi 2 . Since this measurement is made based on pressure, the volume determination can be made for nearly any position of the membrane  15 /pump control region  1482  in the pump chamber  181 , whether for a full or partial pump stroke. However, measurement made at the ends of fill and delivery strokes can be accomplished with little or no impact on pump operation and/or flow rate. 
     One aspect of the invention involves a technique for identifying pressure measurement values that are to be used in determining a volume for the control chamber and/or other purposes. For example, although pressure sensors may be used to detect a pressure in the control chamber and a pressure in the reference chamber, the sensed pressure values may vary with opening/closing of valves, introduction of pressure to the control chamber, venting of the reference chamber to atmospheric pressure or other reference pressure, etc. Also, since in one embodiment, an adiabatic system is assumed to exist from a time before pressure equalization between the control chamber and the reference chamber until after equalization, identifying appropriate pressure values that were measured as close together in time may help to reduce error (e.g., because a shorter time elapsed between pressure measurements may reduce the amount of heat that is exchanged in the system). Thus, the measured pressure values may need to be chosen carefully to help ensure appropriate pressures are used for determining a volume delivered by the pump, etc. 
     For purposes of explanation,  FIG. 43  shows a plot of illustrative pressure values for the control chamber and the reference chamber from a point in time before opening of the valve X 2  until some time after the valve X 2  is opened to allow the pressure in the chambers to equalize. In this illustrative embodiment, the pressure in the control chamber is higher than the pressure in the reference chamber before equalization, but it should be understood that the control chamber pressure may be lower than the reference chamber pressure before equalization in some arrangements, such as during and/or at the end of a fill stroke. Also, the plot in  FIG. 43  shows a horizontal line marking the equalization pressure, but it should be understood that this line is shown for clarity only. The equalization pressure in general will not be known prior to opening of the valve X 2 . In this embodiment, the pressure sensors sense pressure at a rate of about 2000 Hz for both the control chamber and the reference chamber, although other suitable sampling rates could be used. Before opening of the valve X 2 , the pressures in the control chamber and the reference chamber are approximately constant, there being no air or other fluid being introduced into the chambers. Thus, the valves X 1  and X 3  will generally be closed at a time before opening of the valve X 2 . Also, valves leading into the pump chamber, such as the valve ports  190  and  192 , may be closed to prevent influence of pressure variations in the pump chamber, the liquid supply or liquid outlet. 
     At first, the measured pressure data is processed to identify the initial pressures for the control chamber and reference chambers, i.e., Pd and Pr. In one illustrative embodiment, the initial pressures are identified based on analysis of a 10-point sliding window used on the measured pressure data. This analysis involves generating a best fit line for the data in each window (or set), e.g., using a least squares technique, and determining a slope for the best fit line. For example, each time a new pressure is measured for the control chamber or the reference chamber, a least squares fit line may be determined for a data set including the latest measurement and the 9 prior pressure measurements. This process may be repeated for several sets of pressure data, and a determination may be made as to when the slope of the least squares fit lines first becomes negative (or otherwise non-zero) and continues to grow more negative for subsequent data sets (or otherwise deviates from a zero slope). The point at which the least squares fit lines begin to have a suitable, and increasing, non-zero slope may be used to identify the initial pressure of the chambers, i.e., at a time before the valve X 2  is opened. 
     In one embodiment, the initial pressure value for the reference chamber and the control chamber may be determined to be in the last of 5 consecutive data sets, where the slope of the best fit line for the data sets increases from the first data set to the fifth data set, and the slope of the best fit line for the first data set first becomes non-zero (i.e., the slope of best fit lines for data sets preceding the first data set is zero or otherwise not sufficiently non-zero). For example, the pressure sensor may take samples every ½ millisecond (or other sampling rate) starting at a time before the valve X 2  opens. Every time a pressure measurement is made, the cycler  14  may take the most recent measurement together with the prior 9 measurements, and generate a best fit line to the 10 data points in the set. Upon taking the next pressure measurement (e.g., ½ millisecond later), the cycler  14  may take the measurement together with the 9 prior measurements, and again generate a best fit line to the 10 points in the set. This process may be repeated, and the cycler  14  may determine when the slope of the best fit line for a set of 10 data points first turns non-zero (or otherwise suitably sloped) and, for example, that the slope of the best fit line for 5 subsequent sets of 10 data points increases with each later data set. To identify the specific pressure measurement to use, one technique is to select the third measurement in the 5 th  data set (i.e., the 5 th  data set with which it was found that the best fit line has been consistently increasing in slope and the 1 St  measurement is the pressure measurement that was taken earliest in time) as the measurement to be used as the initial pressure for the control chamber or the reference chamber, i.e., Pd or Pr. This selection was chosen using empirical methods, e.g., plotting the pressure measurement values and then selecting which point best represents the time when the pressure began the equalization process. Of course, other techniques could be used to select the appropriate initial pressure. 
     In one illustrative embodiment, a check may be made that the times at which the selected Pd and Pr measurements occurred were within a desired time threshold, e.g., within 1-2 milliseconds of each other. For example, if the technique described above is used to analyze the control chamber pressure and the reference chamber pressure and identify a pressure measurement (and thus a point in time) just before pressure equalization began, the times at which the pressures were measured should be relatively close to each other. Otherwise, there may have been an error or other fault condition that invalidates one or both of the pressure measurements. By confirming that the time at which Pd and Pr occurred are suitably close together, the cycler  14  may confirm that the initial pressures were properly identified. 
     To identify when the pressures in the control chamber and the reference chamber have equalized such that measured pressures for the chamber can be used to reliably determine pump chamber volume, the cycler  14  may analyze data sets including a series of data points from pressure measurements for both the control chamber and the reference chamber, determine a best fit line for each of the data sets (e.g., using a least squares method), and identify when the slopes of the best fit lines for a data set for the control chamber and a data set for the reference chamber are first suitably similar to each other, e.g., the slopes are both close to zero or have values that are within a threshold of each other. When the slopes of the best fit lines are similar or close to zero, the pressure may be determined to be equalized. The first pressure measurement value for either data set may be used as the final equalized pressure, i.e., Pf. In one illustrative embodiment, it was found that pressure equalization occurred generally within about 200-400 milliseconds after valve X 2  is opened, with the bulk of equalization occurring within about 50 milliseconds. Accordingly, the pressure in the control and reference chambers may be sampled approximately 400-800 times or more during the entire equalization process from a time before the valve X 2  is opened until a time when equalization has been achieved. 
     In some cases, it may be desirable to increase the accuracy of the control chamber volume measurement using an alternate FMS technique. Substantial differences in temperature between the liquid being pumped, the control chamber gas, and the reference chamber gas may introduce significant errors in calculations based on the assumption that pressure equalization occurs adiabatically. Waiting to make pressure measurements until full equalization of pressure between the control chamber and the reference chamber may allow an excessive amount of heat transfer to occur. In one aspect of the invention, pressure values for the pump chamber and reference chamber that are substantially unequal to each other, i.e., that are measured before complete equalization has occurred, may be used to determine pump chamber volume. 
     In one embodiment, heat transfer may be minimized, and adiabatic calculation error reduced, by measuring the chamber pressures throughout the equalization period from the opening of valve X 2  through full pressure equalization, and selecting a sampling point during the equalization period for the adiabatic calculations. In one embodiment of an APD system, measured chamber pressures that are taken prior to complete pressure equalization between the control chamber and the reference chamber can be used to determine pump chamber volume. In one embodiment, these pressure values may be measured about 50 ms after the chambers are first fluidly connected and equalization is initiated. As mentioned above, in one embodiment, complete equalization may occur about 200-400 ms after the valve X 2  is opened. Thus, the measured pressures may be taken at a point in time after the valve X 2  is opened (or equalization is initiated) that is about 10% to 50% or less of the total equalization time period. Said another way, the measured pressures may be taken at a point in time at which 50-70% of pressure equalization has occurred (i.e., the reference and pump chamber pressures have changed by about 50-70% of the difference between the initial chamber pressure and the final equalized pressure. Using a computer-enabled controller, a substantial number of pressure measurements in the control and reference chambers can be made, stored and analyzed during the equalization period (for example, 40-100 individual pressure measurements). Among the time points sampled during the first 50 ms of the equalization period, there is a theoretically optimized sampling point for conducting the adiabatic calculations (e.g., see  FIG. 43  in which the optimized sampling point occurs at about 50 ms after opening of the valve X 2 ). The optimized sampling point may occur at a time early enough after valve X 2  opening to minimize thermal transfer between the gas volumes of the two chambers, but not so early as to introduce significant errors in pressure measurements due to the properties of the pressure sensors and delays in valve actuation. However, as can be seen in  FIG. 43 , the pressures for the pump chamber and reference chambers may be substantially unequal to each other at this point, and thus equalization may not be complete. (Note that in some cases, it may be technically difficult to take reliable pressure measurements immediately after the opening of valve X 2 , for example, because of the inherent inaccuracies of the pressure sensors, the time required for valve X 2  to fully open, and the rapid initial change in the pressure of either the control chamber or the reference chamber immediately after the opening of valve X 2 .) 
     During pressure equalization, when the final pressure for the control chamber and reference chambers are not the same, Equation 2 becomes: 
         PriVri   γ   +PdiVdi   γ =Constant= PrfVrf   γ   +PdfVdf   γ   (8)
 
     where: Pri=pressure in the reference chamber prior to opening valve X 2 , Pdi=pressure in the control chamber prior to opening valve X 2 , Prf=final reference chamber pressure, Pdf=final control chamber pressure. 
     An optimization algorithm can be used to select a point in time during the pressure equalization period at which the difference between the absolute values of ΔVd and ΔVr is minimized (or below a desired threshold) over the equalization period. (In an adiabatic process, this difference should ideally be zero, as indicated by Equation 5. In  FIG. 43  the point in time at which the difference between the absolute values of ΔVd and ΔVr is minimized occurs at the 50 ms line, marked “time at which final pressures identified.”) First, pressure data can be collected from the control and reference chambers at multiple points j=1 through n between the opening of valve X 2  and final pressure equalization. Since Vri, the fixed volume of the reference chamber system before pressure equalization, is known, a subsequent value for Vrj (reference chamber system volume at sampling point j after valve X 2  has opened) can be calculated using Equation 3 at each sampling point Prj along the equalization curve. For each such value of Vrj, a value for ΔVd can be calculated using Equations 5 and 7, each value of Vrj thus yielding Vdij, a putative value for Vdi, the volume of the control chamber system prior to pressure equalization. Using each value of Vrj and its corresponding value of Vdij, and using Equations 3 and 4, the difference in the absolute values of ΔVd and ΔVr can be calculated at each pressure measurement point along the equalization curve. The sum of these differences squared provides a measure of the error in the calculated value of Vdi during pressure equalization for each value of Vrj and its corresponding Vdij. Denoting the reference chamber pressure that yields the least sum of the squared differences of |ΔVd| and |ΔVr| as Prf, and its associated reference chamber volume as Vrf, the data points Prf and Pdf corresponding to Vrf can then be used to calculate an optimized estimate of Vdi, the initial volume of the control chamber system. 
     One method for determining where on the equalization curve to capture an optimized value for Pdf and Prf is as follows:
         1) Acquire a series of pressure data sets from the control and reference chambers starting just before the opening of valve X 2  and ending with Pr and Pd becoming close to equal. If Pri is the first reference chamber pressure captured, then the subsequent sampling points in  FIG. 32  will be referred to as Prj=Pr 1 , Pr 2 , . . . Prn.   2) Using Equation 6, for each Prj after Pri, calculate the corresponding ΔVrj where j represents the jth pressure data point after Pri.       

       Δ Vrj=Vrj−Vri=Vri (−1+( Prj/Pri ) −(1/γ)  
         3) For each such ΔVrj calculate the corresponding Vdij using Equation 7. For example:       

       Δ Vr 1= Vri *(−1+( Pr 1/ Pri ) −(1/γ) )
 
       Δ Vd 1=−Δ Vr 1
 
       Therefore, 
         Vdi 1=Δ Vd 1/(−1+( Pd 1/ Pdi ) −(1/γ) )
 
       . 
       . 
         Vdin=ΔVdn /(−1+( Pdn/Pdi ) −(1/γ) )
 
     Having calculated a set of n control chamber system initial volumes (Vdi 1  to Vdin) based on the set of reference chamber pressure data points Pr 1  to Prn during pressure equalization, it is now possible to select the point in time (f) that yields an optimized measure of the control chamber system initial volume (Vdi) over the entire pressure equalization period.
         4) Using Equation 7, for each Vdi 1  through Vdin, calculate all ΔVdj,k using control chamber pressure measurements Pd for time points k=1 to n.
           For the Vdi corresponding to Pr 1 :   
               

     
       
         
           
             
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             5) Take the sum-square error between the absolute values of the ΔVr&#39;s and ΔVdj,k&#39;s 
           
         
       
    
     
       
         
           
             
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                 [S1 represents the sum-square error of |ΔVd| minus |ΔVr| over all data points during the equalization period when using the first data point Pr 1  to determine Vdi, the control chamber system initial volume, from Vr 1  and ΔVr.] 
               
             
           
         
       
    
     
       
         
           
             
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             6) The Pr data point between Pr 1  and Prn that generates the minimum sum-square error S from step 5 (or a value that is below a desired threshold) then becomes the chosen Prf, from which Pdf and an optimized estimate of Vdi, the control chamber initial volume, can then be determined. In this example, Pdf occurs at, or about, the same time as Prf. 
             7) The above procedure can be applied any time that an estimate of the control chamber volume is desired, but can preferably be applied at the end of each fill stroke and each delivery stroke. The difference between the optimized Vdi at the end of a fill stroke and the optimized Vdi at the end of a corresponding delivery stroke can be used to estimate the volume of liquid delivered by the pump. 
           
         
       
    
     Air Detection 
     Another aspect of the invention involves the determination of a presence of air in the pump chamber  181 , and if present, a volume of air present. Such a determination can be important, e.g., to help ensure that a priming sequence is adequately performed to remove air from the cassette  24  and/or to help ensure that air is not delivered to the patient. In certain embodiments, for example, when delivering fluid to the patient through the lower opening  187  at the bottom of the pump chamber  181 , air or other gas that is trapped in the pump chamber may tend to remain in the pump chamber  181  and will be inhibited from being pumped to the patient unless the volume of the gas is larger than the volume of the effective dead space of pump chamber  181 . As discussed below, the volume of the air or other gas contained in pump chambers  181  can be determined in accordance with aspects of the present invention and the gas can be purged from pump chamber  181  before the volume of the gas is larger than the volume of the effective dead space of pump chamber  181 . 
     A determination of an amount of air in the pump chamber  181  may be made at the end of a fill stroke, and thus, may be performed without interrupting a pumping process. For example, at the end of a fill stroke during which the membrane  15  and the pump control region  1482  are drawn away from the cassette  24  such that the membrane  15 /region  1482  are brought into contact with the wall of the control chamber  171 , the valve X 2  may be closed, and the reference chamber vented to atmospheric pressure, e.g., by opening the valve X 3 . Thereafter, the valves X 1  and X 3  may be closed, fixing the imaginary “piston” at the valve X 2 . The valve X 2  may then be opened, allowing the pressure in the control chamber and the reference chamber to equalize, as was described above when performing pressure measurements to determine a volume for the control chamber. 
     If there is no air bubble in the pump chamber  181 , the change in volume of the reference chamber, i.e., due to the movement of the imaginary “piston,” determined using the known initial volume of the reference chamber system and the initial pressure in the reference chamber, will be equal to the change in volume of the control chamber determined using the known initial volume of the control chamber system and the initial pressure in the control chamber. (The initial volume of the control chamber may be known in conditions where the membrane  15 /control region  1482  are in contact with the wall of the control chamber or in contact with the spacer elements  50  of the pump chamber  181 .) However, if air is present in the pump chamber  181 , the change in volume of the control chamber will actually be distributed between the control chamber volume and the air bubble(s) in the pump chamber  181 . As a result, the calculated change in volume for the control chamber using the known initial volume of the control chamber system will not be equal to the calculated change in volume for the reference chamber, thus signaling the presence of air in the pump chamber. 
     If there is air in the pump chamber  181 , the initial volume of the control chamber system Vdi is actually equal to the sum of the volume of the control chamber and lines L 0  and L 1  (referred to as Vdfix) plus the initial volume of the air bubble in the pump chamber  181 , (referred to as Vbi), as shown in Equation 9: 
         Vdi=Vbi+Vdfix   (9)
 
     With the membrane  15 /control region  1482  pressed against the wall of the control chamber at the end of a fill stroke, the volume of any air space in the control chamber, e.g., due to the presence of grooves or other features in the control chamber wall, and the volume of the lines L 0  and L 1 —together Vdfix—can be known quite accurately. (Similarly, with the membrane  15 /control region  1482  pressed against the spacer elements  50  of the pump chamber  181 , the volume of the control chamber and the lines L 0  and L 1  can be known accurately.) After a fill stroke, the volume of the control chamber system is tested using a positive control chamber pre-charge. Any discrepancy between this tested volume and the tested volume at the end of the fill stroke may indicate a volume of air present in the pump chamber. Substituting from Equation 9 into Equation 7, the change in volume of the control chamber ΔVd is given by: 
       Δ Vd =( Vbi+Vdfix )(−1+( Pdf/Pdi ) −(1/γ) )  (10)
 
     Since ΔVr can be calculated from Equation 6, and we know from Equation 5 that ΔVr=(−1) ΔVd, Equation 10 can be re-written as: 
       (−1)Δ Vr =( Vbi+Vdfix )(−1+( Pdf/Pdi ) −(1/γ) )  (11)
 
       and again as: 
         Vbi =(−1)Δ Vr /(−1+( Pdf/Pdi ) −(1/γ) )− Vdfix   (12)
 
     Accordingly, the cycler  14  can determine whether there is air in the pump chamber  181 , and the approximate volume of the bubble using Equation 12. This calculation of the air bubble volume may be performed if it is found, for example, that the absolute values of ΔVr (as determined from Equation 6) and ΔVd (as determined from Equation 7 using Vdi=Vdfix) are not equal to each other. That is, Vdi should be equal to Vdfix if there is no air present in the pump chamber  181 , and thus the absolute value for ΔVd given by Equation 7 using Vdfix in place of Vdi will be equal to ΔVr. 
     After a fill stroke has been completed, and if air is detected according to the methods described above, it may be difficult to determine whether the air is located on the pump chamber side or the control side of the membrane  15 . Air bubbles could be present in the liquid being pumped, or there could be residual air on the control (pneumatic) side of the pump membrane  15  because of a condition (such as, for example, an occlusion) during pumping that caused an incomplete pump stroke, and incomplete filling of the pump chamber. At this point, an adiabatic FMS measurement using a negative pump chamber pre-charge can be done. If this FMS volume matches the FMS volume with the positive precharge, then the membrane is free to move in both directions, which implies that the pump chamber is only partially filled (possibly, for example, due to an occlusion). If the value of the negative pump chamber pre-charge FMS volume equals the nominal control chamber air volume when the membrane  15 /region  1482  is in contact with the inner wall of the control chamber, then it is possible to conclude that there is an air bubble in the liquid on the pump chamber side of the flexible membrane. 
     Head Height Detection 
     In some circumstances, it may be useful to determine the heightwise location of the patient relative to the cassette  24  or other portion of the system. For example, dialysis patients in some circumstances can sense a “tugging” or other motion due to fluid flowing into or out of the patient&#39;s peritoneal cavity during a fill or drain operation. To reduce this sensation, the cycler  14  may reduce the pressure applied to the patient line  34  during fill and/or drain operations. However, to suitably set the pressure for the patient line  34 , the cycler  14  may determine the height of the patient relative to the cycler  14 , the heater bag  22 , drain or other portion of the system. For example, when performing a fill operation, if the patient&#39;s peritoneal cavity is located 5 feet above the heater bag  22  or the cassette  24 , the cycler  14  may need to use a higher pressure in the patient line  34  to deliver dialysate than if the patient&#39;s peritoneal cavity is located 5 ft below the cycler  14 . The pressure may be adjusted, for example, by alternately opening and closing a binary pneumatic source valve for variable time intervals to achieve the desired target pump chamber pressure. An average desired target pressure can be maintained, for example, by adjusting the time intervals to keep the valve open when the pump chamber pressure is below the target pressure by a specified amount, and to keep the valve closed when the pump chamber pressure is above the target pressure by a specified amount. Any adjustments to maintain the delivery of a complete stroke volume can be made by adjusting the fill and/or delivery times of the pump chamber. If a variable orifice source valve is used, the target pump chamber pressure can be reached by varying the orifice of the source valve in addition to timing the intervals during which the valve is opened and closed. To adjust for patient position, the cycler  14  may momentarily stop pumping of fluid, leaving the patient line  34  in open fluid communication with one or more pump chambers  181  in the cassette (e.g., by opening suitable valve ports in the cassette  24 ). However, other fluid lines may be closed, such as the upper valve ports  192  for the pump chambers  181 . In this condition, the pressure in the control chamber for one of the pumps may be measured. As is well known in the art, this pressure correlates with the “head” height of the patient, and can be used by the cycler  14  to control the delivery pressure of fluid to the patient. A similar approach can be used to determine the “head” height of the heater bag  22  (which will generally be known), and/or the solution containers  20 , as the head height of these components may have an effect on pressure needed for pumping fluid in a suitable way. 
     Noise Reduction Features of the Cycler 
     In accordance with aspects of the invention, the cycler  14  may include one or more features to reduce noise generated by the cycler  14  during operation and/or when idle. In one aspect of the invention, the cycler  14  may include a single pump that generates both pressure and vacuum that are used to control the various pneumatic systems of the cycler  14 . In one embodiment, the pump can simultaneously generate both pressure and vacuum, thereby reducing overall run time, and allowing the pump to run more slowly (and thus more quietly). In another embodiment, the air pump start and/or stop may be ramped, e.g., slowly increases pump speed or power output at starting and/or slowly decreases pump speed or power output at shut down. This arrangement may help reduce “on/off” noise associated with start and stop of the air pump so pump noise is less noticeable. In another embodiment, the air pump may be operated at a lower duty cycle when nearing a target output pressure or volume flow rate so that the air pump can continue operating as opposed to shutting off, only to be turned on after a short time. As a result, disruption caused by repeated on and off cycles of the air pump may be avoided. 
       FIG. 44  shows a perspective view of an interior section of the cycler  14  with the upper portion of the housing  82  removed. In this illustrative embodiment, the cycler  14  includes a single air pump  83 , which includes the actual pump and motor drive contained within a sound barrier enclosure. The sound barrier enclosure includes an outer shield, such as a metal or plastic frame, and a sound insulation material within the outer shield and at least partially surrounding the motor and pump. This air pump  83  may simultaneously provide air pressure and vacuum, e.g., to a pair of accumulator tanks  84 . One of the tanks  84  may store positive pressure air, while the other stores vacuum. A suitable manifold and valve arrangement may be coupled to the tanks  84  so as to provide and control air pressure/vacuum supplied to the components of the cycler  14 . 
     In accordance with another aspect of the invention, components that require a relatively constant pressure or vacuum supply during cycler operation, such as an occluder, may be isolated from the source of air pressure/vacuum at least for relatively long periods of time. For example, the occluder  147  in the cycler  14  generally requires a constant air pressure in the occluder bladder  166  so that the patient and drain lines remain open for flow. If the cycler  14  continues to operate properly without power failure, etc., the bladder  166  may be inflated once at the beginning of system operation and remain inflated until shut down. The inventors have recognized that in some circumstances air powered devices that are relatively static, such as the bladder  166 , may “creak” or otherwise make noise in response to slight variations in supplied air pressure. Such variations may cause the bladder  166  to change size slightly, which causes associated mechanical parts to move and potentially make noise. In accordance with an aspect of the bladder  166  and other components having similar pneumatic power requirements, may be isolated from the air pump  83  and/or the tanks  84 , e.g., by the closing of a valve, so as to reduce variations of pressure in the bladder or other pneumatic component, thus reducing noise that may be generated as a result of pressure variations. Another component that may be isolated from the pneumatic supply is the bladder in the door  141  at the cassette mounting location  145  which inflates to press the cassette  24  against the control surface  148  when the door  141  is closed. Other suitable components may be isolated as desired. 
     In accordance with another aspect of the invention, the speed and/or force at which pneumatic components are actuated may be controlled to as to reduce noise generated by component operation. For example, movement of the valve control regions  1481  to move a corresponding portion of the cassette membrane  15  so as to open or close a valve port on the cassette  24  may cause a “popping” noise as the membrane  15  slaps against and/or pull away from the cassette  24 . Such noise may be reduced by controlling the rate of operation of the valve control regions  1481 , e.g., by restricting the flow rate of air used to move the control regions  1481 . Air flow may be restricted by, for example, providing a suitably small sized orifice in the line leading to the associated control chamber, or in other ways. 
     A controller may also be programmed to apply pulse width modulation (“PWM”) to the activation of one or more pneumatic source valves at a manifold of cycler  14 . The pneumatic pressure delivered to various valves and pumps of cassette  24  can be controlled by causing the associated manifold source valves to open and close repeatedly during the period of actuation of a valve or pump in cassette  24 . The rate of rise or fall of pressure against membrane  15 /control surface  148  can then be controlled by modulating the duration of the “on” portion of the particular manifold valve during the actuation period. An additional advantage of applying PWM to the manifold source valves is that variable pneumatic pressure can be delivered to the cassette  24  components using only a binary (on-off) source valve, rather than a more expensive and potentially less reliable variable-orifice source valve. 
     In accordance with another aspect of the invention, the movement of one or more valve elements may be suitably damped so as to reduce noise generated by valve cycling. For example, a fluid (such as a ferro fluid) may be provided with the valve element of high frequency solenoid valves to damp the movement of the element and/or reduce noise generated by movement of the valve element between open and closed positions. 
     In accordance with another embodiment, pneumatic control line vents may be connected together and/or routed into a common, sound-insulated space so that noise associated with air pressure or vacuum release may be reduced. For example, when the occluder bladder  166  is vented to allow the spring plates  165  to move toward each other and occlude one or more lines, the air pressure released may be released into a sound insulated enclosure, as opposed to being released into a space where noise associated with the release may be heard more easily. In another embodiment, lines that are arranged to release air pressure may be connected together with lines that are arranged to release an air vacuum. With this connection (which may include a vent to atmosphere, an accumulator or other), noise generated by pressure/vacuum release may be further reduced. 
     Control System 
     The control system  16  described in connection with  FIG. 1  has a number of functions, such as controlling dialysis therapy and communicating information related to the dialysis therapy. While these functions may be handled by a single computer or processor, it may be desirable to use different computers for different functions so that the implementations of those functions are kept physically and conceptually separate. For example, it may be desirable to use one computer to control the dialysis machinery and another computer to control the user interface. 
       FIG. 45  shows a block diagram illustrating an exemplary implementation of control system  16 , wherein the control system comprises a computer that controls the dialysis machinery (an “automation computer”  300 ) and a separate computer that controls the user interface (a “user interface computer”  302 ). As will be described, safety-critical system functions may be run solely on the automation computer  300 , such that the user interface computer  302  is isolated from executing safety-critical functions. 
     The automation computer  300  controls the hardware, such as the valves, heaters and pumps, that implement the dialysis therapy. In addition, the automation computer  300  sequences the therapy and maintains a “model” of the user interface, as further described herein. As shown, the automation computer  300  comprises a computer processing unit (CPU)/memory  304 , a flash disk file system  306 , a network interface  308 , and a hardware interface  310 . The hardware interface  310  is coupled to sensors/actuators  312 . This coupling allows the automation computer  300  to read the sensors and control the hardware actuators of the APD system to monitor and perform therapy operations. The network interface  308  provides an interface to couple the automation computer  300  to the user interface computer  302 . 
     The user interface computer  302  controls the components that enable data exchange with the outside world, including the user and external devices and entities. The user interface computer  302  comprises a computer processing unit (CPU)/memory  314 , a flash disk file system  316 , and a network interface  318 , each of which may be the same as or similar to their counterparts on the automation computer  300 . The Linux operating system may run on each of the automation computer  300  and the user interface computer  302 . An exemplary processor that may be suitable for use as the CPU of the automation computer  300  and/or for use as the CPU of the user interface computer  302  is Freescale&#39;s Power PC 5200B®. 
     Via the network interface  318 , the user interface computer  302  may be connected to the automation computer  300 . Both the automation computer  300  and the user interface computer  302  may be included within the same chassis of the APD system. Alternatively, one or both computers or a portion of said computers (e.g., display  324 ) may be located outside of the chassis. The automation computer  300  and the user interface computer  302  may be coupled by a wide area network, a local area network, a bus structure, a wireless connection, and/or some other data transfer medium. 
     The network interface  318  may also be used to couple the user interface computer  302  to the Internet  320  and/or other networks. Such a network connection may be used, for example, to initiate connections to a clinic or clinician, upload therapy data to a remote database server, obtain new prescriptions from a clinician, upgrade application software, obtain service support, request supplies, and/or export data for maintenance use. According to one example, call center technicians may access alarm logs and machine configuration information remotely over the Internet  320  through the network interface  318 . If desired, the user interface computer  302  may be configured such that connections may only be initiated by the user or otherwise locally by the system, and not by remote initiators. 
     The user interface computer  302  also comprises a graphics interface  322  that is coupled to a user interface, such as the user interface  144  described in connection with  FIG. 10 . According to one exemplary implementation, the user interface comprises a display  324  that includes a liquid crystal display (LCD) and is associated with a touch screen. For example, a touch screen may be overlaid on the LCD so that the user can provide inputs to the user interface computer  302  by touching the display with a finger, stylus or the like. The display may also be associated with an audio system capable of playing, among other things, audio prompts and recorded speech. The user may adjust the brightness of the display  324  based on their environment and preference. Optionally, the APD system may include a light sensor, and the brightness of the display may be adjusted automatically in response to the amount of ambient light detected by the light sensor. 
     The brightness of the display may be set by the users for two different conditions: high ambient light and low ambient light. The light sensor will detect the ambient light level and the control system  16  will set the display brightness to the preselected levels for either high or low ambient light based on the measured ambient light. The user may select the brightness level for high and low ambient light by selection a value from 1 to 5 for each condition. The user interface may be a slider bar for each condition. In another example the user may select a number. The control system may set the button light levels to match the display light levels. 
     The LCD display and/or the touch screen of the display  324  may develop faults, where they do not display and/or respond correctly. One theory, but not the only theory, of the cause is an electro-static discharge from a user to the screen that changes the values in the memories of the drivers for the LCD display and touch screen. The software processes UIC executive  354  or the AC executive  354  may include a low priority sub-process or thread that checks the constant memory registers of the drivers for the touch screen and LCD display. If thread finds that any of the constant values in the memory registers are different from those stored elsewhere in the User Interface computer  302  or automation computer  300 , then the thread calls for another software process to reinitialize the drivers for LCD display and/or the touch screen. In one embodiment, the LCD display is driven by a Kieko Epson S1d13513 chip and the touch screen is driven by Wolfson Microelectronics WM97156 chip. Examples of the constant register values include but are not limited to the number of pixels display on the screen, the number colors displayed. 
     In addition, the user interface computer  302  comprises a USB interface  326 . A data storage device  328 , such as a USB flash drive, may be selectively coupled to the user interface computer  302  via the USB interface  326 . The data storage device  328  may comprise a “patient data key” used to store patient-specific data. Data from dialysis therapies and/or survey questions (e.g., weight, blood pressure) may be logged to the patient data key. In this way, patient data may be accessible to the user interface computer  302  when coupled to the USB interface  326  and portable when removed from the interface. The patient data key may be used for transferring data from one system or cycler to another during a cycler swap, transferring new therapy and cycler configuration data from clinical software to the system, and transferring treatment history and device history information from the system to clinical software. An exemplary patient data key  325  is shown in  FIG. 65 . 
     As shown, the patient data key  325  comprises a connector  327  and a housing  329  coupled to the connector. The patient data key  325  may be optionally be associated with a dedicated USB port  331 . The port  331  comprises a recess  333  (e.g., in the chassis of the APD system) and a connector  335  disposed within the recess. The recess may be defined, at least in part, by a housing  337  associated with the port  331 . The patient data key connector  327  and the port connector  335  are adapted to be selectively electrically and mechanically coupled to each other. As may be appreciated from  FIG. 65 , when the patient data key connector  327  and the port connector  335  are coupled, the housing  329  of the patient data storage device  325  is received at least partially within the recess  333 . 
     The housing  329  of the patient data key  325  may include visual cues indicative of the port with which it is associated and/or be shaped to prevent incorrect insertion. For example, the recess  333  and/or housing  337  of the port  331  may have a shape corresponding to the shape of the housing  329  of the patient data key  325 . For example, each may have a non-rectangular or otherwise irregular shape, such as an oblong shape with an upper indentation as shown in  FIG. 65 . The recess  333  and/or housing  337  of the port  331  and the housing  329  of the patient data key  325  may include additional visual cues to indicate their association. For example, each may be formed of the same material and/or have the same or a similar color and/or pattern. 
     In a further embodiment, as shown in  FIG. 65A , the housing  329  of the patient data key  325  may constructed to be sloped away from connector  327  to carry any liquids that may splash onto the key  325  away from connector  327  and toward the opposite end of the housing  329 , where a hole  339  in the housing  329  may help drain the liquid off and away from the patient data key  325  and its coupling with the port connector  335 . 
     In one embodiment, the port  331  and recess  333  are located on the front panel  1084  of cycler  14  as shown in  FIG. 9-11 . The patient data key  325  is inserted in the port  331  before the door  141  is closed and therapy is started. The door  141  includes a second recess  2802  to accommodate the patient data key  325 , when the door  141  is closed. Locating the patient data key  325  behind the door  141  assures that all the therapy data may be recorded on to the PDK. This location prevents a user from removing the key mid-therapy. 
     Alternatively or additionally, the patient data key  325  may comprise a verification code that is readable by the APD system to verify that the patient data key is of an expected type and/or origin. Such a verification code may be stored in a memory of the patient data key  325 , and be read from the patient data key and processed by a processor of the APD system. Alternatively or additionally, such a verification code may be included on an exterior of the patient data key  325 , e.g., as a barcode or numeric code. In this case, the code may be read by a camera and associated processor, a barcode scanner, or another code reading device. 
     If the patient data key is not inserted when the system is powered on, an alert may be generated requesting that the key be inserted. However, the system may be able to run without the patient data key as long as it has been previously configured. Thus, a patient who has lost their patient data key may receive therapy until a replacement key can be obtained. Data may be stored directly to the patient data key or transferred to the patient data key after storage on the user interface computer  302 . Data may also be transferred from the patient data key to the user interface computer  302 . 
     In addition, a USB Bluetooth adapter  330  may be coupled to the user interface computer  302  via the USB interface  326  to allow, for example, data to be exchanged with nearby Bluetooth-enabled devices. For example, a Bluetooth-enabled scale in the vicinity of the APD system may wirelessly transfer information concerning a patient&#39;s weight to the system via the USB interface  326  using the USB Bluetooth adapter  330 . Similarly, a Bluetooth-enabled blood pressure cuff may wirelessly transfer information concerning a patient&#39;s blood pressure to the system using the USB Bluetooth adapter  330 . The Bluetooth adapter may be built-in to the user interface computer  302  or may be external (e.g., a Bluetooth dongle). 
     The USB interface  326  may comprise several ports, and these ports may have different physical locations and be used for different USB device. For example, it may be desirable to make the USB port for the patient data key accessible from the front of the machine, while another USB port may be provided at and accessible from the back of the machine. A USB port for the Bluetooth connection may be included on the outside of the chassis, or instead be located internal to the machine or inside the battery door, for example. 
     As noted above, functions that could have safety-critical implications may be isolated on the automation computer. Safety-critical information relates to operations of the APD system. For example, safety-critical information may comprise a state of a APD procedure and/or the algorithms for implementing or monitoring therapies. Non safety-critical information may comprise information that relates to the visual presentation of the screen display that is not material to the operations of the APD system. 
     By isolating functions that could have safety-critical implications on the automation computer  300 , the user interface computer  302  may be relieved of handling safety-critical operations. Thus, problems with or changes to the software that executes on the user interface computer  302  will not affect the delivery of therapy to the patient. Consider the example of graphical libraries (e.g., Trolltech&#39;s Qt® toolkit), which may be used by the user interface computer  302  to reduce the amount of time needed to develop the user interface view. Because these libraries are handled by a process and processor separate from those of the automation computer  300 , the automation computer is protected from any potential flaws in the libraries that might affect the rest of the system (including safety-critical functions) were they handled by the same processor or process. 
     Of course, while the user interface computer  302  is responsible for the presentation of the interface to the user, data may also be input by the user using the user interface computer  302 , e.g., via the display  324 . To maintain the isolation between the functions of the automation computer  300  and the user interface computer  302 , data received via the display  324  may be sent to the automation computer for interpretation and returned to the user interface computer for display. 
     Although  FIG. 45  shows two separate computers, separation of the storage and/or execution of safety-critical functions from the storage and/or execution of non safety-critical functions may be provided by having a single computer including separate processors, such as CPU/memory components  304  and  314 . Thus, it should be appreciated that providing separate processors or “computers” is not necessary. Further, a single processor may alternatively be used to perform the functions described above. In this case, it may be desirable to functionally isolate the execution and/or storage of the software components that control the dialysis machinery from those that control the user interface, although the invention is not limited in this respect. 
     Other aspects of the system architecture may also be designed to address safety concerns. For example, the automation computer  300  and user interface computer  302  may include a “safe line” that can be enabled or disabled by the CPU on each computer. The safe line may be coupled to a voltage supply that generates a voltage (e.g., 12 V) sufficient to enable at least some of the sensors/actuators  312  of the APD system. When both the CPU of the automation computer  300  and the CPU of the user interface computer  302  send an enable signal to the safe line, the voltage generated by the voltage supply may be transmitted to the sensors/actuators to activate and disable certain components. The voltage may, for example, activate the pneumatic valves and pump, disable the occluder, and activate the heater. When either CPU stops sending the enable signal to the safe line, the voltage pathway may be interrupted (e.g., by a mechanical relay) to deactivate the pneumatic valves and pump, enable the occluder, and deactivate the heater. In this way, when either the automation computer  300  or the user interface computer  302  deems it necessary, the patient may be rapidly isolated from the fluid path, and other activities such as heating and pumping may be stopped. Each CPU can disable the safe line at any time, such as when a safety-critical error is detected or a software watchdog detects an error. The system may be configured such that, once disabled, the safe line may not be re-enabled until both the automation computer  300  and user interface computer  302  have completed self-tests. 
       FIG. 46  shows a block diagram of the software subsystems of the user interface computer  302  and the automation computer  300 . In this example, a “subsystem” is a collection of software, and perhaps hardware, assigned to a specific set of related system functionality. A “process” may be an independent executable which runs in its own virtual address space, and which passes data to other processes using inter-process communication facilities. 
     The executive subsystem  332  includes the software and scripts used to inventory, verify, start and monitor the execution of the software running on the CPU of the automation computer  300  and the CPU of the user interface computer  302 . A custom executive process is run on each of the foregoing CPUs. Each executive process loads and monitors the software on its own processor and monitors the executive on the other processor. 
     The user interface (UI) subsystem  334 , handles system interactions with the user and the clinic. The UI subsystem  334  is implemented according to a “model-view-controller” design pattern, separating the display of the data (“view”) from the data itself (“model”). In particular, system state and data modification functions (“model”) and cycler control functions (“controller”) are handled by the UI model and cycler controller  336  on the automation computer  300 , while the “view” portion of the subsystem is handled by the UI screen view  338  on the UI computer  302 . Data display and export functionality, such as log viewing or remote access, may be handled entirely by the UI screen view  338 . The UI screen view  338  monitors and controls additional applications, such as those that provide log viewing and a clinician interface. These applications are spawned in a window controlled by the UI screen view  338  so that control can be returned to the UI screen view  338  in the case of an alert, an alarm or an error. 
     The therapy subsystem  340  directs and times the delivery of the dialysis treatment. It may also be responsible verifying a prescription, calculating the number and duration of therapy cycles based upon the prescription, time and available fluids, controlling the therapy cycles, tracking fluid in the supply bags, tracking fluid in the heater bag, tracking the amount of fluid in the patient, tracking the amount of ultra-filtrate removed from patient, and detecting alert or alarm conditions. 
     The machine control subsystem  342  controls the machinery used to implement the dialysis therapy, orchestrating the high level pumping and control functionality when called upon by the therapy subsystem  340 . In particular, the following control functions may be performed by the machine control subsystem  342 : air compressor control; heater control; fluid delivery control (pumping); and fluid volume measurement. The machine control subsystem  342  also signals the reading of sensors by the I/O subsystem  344 , described below. 
     The I/O subsystem  344  on the automation computer  300  controls access to the sensors and actuators used to control the therapy. In this implementation, the I/O subsystem  344  is the only application process with direct access to the hardware. Thus, the I/O subsystem  344  publishes an interface to allow other processes to obtain the state of the hardware inputs and set the state of the hardware outputs. 
     FPGA 
     In some embodiments, the Hardware Interface  310  in  FIG. 45  may be a separate processor from the automation computer  300  and the User Interface  302  that may perform a defined set of machine control functions and provide an additional layer of safety to the cycler controller  16 . A second processor, such as a field programmable gate array (FPGA) may increase the responsiveness and speed of the cycler  14  by moving some computing tasks from the automation computer  300  to the hardware interface  310  (e.g., an FPGA), so that the automation computer  300  can devote more resources to fluid management and therapy control, as these comprise resource-intensive calculations. The hardware interface  310  may control the pneumatic valves and record and temporarily store data from the various sensors. The real time control of the valves, pressure levels and data recording by the hardware interface  310  allows the automation computer  300  to send commands and receive data, when the software processes or functions running on the automation computer  300  are ready for them. 
     A hardware interface processor  310  may advantageously be implemented on any medical fluid delivery apparatus, including (but not limited to) a peritoneal dialysis cycler  14 , in which fluid is pumped by one or more pumps and an arrangement of one or more valves from one or more source containers of fluid (e.g., dialysate solution bags, or a heater bag containing fluid to be infused) to a patient or user. It may also be implemented on a fluid delivery apparatus that is configured to pump fluid from a patient or user (e.g., peritoneal dialysis cycler) to a receptacle (e.g., drain bag). A main processor may be dedicated to controlling the proper sequence and timing of pumps and valves to perform specific functions (e.g., pumping from a solution bag to a heater bag, pumping from a heater bag to a user, or pumping from a user to a drain receptacle), and to monitor the volumes of fluid pumped from one location to the next. A secondary (hardware interface) processor (e.g. an FPGA) may correspondingly be dedicated to collect and store data received from various sensors (e.g., pressure sensors associated with the pumps, or temperature sensors associated with a heating system) at an uninterrupted fixed rate (e.g., about 100 Hz or 200 Hz), and to store the data until it is requested by the main processor. It may also control the pumping pressures of the pumps at a rate or on a schedule that is independent from any processes occurring in the main processor. In addition to other functions (see below) it may also open or close individual valves on command from the main processor. 
     In one example the Hardware Interface  310  may be a processor that performs a number of functions including but not limited to:
         Acquiring pneumatic pressure sensor data on a predictable and fine resolution time base;   Storing the pressure data with a timestamp until requested by automation computer  300 ;   Validating the messages received from that automation computer  30 ;   Providing automated control of one or more pneumatic valves ______;   Controlling some valves with a variable pulse width modulation (PWM) duty cycle to provide Pick &amp; Hold functionality and/or control some valves with current feedback;   Provide automated and redundant safety checking of valve combinations, maximum pressures and temperatures and ability.   Independent of the other computers  300 ,  302  putting the cycler  14  into a failsafe mode as needed.   Monitoring status of buttons on the cycler  14  and controlling the level of button illumination;   Controlling the Auto Connect screw-drive mechanism  1321  and monitoring the Auto-Connect position sensing;   Detecting the presence of solution caps  31  and/or spike caps  63 ;   Control of the pneumatic pump;   Control of the prime sensor LED and detector;   Detecting over-voltages and testing hardware to detect over-voltages;   Controlling and monitoring one or more fluid detectors;   Monitoring the latch  1080  and proximity sensor  1076  on the door  141 ;   Monitoring critical voltages at the system level.       

     The Hardware Interface  310  may comprise a processor separate from the processors in the automation computer  300  and user interface  302 , A to D converts and one or more IO boards. In another embodiment, the hardware interface is comprised of a FPGA (Field Programmable Gate Array). In one embodiment the FPGA is a SPARTAN® 3A in the 400K gate and 256 ball package made by Xilinx Inc. of California. The Hardware Interface  310  is an intelligent entity that is employed to operate as an independent safety monitor for many of the Control CPU functions. There are several safety critical operations where either the Hardware Interface or the Control CPU serves as a primary controller and the other serves as a monitor. 
     The hardware interface  310  serves to monitor the following automation computer  300  functions including but not limited to:
         Monitoring the integrity of system control data being received from the automation computer  300 ;   Evaluating the commanded valve configurations for combination that could create a patient hazard during therapy;   Monitoring the fluid and pan temperature for excessive high or low temperatures;   Monitoring and testing the overvoltage monitor; and   Provide a means for the automation computer  300  to validate critical data returned from the hardware interface.       

       FIG. 45A  is a schematic representation of one arrangement of the automation computer  300 , the UI computer  302  and the hardware interface processor  310 . The hardware interface  310  is connected via a communication line to the automation computer  300  and connects to the sensors and actuators  312  in the cycler  14 . A voltage supply  2500  provides power for the safety critical actuators that can be enabled or disabled by any of the computers  300 ,  302 ,  310 . The safety critical actuators include but are not limited to the pneumatic valves, the pneumatic pump and a safety relay on the heater circuit. The pneumatic system is configured to safe condition when unpowered. The pneumatic safe condition may include occluding the lines  28 , 34  to the patient, isolating the control chambers  171  and/or closing all the valves  184 ,  186 ,  190 ,  192 , on the cassette  24 . The safety relay  2030  in the heater circuit  2212  is open, preventing electrical heating, when the relay is unpowered. Each computer  300 ,  302 ,  310  controls a separate electrical switch  2510  that can each interrupt power to the valves, pump and safety relay. If any of the three computers detects a fault condition, it can put the cycler  14  in a failsafe condition by opening one of the three switches  2510 . The electrical switches  2510  are controlled by the safety executive process  352 ,  354  in the UI computer  302 , and automation computer  300  respectively. 
       FIG. 45B  is a schematic illustration of the connections between the Hardware Interface  310 , the various sensors, the pneumatic valves, the bag heater and the automation computer  300 . The Hardware Interface  300  controls each of the pneumatic valves  2660 - 2667  and the pneumatic pump or compressor  2600  via pulse-width-modulated DC voltages.  FIG. 45B  presents an alternative embodiment of the safe line  2632  supplying power to the pneumatic valves  2660 - 2667 , pump  2600  and heater safety relay  2030 , in which a single switch  2510  is driven by an AND gate  2532  connected to the three computers  300 ,  302 ,  310 . The prime sensor is controlled and monitored by the Hardware Interface  310 . The brightness of the button LEDs is controlled by the Hardware Interface  310  via a PWM′d voltage. 
     The data signals from the buttons, pressure sensors, temperature sensors and other elements listed in  FIG. 45B  are monitored by the Hardware Interface  310 , and the data is stored in a buffer memory until called for by the automation computer  300 . The digital inputs are connected directly to the Hardware Interface  310 . The analog signals from pressure, temperature, current sensors and others are connected to Analog-to-Digital-Converter (ADC) boards that convert the analog signals to digital values and may a scale and/or offset the digital values. The outputs of the ADCs are communicated over SPI buses to the Hardware Interface  310 . The data is recorded and stored in the buffer at a fixed rate. Some of the data signals may be recorded at a relatively slow rate, including the pressure data on the pressure reservoirs and the fluid trap, temperatures, and current measurements. The low speed data may be recorded at 100 Hz. The adiabatic FMS volume measurement algorithm can be improved with high speed pressure data that is recorded at regular intervals. In a preferred embodiment, the pressure data from the sensors on the control volume  171  and the reference chamber  174  are recorded at 2000 Hz. The data may be stored in random-access-memory (RAM) along with a time stamp. The rate of data collection may preferably proceed independently of the automation computer  300  and of processes or subroutines on the hardware interface. The data is reported to the automation computer  300 , when a process calls for that value. 
     The transfer of data between the hardware interface  310  to the automation computer  300  may occur in a two step process where a data packet transferred and stored in a buffer before being validated and then accepted for use by the receiving computer. In one example, the sending computer transmits a first data packet, followed by a second transmission of the cyclic redundancy check (CRC) value for the first data packet. The receiving computer stores the first data packet in a memory buffer and calculates a new CRC value first data packet. The receiving computer then compares the newly calculated CRC value to the CRC value received and accepts the first data packet if the two CRC values match. The cyclic redundancy check (CRC) is an error-detecting code commonly used in digital networks and storage devices to detect accidental changes to raw data. Blocks of data entering these systems get a short check value attached, based on the remainder of a polynomial division of their contents; on retrieval the calculation is repeated, and corrective action can be taken against presumed data corruption if the check values do not match. The data is not transferred between the automation computer and hardware interface if CRC values do not match. If multiple consecutive data packets fail the CRC test, the receiving computer may signal an alarm and put the machine in a fail-safe condition by de-energizing the safe line  2632 . In one example, the alarm condition occurs on the third consecutive failed CRC check. 
     The automation computer  300  passes commands to open selected valves and set specified pressures in specified volumes to the hardware interface  300 . The hardware interface  310  in turn controls the valve position by providing a PWM′d voltage to each valve. The hardware interface  310  opens valves as requested with a pick-and-hold algorithm, where the valve is initially actuated with a high voltage or current, and then held in place with a lower voltage or current. Pick-and-hold operation of valves may advantageously reduce the power draw and the level of heat dissipation inside the cycler  14 . 
     The hardware interface  310  controls the pressure in the specified volume by opening and closing the valves between the specified volume and the appropriate pressure reservoir based on the measured pressure in the specified volume. The hardware interface  310  may also control the pressure in the pressure reservoirs by opening and closing the valves between a pneumatic pump and one of the pressure reservoirs based on the measured pressure in the reservoir. The specified volumes may include each of the control chambers  171 , the reference volumes  174 , the fluid trap and the positive and negative reservoirs. The hardware interface  310  may control the pressure in each of these specified volumes via a number of control schemes, including but not limited to on-off control, or proportional control of the valve with a PWM signal. In one example, as described above, the hardware interface  310  implements an on-off controller, sometimes referred to as a bang-bang controller, which sets a first and second limit and closes the valve when the pressure exceeds the upper second limit and opens the valve when the pressure is less than the first lower limit. In another example, the hardware interface  310  may operate valves between the specified volume and both pressure reservoirs to achieve a desired pressure. In other examples the automation computer  300  may specify one or more valves and command a specific valve to control the pressure as measured by a specified sensor. 
     The hardware interface  310  controls the position and operation of the Auto-Connect carriage. The movement and positioning of the Auto-Connect carriage  146  is controlled in real time by the hardware interface based on the measured position of the carriage  146 . The automation computer  300  may command a particular function or position for the carriage. The hardware interface  310  carries out the commanded function without burdening memory or processing of the automation computer  300 . The positioning of the carriage  146  is controlled with a feedback loop from a position sensor. In addition, the FPGA detects the presence of solution caps  31  and/or spike caps  63  with sensing elements  1112  as described above. Alternatively, the presence of the caps  31  and/or spike caps  63  can be detected by a range of sensing technologies, including but not limited to vision systems, optical sensors that can be blocked by a solution cap and/or spike cap, or, for example, a micro-switch on the stripper element  1491 . 
     The hardware interface  310  may implement safety functions independently of the automation computer  300  or the user interface computer  302 . The independent action of the hardware interface  310  to disable the safety line  2632  and/or signal an alarm to the safety executives  352 ,  354  further reduces the possibility of an unsafe condition occurring. The hardware interface  310  may send an alarm and/or de-energize the safe line  2632  for defined valve combinations at any time. Shutting the cycler down based on disallowed valve positions protects the patient and preserves the ability to complete the therapy (after a reset if needed). The hardware interface  310  may also alarm and de-energize the safe line at unsafe conditions including excessive temperature on the heater pan and/or bag button, excessive pressure in control chamber or reservoir. The hardware interface may alarm and de-energize the safe line when water is detected in the fluid trap. 
     Heater Control System 
     The control systems described above may be used to ensure that the solution delivered to a patient is maintained within a pre-determined range of temperatures. During the therapy process, the cycler  14  fills the heater bag  22  with solution from the connected solution containers  20 , via a heater bag line  26 . The heater bag  22  rests on the heater pan  142  which may include electrical resistance heaters. The heater bag  22  may be covered with an insulated cover  143 . A heater controller may function so as to control the thermal energy delivered to the heater pan  142  in order to control the temperature of the solution to a desired set point prior to delivering the solution to the patient. The solution temperature should be within a safe range prior to being delivered to the patient&#39;s abdominal cavity in order to avoid injuring or causing discomfort to the patient, or causing hypothermia or hyperthermia. The heater controller may also limit the temperature of the heater pan to touch-safe temperatures. The heater controller is constructed to heat and maintain the solution within a range of acceptable temperatures in a timely manner in order to ensure the most effective therapy. 
       FIG. 49-1  is a schematic view of an exemplary embodiment of a solution heater system  500 . In this example, the solution heater system  500  is located within the housing  82  of the cycler  14 . The housing includes an insulated lid  143  that may be affixed to the top of the housing  82 . The housing  82  and the heater lid  143  may therefore define a region that serves to house the components of the solution heater system  500 . The solution heater system may include the following elements: housing  82 , heater lid  143 , heater pan  22 , heater elements  508 , heater pan temperature sensors  504 , button temperature sensor  506 , insulating ring  507  and heater control electronics  50 . The heater pan  142  is positioned inside the housing  82 , and may accommodate a heater bag  22  when positioned on top of the heater tray  142 . Preferably, the heater pan  142  is inclined to place the inlet and/or outlet of the heater bag in a dependent position, to help ensure that fluid in the bag is always in contact with the inlet/outlet regardless of the amount of fluid in the bag. In an embodiment, there can be up to six or more heater pan temperature sensors  504  (only one exemplary heater pan temperature sensor  504  is shown in  FIG. 49-1 ) positioned along the floor of the heater pan  142 . Additionally, there may be a button temperature sensor  506  positioned within the heater pan  142 . The button sensor  506  is positioned to make good thermal contact with the heater bag, while being thermally isolated from the heater pan  142  by an insulating ring  507 , in order to provide an approximation of the temperature of the fluid or dialysate in the bag. In another embodiment, the button sensor  506  may comprise a pair of thermistors mounted on an aluminum button. The aluminum button is thermally isolated by an insulating ring made of, for example, LEXAN® 3412R plastic or another low thermal conductivity material. The button temperature sensor  506  may be located near the end of the tray where the fluid lines connect to the heater bag  22  in order to better measure the temperature of the fluid within the heater bag when the heater bag is less than approximately one-third full. The button sensor  506  may also be referred to as the fluid or dialysate temperature sensor. There may also be a plurality of heater elements  508  positioned under the heater pan  142 , more toward the superior end of the pan, with the bag sensor located more toward the dependent portion of the pan, in order for the sensor to provide a more accurate reading of the fluid temperature within the bag, and to be relatively unaffected by the heater elements  508 . The thermal output of the heater elements  508  may be controlled by the heater control electronics  505  to achieve the desired fluid temperature in the heater bag. The heater control electronics  505  may include but not be limited to a heater control module  509  that produces a Pulse Width Modulation (PWM) signal (PWM signal  511 , represented in  FIG. 49-2 ). Electrical hardware in the input-output (IO) subsystem  344  connects electrical power to the heater elements  508  based on the PWM signal  511 , and hardware on the IO subsystem  344  reads the output of heater pan temperature sensors  504  and button temperature sensor  506 . The PWM signal  511  may control the power supplied to each of the heater elements  508 , and consequently the solution heater system  500  may then heat the heater bag  22  to a user-settable comfort temperature, which may be controlled within a preferred safe temperature range. The solution heater system  500  may also limit the surface temperature of the heater pan  142  to a safe-to-touch temperature. The hardware components of the heater control circuitry  505  may be part of controller  16 . There may also be insulation  510  positioned below the heater element  508  which functions to thermally isolate the heater pan  142  and heater bag  22  from the electronic and pneumatic components of the cycler  12 . Additionally, the heater lid  143  may insulate the heater bag  22  from the surrounding environment. The solution heater system  500  may thus be constructed to bring the solution temperature inside the heater bag  22 , as measured by the button temperature sensor  506 , to the desired fluid set point temperature  550  (see  FIG. 49-3 ) as quickly as possible, and maintaining that desired fluid set point temperature  550  through the rest of the therapy cycle. In some embodiments, the temperature sensors connect to the hardware interface  310 . The same hardware interface  310  may control a safety relay that disables the heater. 
     In some embodiments, the heater elements may include thermal switches that open when the temperature of the switch exceeds a first pre-determined value. The switch will close again once the temperature of the switch drops below the second lower pre-determined value. The thermal switch may be incorporated directly into the heater elements or may be mounted on the outside of the heater element or on the heater pan. The thermal switches provide an additional layer of protection against unsafe pan temperatures. 
     In another example, the thermal switch may be a thermal fuse with a one-time fusible link. A service call will be required to replace the blown thermal fuse, which may advantageously provide an opportunity to inspect and/or test cycler  14  before restarting therapy.  FIG. 49-2  shows a schematic block diagram of the software context of the heater control subsystem. In an embodiment, the logic of the heater control circuitry  505  may be implemented as a heater control module  509  in the machine control subsystem  342  in the APD System software architecture. The heater controller software may be implemented in the controller  16  ( FIG. 45 ) as described below. Additionally, the therapy subsystem  340  may supply information to the machine control subsystem  342  such as the heater bag volume and the set point for the button temperature sensor  506 . The heater elements  508  may be enabled by the therapy subsystem  340 . The machine control subsystem  342  may also read temperature values from the I/O subsystem  344 , which is located below the machine control subsystem  342 . Furthermore, the heater controller  509  may output a PWM signal  511  which may then control the power supplied to the heater elements  508 . 
     In an embodiment, the machine control subsystem  342  may be called periodically (e.g., approximately every 10 milliseconds) to service the I/O subsystem  344 , update variables, and detect conditions. The machine control subsystem  342  may also send updated signals to the heater control module  509  periodically (e.g., approximately every 10 ms.). The updated signals may include the heater bag volume, heater pan temperatures  515 , the button temperature  517 , the set point temperature  550  and the heater enable function. The heater control module may average some or all of these signals continuously, but only calculate and update its output  511  at a lower frequency (e.g, every 2 seconds). 
     In another aspect, the solution heater system  500  may be able to control the solution temperature in the heater bag  22  within a given range of a desired fluid set point temperature  550  (see  FIG. 49-2  and  FIGS. 49-7-49-9 ). Furthermore, the solution heater system  500  has been designed to function within pre-defined specifications under a variety of different operating conditions, such as a relatively wide range of ambient temperatures (e.g., approximately 5° C. to approximately 37° C.), bag fill volumes (e.g., approximately 0 mL to approximately 3200 mL), and solution container  20  temperatures (e.g., between approximately 5° C. and approximately 37° C.). In addition, the solution heater system  500  is capable of functioning within specifications even if the solution in the heater bag  22  and the solution introduced during the replenish cycle may be at different temperatures. The solution heater system  500  has also been designed to function within specifications with heater supply voltages varying as much as +10% of nominal voltage. 
     The solution heater system  500  may be considered to be an asymmetrical system, in which the solution heater system  500  can increase the solution temperature with the heater elements  508 , but relies on natural convection to lower the solution temperature in the heater bag  22 . The heat loss may be further limited by the insulation  510  and the insulated cover  143 . One possible consequence is that in the event of a temperature overshoot, the APD system  10  may delay a patient fill while the heater bag slowly cools. A possible consequence of placing the heater elements on the heater pan  142  is that the heater pan  142  may be at a substantially higher temperature than that of the heater bag  22  during the heating process. A simple feedback control on the heater bag temperature as recorded by the button temperature sensor  506 , may not turn the heater off soon enough to avoid the thermal energy at a higher temperature in the heater pan from causing the heater bag  22  to overshoot the desired set point temperature  550 . Alternatively controlling the heaters  508  to achieve a heater pan temperature  504  that would not cause the heater bag temperature to overshoot may result in a slow heater system and thus delay therapy. 
     In order to minimize the time for the solution in the heater bag to achieve the set point temperature  550  without overshoot, the heater control module may implement a control loop that varies the electrical power of the heater elements  508  to achieve a desired fluid temperature in the heater bag, in part by controlling the equilibrium temperature of the heater pan  142 , the heater bag  22  and the fluid within the heater bag  22 . In one embodiment, a Proportional-Integral (PI) controller controls an equilibrium temperature  532  that is a function of the temperatures of the heater bag  22  and the heater pan  142  and the volume of solution in the heater bag. The equilibrium temperature may be understood to be the temperature that the solution in the heater bag  22  and the heater pan  142  would reach if the heater were turned off and the two components allowed to reach equilibrium. The equilibrium temperature may also be understood as the weighted average of the target temperature for the heater pan  142  and the measured temperature of the solution-filled heater bag, weighted by the thermal capacitance of each. The equilibrium temperature may also be calculated as the weighted average of the measured heater pan temperature and the solution temperature, in which the temperatures are weighted by their respective thermal capacitances. In an embodiment, the weighted average temperature of the heater pan and fluid in the heater bag may be calculated as the sum of the target heater pan temperature times the thermal capacitance of the heater pan plus the fluid temperature times the thermal capacitance of the fluid in the heater bag, where the sum is divided by the sum of the thermal capacitance of the heater pan plus the thermal capacitance of the fluid in the heater bag. The weighted averages of the heater pan and fluid may be alternatively weighted by the mass of the heater pan and fluid in the bag or the volume of the heater pan and fluid in the bag. 
     The control of the equilibrium temperature may be implemented using a number of control schemes, such as, for example, single feedback loops using proportional, integral and or derivative controllers and nested loops. One embodiment of a control scheme using cascaded nested control loops is shown in  FIG. 49-3 . The outer loop controller  514  may control the heater bag temperature as measured by the button temperature sensor  506  to the fluid set point temperature  550  by varying the heater pan set point temperature  527  supplied to the inner loop controller  512 . Alternatively, the outer loop controller  514  may control the equilibrium temperature of the heater bag  22 , fluid and heater pan  142  to the fluid set point temperature  550  by varying the heater pan set point temperature  527 . The temperature of the heater bag  22  and fluid may be measured by the button temperature sensor  506  and the heater pan temperature may be measured by one or more of the heater pan temperature sensors  504 . The outer loop controller may include one or more of the following elements: proportional controller, integral controller, derivative controller, saturation limits, anti-windup logic and zero-order hold logic elements. 
     The inner loop controller  512  may control the heater pan temperature to the heater pan set point temperature  527  by varying the thermal output of the heater elements  508 . The temperature of the pan may be measured by one or more of the heater pan temperature sensors  504 . The inner loop controller may include one or more of the following elements: proportional controller, integral controller, derivative controller, saturation limits, anti-windup logic and zero-order hold logic elements. 
     An exemplary implementation of the heater control module  509  utilizes a PI regulator cascade-coupled with a Proportional-Integral-Derivative (PID) controller. In the  FIG. 49-3  embodiment, a PID inner loop controller  512  may control the temperature of the heater pan  142 , and a PI outer loop controller  514  may control the equilibrium temperature of the heater bag, the fluid in the heater bag and the heater pan as measured by the heater pan temperature sensors  504  and button temperature sensor  506 . The loop controller  514  differs from a standard PI regulator in that any overshoot of the desired fluid set point  550  by the solution heater system  500  may be minimized by a logic controllable integrator as described below. In an embodiment, the heater pan temperature signal  515  and the button temperature sensor (heater bag) signal  517  are low-pass filtered through a pair of control filters  519  at a relatively high frame rate (e.g., a full 100 Hz frame rate), while the heater control module  509  may change the output of the heaters at a lower rate (e.g., rate of ½ Hz). 
       FIG. 49-4  shows a schematic diagram of one embodiment of the inner loop controller  512  (heater pan controller). In this embodiment, the inner loop controller  512  uses a standard PID regulator including but not limited to a differencing element  519  to produce a temperature error and a proportional gain element  522  to create an PWM signal  511 . The inner loop controller  512  may further include a discrete-time integrator  516  to reduce the offset error. The inner loop controller  512  may also include an anti-windup logic element  518  to minimize overshoot due a temperature error existing for a long period of time when the output of the inner loop controller  512  is saturated. The inner loop controller  512  may further include a discrete derivative term  520  that acts on the heater pan actual temperature  515  to improve heater responsiveness. The inner loop controller  512  may further include a saturation limit element  521  that sets a maximum and/or minimum allowed heater command or PWM signal  511 . The inner loop controller  512  may further include zero-order hold logic  523  to hold the PWM signal  511  constant between controller calculations that occur approximately every 2 seconds. 
       FIG. 49-5  shows a schematic diagram of the outer loop controller  514  (button temperature sensor controller). In this example, the outer loop controller  514  utilizes a modified PI-type regulator, which may include differencing elements  531 , an integrator  534  and a proportional gain element  526 . The outer loop controller  514  may further include an integrator switching logic  522  and corresponding switch  529 , to allow the integrator to be switched on or off by logic in the heater control module  509 . The outer loop controller  514  may further include a command feed forward  524  to improve the responsiveness of the outer loop controller  514 . The outer loop controller  514  may further include a proportional feedback term  526  to act on a weighted combination of the button temperature sensor target temperature  517  and the heater pan target temperature  527 . The resulting measurement is an equilibrium temperature  532  as described above. The outer loop controller  514  may further include a saturation limit element  521  and/or a low pass filter  542 . The saturation limit element  521  in the outer loop sets a maximum allowed target pan temperature  527 . The low pass filter  542  may be designed to filter out transient control signals at frequencies outside the bandwidth of the solution heater system  500 . 
     The integral elements  534  in the outer loop controller  514  may be turned on by a switch  529  when some or all of the following conditions are present: the rate of change of the button temperature  517  is below a pre-determined threshold, the button temperature  517  is within a pre-determined number of degrees of the fluid set point temperature  550 , or the bag volume is greater than a pre-determined minimum and neither of the controllers  512 ,  514  are saturated. An equilibrium temperature feedback loop may control the transient behavior of the solution heater system  500 , and may be dominant when the surrounding ambient temperature is in a normal to elevated range. The action of the integrator  516  may only be significant in colder environments, which may result in a substantial temperature difference between the button sensor actual temperature  517  and the heater pan actual temperature  515  at equilibrium. The feed-forward term  524  may pass the fluid set point temperature  550  through to the heater pan target temperature  527 . This action will start the heater pan target temperature  527  at the fluid set point temperature  550 , instead of zero, which thereby improves the transient response of the solution heater system  500 . 
     The heater module  509  may also include a check that turns off the PWM signal  511  if the heater pan actual temperature  515  crosses a pre-determined threshold (this threshold may be set to be slightly higher than the maximum allowed heater pan target temperature  527 ). This check may not be triggered under normal operation, but may be triggered if the heater bag  22  is removed while the temperature of the heater pan  142  is at a pre-determined maximum value. 
     The PI controller  514  may include a proportional term that acts on the equilibrium temperature  532 . The equilibrium temperature is the heater bag temperature measured by the button sensor  506  that would result if the heater  508  was turned off and the heater pan  142  and the solution-filled heater bag  22  were allowed to come to equilibrium. The equilibrium temperature can be better understood by referring to  FIG. 49-6 , which shows a schematic block diagram of the heater pan  142  and heater bag  22  in a control volume analysis  546 . The control volume analysis  546  depicts a model environment in which the equilibrium temperature  532  may be determined. In this illustrative embodiment, the solution heater system  500  may be modeled in as control volume  548 , which may comprise at least two thermal masses: the heater pan  142  and the heater bag  22 . The boundary of the control volume  548  may be assumed to function as a perfect insulator, in which the only heat transfer is between the heater pan  142  and the heater bag  22 . In this model, thermal energy  549  may be added to the system via the heater elements  508 , but thermal energy may not be removed from the heater pan  142  and heater bag  22 . In this model, as in the solution heater system  500 , it is desirable to heat the heater pan  142  just enough that the heater bag  22  reaches its target temperature as the heater pan  142  and heater bag  22  come to equilibrium. Therefore, the equilibrium temperature  532  may be calculated as a function of the initial temperature of the heater bag  22  and the initial temperature of the heater pan  142 : 
         E=M   p   c   p   T   p   +V   b ρ b   c   b   T   b =( M   p   c   p )+ V   b ρ b   c   b ) T   e  
 
     where M P , c p  are the mass and specific heat of the heater pan  142 , V P , ρ b , c b  are the volume, density and specific heat of the solution in the bag, T p  and T b  are the temperatures of the heater pan  515  and the button  517  respectively. Solving for the equilibrium temperature yields a linear combination of pan and button temperatures: 
         T   e   =cT   b +(1− c ) T   p 
 
     
       
         
           
             C 
             = 
             
               
                 
                   
                     V 
                     b 
                   
                   
                     k 
                     + 
                     
                       V 
                       b 
                     
                   
                 
                  
                 
                     
                 
                  
                 and 
                  
                 
                     
                 
                  
                 k 
               
               = 
               
                 
                   
                     M 
                     p 
                   
                    
                   
                     C 
                     p 
                   
                 
                 
                   
                     ρ 
                     b 
                   
                    
                   
                     C 
                     b 
                   
                 
               
             
           
         
       
         
         
           
             where 
           
         
       
    
     The constant c is an equilibrium constant, k is the thermal capacitance ratio of the heater pan over the solution. The subscript b denotes the solution in the heater bag  22 , while p denotes the heater pan  142 . 
     In this model, allowing the heater module  509  to control the equilibrium temperature  532  during the initial transient may allow for rapid heating of the heater bag  22  while also reducing the heater pan actual temperature  515  sufficiently early to prevent thermal overshoot. The c parameter may be determined empirically. The heater module  509  may set c to a value larger than the measured value to underestimate the total energy required to reach the desired set point  550 , further limiting the thermal overshoot of the solution heater system  500 . 
       FIG. 49-7  shows graphically the performance of solution heater system  500  of the disclosed embodiment operating under normal conditions. The measured temperatures of the heater pan sensors  504 , the button temperature sensor  506  and an additional temperature probe are plotted against time. The fluid temperature probe was part of the experimental setup up to verify the control scheme. The fluid probe temperature is shown as line  552 . The button temperature is shown as line  517  and the heat pan temperatures are shown as line  515 . Line  550  is the target temperature for the button temperature sensor  506 . At the start of this trial, the heater bag is substantially empty, the heater is off and fluid is not moving, so that all the temperatures are at a nominal value. At a time T=1, the fluid at 25 C starts to flow into the heater bag  22  bringing down the probe and button temperatures  552 ,  517 , while the heater turns on and increases the heater pan temperature  515 . Under normal operation, proportional control of the equilibrium temperature  532  may be sufficient to heat the solution within the heater bag  22  to a temperature close to the desired fluid set point temperature  550 . Therefore, in  FIG. 49-7 , the solution heater system  500  functions effectively, and the heater pan actual temperature  515 , the button sensor actual temperature  517 , and a probe temperature  552  all converge to the fluid set point temperature  550  within approximately 50 minutes. 
       FIG. 49-8  shows graphically the performance of the solution heater system  500  operated in a high temperature environment in which the ambient temperature is 35 C. As described above, the trial begins with the heater bag being substantially empty. Once the fluid starts to flow and the heater turns on, the probe and button temperatures  552 ,  517  decrease and the heater pan temperature  515  increases. In a high temperature environment, the solution heater system  500  functions in a manner substantially similar to normal conditions. Thus, proportional control of the equilibrium temperature  532  may again be sufficient to heat the solution within the heater bag  22  to a temperature close to the desired fluid set point temperature  550 . In  FIG. 49-7 , the solution heater system  500  functions effectively and within desired specifications, and the heater pan actual temperature  515 , the button sensor actual temperature  517 , and a probe temperature  552  all converge to the desired set point temperature  550  within approximately 30 minutes. 
       FIG. 49-9  shows graphically the performance of the solution heater system  500  operated in a cold environment where the ambient temperature is 10 degrees C. and the source fluid is 5 degrees C. As described above, the trial begins with the heater bag being substantially empty. Once the fluid starts to flow and the heater turns on, the probe and button temperatures  552 ,  517  decrease and the heater pan temperature  515  increases. In a cold environment, setting the desired fluid set point temperature  550  equal to the equilibrium temperature  532  may lead to a steady-state error in the temperature of the button sensor  506 . The heat loss in cold environments may necessitate a large temperature difference between the heater pan  142  and the button sensor  506  during thermal equilibrium. Since the equilibrium temperature  532  is a weighted sum of the heater pan  142  and the button sensor  506 , the temperature of the button sensor  506  may be below the fluid set point temperature  550  if the temperature of the heater pan  142  is above the desired fluid set point temperature  550  at equilibrium. This may occur even if the equilibrium temperature  532  is equal to the fluid set point temperature  550 . To compensate for this steady-state-error an integral term may be added to outer PI controller  514  that acts on the temperature error of the button sensor  506 . The integrator  538  may be turned on when one or more of the following conditions are met: a first derivative of the temperature of the button sensor  506  is low; the button sensor  506  is close to the fluid set point temperature  550 , the volume of the heater bag  22  exceeds a minimum threshold; and neither inner PID loop  512  or outer PI controller  514  are saturated. In this illustrative embodiment, the switching of the integral term may minimize the effect of the integrator  538  during normal operation and may also minimize the overshoot caused by integration during temperature transients. Therefore, in  FIG. 49-9 , the solution heater system  500  functions effectively and within desired specifications, and the heater pan actual temperature  515 , the button sensor actual temperature  517 , and a probe temperature  552  all converge to the fluid set point temperature  550  within approximately 30 minutes. 
     In summary, the disclosed temperature controller can achieve good thermal control of a two component system, in which the mass of the first component varies over time, and in which the second component includes a heater or cooler, and both components are in an insulated volume. This thermal control can be achieved by controlling the equilibrium temperature. The temperature controller determines the temperature of both components as well as the mass of the variable component. The temperature controller varies the heating or cooling of the second component to bring the equilibrium temperature to the desired set point temperature. The equilibrium temperature is the thermal capacitance weighted average temperature of the two components. The controller may use a proportional feedback loop to control the equilibrium temperature. 
     The temperature controller may also include an integral term that responds to the difference between the set point temperature and the temperature of the first component. The integral term may optionally be turned on when some or all of the following conditions are met: 
     the rate of temperature change of the first component is low; 
     the temperature of the first part is near the set point temperature; 
     the volume of the first part exceeds some minimum level; 
     the control output signal is not saturated. 
     The temperature controller may also include a feed-forward term that adds the set point temperature to the output of the proportional and integral terms. 
     Further, the temperature controller may be the outer loop controller of a cascade temperature controller in which the outer loop controller includes at least a proportional control term on the equilibrium temperature and outputs a set point temperature for the inner controller. The inner controller controls the temperature of the first component with the heater or cooler elements to the set point temperature produced by the outer controller. 
     Universal Power Supply 
     In accordance with an aspect of the disclosure, the APD system  10  may include a universal power supply that converts line voltage to one or more levels of DC voltage for some or all of the electro-mechanical elements and electronics in the cycler  14 , and provides AC power to the electric heater for the heater pan  142 . The electro-mechanical elements in the cycler  14  may include pneumatic valves, electric motors, and pneumatic pumps. The electronics in the cycler  14  may include the control system  16 , display  324 , and sensors. AC power is supplied to a heater controller to control the temperature of the solution in the heater bag  22  on the heater tray  142  to a desired set point prior to delivering the solution to the user/patient. The universal power supply changes the configuration of two (or more) heater elements to accommodate two ranges of AC line voltages: e.g., a first range of 110±10 volts rms; and a second range of 220±20 volts rms. This arrangement is intended to accommodate using the APD system  10  in a number of different countries. During the start of a therapy session, the APD cycler  14  fills the heater bag  22  with solution from the connected solution containers  20 , via a heater bag line  26 . In an alternative embodiment, a pre-filled bag of solution may be placed on a heater pan  142  at the start of a therapy. 
     PWM Heater Circuit 
     The heater controller in the APD cycler modulates the electrical power delivered to the heater elements attached to the heater pan  142 . The APD cycler may be used in various locations around the world and may be plugged into AC mains that supply power from 100 to 230 volts rms. The heater controller and circuits may adapt to the variety of AC voltages while continuing to supply sufficient heater power and not blowing fuses or damaging heater elements in a number of ways. 
     One embodiment of a heater circuit is presented in  FIG. 49-10 , where a pulse width modulator (PWM) based circuit  2005  controls the temperature of the heater pan  142  with a pulse-width-modulated (PWM) element  2010  connected between one lead of the AC mains  2040  and the heater element  2000 . The controller  2035  is operably connected to the relay  2030  and the PWM element  2010 . The controller  2035  monitors the operation of the heater by interrogating the voltage detect  2020  and temperature sensor  2007 . The controller  2035  may modulate the amount of power delivered to the heater  2000  via a signal to the PWM element  2010 . The PWM or pulse-width-modulated element is closed for some fraction of a fixed period between 0 and 100%. When the PWM element  2010  is closed 0% of the time, no electrical energy flows to the heater  2000 . The heater is continuously connected to the AC mains  2040  when the PWM element is closed 100%. The controller  2035  can modulate the amount of power dissipated by the heater  2000  by setting the PWM element  2010  to a range of values between 0 and 100%, inclusive. 
     The PWM elements  2010  switch large current flows on and off multiple times a second. PWM elements  2010  are typically some kind of solid state relay (SSR). SSRs for AC voltage typically include a triggering circuit that controls the power switch. The triggering circuit may be, for example, a reed relay, a transformer or an optical coupler. The power switch may be a silicon control rectifier (SCR) or a TRIAC. The SCR or TRIAC are also referred to as thyristors. One example of a SSR is the MCX240D5® by Crydom Inc. 
     In one example, the controller  2035  may modulate the PWM element value in order to control the temperature of the heater pan  142  as measured by temperature sensor  2007 . In another example, the controller  2035  may modulate the PWM element value to control the temperature of the fluid in the heater bag  22 . In another example the controller  2935  may control the PWM element  2010  to provide a fixed schedule of heater power. The controller  2035  may command a safety relay  2030  that opens the heater circuit and stops the flow of electrical power to the heater  2000 . The safety relay  2030  may be controlled by a separate controller (not shown) in order to provide a safety circuit independent of the controller  2035 . 
     The PWM based circuit  2005  may include a voltage detect element  2020  that provides a signal to the controller  2035  indicative of the voltage on the AC mains  2040 . In one example, the voltage detect element  2020  may measure the AC potential across the AC mains  2040 . In another example the voltage detect element  2020  may measure the current flow through the heater  2000 . The controller  2035  may calculate the voltage across the AC mains from a known resistance of the heater element  2000 , the PWM element  2010  signal and the measured current. 
     The PWM based circuit  2005  may vary the maximum allowed duty cycle of PWM element  2010  to accommodate different AC Mains voltage. The heater element  2000  may be designed to provide the maximum required power with the lowest possible AC voltage. The controller may vary the duty cycle of the PWM element  2010  to provide a constant maximum heater power for a range of voltages at the AC mains. For example, the voltage supplied to the heater  2000  from a 110 volt AC line may be supplied at a 100% duty cycle, and the same amount of electrical power may be delivered to the heater  2000  from a 220 volt AC line if the PWM element  2010  is set to 25%. The duty cycle of the PWM element  2010  may be further reduced below the maximum value to control the temperature of the heater pan  142 . 
     The temperature of the heater element  2000  and the heater pan  142  may be controlled by the average heater power over a time constant that is a function of the thermal mass of the element and heater pan. The average heater power may be calculated from the heater resistance, which is relatively constant, and the rms voltage across the heater element  2000 . In a practical sized heater, the PWM frequency is much faster than the time constant of the heater system, so the effective voltage across the heater element is simply the PWM duty cycle multiplied by the rms voltage. 
     One method to control the heater pan temperature of the circuit in  FIG. 49-10  may direct the controller  2035  to set a maximum PWM duty cycle based on the measured voltage at  2020 . The maximum duty cycle may be calculated from the desired maximum heater power, known resistance of the heater element  2000  and the measured voltage. One possible example of the calculation is: 
       PWM MAX =( P   MAX   *R   HEATER )/ V   rms    
     where PWM MAX  is the maximum allowed PWM duty cycle, P MAX  is the maximum heater power, R HEATER  is the nominal resistance of the heater element  2000 , and V rms  is the supplied voltage as measured by the Voltage Detect  2020 . Another example of the calculation is: 
       PWM MAX   =P   MAX /( I   2   *R   HEATER ) 
     where I is the current flow through heater when the voltage is applied. The controller  2035 , after setting the maximum PWM duty cycle, then varies the PWM duty cycle of the PWM element  2010  to control the temperature of the heater pan  142  as measured by a temperature sensor  2007 . The controller may control the PWM element to achieve a desired temperature in a number of ways, including, for example, a PID feedback loop, or a PI feedback system. 
     In an alternative method and configuration, the PWM circuit  2005  does not include the voltage detect  2020 . In this alternative method the controller  2035  varies the PWM duty cycle of the PWM element  2010  to achieve the desired heater pan temperature as measured by temperature sensor  2007 . The controller  2035  begins the heating cycle at a minimum PWM duty cycle and increases the PWM duty cycle until the temperature sensor reports the desired temperature to the controller  2035 . The rate of increase of the PWM rate may be limited or controlled to avoid excessive currents that could trip and blow the fuses  2050 . The controller  2035  may alternatively use small gains in a feedback calculation to limit rate of PWM duty cycle increase. Alternatively the controller may use a feed forward control to limit the rate of PWM duty cycle increase. 
     Dual-Voltage Heater Circuit 
     An example of a dual-voltage heater circuit  2012  that changes the resistance of the heater is shown as a schematic block diagram in  FIG. 49-11 . The block diagram in  FIG. 49-11  presents one example of a dual-voltage heater circuit  2012  to provide approximately constant heater power for the two standard AC voltages of 110 and 220 volts rms. Dual-voltage heater circuit  2012  limits the maximum current flow by reconfiguring the heater and thus is less sensitive to software errors setting the duty cycle of the PWM element as in circuit  2005 . Circuit  2012  lowers the maximum current flows through the PWM element  2010  which allows for smaller and less expensive SSRs. The selection of the heater configuration in circuit  2012  is separated from the heater modulation to improve control and reliability. The PWM elements  2010 A,  2010 B that modulate the heater power are typically SSR, which typically fail closed, thus providing maximum power. The heater select relay  2014  may be an electromechanical relay, which while less than ideal for high cycle applications, may typically be preferred for safety critical circuits, due in part to the tendency of electromechanical relays to fail open. The selection of the heater configuration by the processor allows more control of heater configuration. 
     In the event of the AC Mains voltage fluctuating, perhaps due to a brown-out, the controller preferably holds the heater configuration constant. In contrast, a circuit that automatically changes the heater configuration based on the instantaneous voltage could fluctuate between heater configurations. This may result in high current flows if the circuit does not respond fast enough to line voltage that returns to its original level from a temporarily lower level. In an embodiment, the processor receives input from the user or patient in selecting the heater configuration (parallel or series), and the dual-voltage heater circuit  2012  does not automatically switch between configurations in response to fluctuating line voltage. In another embodiment, the processor measures the current flow in the series configuration (i.e. the higher resistance configuration) at full power, selects a heater configuration appropriate to the AC mains voltage at the start of therapy, and does not change configuration for the duration of therapy. 
     The dual-voltage heater circuit  2012  may comprise two heater elements  2001 ,  2002  that can be connected in parallel or in series with one another to provide the same heater power for two different voltages at the AC mains  2040 . Each heater element  2001 ,  2002  may comprise one or more heater sub-elements. The electrical resistance of heater elements  2001 ,  2002  is preferably approximately equal. The controller  2035  may receive a signal from the current sense  2022  and control the heater select relay  2014  to connect the heater elements  2001 ,  2002  in either series or parallel. The controller  2035  may change the electrical arrangement of the two heater elements to limit the current flow resulting from different AC mains voltages. One example of a current sense  2022  is a current sense transformer AC-1005 made by Acme Electric. 
     The power in the heater elements  2001 ,  2002  may be further modulated by the PWM elements  2010 A,  2010 B controlled by the controller  2035  to achieve a desired temperature as measured by temperature sensor  2007 , or to achieve other control goals as described above. The PWM elements  2010 A,  2010 B may be a solid state relays such as MCX240D5® by Crydom Inc. The safety relay  2030  may be configured to disconnect the heater elements  2001 ,  2002  from the AC mains  2040 . The safety relay  2030  may be controlled by the controller  2035  or another processor or safety circuit (not shown). 
     The safety relay  2030  and heater select relay  2014  may be solid state or electro-mechanical relays. In a preferred embodiment, the safety relay  2030  and/or heater select relay  2014  are electro-mechanical relays. One example of an electro-mechanical relay is a G2AL-24-DC12 relay made by OMRON ELECTRONIC COMPONENTS and other manufacturers. Electro-mechanical relays are often preferred for safety critical circuits as they are considered to be more robust and more reliable than solid state relays, and have a tendency to fail open. They may also be less susceptible to various failures in the controller software. 
     In one example, the heater select relay  2014  comprises a double-pole double-throw relay, in which the outputs connect to the heater elements  2001 ,  2002 . The heater select relay  2014 , in the non-energized state, connects the heater elements  2001 ,  2002  in series such that the current flows through one element and then the other. The series configuration may be achieved, in one example circuit, by the following; connect the first end of the heater element  2001  to L 1  circuit  2041  via PWM element  2010 A; connect the joined ends of heater elements  2001 ,  2002  to an open circuit via the first pole  2014 A; connect second end of heater element  2002  to the L 2  circuit  2042  via the second pole  2014 B. In an energized state, the heater select relay  2014  connects the heater elements in parallel such that approximately half the current flows through each PWM and heater element. The parallel configuration may be achieved in the same example circuit by the following: connect the first end of the heater element  2001  to L 1  circuit  2041  via PWM element  2010 A; connect the second end of heater element  2002  to the L 1  circuit  2041  via PWM element  2010 B; connect the joined ends of heater elements  2001 ,  2002  to L 2  circuit  2042  via the first pole  2014 A. The preferred circuit connects the heater elements  2001 ,  2002  in series in the unpowered condition as it is a safer configuration because the resulting higher resistance will limit current flows and avoid overloading the fuses  2050 , or overheating the heating elements  2001 ,  2002  if connected to a higher voltage AC main. 
     Another example of a heater circuit  2112  that changes the effective resistance of the heater by changing the heater configuration is shown in  FIG. 49-12  as a schematic block diagram. The heater circuit  2112  is similar to heater circuit  2012  (shown in  FIG. 49-11 ) except that heater circuit  2112  provides better leakage current protection in the event that the L 1  and L 2  power circuits are reversed at the wall socket. The reversal of the L 1  and L 2  power circuits is possible if the power was incorrectly wired in the building that supplies power to the heater circuit. Wiring in a residential building may not be as reliable as a hospital, where all the electrical system is installed and maintained by qualified personnel. 
     The electrical components and connections between the PWM elements  2010 A,  2010 B, the nominal L 1  circuit  2041 , heater elements  2001 ,  2002 , heater select relay  2014  and the nominal L 2  circuit  2042  in heater circuit  2112  are arranged to minimize leakage current regardless of wall socket polarity. In the non-energized state as shown in  FIG. 49-12 , the heater select relay  2014  connects the heater elements  2001 ,  2002  in series with the PWM element  2010 A. One possible circuit that connects the heater elements in series includes: the first end of heater element  2001  connected to the L 1  circuit  2041  via PWM element  2010 A; the second end of heater element  2001  connected to the first end of heater element  2002  via the first pole  2014 A, a L 1   2014 C and the second pole  2014 B; and the second end of heater element  2002  connected to the L 2  circuit  2042  via PWM element  2010 B. In the energized state, the heater elements  2001 ,  2002  and PWM elements  2010 A,  2010 B are connected in parallel. In an energized state, the heater select relay  2014  connects the heater elements in circuit  2122  in parallel such that approximately half the current flows through each PWM and heater element. One possible circuit to connect the two heater and PWM elements in parallel includes: the first end of heater element  2001  connected to the L 1  circuit  2041  via PWM element  2010 A; the second end of heater element  2001  connected via the first pole  2014 A to the L 2  circuit; the first end of heater element  2002  is connected to the L 1  circuit  2041  via the second pole  2014 B; the second end of heater element  2002  is connected to the L 2  circuit  2042  via the PWM element  2010 B. The safety relay  2030  is located on the L 2  circuit  2042  and creates a fail-safe condition of no current flow by opening if a fault occurs. The control of the safety relay is described below. The controller  2035  controls the heater configuration to limit the current flow as measured by the current sense  2022  to levels below the current rating for the fuses  2050 , heater elements  20001 ,  2002 , the PWM elements  2010 A,  2010 B and limits total heater power. The controller  2035  varies the duty cycle of the PWM elements  2010 A,  2010 B to control the heater pan  142  temperature as measured by the sensor  2007 . 
     Dual-Voltage Heater Circuit Implementation 
     A circuit diagram  2212  of one embodiment of the present invention is shown in  FIG. 49-13 , which is equivalent to heater circuit  2012  in  FIG. 49-11 . In the circuit  2212 , the heater elements  2001 ,  2002  are connected in series by the heater select relay  2014  when the relay coil  2014 D is not energized. The controller (not shown) connects the heater elements  2001 ,  2002  and PWM elements  2010 A,  2010 B in parallel by supplying a signal at node  2224 , which closes transistor switch  2224 A, and energizing the relay coil using the Vs DC power  2214 , The controller modulates the heater power by varying the duty cycle of the PWM elements  2010 A,  2010 B through a signal at node  2220  and powered with Vsupply  2210 . The current flow is measured with the current sense  2022 . The safety relay  2030  is normally open. The safety relay  2030  may be controlled by an FPGA board that is separate from the controller. The FPGA board monitors the operation of the APD cycler, including the heater pan temperature and the current sense and several other parameters. The FPGA board may open the relay by removing the signal at node  2228 . The safety relay coil  2030 D is powered by the Vsafety  2218 . 
     In one example, the voltage supplying Vsupply  2210 , Vs  2214 , Vsafety  2218  may be the same voltage source. In another example each voltage source be controllable to provide additional operation control of the heater circuit for added safety. In one example the Vsafety  2218  may be controlled by multiple processors in the APD cycler  14 . If any of the processors detects an error and fails, then the Vsafety circuit is opened, the Safety Relay  2030  is opened and heater power is turned off. 
     Dual-Voltage Heater Circuit Operation 
     The heater circuit is operated to provide adequate heater power without allowing damaging currents to flow through the heater elements  2001 ,  2002  or the fuses  2050 . The heater circuit  2212  may be configured before the therapies are run on the APD cycler  14  and not changed during operation regardless of the voltage changes in the AC mains. The control system  16  (in  FIG. 45 ) starts up the heater control circuit  2212  with the heater select relay  2014  un-energized, so the heater elements are connected in series to minimize the current. As one part of the startup processes, software in the automation computer  300  may run a current flow test of the heaters by commanding the PWM elements  2010 A,  2010 B to 100% duty cycle and the resulting test current is measured by the current sense  2022  and communicated to the automation computer  300 . The duty cycle of the PWM elements  2010  may be reset to zero after current flow test. 
     In one example method, the automation computer  300  evaluates the measured test current against a predetermined value. If the measured test current is above a given value, the automation computer  300  will proceed with the ADP cycler startup procedure. If the measured test current value is below that same given value, then the automation computer  300  will energize the heater select relay to reconfigure the heater elements  2001 ,  2002  in parallel. The current flow test is repeated and if the new measured test current is above the predetermined value the automation computer  300  will proceed with the ADP cycler startup procedure. If the measure test current from the current flow test with parallel heater elements, is below above the predetermined value, the automation computer  300  will signal an error to the user interface computer  302 . 
     Alternatively, the automation computer  300  may calculate a test voltage based on the measured test current and heater element configuration. If the test voltage is in the range of 180 to 250 volts rms, then the automation computer  300  will proceed with the ADP cycler startup procedure. If the test voltage is in the range of 90 to 130 V rms, then the automation computer  300  will energize the heater select relay to reconfigure the heater elements  2001 ,  2002  in parallel, repeat the current flow test, and recalculate the test voltage. If the test voltage is in the range of 90 to 130 V rms, the automation computer  300  will proceed with the ADP cycler startup procedure, if not automation computer  300  will signal an error to the user interface computer  302 . 
     In another example method, the automation computer  300  compares the measured test current with the heater elements configured in series to a series-low-range and series-high-range of current values. The series-low-range is consistent with a low AC voltage flowing through the heater elements arranged in series. The series-high-range is consistent with a high AC voltage flowing through the heater elements arranged in series. In an exemplary embodiment, the low AC voltage includes rms values from 100 to 130 volts, while the high AC voltage includes rms values from 200 to 250 volts. 
     If the measured test current is outside of low-range and the high-range, then the automation computer  300  may determine that the heater circuit is broken and signal an error to the user interface computer  302 . If the measured test current is within the high-range, the heater configuration is left unchanged and the startup of the APD cycler  14  may continue. If the measured test current is within the low-range and the heater elements are arranged in series, then the automation computer  300  may reconfigure the heater elements  2001 ,  2002  to a parallel arrangement by energizing the heater select relay  2014  through a signal at node  2224 . The automation computer  300  may control the heater select relay  2014  via a command sent to the hardware interface  310  that in turn provides the signal to actuate the heater select relay  2014 . 
     The automation computer  300  may repeat the current flow test after reconfiguring the heater elements into a parallel arrangement by again commanding the PWM elements  2010 A,  2010 B to 100% duty cycle and measuring the current flow with the current sense  2022 . The measured test current may be evaluated against the parallel-low-range of current values. If the measured test current is within the parallel-low-range values proceed with the ADP cycler startup procedure. If the newly measured test current is outside the parallel-low-range values, then automation computer  300  will signal an error to the user interface computer  302 . 
     The FPGA controller implemented in the hardware interface  310  may be programmed to command the safety relay  2030  to open through a signal at node  2228  while the heater select relay  2014  is switched. The safety relay  2030  may be opened each time the heater select relay  2014  is opened or closed to prevent a short circuit from one pole to the other within the heater select relay  2014 . 
     Dual-Voltage Heater Circuit Operation with User Input 
     In an alternative embodiment, the automation computer  300  may require user intervention before reconfiguring the heater elements  2001 ,  2002 . Requiring user input provides a valuable safety feature of one embodiment of the present invention.  FIG. 49-14  shows a logic flow chart illustrating a method  2240  to include the user in configuring the heater elements appropriately for the available AC voltage. In step  2241 , the control system  16  (in  FIG. 45 ) starts up the heater control circuit  2212  ( FIG. 49-13 ) with the heater select relay  2014  un-energized, so the heater elements are connected in series to minimize the current. In setup  2242 , the automation computer  300  commands the PWM elements  2010 A,  2010 B to 100% duty cycle and the current is measured by the current sense  2022  and the measure test current is communicated to the processor. The duty cycle of the PWM elements  2010  may be reset to zero after the test current is measured. In step  2244 , the automation computer  300  compares the measured test current to a first range. In step  2245 , if the measured test current is within the first range, then the heater configuration is correct and the APD operation proceeds in step  2254 . In an alternative embodiment, method  2240  includes step  2245 A where the user interface computer  302  ask the user to confirm the AC mains voltage that the automation computer  300  determined from measured test current and the heater configuration before proceeding from step  2245 . If the user does not confirm the AC voltage level, method  2240  will proceed to step  2252  and displays an error. 
     In step  2246 , if the measured current is outside the second range, then method  2240  displays an error in step  2252 , otherwise the method  2240  proceeds to step  2247 . In step  2247 , if the user confirms low AC voltage then the heater configuration will be changed in step  2248 , otherwise the method  2240  displays an error in step  2252 . In step  2248 , the automation computer  300  reconfigures the heater elements  2001 ,  2002  to a parallel arrangement by energizing the heater select relay  2014  through a signal at node  2224 . After reconfiguring the heater elements in step  2248 , the method  2240  retests the heater in step  2242  and continues through the logic flow chart of method  2240 . 
     An alternative embodiment, a user or patient may store the AC voltage as high or low in the memory of the control system  16  so that the automation computer  300  need not query the user or patient at each treatment to confirm the AC voltage.  FIG. 49-15  shows a logic flow chart illustrating a method  2260  where the AC voltage value is stored in the memory of the control system  16 . The steps  2241  through  2246  are the same as method  2240  described above. In step  2249 , the memory is queried for the stored AC voltage value. If the stored AC voltage value is low, then the method  2260  proceeds to step  2248  and reconfigures the heater elements into a parallel arrangement. If the stored AC voltage is high nor zero, then the user interface computer  302  may query the user to confirm a low AC mains voltage. If a user confirms the low AC voltage, then the method  2260  proceeds to step  2248  and reconfigures the heater elements into a parallel arrangement. Step  2248  may also include the setting the stored AC voltage to low. After reconfiguring the heater elements in step  2248 , the method  2260  retests the heater in step  2242  and continues through the logic flow chart of method  2260 . 
     In one example, method  2260  may include a step  2245 A which reads from memory or calculates the test voltage from the measured test current and heater configuration and then has the user interface computer  302  asks the user to confirm the test voltage. The method may include a step between  2245  and  2246 , where if the heater has been reconfigured to a parallel arrangement and the current is not within the high range, then the method proceeds to step  2252  and shuts down the APD cycler  14 . 
     The methods  2240  and  2260  may evaluate the measured test current by a number of different methods. A preferred method was described above and alternative examples are es are described below. The first range in step  2245  may be a range of current levels that would provide the desired amount of maximum heater power for the current heater element configuration. Alternatively step  2245  may calculate a test voltage from the measured test current and heater element configuration and evaluate if the test voltage is correct for the heater configuration: approximately 110 V rms for parallel configuration and approximately 220 V rms for series configuration. Alternatively step  2245  may test if the measured test current is above a given predetermined value. The second range in step  2246  may be a range of current values corresponding to approximately 110 V rms in a series configuration. Alternatively step  2246  may calculate a test voltage from the measured test current and heater element configuration and evaluate if the test voltage approximately 110 V rms for a series configuration. Alternatively, step  2246  may evaluate if the measure test current is below a given predetermined value. 
     In another embodiment, the selected AC voltage value in method  2260  may be preloaded in the factory or distribution center based on the expected location of usage. For example, the AC voltage value may be selected for low if the APD cycler will be used in the US, Canada or Japan. For another example, the AC voltage value may be selected for high if the APD cycler will be used in Europe, or Asia. 
     For machines expected to operate in a given region, this database may be as simple as a regional voltage being loaded on the machine at the factory, or loaded by a technician during initial set-up at a place of operation. These regional AC voltage value prescriptions may be entered manually, using a memory stick or similar device, using a personal data key (PDK), a compact disc, bar code reader over the world wide web using an Ethernet or wireless connection or by any other data transfer mechanism obvious to one skilled in the art. In other embodiments, sets of regional voltages may be accessible to control system  16  and may be used to inform a user of the typical operating voltage in his or her area. In one embodiment, prior to accepting a user input in step  2247  to change voltage from a previous setting, a user would be informed of the typical voltage of a region; thus a user unfamiliar with the value of regional voltages would only be required to know his or her current location to provide a safeguard against voltage incompatibility. 
     In another embodiment, APD cycler  14  would be equipped with a mechanism to determine its current location, for example a GPS tracker, an Ethernet connection and a mechanism to determine the location of the connection, or a mode where user interface  302  can be used to enter the present location, such as country or continent. In an embodiment, after starting up in a series heater configuration and running a current flow test, a user may simply be queried as to his or her present location; if the response to that query matches both the voltage associated with the measured test current and heater configuration and the typical voltage for that region, then treatment is allowed to proceed. 
     In one embodiment of the present invention a manual switch (not shown), or alternately a logic switch, is used to set the APD machine to the appropriate, safe voltage for use. The instantaneous voltage is measured and this measurement, either as the specific value or as a categorical descriptor, is displayed to the user. The user must respond that the measured voltage is within the safe operating range for the machine as currently configured, or alternately must respond by altering the configuration of the machine, before power is allowed to flow to the heating element. The configuration could be altered electronically, for example via the user interface computer  302 , or could be performed manually by flipping a switch. 
     In another embodiment of the present invention, a rectifier converts any incoming alternating current (AC) into a single direct current (DC). The heater circuit would resemble heater circuit  2005  in  FIG. 49-8  except the voltage detect  2020  element is replaced with a universal DC supply that rectifies the AC voltage into a selected DC voltage. The electrical power supplied to the heater elements  2001 ,  2002  may be modulated by a PWM element in the rectifier or by a separate PWM element  2030 . The heater circuit may include a safety relay  2010 . The single voltage DC power source allows the use of one heater configuration. The PWM element in this embodiment may comprise one or more IGBT or an MOSFET switches and related electrical hardware. In a preferred embodiment, the incoming alternating current would be converted to direct current in the range of 12V to 48V. 
     In another embodiment, the heater element  2000  may comprise a Positive Temperature Coefficient (PTC) element that self limits the power dissipated. The internal electrical resistance of a PTC element increases with temperature, so the power level is self limiting. PTC heater elements are commercially available from companies such as STEGO that are rated to run on voltages from 110 to 220 V rms. A heater circuit employing a PTC heating element would resemble heater circuit  2005  with the voltage detect element  2020  removed. The heater power would be controlled with the PWM element  2010  using a Triac. 
     Database and User Interface Systems 
     The database subsystem  346 , also on the user interface computer  302 , stores all data to and retrieves all data from the databases used for the onboard storage of machine, patient, prescription, user-entry and treatment history information. This provides a common access point when such information is needed by the system. The interface provided by the database subsystem  346  is used by several processes for their data storage needs. The database subsystem  346  also manages database file maintenance and back-up. 
     The UI screen view  338  may invoke a therapy log query application to browse the therapy history database. Using this application, which may alternatively be implemented as multiple applications, the user can graphically review their treatment history, their prescription and/or historical machine status information. The application transmits database queries to the database subsystem  346 . The application can be run while the patient is dialyzing without impeding the safe operation of the machine. 
     The remote access application, which may be implemented as a single application or multiple applications, provides the functionality to export therapy and machine diagnostic data for analysis and/or display on remote systems. The therapy log query application may be used to retrieve information requested, and the data may be reformatted into a machine neutral format, such as XML, for transport. The formatted data may be transported off-board by a memory storage device, direct network connection or other external interface  348 . Network connections may be initiated by the APD system, as requested by the user. 
     The service interface  356  may be selected by the user when a therapy is not in progress. The service interface  356  may comprise one or more specialized applications that log test results and optionally generate a test report which can be uploaded, for example, to a diagnostic center. The media player  358  may, for example, play audio and/or video to be presented to a user. 
     According to one exemplary implementation, the databases described above are implemented using SQLite®, a software library that implements a self-contained, server-less, zero-configuration, transactional SQL database engine. 
     The executive subsystem  332  implements two executive modules, the user interface computer (UIC) executive  352  on the user interface computer  302  and the automation computer (AC) executive  354  on the automation computer  300 . Each executive is started by the startup scripts that run after the operating system is booted and includes a list of processes it starts. As the executives go through their respective process lists, each process image is checked to ensure its integrity in the file system before the process is launched. The executives monitor each child process to ensure that each starts as expected and continue monitoring the child processes while they run, e.g., using Linux parent-child process notifications. When a child process terminates or fails, the executive either restarts it (as in the case of the UI view) or places the system in fail safe mode to ensure that the machine behaves in a safe manner. The executive processes are also responsible for cleanly shutting down the operating system when the machine is powering off. 
     The executive processes communicate with each other allowing them to coordinate the startup and shutdown of the various application components. Status information is shared periodically between the two executives to support a watchdog function between the processors. The executive subsystem  332  is responsible for enabling or disabling the safe line. When both the UIC executive  352  and the AC executive  354  have enabled the safe line, the pump, the heater, and the valves can operate. Before enabling the lines, the executives test each line independently to ensure proper operation. In addition, each executive monitors the state of the other&#39;s safe line. 
     The UIC executive  352  and the AC executive  354  work together to synchronize the time between the user interface computer  302  and the automation computer  300 . The time basis is configured via a battery backed real-time clock on the user interface computer  302  that is accessed upon startup. The user interface computer  302  initializes the CPU of the automation computer  300  to the real-time clock. After that, the operating system on each computer maintains its own internal time. The executives work together to ensure sufficiently timekeeping by periodically performing power on self tests. An alert may be generated if a discrepancy between the automation computer time and the user interface computer time exceeds a given threshold. 
       FIG. 47  shows the flow of information between various subsystems and processes of the APD system. As discussed previously, the UI model  360  and cycler controller  362  run on the automation computer. The user interface design separates the screen display, which is controlled by the UI view  338 , from the screen-to-screen flow, which is controlled by the cycler controller  362 , and the displayable data items, which are controlled by the UI model  360 . This allows the visual representation of the screen display to be changed without affecting the underlying therapy software. All therapy values and context are stored in the UI model  360 , isolating the UI view  338  from the safety-critical therapy functionality. 
     The UI model  360  aggregates the information describing the current state of the system and patient, and maintains the information that can be displayed via the user interface. The UI model  360  may update a state that is not currently visible or otherwise discernable to the operator. When the user navigates to a new screen, the UI model  360  provides the information relating to the new screen and its contents to the UI view  338 . The UI model  360  exposes an interface allowing the UI view  338  or some other process to query for current user interface screen and contents to display. The UI model  360  thus provides a common point where interfaces such as the remote user interface and online assistance can obtain the current operational state of the system. 
     The cycler controller  362  handles changes to the state of the system based on operator input, time and therapy layer state. Acceptable changes are reflected in the UI model  360 . The cycler controller  362  is implemented as a hierarchical state machine that coordinates therapy layer commands, therapy status, user requests and timed events, and provides view screen control via UI model  360  updates. The cycler controller  362  also validates user inputs. If the user inputs are allowed, new values relating to the user inputs are reflected back to the UI view  338  via the UI model  360 . The therapy process  368  acts as a server to the cycler controller  362 . Therapy commands from the cycler controller  362  are received by the therapy process  368 . 
     The UI view  338 , which runs on the UI computer  302 , controls the user interface screen display and responds to user input from the touch screen. The UI view  338  keeps track of local screen state, but does not maintain machine state information. Machine state and displayed data values, unless they are in the midst of being changed by the user, are sourced from the UI model  360 . If the UI view  338  terminates and is restarted, it displays the base screen for the current state with current data. The UI view  338  determines which class of screens to display from the UI model  360 , which leaves the presentation of the screen to the UI view. All safety-critical aspects of the user interface are handled by the UI model  360  and cycler controller  362 . 
     The UI view  338  may load and execute other applications  364  on the user interface computer  302 . These applications may perform non-therapy controlling tasks. Exemplary applications include the log viewer, the service interface, and the remote access applications. The UI view  338  places these applications within a window controlled by the UI view, which allows the UI view to display status, error, and alert screens as appropriate. Certain applications may be run during active therapy. For example, the log viewer may be run during active therapy, while the service interface and the remote access application generally may not. When an application subservient to the UI view  338  is running and the user&#39;s attention is required by the ongoing therapy, the UI view  338  may suspend the application and regain control of the screen and input functions. The suspended application can be resumed or aborted by the UI view  338 . 
       FIG. 48  illustrates the operation of the therapy subsystem  340  described in connection with  FIG. 46 . The therapy subsystem  340  functionality is divided across three processes: therapy control; therapy calculation; and solution management. This allows for functional decomposition, ease of testing, and ease of updates. 
     The therapy control module  370  uses the services of the therapy calculation module  372 , solution management module  374  and machine control subsystem  342  ( FIG. 46 ) to accomplish its tasks. Responsibilities of the therapy control module  370  include tracking fluid volume in the heater bag, tracking fluid volume in the patient, tracking patient drain volumes and ultra filtrate, tracking and logging cycle volumes, tracking and logging therapy volumes, orchestrating the execution of the dialysis therapy (drain-fill-dwell), and controlling therapy setup operations. The therapy control module  370  performs each phase of the therapy as directed by the therapy calculation module  370 . 
     The therapy calculation module  370  tracks and recalculates the drain-fill-dwell cycles that comprise a peritoneal dialysis therapy. Using the patient&#39;s prescription, the therapy calculation module  372  calculates the number of cycles, the dwell time, and the amount of solution needed (total therapy volume). As the therapy proceeds, a subset of these values is recalculated, accounting for the actual elapsed time. The therapy calculation module  372  tracks the therapy sequence, passing the therapy phases and parameters to the therapy control module  370  when requested. 
     The solution management module  374  maps the placement of solution supply bags, tracks the volume in each supply bag, commands the mixing of solutions based upon recipes in the solution database, commands the transfer of the requested volume of mixed or unmixed solution into the heater bag, and tracks the volume of mixed solutions available using the solution recipe and available bag volume. 
       FIG. 49  shows a sequence diagram depicting exemplary interactions of the therapy module processes described above during the initial ‘replenish’ and ‘dialyze’ portions of the therapy. During the exemplary initial replenish process  376 , the therapy control module  370  fetches the solution ID and volume for the first fill from the therapy calculation module  372 . The solution ID is passed to the solution management module  374  with a request to fill the heater bag with solution, in preparation for priming the patient line and the first patient fill. The solution management module  374  passes the request to the machine control subsystem  342  to begin pumping the solution to the heater bag. 
     During the exemplary dialyze process  378 , the therapy control module  370  executes one cycle (initial drain, fill, dwell-replenish, and drain) at a time, sequencing these cycles under the control of the therapy calculation module  372 . During the therapy, the therapy calculation module  372  is updated with the actual cycle timing, so that it can recalculate the remainder of the therapy if needed. 
     In this example, the therapy calculation module  372  specifies the phase as “initial drain,” and the therapy control module makes the request to the machine control subsystem  342 . The next phase specified by the therapy calculation module  372  is “fill.” The instruction is sent to the machine control subsystem  342 . The therapy calculation module  372  is called again by the therapy control module  370 , which requests that fluid be replenished to the heater bag during the “dwell” phase. The solution management module  374  is called by the therapy control module  370  to replenish fluid in the heater bag by calling the machine control subsystem  342 . Processing continues with therapy control module  370  calling the therapy calculation module  372  to get the next phase. This is repeated until there are no more phases, and the therapy is complete. 
     Pump Monitor/Math Repeater 
     The Pump Monitor/Math Repeater process is a software process or function that runs on the automation computer  300  separate from the safety executive  354 . The Pump Monitor/Math Repeater process is implemented in as two separate threads or sub-functions that run independently. The math repeater thread, herein referred to as the MR thread, confirms the FMS calculation result. The Pump Monitor thread, referred to as the PM thread, monitors the net fluid and air flow across relevant endpoints from information provided in the routine status messages from the Machine process  342 . The relevant endpoints may include but not be limited to 5 potential bag spikes, the heater bag, patient port and drain port. The PM thread will also monitor the heater pan temperature via information from the IO Server process. The PM thread will signal an alarm to the safety executive  354 , if predefined limits for fluid flow, air flow or temperature are exceeded. 
     The MR thread accepts the high speed pressure data and repeats the FMS calculation described above to recalculate the fluid volume displaced. The MR thread compares its recalculated fluid volume to the volume calculated by the Machine process  342  and sends a message to the safety executive. In another example, the MR thread declares and error condition if the two fluid volume values do not match. 
     The PM thread monitors several aspects of the pumping process as a safety check on the functioning of the cycler  14 . The PM thread will declare an invalid pump operation error condition if the Hardware Interface  310  reports valves open that do not correspond to the commanded pump action by the Machine subsystem  342 . An example of an invalid valve condition would be if any port valve  186 ,  184  ( FIG. 6 ) are open, while the pump was in an idle mode. The state of valves in the cassette is mapped to the state of the corresponding pneumatic valves  2710 , which are energized by the hardware interface  310 . Another example of an invalid valve condition would be a port valve  184 ,  186  that is open that does not correspond to the specified source of sink of fluid. 
     The PM thread will declare an error condition if excess fluid is pumped to the patient while the heater button temperature sensor  506  reports less than a given temperature. In a preferred embodiment, the PM thread will declare a error condition more than 50 ml of fluid is pumped to the patient while the button temperature is less than 32° C. 
     The PM thread will maintain a numerical accumulator on the amount of fluid pumped to the patient. If total volume of fluid pumped to the patient exceeds a specified amount, the PM thread will declare an error. The specified amount may be defined in the prescription information and may include an additional volume equal to one chamber volume or approximately 23 ml. 
     The PM thread will maintain a numerical accumulator on the amount of air measured in the pumping chamber by the FMS method for air taken from each bag. If the total amount of air from any bag exceeds the maximum allowed volume of air for that bag, then the PM thread will declare an error. In a preferred embodiment, the maximum allowed air volume for the heater bag is 350 ml and the maximum allowed air volume for a supply bag is 200 ml. A large air volume from a bag indicates that it may contain a leak to the atmosphere. The maximum allowed air volume for the heater bag may be larger to account for out-gassing when the fluid is heated. 
     Alert/Alarm Functions 
     Conditions or events in the APD system may trigger alerts and/or alarms that are logged, displayed to a user, or both. These alerts and alarms are a user interface construct that reside in the user interface subsystem, and may be triggered by conditions that occur in any part of the system. These conditions may be grouped into three categories: (1) system error conditions, (2) therapy conditions, and (3) system operation conditions. 
     “System error conditions” relate to errors detected in software, memory, or other aspects of the processors of the APD system. These errors call the reliability of the system into question, and may be considered “unrecoverable.” System error conditions cause an alarm that is displayed or otherwise made known to the user. The alarm may also be logged. Since system integrity cannot be guaranteed in the instance of a system error condition, the system may enter a fail safe mode in which the safe line described herein is disabled. 
     Each subsystem described in connection with  FIG. 46  is responsible for detecting its own set of system errors. System errors between subsystems are monitored by the user interface computer executive  352  and automation computer executives  354 . When a system error originates from a process running on the user interface computer  302 , the process reporting the system error terminates. If the UI screen view subsystem  338  is terminated, the user interface computer executive  352  attempts to restart it, e.g., up to a maximum of three times. If it fails to restart the UI screen view  338  and a therapy is in progress, the user interface computer executive  352  transitions the machine to a fail safe mode. 
     When a system error originates from a process running on the automation computer  300 , the process terminates. The automation computer executive  354  detects that the process has terminated and transitions to a safe state if a therapy is in progress. 
     When a system error is reported, an attempt is made to inform the user, e.g., with visual and/or audio feedback, as well as to log the error to a database. System error handling is encapsulated in the executive subsystem  332  to assure uniform handling of unrecoverable events. The executive processes of the UIC executive  352  and AC executive  354  monitor each other such that if one executive process fails during therapy, the other executive transitions the machine to a safe state. 
     “Therapy conditions” are caused by a status or variable associated with the therapy going outside of allowable bounds. For example, a therapy condition may be caused by an out-of-bounds sensor reading. These conditions may be associated with an alert or an alarm, and then logged. Alarms are critical events, generally requiring immediate action. Alarms may be prioritized, for example as low, medium or high, based on the severity of the condition. Alerts are less critical than alarms, and generally do not have any associated risk other than loss of therapy or discomfort. Alerts may fall into one of three categories: message alerts, escalating alerts, and user alerts. 
     The responsibility for detecting therapy conditions that may cause an alarm or alert condition is shared between the UI model and therapy subsystems. The UI model subsystem  360  ( FIG. 47 ) is responsible for detecting alarm and alert conditions pre-therapy and post-therapy. The therapy subsystem  340  ( FIG. 46 ) is responsible for detecting alarm and alert conditions during therapy. 
     The responsibility for handling alerts or alarms associated with therapy conditions is also shared between the UI model and therapy subsystems. Pre-therapy and post-therapy, the UI model subsystem  360  is responsible for handling the alarm or alert condition. During a therapy session, the therapy subsystem  340  is responsible for handling the alarm or alert condition and notifying the UI Model Subsystem an alarm or alert condition exists. The UI model subsystem  360  is responsible for escalating alerts, and for coordinating with the UI view subsystem  338  to provide the user with visual and/or audio feedback when an alarm or alert condition is detected. 
     “System operation conditions” do not have an alert or alarm associated with them. These conditions are simply logged to provide a record of system operations. Auditory or visual feedback need not be provided. 
     Actions that may be taken in response to the system error conditions, therapy conditions, or system operation conditions described above are implemented by the subsystem (or layer) that detected the condition, which sends the status up to the higher subsystems. The subsystem that detected the condition may log the condition and take care of any safety considerations associated with the condition. These safety considerations may comprise any one or combination of the following: pausing the therapy and engaging the occluder; clearing states and timers as needed; disabling the heater; ending the therapy entirely; deactivating the safe line to close the occluder, shut off the heater, and removing power from the valves; and preventing the cycler from running therapies even after a power cycle to require the system to be sent back to service. The UI subsystem  334  may be responsible for conditions that can be cleared automatically (i.e., non-latching conditions) and for user recoverable conditions that are latched and can only be cleared by user interaction. 
     Each condition may be defined such that it contains certain information to allow the software to act according to the severity of the condition. This information may comprise a numeric identifier, which may be used in combination with a lookup table to define priority; a descriptive name of the error (i.e., a condition name); the subsystem that detected the condition; a description of what status or error triggers the condition; and flags for whether the condition implements one or more actions defined above. 
     Conditions may be ranked in priority such that when multiple conditions occur, the higher priority condition may be handled first. This priority ranking may be based on whether the condition stops the administration of therapy. When a condition occurs that stops therapy, this condition takes precedence when relaying status to the next higher subsystem. As discussed above, the subsystem that detects a condition handles the condition and sends status information up to the subsystem above. Based on the received status information, the upper subsystem may trigger a different condition that may have different actions and a different alert/alarm associated with it. Each subsystem implements any additional actions associated with the new condition and passes status information up to the subsystem above. According to one exemplary implementation, the UI subsystem only displays one alert/alarm at a given time. In this case, the UI model sorts all active events by their priority and displays the alert/alarm that is associated with the highest priority event. 
     A priority may be assigned to an alarm based on the severity the potential harm and the onset of that harm. Table 1, below, shows an example of how priorities may be assigned in this manner 
     
       
         
           
               
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 POTENTIAL RESULT 
                   
               
               
                 OF FAILURE TO 
               
               
                 RESPOND TO THE 
               
               
                 CAUSE OF ALARM 
                 ONSET OF POTENTIAL HARM 
               
            
           
           
               
               
               
               
            
               
                 CONDITION 
                 IMMEDIATE 
                 PROMPT 
                 DELAYED 
               
               
                   
               
               
                 death or irreversible 
                 high priority 
                 high priority 
                 medium 
               
               
                 injury 
                   
                   
                 priority 
               
               
                 reversible injury 
                 high priority 
                 medium 
                 low priority 
               
               
                   
                   
                 priority 
               
               
                 minor discomfort or 
                 medium 
                 low priority 
                 low priority or 
               
               
                 injury 
                 priority 
                   
                 no alarm signal 
               
               
                   
               
            
           
         
       
     
     In the context of Table 1, the onset of potential harm refers to when an injury occurs and not to when it is manifested. A potential harm having an onset designated as “immediate” denotes a harm having the potential to develop within a period of time not usually sufficient for manual corrective action. A potential harm having an onset designated as “prompt” denotes a harm having the potential to develop within a period of time usually sufficient for manual corrective action. A potential harm having an onset designated as “delayed” denotes a harm having the potential to develop within an unspecified time greater than that given under “prompt.” 
     FIGS. F-K show exemplary screen views relating to alerts and alarms that may be displayed on a touch screen user interface.  FIG. 50  shows the first screen of an alarm, which includes a diagram  380  and text  382  instructing a user to close their transfer set. The screen includes a visual warning  384 , and is also associated with an audio warning. The audio warning may be turned off my selecting the “audio off” option  386  on the touch screen. When the user has closed the transfer set, the user selects the “confirm” option  388  on the touch screen.  FIG. 51  shows a similar alarm screen instructing a user to close their transfer set. In this case, an indication that draining is paused  390  and an instruction to select “end treatment” are provided  392 . 
     As previously discussed, alerts generally do not have associated risk other than loss of therapy or discomfort. Thus, an alert may or may not cause the therapy to pause. Alerts can be either “auto recoverable,” such that if the event clears the alert automatically clears, or “user recoverable,” such that user interaction with the user interface is needed to clear the alert. An audible alert prompt, which may have a volume that may be varied within certain limits, may be used to bring an alert to the attention of a user. In addition, information or an instruction may be displayed to the user. So that such information or instruction may be viewed by the user, an auto-dim feature of the user interface may be disabled during alerts. 
     In order to reduce the amount of disturbance the user, alerts may be categorized into different types based on how important an alert is and how quick a user response is required. Three exemplary types of alerts are a “message alert,” an “escalating alert,” and a “user alert.” These alerts have different characteristics based on how information is visually presented to the user and how the audible prompt is used. 
     A “message alert” may appear at the top of a status screen and is used for informational purposes when a user interaction is not required. Because no action needs to be taken to clear the alert, an audible prompt is generally not used to avoid disturbing, and possibly waking, the patient. However, an audible alert may be optionally presented.  FIG. 52  shows an exemplary message alert. In particular,  FIG. 52  shows an under-temperature message alert  394  that may be used to inform a user when the dialysate is below a desired temperature or range. In this case, a user does not need to take any action, but is informed that therapy will be delayed while the dialysate is heated. If the patient desires more information, the “view” option  396  may be selected on the touch screen. This causes additional information  398  concerning the alert to appear on the screen, as shown in  FIG. 53 . A message alert may also be used when there is a low flow event that the user is trying to correct. In this case, a message alert may be displayed until the low flow event is cleared to provide feedback to the user on whether the user fixed the problem. 
     An “escalating alert” is intended to prompt the user to take action in a non-jarring manner During an escalating alert, a visual prompt may displayed on the touch screen and an audible prompt may be presented (e.g., once). After a given period of time, if the event that caused the alert is not cleared, a more emphatic audible prompt may be presented. If the event causing the alert is not cleared after an additional period of time, the alert is escalated to a “user alert.” According to one exemplary implementation of a user alert, a visual prompt is displayed until the alert is cleared and an audible prompt, which can be silenced, is presented. The UI subsystem does not handle the transition to from escalating alert to user alert. Rather, the subsystem that triggered the original event will trigger a new event associated with the user alert.  FIG. 54  shows a screen view displaying information concerning an escalating alert. This exemplary alert includes an on-screen alert message  400  and a prompt  402  instructing the user to check the drain line for kinks and closed clamps, as well as and an audible prompt. The audible prompt may be continuous until it is silenced by the user.  FIG. 55  shows a screen view including an “audio off” option  404  that may be selected to silence the audible prompt. This alert can be used directly, or as part of the escalating alert scheme. 
     Each alert/alarm is specified by: an alert/alarm code, which is a unique identifier for the alert/alarm; an alert/alarm name, which is a descriptive name of the alert/alarm; an alert/alarm type, which comprises the type of alert or level of alarm; an indication of whether an audible prompt is associated with the alert/alarm; an indication of whether the alert and associated event can be bypassed (or ignored) by the user; and the event code of the event or events that trigger the alert/alarm. 
     During alarms, escalating alerts and user alerts, the event code (which may be different from the alert or alarm code, as described above) may be displayed on the screen so that the user can read the code to service personnel if needed. Alternatively or additionally, a voice guidance system may be used so that, once connected to a remote call center, the system can vocalize pertinent information about the system configuration, state, and error code. The system may be connected to the remote call center via a network, telephonic connection, or some other means. 
     An example of a condition detected by the therapy subsystem is described below in connection with  FIG. 56 . The condition results when the APD system is not positioned on a level surface, which is important for air management. More particularly, the condition results when a tilt sensor detects that APD system is tilted beyond a predetermined threshold, such as 35°, with respect to a horizontal plane. As described below, a recoverable user alert may be generated by the therapy subsystem if the tilt sensor senses an angle with an absolute value greater than the predetermined threshold. To avoid nuisance alarms, the user may be directed to level the APD system before therapy begins. The tilt threshold may be lower during this pre-therapy period (e.g., 35°). The user may also be given feedback concerning whether the problem is corrected. 
     When the tilt sensor detects an angle of tilt exceeding a threshold value during therapy, the machine subsystem  342  responds by stopping the pump in a manner similar to detecting air in the pump chamber. The therapy subsystem  340  asks for status and determines that the machine layer  342  has paused pumping due to tilt. It also receives status information concerning the angle of the machine. At this point, the therapy subsystem  340  generates a tilt condition, pauses therapy, and sends a command to the machine subsystem  342  to pause pumping. This command triggers clean-up, such as taking fluid measurement system (FMS) measurements and closing the patient valve. The therapy subsystem  340  also starts a timer and sends an auto recoverable tilt condition up to the UI model  360 , which sends the condition to the UI view  338 . The UI view  338  maps the condition to an escalating alert. The therapy subsystem  340  continues to monitor the tilt sensor reading and, if it drops below the threshold, clears the condition and restarts therapy. If the condition does not clear before the timer expires, the therapy subsystem  340  triggers a user recoverable “tilt timeout” condition that supersedes the auto-recoverable tilt condition. It sends this condition to the UI model  360 , which sends the condition to the UI view  338 . The UI view  338  maps the condition to a user alert. This condition cannot be cleared until a restart therapy command is received from the UI subsystem (e.g., the user pressing the resume button). If the tilt sensor reading is below the threshold, the therapy resumes. If it is not below the threshold, the therapy layer triggers an auto recoverable tilt condition and starts the timer. 
     Prioritized Audible Signals 
     The cycler may provide audible signals and voice guidance to the user to communicate a range of information including but not limited to number selection, sound effects (button selection, action selection), machine condition, operational directions, alerts, and alarms. The cycler controller  16  may cause a speaker to annunciate audible signals and vocalizations from stored sound files stored in memory on one or both of the computers  300 ,  302  in the control system  16 . Alternatively, vocalizations may be stored and produced by a specialized voice chip. 
     In some instances, the cycler may have multiple audible signals to annunciate at the same time or sequentially in a very short time. The annunciation of several signals in a short period of time may overwhelm the user resulting in annoyance or the loss of critical safety information. The cycler controller  16  may assign priorities to each audible signal and suppress the lower priority signals to allow the clear communication of higher priority audible signals. In one instance, the audible signals are prioritized from the highest priority alarm signals to the lowest priority annunciation of a sequence of numbers: 
     1. Alarms 
     2. Alerts 
     3. Sound Effects 
     4. Voice Guidance 
     5. Annunciation for a sequence of numbers. 
     Alarms and alerts are described above. Sound effects may confirm sounds to indicate that a button, or choice has been selected. Sound effects may also announce or confirm a particular action is being taken by the cycler. Voice guidance may include voiced instructions to execute a particular procedure, access help, contact a call center and other directing instructions. Annunciation for a sequence of numbers may include reading back to the user or the call center the number that the user had just keyed in or it may read the user allowable values for requested input. 
     Audible Sleep Aid 
     The cycler  14  may include an option to play soothing sounds at night to aid sleeping. The playing of sounds such as rain, ocean waves, etc are referred to as sound therapy. Sound therapy for sleep can provide some users with a higher tolerance for nighttime noises and the masking or replacing of nighttime noise with more rhythmic, soothing sounds that minimize sleep disturbance. Sound therapy may help individuals suffering from hearing conditions such as hyperacusis and tinnitus. The user interface  324  may provide the user with a menu to select types of sound, volume levels and duration so that the sound therapy can play before during the initial period of sleep. The sound files may be stored in the memories of the computers  300 ,  302  and played by the speaker in the cycler  14 . In another example, the cycler may include an output jack to drive external speakers. In another example, the sound files and/or the speaker driver electronics may be separate from either the automation computer  300  or the user interface computer  302 . The sound files may include the but be limited to rain sounds, thunder storms, ocean waves, thunder, forest sounds, crickets, white noise, and pink noise (varying amplitude and more bass). 
     Battery Operation 
     The cycler may include a rechargeable lithium ion battery for use as a backup power source. At a minimum this battery helps to ensure that the cycler does not turn off without alerting the user and saving the current state of the treatment. A power management system may be implemented by the cycler when on battery power that is contingent on the amount of charge remaining in the battery. If the battery is sufficiently charged, the cycler can prevent brownouts or short power outages from interfering with the completion of a therapy. The cycler control circuitry can measure the state of charge of the battery, and can correlate the battery charge level with operable states. This information may be obtained empirically through testing, and the correlations between battery charge level and the ability to operate the various subsystems may be stored in memory. The following functions may be associated with the battery charge level: 
     Level 4: Enough power to perform one cycle of therapy. Implemented if, for example, the charge level of the battery is equal to or greater than approximately 1100 milliamp-hours.
 
Level 3: Enough power to perform a user drain. Implemented if, for example, the charge level of the battery is equal to or greater than approximately 500 milliamp-hours.
 
Level 2: Enough power to end therapy, display alert, and guide user through post-therapy breakdown. Implemented if, for example, the charge level of the battery is equal to or greater than approximately 300 milliamp-hours.
 
Level 1: Enough power to end therapy and display an alert. Implemented if, for example, the charge level of the battery is equal to or greater than approximately 200 milliamp-hours.
 
Level 0: Not enough power to operate.
 
If there is enough charge in the battery (Level 4), the cycler will continue with the therapy until the current cycle is finished. This may not include replenishing the heater bag or heating the solution. Therefore, if already in a fill phase, the cycler may continue the therapy if the solution in the heater bag is in the proper temperature range and there is enough solution in the heater bag. If the battery only has enough capacity to perform a 20 minute drain (Level 3), the cycler will alert the user, and give the user the option to either drain or end treatment without draining. If the battery only has enough power to alert the user (Level 2) it will not give the user the option to drain and the user will be guided through the post-therapy breakdown. If there is not enough power to guide the user through breakdown (Level 1), the user will be prompted to disconnect and then the cycler will power down. At this battery level the cycler may not have enough power to release the door, so the user may not be able to breakdown the therapy. During start up, the cycler can assess the state of the batter, and alert the user if the battery has a fault or if the battery does not have a sufficient charge to at least alert the patient if main power is lost. The cycler may be programmed to not allow the user to start a treatment without the battery having enough capacity to provide and alert and guide the user through post-therapy breakdown (Battery Level 2).
 
Another example of battery charge levels and available therapy choices or machine actions sets  4  battery charge levels and the available therapy choices or machine actions:
 
     Level 4: 
     If the fill process has not started, then suspend operation until the AC power is restored. The suspend is limited to 30 mins. 
     If the fill process has started, then complete cycle including the fill, dwell and drain processes. 
     The heater bag will not be refilled as there is no heating during battery operation. 
     End therapy, and guide user through post-therapy breakdown including removal of the of the dialysate delivery set  12   a  from the cycler  14 . 
     Level 3: 
     If in the fill or drain process, then suspend operation until the AC power is restored. The suspend is limited to 30 mins. 
     If the drain process has started, then complete the cycle. 
     The heater bag will not be refilled as there is no heating during battery operation. 
     End therapy, and guide user through post-therapy breakdown including removal of the of the dialysate delivery set  12   a  from the cycler  14 . 
     Level 2: 
     End therapy, and guide user through post-therapy breakdown including removal of the of the dialysate delivery set  12   a  from the cycler  14 . 
     Level 1: 
     End therapy. 
     Level 0: 
     Not enough power to operate. 
     An alert will be displayed to the user or patient at levels 1-4. The control system  16  may extend the cycler operation on battery power by dimming the display screen  324  after a given time period from the last screen touch. In another example the display screen  324  may dim after a given period from the appearance of the most recent message, alert or warning. In one example, the display screen  324  will dim 2 minutes after the more recent screen touch or last. The display screen  324  may include a message or symbol indicating operation on battery power. 
     The electrical circuitry connecting the battery to the pneumatic valves may include a regulated voltage boost converter that steps-up the supplied variable battery voltage to a consistent voltage. The supplied battery voltage may drop as the battery is discharged, In one example, an Li-Ion battery at full charge may supply 12.3 volts. The supplied voltage may drop as the battery is depleted to as low as 9 volts when the battery is fully discharged. The pneumatic valves may require a minimum voltage to reliably open fully. In one example, the minimum voltage to reliably open the valve may be 12 volts. 
     A regulated voltage boost converter may be placed between the supply batter and the valves to assure sufficient voltage to reliably open the valves as battery discharges. The regulated voltage boost converter will output a regulated voltage at a higher value than the variable battery voltage input. In one example, the regulated voltage boost converter may be an integrated chip such as the TPS61175 made by Texas Instruments. A regulated voltage buck/boost converter may also be used between the battery and the valves. The buck/boost converter is able to supply a regulated voltage output from supplied voltages that are higher, equal to, or lower than the input voltage. 
     In one embodiment, the PWM duty cycle of the valve drivers may vary with the measured battery voltage. The valves may be operated in a pick-and-hold manner, where an initially higher voltage is applied to open the valve and then a lower voltage is applied to hold the valve in desired condition. The PWM duty cycle for the hold function may be scaled inversely with the measure battery voltage to provide a consistent averaged voltage or current to the valves. The PWM duty cycle may be scaled inversely with measured battery voltage for the higher voltage open or pick operation. 
     Screen Display 
     As discussed previously, the UI view subsystem  338  ( FIG. 47 ) is responsible for the presentation of the interface to the user. The UI view subsystem is a client of and interfaces with the UI model subsystem  360  ( FIG. 47 ) running on the automation computer. For example, the UI view subsystem communicates with the UI model subsystem to determine which screen should be displayed to the user at a given time. The UI view may include templates for the screen views, and may handle locale-specific settings such as display language, skin, audio language, and culturally sensitive animations. 
     There are three basic types of events that occur in the UI view subsystem. These are local screen events that are handled by the individual screens, model events in which a screen event must propagate down to the UI model subsystem, and polling events that occur on a timer and query the UI model subsystem for status. A local screen event only affects the UI view level. These events can be local screen transitions (e.g., in the case of multiple screens for a single model state), updates to view settings (e.g., locality and language options), and requests to play media clips from a given screen (e.g., instructional animations or voice prompts). Model events occur when the UI view subsystem must consult with the UI model subsystem to determine how to handle the event. Examples that fall into this category are the confirmation of therapy parameters or the pressing of the “start therapy” button. These events are initiated by the UI view subsystem, but are handled in the UI model subsystem. The UI model subsystem processes the event and returns a result to the UI view subsystem. This result drives the internal state of the UI view subsystem. Polling events occur when a timer generates a timing signal and the UI model subsystem is polled. In the case of a polling event, the current state of the UI view subsystem is sent to the UI model subsystem for evaluation. The UI model subsystem evaluates the state information and replies with the desired state of the UI view subsystem. This may constitute: (1) a state change, e.g., if the major states of the UI model subsystem and the UI view subsystem are different, (2) a screen update, e.g., if values from the UI model subsystem change values displayed on-screen, or (3) no change in state, e.g., if the state of the UI model subsystem and the UI view subsystem are identical.  FIG. 57  shows the exemplary modules of the UI view subsystem  338  that perform the functions described above. 
     As shown in  FIG. 57 , the UI model client module  406  is used to communicate events to the UI model. This module  406  is also used to poll the UI model for the current status. Within a responsive status message, the UI model subsystem may embed a time to be used to synchronize the clocks of the automation computer and the user interface computer. 
     The global slots module  408  provides a mechanism by which multiple callback routines (slots) can subscribe to be notified when given events (signals) occur. This is a “many-to-many” relationship, as a slot can be bound to many signals, and likewise a signal can be bound to many slots to be called upon its activation. The global slots module  408  handles non-screen specific slots, such as application level timers for UI model polling or button presses that occur outside of the screen (e.g., the voice prompt button). 
     The screen list class  410  contains a listing of all screens in the form of templates and data tables. A screen is made up of a template and an associated data table that will be used to populate that screen. The template is a window with widgets laid out on it in a generic manner and with no content assigned to the widgets. The data table includes records that describe the content used to populate the widgets and the state of the widgets. A widget state can be checked or unchecked (in the case of a checkbox style widget), visible or hidden, or enabled or disabled. The data table can also describe the action that occurs as a result of a button press. For example, a button on window ‘A’ derived from template ‘1’ could send an event down to the UI model, whereas that same button on window ‘B’ also derived from template ‘1’ could simply cause a local screen transition without propagating the event down to the UI model. The data tables may also contain an index into the context-sensitive help system. 
     The screen list class  410  forwards data from the UI model to the intended screen, selects the proper screen-based data from the UI model, and displays the screen. The screen list class  410  selects which screen to display based on two factors: the state reported by the UI model and the internal state of the UI view. In some cases, the UI model may only inform the UI view that it is allowed to display any screen within a category. For example, the model may report that the machine is idle (e.g., no therapy has been started or the setup phase has not yet occurred). In this case, it is not necessary to confer with the UI model when the user progresses from a menu into its sub-menu. To track the change, the UI view will store the current screen locally. This local sequencing of screens is handled by the table entries described above. The table entry lists the actions that respective buttons will initiate when pressed. 
     The language manager class  412  is responsible for performing inventory on and managing translations. A checksum may be performed on the list of installed languages to alert the UI view if any of the translations are corrupted and or missing. Any class that wants a string translated asks the language manager class  412  to perform it. Translations may be handled by a library (e.g., Qt®). Preferably, translations are requested as close as possible to the time of rendering. To this end, most screen template member access methods request a translation right before handing it to the widget for rendering. 
     A skin comprises a style-sheet and images that determine the “look and feel” of the user interface. The style-sheet controls things such as fonts, colors, and which images a widget will use to display its various states (normal, pressed, disabled, etc.). Any displayed widget can have its appearance altered by a skin change. The skin manager module  414  is responsible for informing the screen list and, by extension, the screen widgets, which style-sheet and skin graphics should be displayed. The skin manager module  414  also includes any animated files the application may want to display. On a skin change event, the skin manager will update the images and style-sheet in the working set directory with the proper set, which is retrieved from an archive. 
     The video manager module  416  is responsible for playing locale-appropriate video given a request to display a particular video. On a locale change event, the video manager will update the videos and animations in the working set directory with the proper set from an archive. The video manager will also play videos that have accompanying audio in the audio manager module  418 . Upon playback of these videos, the video manager module  416  will make the appropriate request to the audio manager module  418  to play the recording that belongs to the originally requested video clip. 
     Similarly, the audio manager module  418  is responsible for playing locale-appropriate audio given a request to play a particular audio clip. On a locale change event, the audio manager will update the audio clips in the working set directory with the proper set from an archive. The audio manager module  418  handles all audio initiated by the UI view. This includes dubbing for animations and sound clips for voice prompts. 
     The database client module  420  is used to communicate with the database manager process, which handles the interface between the UI view subsystem and the database server  366  ( FIG. 47 ). The UI view uses this interface to store and retrieve settings, and to supplement therapy logs with user-provided answers to questions about variables (e.g., weight and blood pressure). 
     The help manager module  422  is used to manage the context-sensitive help system. Each page in a screen list that presents a help button may include an index into the context-sensitive help system. This index is used so that the help manager can display the help screen associated with a page. The help screen may include text, pictures, audio, and video. 
     The auto ID manager  424  is called upon during pre-therapy setup. This module is responsible for capturing an image (e.g., a photographic image) of a solution bag code (e.g., a datamatrix code). The data extracted from the image is then sent to the machine control subsystem to be used by the therapy subsystem to identify the contents of a solution bag, along with any other information (e.g., origin) included in the code. 
     Using the modules described above, the UI view subsystem  338  renders the screen views that are displayed to the user via the user interface (e.g., display  324  of  FIG. 45 ). FIGS. N-T show exemplary screen views that may be rendered by the UI view subsystem. These screen views illustrate, for example, exemplary input mechanisms, display formats, screen transitions, icons and layouts. Although the screens shown are generally displayed during or before therapy, aspects of the screen views may be used for different input and output functions than those shown. 
     The screen shown in  FIG. 58  is an initial screen that provides the user the option of selecting between “start therapy”  426  to initiate the specified therapy  428  or “settings”  430  to change settings. Icons  432  and  434  are respectively provided to adjust brightness and audio levels, and an information icon  436  is provided to allow the user to solicit more information. These icons may appear on other screens in a similar manner. 
       FIG. 59  shows a status screen that provides information the status of the therapy. In particular, the screen indicates the type of therapy being performed  438 , the estimated completion time  440 , and the current fill cycle number and total number of fill cycles  442 . The completion percentage of the current fill cycle  444  and the completion percentage of the total therapy  446  are both numerically and graphically displayed. The user may select a “pause” option  448  to pause therapy. 
       FIG. 60  shows a menu screen with various comfort settings. The menu includes brightness arrows  450 , volume arrows  452  and temperature arrows  454 . By selecting either the up or down arrow in each respective pair, a user can increase or decrease screen brightness, audio volume, and fluid temperature. The current brightness percentage, volume percentage and temperature are also displayed. When the settings are as desired, a user may select the “OK” button  456 . 
       FIG. 61  shows a help menu, which may be reached, for example, by pressing a help or information button on a prior screen. The help menu may include text  458  and/or an illustration  460  to assist the user. The text and/or illustration may be “context sensitive,” or based on the context of the prior screen. If the information provided to the user cannot conveniently be provided in one screen, for example in the case of a multi-step process, arrows  462  may be provided to allow the user to navigate backward and forward between a series of screens. When the user has obtained the desired information. he or she may select the “back” button  464 . If additional assistance is required, a user may select the “call service center” option  466  to have the system contact the call service center. 
       FIG. 62  illustrates a screen that allows a user to set a set of parameters. For example, the screen displays the current therapy mode  468  and minimum drain volume  470 , and allows a user to select these parameters to be changed. Parameters may be changed in a number of ways, such as by selecting a desired option from a round robin style menu on the current screen. Alternatively, when the user selects a parameter to be changed, a new screen may appear, such as that shown in  FIG. 63 . The screen of  FIG. 63  allows a user to adjust the minimum drain volume by inputting a numeric value  472  using a keypad  474 . Once entered, the user may confirm or cancel the value using buttons  476  and  478 . Referring again to  FIG. 62 , a user may then use the “back” and “next” arrows  480 ,  482  to navigate through a series of parameters screens, each including a different set of parameters. 
     Once all desired parameters have been set or changed (e.g., when the user has navigated through the series of parameters screens), a screen such as that shown in  FIG. 64  may be presented to allow a user to review and confirm the settings. Parameters that have changed may optionally be highlighted in some fashion to draw the attention of the user. When the settings are as desired, a user may select the “confirm” button  486 . 
     Automated Peritoneal Dialysis Therapy Control 
     Continuous ambulatory peritoneal dialysis (“CAPD”) is traditionally performed manually, with a patient or user transferring dialysis solution from a bag into his or her peritoneal cavity, having the fluid dwell in the abdomen for three to six hours, and then allowing the fluid to empty into a collection or drain bag. This is typically done three or four times a day. Automated peritoneal dialysis (“APD”) differs from CAPD in that APD is achieved with the aid of a peritoneal dialysis machine (“cycler”) that performs a series of fill-dwell-drain cycles during a period of several hours (e.g. when asleep or at night). In APD, the fluid introduced during a fill phase of a cycle, plus any ultrafiltration fluid, may not drain completely during the following drain phase of the cycle. This may be a result of the user&#39;s position in bed, leading to sequestration of fluid, for example, in a recess in the peritoneal cavity, and preventing an indwelling catheter from accessing all of the fluid present. In continuous cycling peritoneal dialysis (“CCPD”), the cycler attempts to perform a full drain after a fill and dwell phase in order to prevent accumulation of retained fluid (a residual intraperitoneal volume) with each succeeding cycle. APD generally comprises a plurality of short nighttime exchanges of dialysate while the user is connected to the cycler and asleep. At the end of a nighttime therapy, a volume of dialysis fluid—possibly of different composition—may be left in the peritoneal cavity during the day for continued exchange of solutes, transfer of waste compounds, and ultrafiltration. In intermittent peritoneal dialysis (“IPD”), multiple exchanges of dialysate are performed over a period of time (e.g., at night), without having a prolonged residual (or daytime) dwell cycle. 
     Therapy with a cycler generally begins with an initial drain phase to attempt to ensure that the peritoneal cavity is empty of fluid. The characteristics of the dialysate solution usually cause some transfer of fluid from the patient&#39;s tissues to the intraperitoneal space—ultrafiltration. As therapy proceeds through a series of cycles, fluid may accumulate in the intraperitoneal cavity if the drain phase does not yield the volume of fluid infused during the fill phase, plus the volume of ultrafiltered fluid produced during the time that dialysate solution is in the peritoneal cavity. In some modes, the cycler may be programmed to issue an alarm to the user when the drain volume has not matched the volume of fluid infused plus the expected ultrafiltration (“UF”) volume. (The expected UF volume is a function of—among other things—the individual patient&#39;s physiology, the chemical composition of the dialysate solution, and the time during which the dialysate solution is expected to be present in the peritoneal cavity). 
     In other modes, the cycler may proceed to the next fill-dwell-drain cycle if a pre-determined amount of drain time has passed and a pre-determined minimum percentage (e.g. 85%) of the preceding fill volume has been drained. In this case, the cycler may be programmed to alarm if the drain flow decreases below a pre-determined rate after the minimum drain time and before the minimum drain percentage has been reached. The cycler may be programmed to alert the user after several minutes (e.g., two minutes) of attempting but failing to maintain a pre-determined flow rate when pumping fluid from the peritoneal cavity. A low-flow condition may be detectable by the cycler because of the increased amount of time required to fill a pump chamber before end-of-stroke is detected by the controller. A zero-flow or no-flow condition may be detectable by the cycler because of the detection by the controller of a premature end-of-stroke state. The duration of the time delay before alerting the user or initiating a new fill-dwell-drain cycle may be programmed to be a few minutes in a low-flow condition (e.g., 2 minutes), and may be shorter (e.g., 30 seconds) in a no-flow condition. A shorter wait-time during a no-flow condition may be preferable, for example, because it may be associated with a greater degree of patient discomfort, or may be the result of a quickly correctable problem, such as a bend in the patient line or catheter. This time delay may be programmed at the cycler manufacturing stage or may be selectable by a clinician as a prescription parameter. The extent of the delay may be governed, among other things, by the countervailing desire of the user or clinician to stay within the targeted total therapy time (keeping in mind that little dialysis is likely to occur when the intraperitoneal volume (“IPV”) is low or close to zero). If a full drain is not achieved, the cycler may also track the amount of fluid estimated to be accumulating with each cycle, and issue a warning or alarm if the cumulative IPV exceeds a pre-determined amount. This maximum IPV may be a parameter of the therapy prescription programmed into the cycler by the clinician, taking account of the particular physiological characteristics of the individual patient/user. 
     One method of dealing with the cumulative retention of fluid during a series of CCPD cycles is to convert the CCPD therapy to a tidal peritoneal dialysis (“TPD”) therapy. TPD generally comprises a fill-dwell-drain cycle in which a drain volume is intentionally made a prescribed fraction of the initial fill volume (which may also be initially be entered by the clinician as a prescription parameter). A pre-determined percentage of the infused fluid, or a pre-determined amount of fluid is arranged to remain in the peritoneal cavity during the subsequent fill-dwell-drain cycles during a therapy. Preferably, the subsequent fill volumes are also reduced to match the drain volume (minus the expected UF) in order to maintain a relatively constant residual intraperitoneal volume. For example, an initial fill volume of 3000 ml may be introduced at the beginning of therapy, followed by subsequent drain and [fill plus expected UF] volumes amounting to only 1500 ml, i.e. 50% of the initial fill volume. The reserve or residual fluid in the peritoneal cavity is then drained completely at the end of therapy. In an alternative mode, a complete drain may be attempted after a pre-determined or prescribed number of fill-dwell-drain cycles (e.g., a complete drain may be attempted after three cycles of tidal therapy, this grouping comprising a therapy “cluster”). TPD may be beneficial in that users may experience less discomfort associated with repeated large fill volumes or repeated attempts to fully empty the peritoneal cavity. Low-flow conditions associated with small intraperitoneal fluid volumes may also be reduced, thus helping to avoid extending the total therapy time. To reduce the discomfort associated with attempting to drain small residual volumes, for example, the tidal drain volume may be set at 75% of the initial fill volume (plus-or-minus expected UF volume), for example, leaving approximately 25% as a reserve or residual volume in the peritoneal cavity for the duration of therapy, or for the duration of a cluster of cycles. 
     A cycler may also be programmed to convert a CCPD mode of therapy to a TPD mode of therapy during the course of therapy if the user chooses to keep a residual volume of fluid in the peritoneal cavity at the end of the subsequent drain phases (e.g., for comfort reasons). In this case, the cycler is programmed to calculate a choice of residual volumes (or volumes as a percent of initial fill volume) based on the number of extra cycles to be added to the therapy and the volume of remaining dialysate to be infused. For example, the cycler controller can calculate the remaining fill volumes based on the remaining cycles that include an additional one, two or more cycles. Having determined the fill volumes for each of these possibilities, the cycler controller can calculate how much residual volume can be left at the end of each remaining drain phase while ensuring that the IPV remains under a maximum prescribed IPV (Max IPV). The cycler may then present the user with a range of possible residual volumes (as a percentage of the initial fill volume or in volumetric terms) available for each remaining cycle in a therapy extended by one, two or more cycles. The user may make the selection based on the number of extra cycles chosen and the desired amount of post-drain residual volume. Switching to tidal therapy may help to reduce the number of low-drain-flow alerts to the user, which can be particularly advantageous during nighttime therapy. 
     In switching to tidal mode, the cycler may be programmed to select a reserve or residual volume percentage (volume remaining in the peritoneal cavity as a percent of the fill volume plus expected UF). Alternatively, the reserve volume may be user-selectable or clinician-selectable from a range of values, optionally with the clinician having the ability to select a wider range of possible values than the user. In an embodiment, the cycler may calculate the effects of adding one, two or three additional cycles on the remaining fill volumes and the expected residual IP volume percentage, and give the user or clinician the option of selecting among those calculated values. Optionally, the cycler may be constrained to keep the residual IP volume percentage below a pre-determined maximum value (e.g., a percentage of the initial fill volume plus expected UF, or a percentage of the maximum permissible IPV). 
     If CCPD is converted to TPD, one or more therapy cycles (fill-dwell-drain cycles) may need to be added to a therapy to use all of the prescribed volume of dialysate for the therapy session. The remaining volume to be infused going forward would then be divided by the remaining number of cycles. Furthermore, the cycler may be programmed to allow the clinician or user to select between extending the targeted total therapy time to accommodate the additional cycles (cycle-based therapy), or to attempt to maintain the targeted therapy time by adjusting the dwell times (i.e., shortening them) if necessary to reduce the fill-dwell-drain cycle durations going forward (time-based therapy). 
     In an alternative embodiment, the cycler may allow the residual IP volume to fluctuate (optionally within pre-determined limits) from one cycle to the next, depending on how much fluid can be drained within a specified drain time interval. The time available for the drain phase may be limited if the cycler has been programmed to complete the therapy within the previously scheduled time, or the drain phase may be terminated to prevent the cycler from attempting to pull fluid at a slow rate for a prolonged period of time. In switching from CCPD to TPD, if the cycler adds one or more additional cycles to perform a complete therapy with the available dialysate solution, then meeting the scheduled therapy end-time may require shortening the dwell times, or reducing each drain phase, which could cause the residual volume for the tidal mode to vary, depending on the drain flow conditions. As the cycler estimates and tracks the amount of residual volume, it may be programmed to calculate whether the subsequent fill volume plus expected UF volume will reach or exceed a prescribed maximum IPV. If so, the cycler can alert and provide the user with two or more options: the user may terminate treatment, repeat or extend a drain phase in an attempt to lower the residual intraperitoneal volume, or add a cycle to reduce the subsequent fill volumes. After calculating the effect on treatment time of adding an additional one or more cycles (increased number of cycles vs. reduced fill and drain times at lower volumes) the cycler may optionally reduce subsequent dwell times by an amount of time necessary to offset the additional therapy time generated by an additional one or more cycles. The cycler may be programmed to deliver an optional last-fill phase that delivers fresh dialysate of the same or a different composition to the user&#39;s peritoneal cavity for an extended dwell time while not connected to the cycler (e.g., a prolonged dwell phase for a “day therapy,” i.e., during the day following a nighttime therapy). At the user&#39;s option, the last fill volume may be selected to be less than the fill volumes used during nighttime therapy. The cycler may also optionally prompt the user to select an optional extra last drain to give the user the chance to completely empty the peritoneal cavity prior to the infusion of a last fill volume (which may be carried by the user for a relatively prolonged period of time after the end of nighttime therapy). If this function is enabled, the cycler may prompt the user to sit up or stand, or otherwise move about to mobilize any trapped fluid in the peritoneal cavity during this last drain phase. 
     The cycler may also be programmed to account for an expected amount of ultrafiltration (“UF”) fluid produced during a dwell phase on or off the machine, and to alert the user if a minimum drain volume that includes the volume infused plus this expected UF is not drained either initially at the beginning of therapy, or during a fill-dwell-drain cycle during therapy. In an embodiment, the cycler may be programmed for a minimum initial drain volume and a minimum initial drain time, and to pause or terminate the drain phase if the measured drain flow rate has decreased below a pre-determined threshold value for a pre-determined number of minutes. The minimum initial drain volume may comprise the volume of the last fill phase in the preceding nighttime therapy, plus an expected UF volume from the day therapy dwell phase. If the minimum (or more) initial drain volume is achieved, the minimum initial drain time is reached, and/or the drain flow rate has decreased, the IPV tracked by the cycler controller may be set to zero at the end of the initial drain phase. If not, the cycler may alert the user. The cycler may allow the user to bypass the minimum initial drain volume requirement. For example, the user may have manually drained at some time before initiating APD. If the user elects to forego adherence to the minimum initial drain volume, the cycler may be programmed to perform a full drain at the end of the first cycle regardless of the type of therapy selected by the user. If enabled, this feature helps to ensure that the second fill-dwell-drain cycle begins at an IPV that is as close to zero as possible, helping to ensure that a prescribed maximum IPV should not be exceeded during subsequent cycles of the therapy. 
     The cycler may also be programmed to allow the user to pause therapy. During a pause, the user may have the option to alter the therapy by reducing the fill volume, reducing therapy time, terminating a planned “day therapy,” or ending therapy altogether. In addition, the user may have the option to perform an immediate drain at any time during therapy. The volume of an unscheduled drain may be selected by the user, whereupon the cycler may resume the cycle at the stage at which it was interrupted. 
     The cycler may be programmed to have a prescriber or “clinician” mode. A software application may be enabled to allow a clinician to create or modify a set of parameters forming the therapy prescription for a particular patient or user, as well as setting the limits within which a user may adjust user-accessible parameters. The clinician mode may also allow a clinician to fix one or more treatment parameters that would otherwise be accessible to a user, as well as lock a parameter to prevent a user from changing it. A clinician mode may be password-protected to prevent unauthorized access. The clinician mode application may be constructed to interface with a database to read and write the parameters comprising a prescription. Preferably, a “user mode” permits a user to access and adjust user-accessible parameters during a pre-therapy startup phase of a therapy. In addition, an “active therapy mode” may optionally be available to a user during therapy, but with access to only a subset of the parameters or parameter ranges available in the user mode. In an embodiment, the cycler controller may be programmed to allow parameter changes during active therapy mode to affect only the current therapy, the parameter settings being reset to previously prescribed values before subsequent therapies. Certain parameters preferably are not user-adjustable at all, user-adjustable with concurrence of a clinician through a prescription setting, or user-adjustable only within a range of values set by a clinician in programming a prescription. Examples of parameters that may not be adjustable solely by the user include, for example, the minimum initial drain volume or time, maximum initial fill volume, and maximum IPV. User-adjustable parameters may include, for example, the tidal drain frequency in a cluster (e.g., adjustable between 1 and 5 cycles), and the percentage of a tidal therapy fill volume to be drained (e.g., adjustable up or down by a pre-determined amount from a default value of, for example, 85%). In an alternative embodiment, the clinician mode may allow a clinician to prevent a user from programming a maximum IPV to be greater than a pre-determined multiple (e.g., 200%) of the initial fill volume assigned to a nighttime fill-dwell-drain cycle. 
     The cycler may also be programmed to routinely alert the user and to request confirmation when a user-adjustable parameter is entered that is outside of pre-determined ranges. For example, if the maximum IPV has been made user-adjustable in the clinician mode, the cycler may alert the user if he or she attempts to select a Max IPV value outside of a fractional range (e.g., 130-160%) of the programmed fill volume for nighttime therapy. 
     The cycler may also be programmed to alert the user (and possibly seek confirmation) if the initial drain volume has been made user-adjustable in the clinician mode, and the user selects an initial drain volume below a pre-determined percentage of the fill volume of the last therapy (e.g., if it is adjusted to be less than 70% of the last fill volume). In another example, the cycler may be programmed to alert the user (and possibly seek confirmation) if the total expected UF volume has been made user-adjustable by the clinician mode, and the user selects a total expected UF volume to be below a certain percentage of the total volume processed for a nighttime therapy (e.g., if the total expected UF volume is set at less than 7% of the total nighttime therapy volume). Generally the expected UF volume may be determined empirically by a clinician based on a user&#39;s prior experience with peritoneal dialysis. In a further embodiment, the cycler may be programmed to adjust the expected UF volume value according to the actual UF volume in one or more preceding cycles of a therapy. This volume may be calculated in a CCPD mode by calculating the difference between a measured full drain volume and the measured fill volume that preceded it. In some cases, it may be difficult to determine when the peritoneal cavity is fully drained of fluid, and it may be preferable to take an average value of the difference between a full drain volume and a preceding fill volume over a number of cycles. 
     Some of the programmable treatment settings may include:
         the number of daytime exchanges using the cycler;   the volume of solution to be used for each daytime exchange;   the total time for a nighttime therapy;   the total volume of dialysis solution to be used for nighttime therapy (not including a last fill volume if a daytime dwell phase is used);   the volume of dialysis solution to be infused per cycle;   in a Tidal therapy, the volume of fluid to be drained and refilled during each cycle (a percentage of the initial fill volume in a nighttime therapy);   the estimated ultrafiltration volume to be produced during a nighttime therapy;   the volume of solution to be delivered at the end of a therapy and to be left in the peritoneal cavity for an extended period (e.g, daytime dwell);   the minimum initial drain volume required to proceed with a therapy;   the maximum intraperitoneal volume known or estimated to be present that the cycler will allow to reside in the patient&#39;s peritoneal cavity (which may be based on the measured volumes introduced into the peritoneal cavity, the measured volume removed from the peritoneal cavity, and the estimated volume of ultrafiltration produced during therapy).       

     Some of the more advanced programmable treatment settings for the cycler may include:
         the frequency of full drains to be conducted during tidal peritoneal dialysis;   the minimum percentage of the volume delivered to the peritoneum during a day therapy that must be drained before a subsequent fill is allowed;   prompting the user to perform an extra drain phase at the end of therapy if a pre-determined percentage of the estimated total UF is not collected;   a minimum length of time required to perform an initial drain before therapy begins;   a minimum length of time required to perform subsequent drains, either in day-therapy mode or night-therapy mode;   variable dwell times, adjusted by the cycler controller to maintain a fixed total therapy time when either the fill times or drain times have been changed (thus helping to avoid disruptions of the user&#39;s schedule;
 
The cycler can provide the user with alerts or warnings about parameters that have been entered outside a recommended range of values. For example, a warning may be issued if:
   the minimum initial drain volume before a therapy is less than a pre-determined percentage of the currently prescribed last-fill volume at the end of the previous therapy (e.g., &lt;70%);   the maximum IPV is outside a pre-determined percentage range of the fill volume per cycle (e.g., &lt;130% or &gt;160%);   the UF volume threshold to trigger an alert to perform an extra drain at the end of therapy is less than a pre-determined percentage of the estimated UF volume per therapy (e.g. &lt;60%);   the calculated or entered dwell time is less than a pre-determined number of minutes (e.g., &lt;30 minutes);   the estimated UF volume per therapy is more than a pre-determined percentage of the total dialysis solution volume per therapy (e.g., &gt;25%);   the sum of all the solution bag volumes for a therapy should be somewhat greater than the volume of solution used during a CCPD therapy session, in order to account for priming of fluid lines and for loss of fluid to drain during air mitigation procedures.       

     In the clinician mode, in addition to having a selectable maximum IPV, the cycler may be programmed to accept separate minimum drain times for initial drains, day-therapy drains, and night-therapy drains. In the user mode or in the active-therapy mode, the cycler may be programmed to prevent a user from skipping or shortening the initial drain phase at the start of a therapy. In addition, the cycler may permit early termination of the initial drain phase only after a series of escalating low-drain-flow alerts have been issued. (An initial alert may instruct the user to change positions or re-position the peritoneal dialysis catheter, which may then be followed by additional alternative instructions if low flow conditions persist, up to a maximum number of alerts). The cycler may also require the user to confirm any change the user makes to the planned therapy, including bypassing a phase. The clinician may specify in a prescription setting to prevent the user from bypassing a drain phase during nighttime therapy. During therapy, the cycler controller may be programmed to not reset the IPV to zero unless the drain volume exceeds the preceding fill volume (to account for the additional IPV produced by ultrafiltration). The cycler may also be programmed to display to the user the estimated IPV during fills, and may notify the user if any drain volume exceeds the fill volume by a pre-determined amount (e.g. drain volume greater than fill volume plus expected UF volume). The cycler may also be programmed to identify errors in user input and to notify the user of apparent input errors. For example, the number of cycles during a therapy calculated by the cycler, based on the prescription parameters entered by the clinician or user, should be within a pre-determined range (e.g. 1-10). Similarly, the dwell time calculated by the cycler should be greater than zero. In addition, the maximum IPV entered by the user or clinician should be greater than or equal to the fill volume per cycle, plus the expected UF volume. Furthermore, the cycler may be programmed to reject an entered value for maximum IPV that is greater than a pre-determined amount over the fill volume per cycle (e.g., maximum IPV≤200% of initial fill volume). In some cases, it may be desirable for the cycler to be programmed to set the maximum IPV to no greater than the last fill volume if the solution is to remain in the peritoneal cavity for a prolonged period of time, such as during a daytime therapy. In this case, the cycler may be programmed to alert the user if the cycler controller calculates that the last drain volume amounts to less than a complete drain, whereupon the cycler may provide the user with a choice to terminate therapy or undertake another drain phase. 
     Managing Increasing IPV while Minimizing Alarms 
     In an embodiment, the cycler may be programmed to track and manage an increasing IPV during a therapy without converting the therapy from continuous cycling peritoneal dialysis (“CCPD”) therapy to a standard tidal peritoneal dialysis (“TPD”) therapy, which would fix the residual volume to a percentage of the initial fill volume. Rather, an adaptive tidal therapy mode may be initiated, in which the residual volume is allowed to fluctuate or ‘float’ in response to any slow-drain conditions that may be encountered during any drain phase. The cycler may be programmed to permit this mode to operate as long as any subsequent fill volume plus expected UF does not exceed a prescribed maximum IPV (“Max IPV”). Thus the dwell-phase IPV may be permitted to increase or decrease during a therapy up to a maximum IPV, preferably set by a clinician in the clinician mode. In this adaptive tidal therapy mode, at each drain phase during a therapy, the cycler continues to attempt a complete drain within the allotted time, or as long as a low-flow or no-flow condition has not been detected for a prescribed or pre-set number of minutes. The residual volume at the end of the drain phase is allowed to vary or ‘float’ as long as it does not exceed an amount that would lead to exceeding the maximum IPV in the next fill phase or during the next dwell phase. In a preferred embodiment, the cycler may be programmed to not issue an alert or alarm to the user as long as it calculates that the subsequent fill phase or dwell phase will not reach or exceed maximum IPV. 
     The cycler may be programmed to deliver full fill volumes during each cycle of a therapy until the cycler controller calculates that the next fill volume will likely cause the IPV to exceed the maximum IPV. At a convenient time (such as, e.g., the end of a drain phase), the cycler controller may be programmed to calculate a maximum residual IP volume, which represents the maximum permissible residual IP volume at the end of a drain to allow the next cycle to proceed with the previously programmed fill volume. Partial drains will be permitted by the cycler without alarming or issuing an alert as long as the amount of fluid drained brings the residual IPV below the maximum residual IPV. If the estimated or predicted IPV at the end of a drain phase is less than the maximum residual IPV, the cycler can proceed with a full fill phase in the next cycle without risking exceeding the Max IPV. If the estimated IPV at the end of a drain is greater than the maximum residual IPV, the cycler controller may trigger an alert to the user that the subsequent fill plus UF may exceed the maximum IPV. In an embodiment, the cycler may display several options for the user to respond to this alert: it may allow the user to terminate therapy, to attempt another drain phase, or to proceed to enter a revised-cycle therapy mode, in which each subsequent fill volume is reduced and one or more cycles are added to the therapy (thereby ensuring that the remaining volume of fresh dialysate is used during that therapy). In an embodiment, a clinician or user may enable the cycler at the beginning of therapy to automatically enter this revised-cycle therapy mode without having to alert the user during therapy. 
     In some circumstances, the number of additional cycles may be limited by the planned total therapy time. For example, the duration of night time therapy may be limited by the time at which the user is scheduled to wake up or to get up to go to work. For nighttime therapy, the cycler controller may be programmed, for example, to prioritize the use of all dialysate solution that was planned for therapy in favor of ending therapy at the scheduled time. If the clinician or user has selected the dwell time to be adjustable, then the cycler controller will (1) add one or more cycles to ensure that the fill volume plus expected UF does not exceed maximum IPV; (2) ensure that all of the dialysis solution is used for therapy; and (3) attempt to reach the targeted end-of-therapy time by shortening the dwell times of the remaining cycles. An alternative option available to the user is to extend the end-of-therapy time. In a preferred embodiment, the cycler is programmed to add one or two additional cycles to the therapy to permit a reduced fill volume in order to prevent exceeding the maximum IPV. The cycler controller is programmed to recalculate the maximum residual IPV using the reduced fill volume occasioned by the increased number of cycles. Thus, if a low flow condition during drain occurs at the same IPV, the new higher maximum residual IPV may permit dialysis to proceed without exceeding maximum IPV. If the fill volume cannot be reduced enough by adding a maximum allowable number of extra cycles (e.g., 2 cycles in an exemplary night time therapy scenario), then the cycler may present the user with two options: re-attempt a drain phase, or end therapy. The cycler may be programmed to reset the fill volume again after an adjustment of the fill volume, possibly adding an additional cycle, if a low flow condition at the end of drain is again encountered at an IPV above the newly recalculated and reset maximum residual IPV. Thus the cycler may be programmed to repeatedly adjust the subsequent fill volumes to prevent exceeding maximum IPV if a premature low flow condition is repeatedly encountered. 
     Replenishment Limitation on Dwell Time Reductions 
     In an embodiment, if the cycler reduces fill volumes by adding one or more cycles, then it may also reduce the dwell time in order to attempt to keep the therapy session within the total scheduled therapy time. This mode may be useful for nighttime therapy, so that the patient may be reasonably assured that therapy will have ended before a planned time of awakening in the morning. However, the cycler will continue to replenish the heater bag as needed during therapy, the replenishment generally occurring during dwell phases (when the PD cassette is not otherwise pumping to or from the patient). Therefore, in some circumstances, total therapy time may need to be extended when the required reduction in remaining dwell times leads to a total remaining dwell time that is less than the total estimated time needed to replenish the heater bag with the remaining fresh dialysate. The cycler controller may therefore calculate a maximum dwell time reduction available for the remaining therapy cycles, and extend total therapy time to ensure that the remaining fresh dialysate is properly heated. Because the cycler controller keeps track of the volume of dialysate in the heater bag, the temperature of the dialysate in the heater bag, and the volume of remaining fresh dialysate that is scheduled to be infused, it can calculate an estimate of the amount of time needed to replenish the heater bag to a pre-determined volume (given its intrinsic pumping capacity), and the time needed to bring the dialysate in the heater bag up to the prescribed temperature before it is infused into the user. In an alternative embodiment, the cycler controller may interrupt pumping operations to or from the user at any time in order to engage the pumps for replenishment of the heater bag. The cycler controller may be programmed, for example, to prevent the volume of fluid in the heater bag from dropping below a pre-determined volume at any time during therapy, other than during the last cycle. 
     In an embodiment, the cycler may be programmed to deliver fluid to the heater bag at a greater flow rate than when it is transferring fluid to or from the user. If binary valves are used to regulate the flow of control fluid or gas between the positive/negative pressure reservoirs and the control or actuation chambers of the cassette pumps, the controller may issue on-off commands to the valves at different pressure levels measured in the control or actuation chambers of the pumps. Thus the pressure threshold in the pump control or actuation chamber at which the controller triggers an ‘off’ command to the binary valve may have an absolute value that is greater during delivery to or from the heater bag than the corresponding pressure threshold when the cycler is delivering or pulling fluid to or from the user&#39;s peritoneal cavity. A higher average pressure applied to the pump membrane may be expected to result in a greater flow rate of the liquid being pumped. A similar approach may be used if variable orifice valves are used to regulate the flow of control fluid or gas between the pressure reservoirs and the control or actuation chambers of the cassette pumps. In this case, the controller may modulate the flow resistance offered by the variable orifice valves to maintain a desired pressure in the pump control chamber within pre-determined limits as the pump membrane is moving through its stroke. 
     Exemplary Modes of Therapy 
       FIG. 67  is a graphical illustration (not to scale in either volumes or time) of an adaptive tidal mode of the cycler when in a CCPD mode. The initial drain at the beginning of therapy is omitted for clarity. The maximum IPV (Max IPV)  700  is a prescription parameter preferably set by the clinician. The initial fill volume  702  is also preferably set by the clinician as a prescription parameter. The expected UF volume is represented by the additional IPV increase  704  during the dwell phase  706 . The expected UF volume for an entire therapy may be entered by a clinician into the prescription, and the cycler may then calculate the dwell time per cycle based on the number of cycles during the therapy, and thus the expected UF volume per cycle. It should be noted that ultrafiltration is expected to occur throughout the fill-dwell-drain cycle, and the expected UF volume may include the volume of fluid ultrafiltered throughout the cycle period. In most cases, the dwell time is much larger than the fill or drain times, rendering the ultrafiltration volumes during fill or drain relatively insignificant. (The fill and drain times may be adjustable by altering the pressure set points used by the controller to regulate the control valves between the pressure reservoirs and the pumps. However, the adjustability of liquid delivery flow rates and pressures to the user is preferably limited in order to ensure user comfort). Thus the expected UF volume per cycle  704  may be reasonably representative of ultrafiltration during the cycle. The drain phase  708  of the cycle in this example is a full drain, as would occur in a CCPD mode of therapy. 
     The maximum residual volume  710  can be calculated by the cycler controller once the Max IPV  700 , the initial fill volume  702 , and the expected UF volume are entered by the clinician. The maximum residual volume  710  is an indication of the ‘headroom’  712  available in the peritoneal cavity to accommodate more fluid before reaching Max IPV  700 . In an adaptive tidal mode within a CCPD mode of therapy, as long as a drain volume  714 ,  716  leaves an estimated residual volume  718 ,  720  less than the maximum residual volume  710 , the subsequent fill volume  722 ,  724  can remain unchanged, because Max IPV  700  is not expected to be breached. As shown in  FIG. 67 , the occurrence of a low flow condition at the residual volumes  718  and  720  triggers the cycler to initiate the next fill phase  722  and  724 . During this form of therapy, the cycler will continue to attempt to perform a full drain  726  within an allotted time assuming a low-flow or no-flow condition is not encountered before the estimated zero IPV is reached. Thus, even if a full drain is not performed (because of a low-flow or no-flow condition), in this case, full fill volumes will continue to be infused, the residual IPV will be allowed to float within a pre-determined range, and the user preferably will not be disturbed by any alarms or alert notifications. 
       FIG. 68  is a graphical illustration of how the cycler may handle incomplete drains that fail to reach the maximum residual IPV  710 . In this case, the drain phase  730  of the third cycle encounters a low-flow or no-flow condition that prevents the cycler from draining the peritoneal cavity below the maximum residual IPV  710 . Given the estimated residual volume  732  (the estimated residual volume after a pre-determined duration of a low-flow condition), the cycler calculates that a subsequent fill phase volume  734  will likely cause the prescribed Max IPV  700  to be reached or exceeded  736 . Therefore, at the end of drain phase  730 , the cycler may alert the user to this issue. The user may then have the option to terminate therapy, instruct the cycler to re-attempt a drain phase (after possibly changing positions or repositioning the PD catheter), or instruct the cycler to enter into a revised-cycle therapy mode in which the subsequent fill volumes are reduced and one or more cycles added to complete the therapy with the planned total volume of dialysate. To keep within the allotted or prescribed total therapy time, the cycler can calculate the duration of the modified cycles by reducing the fill and drain times to account for the reduced fill and drain volumes, and then determining whether and how much the dwell times need to be reduced to meet the designated ending time of the therapy session. 
     A user may optionally enable a revised-cycle mode of CCPD at the beginning of a therapy, so that the occurrence of a low-flow condition during therapy can trigger the revised-cycle mode without disturbing the user with an alert or alarm. Otherwise, the user may select the revised-cycle mode upon the occurrence of a low-flow condition above the maximum residual IPV. If the user elects to enter a revised-cycle mode, the cycler controller may calculate the required fill volumes for each of an additional one, two or more cycles (remaining fill volume divided by the remaining planned cycles plus the additional one or more cycles). If one additional cycle yields a fill volume (plus expected UF) low enough to avoid reaching or exceeding Max IPV, the cycler (either automatically or at the user&#39;s option) will resume CCPD at that new fill volume  738 . Otherwise, the cycler controller will calculate a new fill volume based on an additional two cycles of therapy. (Rarely, more than two additional cycles may be required to ensure that Max IPV is not breached during the remaining therapy. If the additional cycles require a substantial reduction in the remaining dwell times, the cycler may alert the user, particularly if a minimum dwell time has been prescribed, or heater bag replenishment limitations will require a lengthening of the total therapy time). The now-reduced fill volume  738  allows the cycler controller to re-calculate a revised maximum residual IPV  740 , which is a function of the sum of the new fill volume plus the expected UF volume per cycle. Any subsequent drain phases that leave an estimated residual IP volume less than the revised maximum residual volume  740  will preferably not trigger any further alerts or alarms to the user, allowing for the adaptive mode of tidal therapy to remain enabled. In an embodiment, the cycler may re-calculate the expected UF volume if it has reduced the duration of the remaining dwell phases in order to stay within the planned total therapy time. Any re-calculated reduction in the expected UF volume may further increase the revised maximum residual IPV. In the example shown in  FIG. 68 , the cycler continues to perform CCPD mode therapy, and happens to be able to drain fully in the remaining cycles. In order not to further inconvenience the user, the cycler may optionally refrain from making any further adjustments to the therapy (particularly if the total volume of dialysate and the total therapy time have been kept within the prescribed parameters). 
       FIG. 69  illustrates that a planned standard tidal peritoneal dialysis (TPD) therapy may also be subject to a revised-cycle mode of TPD therapy if the cycler controller calculates that the user&#39;s Max IPV  700  is likely to be reached or exceeded during therapy. In this example, a user or clinician has selected a standard tidal therapy, in which a planned residual IP volume  742  (in actual volumetric terms or as a percentage of the initial fill volume) has been selected. As an optional feature of the cycler, the user or clinician has also chosen to perform a complete drain  744  after every three tidal fill-dwell-drain cycles, comprising a cycle cluster during a therapy session. In this example, a low-flow condition preventing draining below the maximum residual volume  710  occurs at the end of the third cycle  746 . At the option of the user or clinician, the cycler either alerts the user to choose to end therapy, repeat a drain phase, or initiate a revised-cycle TPD therapy, or the cycler is allowed to automatically initiate a revised-cycle TPD therapy. In this case, the addition of a sixth cycle with a consequent reduction of the fill volume to a revised fill volume  748 , is sufficient to avoid exceeding the Max IPV  700 , which otherwise would have occurred  750 . In this example, the cycler proceeds to perform a complete drain  744  at the end of a cluster, but resumes a standard TPD therapy thereafter. If the planned residual volume has been specified to be a percentage of the initial fill volume of the cluster, then that percentage may be applied to a revised residual IPV  752 . The cycler may then calculate the subsequent drain volumes  754  by calculating the appropriate fraction of the revised fill volume  748  plus expected UF volume in order to drain to the revised residual IPV  752 . Any subsequent fill volumes  758  may remain similar to the revised fill volume  748 , as long as the cycler calculates that the Max IPV  700  will not be breached. Alternatively, the subsequent fill volumes may be reduced in a manner designed to maintain a relatively constant revised dwell-phase IPV  756 . In this case, the cycler controller may be programmed to make the additional calculations necessary to ensure that the entire remaining dialysate solution will be properly divided among a revised fill volume  748  and later fill volumes reduced to maintain a revised dwell-phase IPV  756 . In an alternative embodiment, the clinician or user may select the prescribed residual IP volume  742  to be relatively fixed volumetrically throughout therapy. In this case, the cycler controller may convert the percentage value of the residual IP volume  742  into a volumetric value (e.g. in milliliters), and continue to use that targeted residual volume after the revised-cycle mode has been instituted. In any event, the cycler controller may continue to apply the Max IPV  700  limitation in calculating any revised fill volumes. 
       FIG. 70  illustrates how an adaptive tidal therapy mode may be employed during a standard tidal therapy. In this example, a slow-drain condition  760  is encountered below the maximum residual volume  710 . As an optional feature of the cycler, the user or clinician has also chosen in this example to perform a complete drain  764  after every four tidal fill-dwell-drain cycles, comprising a cycle cluster during a therapy session. In this case, the cycler calculates that the Max IPV  700  will not be reached if the tidal fill volume  762  is maintained. The cycler may be programmed to continue the tidal therapy at a revised residual IP volume  760  in order to avoid another slow-drain condition. (Alternatively, the cycler may be programmed to attempt to drain back to the previously prescribed residual IP volume  742 ). Since tidal therapy can continue without risk of breaching Max IPV  700 , the user need not be alerted to the institution of a revised or floating residual volume of the adaptive tidal therapy mode. A full drain  764  is initiated as prescribed, and if successful, the cycler controller may re-institute the originally prescribed tidal therapy parameters. In an embodiment, the cycler may be programmed to alert the user if a full drain cannot be achieved at the end of a tidal therapy cluster. 
     While aspects of the invention have been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art. Accordingly, embodiments of the invention as set forth herein are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention.