Patent ID: 12246119

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

A dialysis machine (e.g., a peritoneal dialysis (PD) machine) can include a pressure sensor mounted at a proximal end of a patient line made of a distensible material (e.g., an elastomeric patient line) that provides PD solution to a patient through a catheter. During treatment, an occlusion can occur at different locations in the patient line and/or the catheter. When an incremental volume ΔVfof additional solution is provided to the patient line while the occlusion is present, a change in pressure ΔP (e.g., a pressure rise) results. The change in pressure ΔP depends on the dimensions and the distensibility of the non-occluded portion of the patient line. If the change in pressure ΔP, the incremental volume ΔVf, the properties related to the distensibility of the patient line, and some of the dimensions of the patient line are known, the location of the occlusion (e.g., the distance x between the patient line port and the occlusion) can be inferred. Because some types of occlusions typically occur in certain parts of the patient line, the occlusion type can be inferred based on the determined location.

In some implementations, the location of the occlusion can be determined by measuring a change in pressure measurements over time while an additional volume of solution is provided to the patient line. In some implementations, the location of the occlusion can be determined by measuring an amount of time required for pressure measurements to decay below a predetermined threshold after an additional volume of solution is provided to the patient line.

In some implementations, the patient line may include a fluid capacitive element that is located between a patient line region and a catheter region of the patient line. The fluidic capacitive element may have a distensibility that is substantially greater than that of the patient line itself. Accordingly, occlusions that occur between the dialysis machine and the fluid capacitive element do not cause the pressure sensor to experience the effects of the fluid capacitive element, and occlusions that occur between the fluid capacitive element and the tip of the catheter do cause the pressure sensor to experience the effects of the fluid capacitive element. That is, the fluid capacitive element may be positioned strategically such that the generated information can localize the occlusion to a region of particular interest. For example, by analyzing characteristics of a plurality of pressure measurements over time, including steady-state measurements and measurements of a transient (e.g., fluctuating) component of the measured pressures over time, a determination can be made as to whether the occlusion is present in the patient line region (e.g., outside of the patient) or the catheter region (e.g., inside the patient).

FIG.1shows a PD system100that includes a PD machine (also generally referred to as a PD cycler)102seated on a cart104. Referring also toFIG.2, the PD machine102includes a housing106, a door108, and a cassette interface110that contacts a disposable PD cassette112when the cassette112is disposed within a cassette compartment114formed between the cassette interface110and the closed door108. A heater tray116is positioned on top of the housing106. The heater tray116is sized and shaped to accommodate a bag of PD solution such as dialysate (e.g., a 5 liter bag of dialysate). The PD machine102also includes a user interface such as a touch screen display118and additional control buttons120that can be operated by a user (e.g., a caregiver or a patient) to allow, for example, set up, initiation, and/or termination of a PD treatment.

Dialysate bags122are suspended from fingers on the sides of the cart104, and a heater bag124is positioned in the heater tray116. The dialysate bags122and the heater bag124are connected to the cassette112via dialysate bag lines126and a heater bag line128, respectively. The dialysate bag lines126can be used to pass dialysate from dialysate bags122to the cassette112during use, and the heater bag line128can be used to pass dialysate back and forth between the cassette112and the heater bag124during use. In addition, a patient line130and a drain line132are connected to the cassette112. The patient line130can be connected to a patient's abdomen via a catheter (e.g., the catheter1002ofFIG.10) and can be used to pass dialysate back and forth between the cassette112and the patient's peritoneal cavity during use. The catheter1002may be connected to the patient line130via a port (1004ofFIG.10) such as a fitting. The drain line132can be connected to a drain or drain receptacle and can be used to pass dialysate from the cassette112to the drain or drain receptacle during use.

The PD machine102also includes a control unit139(e.g., a processor). The control unit139can receive signals from and transmit signals to the touch screen display118, the control panel120, and the various other components of the PD system100. The control unit139can control the operating parameters of the PD machine102. In some implementations, the control unit139is an MPC823 PowerPC device manufactured by Motorola, Inc.

FIG.3shows a more detailed view of the cassette interface110and the door108of the PD machine102. As shown, the PD machine102includes pistons133A,133B with piston heads134A,134B attached to piston shafts135A,135B (piston shaft135A shown inFIGS.9A-G) that can be axially moved within piston access ports136A,136B formed in the cassette interface110. The pistons133A,133B, piston heads134A,134B, and piston shafts135A,135B are sometimes referred to herein as pumps. The piston shafts135A,135B are connected to stepper motors that can be operated to move the pistons133A,133B axially inward and outward such that the piston heads134A,134B move axially inward and outward within the piston access ports136A,136B. The stepper motors drive lead screws, which move nuts inward and outward along the lead screws. The stepper motors may be controlled by driver modules (e.g., the driver modules1538a,1538bofFIG.15). The nuts, in turn, are connected to the pistons133A,133B and thus cause the pistons133A,133B to move inward and outward as the stepper motors rotate the lead screws. Stepper motor controllers (e.g., the microcontroller1436ofFIG.14) provide the necessary current to be driven through the windings of the stepper motors to move the pistons133A,133B. The polarity of the current determines whether the pistons133A,133B are advanced or retracted. In some implementations, the stepper motors require 200 steps to make a full rotation, and this corresponds to 0.048 inch of linear travel.

The PD system100also includes encoders (e.g., optical encoders) that measure the rotational movement of the lead screws. The axial positions of the pistons133A,133B can be determined based on the rotational movement of the lead screws, as determined by the encoders. Thus, the measurements of the encoders can be used to accurately position the piston heads134A,134B of the pistons133A,133B.

As discussed below, when the cassette112(shown inFIGS.2and4-7) is positioned within the cassette compartment114of the PD machine102with the door108closed, the piston heads134A,134B of the PD machine102align with pump chambers138A,138B of the cassette112such that the piston heads134A,134B can be mechanically connected to dome-shaped fastening members161A,161B of the cassette112overlying the pump chambers138A,138B. As a result of this arrangement, movement of the piston heads134A,134B toward the cassette112during treatment can decrease the volume of the pump chambers138A,138B and force dialysate out of the pump chambers138A,138B, while retraction of the piston heads134A,134B away from the cassette112can increase the volume of the pump chambers138A,138B and cause dialysate to be drawn into the pump chambers138A,138B.

As shown inFIG.3, the cassette interface110includes two pressure sensors151A,151B that align with pressure sensing chambers163A,163B (shown inFIGS.2,4,6, and7) of the cassette112when the cassette112is positioned within the cassette compartment114. Portions of a membrane140of the cassette112that overlie the pressure sensing chambers163A,163B adhere to the pressure sensors151A,151B using vacuum pressure. Specifically, clearance around the pressure sensors151A,151B communicates vacuum to the portions of the cassette membrane140overlying the pressure sensing chambers163A,163B to hold those portions of the cassette membrane140tightly against the pressure sensors151A,151B. The pressure of fluid within the pressure sensing chambers163A,163B causes the portions of the cassette membrane140overlying the pressure sensing chambers163A,163B to contact and apply pressure to the pressure sensors151A,151B.

The pressure sensors151A,151B can be any sensors that are capable of measuring the fluid pressure in the sensing chambers163A,163B. In some implementations, the pressure sensors are solid state silicon diaphragm infusion pump force/pressure transducers. One example of such a sensor is the Model1865force/pressure transducer manufactured by Sensym Foxboro ICT. In some implementations, the force/pressure transducer is modified to provide increased voltage output. The force/pressure transducer can, for example, be modified to produce an output signal of 0 to 5 volts.

Still referring toFIG.3, the PD machine102also includes multiple inflatable members142positioned within inflatable member ports144in the cassette interface110. The inflatable members142align with depressible dome regions146of the cassette112(shown inFIGS.4-6) when the cassette112is positioned within the cassette compartment114of the PD machine102. While only a couple of the inflatable members142are labeled inFIG.3, it should be understood that the PD machine102includes an inflatable member142associated with each of the depressible dome regions146of the cassette112. The inflatable members142act as valves to direct dialysate through the cassette112in a desired manner during use. In particular, the inflatable members142bulge outward beyond the surface of the cassette interface110and into contact with the depressible dome regions146of the cassette112when inflated, and retract into the inflatable member ports144and out of contact with the cassette112when deflated. By inflating certain inflatable members142to depress their associated dome regions146on the cassette112, certain fluid flow paths within the cassette112can be occluded. Thus, dialysate can be pumped through the cassette112by actuating the piston heads134A,134B, and can be guided along desired flow paths within the cassette112by selectively inflating and deflating the various inflatable members142.

Still referring toFIG.3, locating pins148extend from the cassette interface110of the PD machine102. When the door108is in the open position, the cassette112can be loaded onto the cassette interface110by positioning the top portion of the cassette112under the locating pins148and pushing the bottom portion of the cassette112toward the cassette interface110. The cassette112is dimensioned to remain securely positioned between the locating pins148and a spring loaded latch150extending from the cassette interface110to allow the door108to be closed over the cassette112. The locating pins148help to ensure that proper alignment of the cassette112within the cassette compartment114is maintained during use.

The door108of the PD machine102, as shown inFIG.3, defines cylindrical recesses152A,152B that substantially align with the pistons133A,133B when the door108is in the closed position. When the cassette112(shown inFIGS.4-7) is positioned within the cassette compartment114, hollow projections154A,154B of the cassette112, inner surfaces of which partially define the pump chambers138A,138B, fit within the recesses152A,152B. The door108further includes a pad that is inflated during use to compress the cassette112between the door108and the cassette interface110. With the pad inflated, the portions of the door108forming the recesses152A,152B support the projections154A,154B of the cassette112and the planar surface of the door108supports the other regions of the cassette112. The door108can counteract the forces applied by the inflatable members142and thus allows the inflatable members142to actuate the depressible dome regions146on the cassette112. The engagement between the door108and the hollow projections154A,154B of the cassette112can also help to hold the cassette112in a desired fixed position within the cassette compartment114to further ensure that the pistons133A,133B align with the fluid pump chambers138A,138B of the cassette112.

The control unit (139ofFIG.1) is connected to the pressure sensors151A,151B, to the stepper motors (e.g., the drivers of the stepper motors) that drive the pistons133A,133B, and to the encoders that monitor rotation of the lead screws of the stepper motors such that the control unit139can receive signals from and transmit signals to those components of the system. The control unit139monitors the components to which it is connected to determine whether any complications exists within the PD system100, such as the presence of an occlusion.

FIG.4is an exploded, perspective view of the cassette112,FIG.5is a cross-sectional view of the fully assembled cassette112, andFIGS.6and7are perspective views of the assembled cassette112, from the membrane side and from the rigid base side, respectively. Referring toFIGS.4-6, the flexible membrane140of the cassette112is attached to a periphery of the tray-like rigid base156. Rigid dome-shaped fastening members161A,161B are positioned within recessed regions162A,162B of the base156. The dome-shaped fastening members161A,161B are sized and shaped to receive the piston heads134A,134B of the PD machine102. In some implementations, the dome-shaped fastening members161A,161B have a diameter, measured from the outer edges of flanges164A,164B, of about 1.5 inches to about 2.5 inches (e.g., about 2.0 inches) and take up about two-thirds to about three-fourths of the area of the recessed regions162A,162B. The annular flanges164A,164B of the rigid dome-shaped fastening members161A,161B are attached in a liquid-tight manner to portions of the inner surface of the membrane140surrounding substantially circular apertures166A,166B formed in the membrane140. The annular flanges164A,164B of the rigid dome-shaped fastening members161A,161B can, for example, be thermally bonded or adhesively bonded to the membrane140. The apertures166A,166B of the membrane140expose the rigid dome-shaped fastening members161A,161B such that the piston heads134A,134B are able to directly contact and mechanically connect to the dome-shaped fastening members161A,161B during use.

The annular flanges164A,164B of the dome-shaped fastening members161A,161B, as shown inFIG.5, form annular projections168A,168B that extend radially inward and annular projections176A,176B that extend radially outward from the side walls of the dome-shaped fastening members161A,161B. When the piston heads134A,134B are mechanically connected to the dome-shaped fastening members161A,161B, the radially inward projections168A,168B engage the rear angled surfaces of the sliding latches145A,147A of the piston heads134A,134B to firmly secure the dome-shaped fastening members161A,161B to the piston heads134A,134B. Because the membrane140is attached to the dome-shaped fastening members161A,161B, movement of the dome-shaped fastening members161A,161B into and out of the recessed regions162A,162B of the base156(e.g., due to reciprocating motion of the pistons133A,133B) causes the flexible membrane140to similarly be moved into and out of the recessed regions162A,162B of the base156. This movement allows fluid to be forced out of and drawn into the fluid pump chambers138A,138B, which are formed between the recessed regions162A,162B of the base156and the portions of the dome-shaped fastening members161A,161B and membrane140that overlie those recessed regions162A,162B.

Referring toFIGS.4and6, raised ridges167extend from the substantially planar surface of the base156towards and into contact with the inner surface of the flexible membrane140when the cassette112is compressed between the door108and the cassette interface110of the PD machine102to form a series of fluid passageways158and to form the multiple, depressible dome regions146, which are widened portions (e.g., substantially circular widened portions) of the fluid pathways158, as shown inFIG.6. The fluid passageways158fluidly connect the fluid line connectors160of the cassette112, which act as inlet/outlet ports of the cassette112, to the fluid pump chambers138A,138B. As noted above, the various inflatable valve members142of the PD machine102act on the cassette112during use. During use, the dialysate flows to and from the pump chambers138A,138B through the fluid pathways158and dome regions146. At each depressible dome region146, the membrane140can be deflected to contact the planar surface of the base156from which the raised ridges167extend. Such contact can substantially impede (e.g., prevent) the flow of dialysate along the region of the pathway158associated with that dome region146. Thus, the flow of dialysate through the cassette112can be controlled through the selective depression of the depressible dome regions146by selectively inflating the inflatable members142of the PD machine102.

Still referring toFIGS.4and6, the fluid line connectors160are positioned along the bottom edge of the cassette112. As noted above, the fluid pathways158in the cassette112lead from the pumping chambers138A,138B to the various connectors160. The connectors160are positioned asymmetrically along the width of the cassette112. The asymmetrical positioning of the connectors160helps to ensure that the cassette112will be properly positioned in the cassette compartment114with the membrane140of the cassette112facing the cassette interface110. The connectors160are configured to receive fittings on the ends of the dialysate bag lines126, the heater bag line128, the patient line130, and the drain line132. One end of the fitting can be inserted into and bonded to its respective line and the other end can be inserted into and bonded to its associated connector160. By permitting the dialysate bag lines126, the heater bag line128, the patient line130, and the drain line132to be connected to the cassette, as shown inFIGS.1and2, the connectors160allow dialysate to flow into and out of the cassette112during use. As the pistons133A,133B are reciprocated, the inflatable members142can be selectively inflated to allow fluid to flow from any of the lines126,128,130, and132to any of ports185A,185B,187A, and187B of the pump chambers138A,138B, and vice versa.

The rigidity of the base156helps to hold the cassette112in place within the cassette compartment114of the PD machine102and to prevent the base156from flexing and deforming in response to forces applied to the projections154A,154B by the dome-shaped fastening members161A,161B and in response to forces applied to the planar surface of the base156by the inflatable members142. The dome-shaped fastening members161A,161B are also sufficiently rigid that they do not deform as a result of usual pressures that occur in the pump chambers138A,138B during the fluid pumping process. Thus, the deformation or bulging of the annular portions149A,149B of the membrane140can be assumed to be the only factor other than the movement of the pistons133A,133B that affects the volume of the pump chambers138A,138B during the pumping process.

The base156and the dome-shaped fastening members161A,161B of the cassette112can be formed of any of various relatively rigid materials. In some implementations, these components of the cassette112are formed of one or more polymers, such as polypropylene, polyvinyl chloride, polycarbonate, polysulfone, and other medical grade plastic materials. In some implementations, these components can be formed of one or more metals or alloys, such as stainless steel. These components of can alternatively be formed of various different combinations of the above-noted polymers and metals. These components of the cassette112can be formed using any of various different techniques, including machining, molding, and casting techniques.

As noted above, the membrane140is attached to the periphery of the base156and to the annular flanges164A,164B of the dome-shaped fastening members161A,161B. The portions of the membrane140overlying the remaining portions of the base156are typically not attached to the base156. Rather, these portions of the membrane140sit loosely atop the raised ridges165A,165B, and167extending from the planar surface of the base156. Any of various attachment techniques, such as adhesive bonding and thermal bonding, can be used to attach the membrane140to the periphery of the base156and to the dome-shaped fastening members161A,161B. The thickness and material(s) of the membrane140are selected so that the membrane140has sufficient flexibility to flex toward the base156in response to the force applied to the membrane140by the inflatable members142. In some implementations, the membrane140is about 0.100 micron to about 0.150 micron in thickness. However, various other thicknesses may be sufficient depending on the type of material used to form the membrane140.

Any of various different materials that permit the membrane140to deflect in response to movement of the inflatable members142without tearing can be used to form the membrane140. In some implementations, the membrane140includes a three-layer laminate. In some implementations, for example, inner and outer layers of the laminate are formed of a compound that is made up of 60 percent Septon® 8004 thermoplastic rubber (i.e., hydrogenated styrenic block copolymer) and 40 percent ethylene, and a middle layer is formed of a compound that is made up of 25 percent Tuftec® H1062 (SEBS: hydrogenated styrenic thermoplastic elastomer), 40 percent Engage® 8003 polyolefin elastomer (ethylene octene copolymer), and 35 percent Septon® 8004 thermoplastic rubber (i.e., hydrogenated styrenic block copolymer). The membrane can alternatively include more or fewer layers and/or can be formed of different materials.

As shown inFIG.8, before treatment, the door108of the PD machine102is opened to expose the cassette interface110, and the cassette112is positioned with its dome-shaped fastening members161A,161B aligned with the pistons133A,133B of the PD machine102, its pressure sensing chambers163A,163B aligned with the pressure sensors151A,151B of the PD machine102, its depressible dome regions146aligned with the inflatable members142of the PD machine102, and its membrane140adjacent to the cassette interface110. In order to ensure that the cassette112is properly positioned on the cassette interface110, the cassette112is positioned between the locating pins148and the spring loaded latch150extending from the cassette interface110. The asymmetrically positioned connectors160of the cassette act as a keying feature that reduces the likelihood that the cassette112will be installed with the membrane140and dome-shaped fastening members161A,161B facing in the wrong direction (e.g., facing outward toward the door108). Additionally or alternatively, the locating pins148can be dimensioned to be less than the maximum protrusion of the projections154A,154B such that the cassette112cannot contact the locating pins148if the membrane140is facing outward toward the door108. The pistons133A,133B are typically retracted into the piston access ports136A,136B during installation of the cassette112to avoid interference between pistons133A,133B and the dome-shaped fastening members161A,161B and thus increase the ease with which the cassette112can be positioned within the cassette compartment114.

After positioning the cassette112as desired on the cassette interface110, the door108is closed and the inflatable pad within the door108is inflated to compress the cassette112between the inflatable pad and the cassette interface110. This compression of the cassette112holds the projections154A,154B of the cassette112in the recesses152A,152B of the door108and presses the membrane140tightly against the raised ridges167extending from the planar surface of the rigid base156to form the enclosed fluid pathways158and dome regions146(shown inFIG.6). Referring briefly also toFIGS.1and2, the patient line130is then connected to a patient's abdomen via a catheter, and the drain line132is connected to a drain or drain receptacle. In addition, the heater bag line128is connected to the heater bag124, and the dialysate bag lines126are connected to the dialysate bags122. At this point, the pistons133A,133B can be coupled to dome-shaped fastening members161A,161B of the cassette112to permit priming of the cassette112and the lines126,128,130,132. Once these components have been primed, treatment can be initiated.

FIGS.9A-9G, which will be discussed below, are cross-sectional views of the system during different stages of the setup, priming, and treatment. These figures focus on the interaction between the piston133A of the PD machine102and the pump chamber138A of the cassette112during the setup, priming, and treatment. The interaction between the other piston133B and pump chamber138B is identical and thus will not be separately described in detail.

FIG.9Ashows the piston133A fully retracted into the piston access port136A of the cassette interface110. The cassette112is positioned in the cassette compartment114of the PD machine102and the inflatable pad in the door108of the PD machine102is inflated such that the cassette112is pressed tightly against the cassette interface110of the PD machine102, as explained above.

Referring toFIG.9B, with the cassette112properly installed within the cassette compartment114of the PD machine102and the appropriate line connections made, the piston133A is advanced to initiate the process of mechanically connecting the piston head134A of the PD machine102to the dome-shaped fastening member161A of the cassette112. As the piston133A is advanced, a front angled surface188A of a sliding latch145A and a front angled surface191A of a sliding latch147A contact a rear surface of the annular projection168A, which extends radially inward from the dome-shaped fastening member161A. The rear surface of the annular projection168A is approximately perpendicular to the longitudinal axis of the piston133A.

As the piston133A continues to advance, the dome-shaped fastening member161A contacts the inner surface of the portion of the rigid base156that forms the recessed region162A, as shown inFIG.9B. The rigid base156prevents further forward movement of the dome-shaped fastening member161A. The membrane140, which is attached to the peripheral flange164A of the dome-shaped fastening member161A, also stretches and moves into the recessed region162A due to the advancing piston133A. Due to the angled geometries of the front angled surfaces188A,191A of the sliding latches145A,147A and the resistance provided by the rigid base156to the forward motion of the dome-shaped fastening member161A, the sliding latches145A,147A are caused to move radially inward (i.e., toward the longitudinal axis of the piston133A) as the piston head134A continues to be advanced relative to the dome-shaped fastening member161A. More specifically, the forward motion of the sliding latches145A,147A is converted into a combined forward and radially inward motion due to the sliding motion of the front angled surfaces188A,191A of the sliding latches145A,147A against the rear surface of the annular projection168A of the dome-shaped fastening member161A. The radial inward movement of each of the sliding latches145A,147A in turn causes a forward movement of a latch lock141A of the piston head134A due to the mated geometries of the outer surfaces of legs155A,157A of the latch lock141A and the surfaces of the sliding latches145A,147A that are positioned adjacent to and brought into contact with those outer surfaces of the legs155A,157A. This forward movement of the latch lock141A is resisted by a spring143A in the piston head.

FIG.9Cshows the piston head134A at a point during the connection process at which the sliding latches145A,147A have been deflected radially inward a sufficient distance to allow the sliding latches145A,147A to pass beyond the annular projection168A that extends radially inward from the dome-shaped fastening member161A. In this position, outer peripheral surfaces of the sliding latches145A,147A, which are substantially parallel to the longitudinal axis of the piston133A, contact and slide along an inner surface of the annular projection168A of the dome-shaped fastening member161A, which is also substantially parallel to the longitudinal axis of the piston133A. The spring143A is further compressed due to the radially inwardly deflected positions of the sliding latches145A,147A.

Referring toFIG.9D, as the sliding latches145A,147A pass beyond the annular projection168A, the spring143A is allowed to expand. The expansion of the spring143A causes the latch lock141A to move rearward. As a result, the outer surfaces of the legs155A,157A of the latch lock141A contact the correspondingly angled adjacent surfaces of the sliding latches145A,147A, causing the sliding latches145A,147A to move radially outward underneath the projection168A of the dome-shaped fastening member161A. Rear angled surfaces190A,193A of the sliding latches145A,147A ride along the front surface of the projection168A of the dome-shaped fastening member161A, which is slightly angled toward the rear of the dome-shaped fastening member161A, as the sliding latches145A,147A move radially outward. The sliding latches145A,147A become wedged beneath the projection168A as the sliding latches145A,147A move radially outward.

FIG.9Eillustrates the completed mechanical connection between the piston head134A and the dome-shaped fastening member161A in which the sliding latches145A,147A have moved to maximum outwardly displaced positions within the dome-shaped fastening member161A. In this configuration, the projection168A of the dome-shaped fastening member161A is effectively pinched between a rear member137A of the piston head134A and the sliding latches145A,147A, resulting in a secure engagement between the piston head134A and the dome-shaped fastening member161A. As a result of the secure engagement of the piston head134A to the dome-shaped fastening member161A, the amount of slippage of the piston head134A relative to the dome-shaped fastening member161A can be reduced (e.g., minimized) and thus precise pumping can be achieved.

After mechanically coupling the piston head134A of the PD machine102to the dome-shaped fastening member161A of the cassette112, a priming technique is carried out to remove air from the cassette112and from the various lines126,128,130,132connected to the cassette112. To prime the cassette112and the lines126,128,130,132, the piston133A and inflatable members142are typically operated to pump dialysate from the heater bag124to the drain and from each of the dialysate bags122to the drain. Dialysate is also passed (e.g., by gravity) from the heater bag124to the patient line130to force any air trapped in the patient line out of a hydrophobic filter positioned at the distal end of the patient line130.

After priming is complete, the patient line130is connected to the patient and the PD machine102is operated to drain any spent dialysate that was left in the patient's peritoneal cavity from a previous treatment. To drain the spent dialysate from the patient's peritoneal cavity, the inflatable members142of the PD machine102are configured to create an open fluid flow path between the patient line130and the port187A (shown inFIG.4) of the pump chamber138A, and the piston133A is retracted to draw spent dialysate from the peritoneal cavity of the patient into the pump chamber138A via the patient line130, as shown inFIG.9F. Because the piston head134A is mechanically connected to the dome-shaped fastening member161A and the dome-shaped fastening member161A is attached to the membrane140of the cassette112, the retraction of the piston133A causes the dome-shaped fastening member161A and the portion of the membrane140attached to the dome-shaped fastening member161A to move rearwardly. As a result, the volume of the pump chamber138A is increased and spent dialysate is drawn into the pump chamber138A from the peritoneal cavity of the patient. The spent dialysate travels from the patient line130through the pressure sensing chamber163A and then enters the pump chamber138A via the port187A. The pressure sensor151A is able to monitor the pressure in the pressure sensing chamber163A, which is approximately equal to the pressure in the pump chamber138A, during this process.

Referring toFIG.9G, after drawing the dialysate into the pump chamber138A from the peritoneal cavity of the patient, the inflatable members142are configured to create an open fluid flow path between the port185A (shown inFIG.4) of the pump chamber138A and the drain line132, and the dialysate is forced out of the pump chamber138A to the drain by advancing the piston133A and decreasing the volume of the pump chamber138A. The piston133A is typically advanced until the dome-shaped fastening member161A contacts or nearly contacts the inner surface of the recessed region of the base156so that substantially all of the dialysate is forced out of the fluid pump chamber138A via the port185A.

During the patient drain phase of the treatment, the pistons133A,133B are typically alternately operated such that the piston133A is retracted to draw spent dialysate solution into the pump chamber138A from the patient while the piston133B is advanced to pump spent dialysate solution from the pump chamber138B to the drain and vice versa.

To begin the patient fill phase, the inflatable members142are configured to create a clear fluid flow path between the pump chamber138A and the heater bag line128, and then the piston133A is retracted, as shown inFIG.9F, to draw warm dialysate from the heater bag124to the pump chamber138A. The warm dialysate travels from the heater bag124through the heater bag line128and into the pump chamber via the port185A.

The warm dialysate is then delivered to the peritoneal cavity of the patient via the patient line130by configuring the inflatable members142to create a clear fluid flow path between the pump chamber138A and the patient line130and advancing the piston133A, as shown inFIG.9G. The warm dialysate exits the pump chamber138A via the port187A and travels through the pressure sensing chamber163A to the patient line130before reaching the peritoneal cavity of the patient. The pressure sensor151A is able to monitor the pressure in the pressure sensing chamber163A, which is approximately equal to the pressure in the pump chamber138A, during this process.

During the patient fill phase of the treatment, the pistons133A,133B are typically alternately operated such that the piston133A is retracted to draw warm dialysate into the pump chamber138A from the heater bag124while the piston133B is advanced to pump warm dialysate from the pump chamber138B to the patient and vice versa. When the desired volume of dialysate has been pumped to the patient, the machine102transitions from the patient fill phase to a dwell phase during which the dialysate is allowed to sit within the peritoneal cavity of the patient for a long period of time.

During the dwell period, toxins cross the peritoneum of the patient into the dialysate from the patient's blood. As the dialysate dwells within the patient, the PD machine102prepares fresh dialysate for delivery to the patient in a subsequent cycle. In particular, the PD machine102pumps fresh dialysate from one of the four full dialysate bags122into the heater bag124for heating. To do this, the pump of the PD machine102is activated to cause the pistons133A,133B to reciprocate and certain inflatable members142of the PD machine102are inflated to cause the dialysate to be drawn into the fluid pump chambers138A,138B of the cassette112from the selected dialysate bag122via its associated line126. The dialysate is then pumped from the fluid pump chambers138A,138B to the heater bag124via the heater bag line128.

After the dialysate has dwelled within the patient for the desired period of time, the spent dialysate is pumped from the patient to the drain in the manner described above. The heated dialysate is then pumped from the heater bag124to the patient where it dwells for a desired period of time. These steps are repeated with the dialysate from two of the three remaining dialysate bags122. The dialysate from the last dialysate bag122is typically delivered to the patient and left in the patient until the subsequent PD treatment.

After completion of the PD treatment, the pistons133A,133B are retracted in a manner to disconnect the piston heads134A,134B from the dome-shaped fastening members161A,161B of the cassette. The door108of the PD machine102is then opened and the cassette112is removed from the cassette compartment114and discarded.

FIG.10shows a schematic diagram of the PD machine102connected to a patient. A proximal end of the patient line130is connected to the PD machine102at a port (e.g., an inlet/outlet), and a distal end of the patient line130is connected to the patient's abdomen via the catheter1002. The catheter1002is connected to the patient line via a port1004. The patient line130may be a tube made of a distensible and/or flexible material that is at least partially distended by operating pressures in the PD machine102. For example, the patient line130may be made of an elastomeric material such as a polymer that develops a swell in response to positive operating pressures in the PD machine102. The patient line130, the port1004, and the catheter1002are sometimes referred to herein as the patient line-catheter conduit, or simply the conduit. One of the pressure sensors151A is located at the proximal end of the patient line130(e.g., at the end of the patient line130that is nearest to the PD machine102). The pressure sensor151A is configured to measure the pressure in the patient line130. In some implementations, the pressure sensor151A include a transducer that generates a signal as a function of the pressure imposed. The signal is indicative of the magnitude and sign of the measured pressure.

During a PD treatment cycle, an occlusion can occur at different locations in the conduit. For example, the patient line130may become kinked or pinched, holes in the catheter1002may become occluded (e.g., with omental fat), or the patient line130may develop an internal blockage at some location (e.g., from a deposit of omental fat). The PD machine102is configured to adjust its operation in response to an occlusion being detected. For example, the control unit139may be configured to adjust one or more operating parameters of the PD machine102in an attempt to clear the occlusion and/or to modulate the flow in the patient line to avoid an overpressure condition. In some implementations, the control unit139may be configured to provide an alert indicating that an occlusion has been detected. For example, a visual, tactile, and/or audible alert may be directed to the patient (e.g., to wake the patient).

In order to determine an appropriate response, the PD machine102is configured to ascertain the type of occlusion that is present. In some implementations, the type of occlusion can be inferred based on the location of the occlusion in the conduit. For example, if an occlusion is detected in the catheter1002, the PD machine102can infer that holes in the catheter1002may be occluded. Similarly, if the occlusion is detected somewhere along the patient line130, the PD machine102can infer that the patient line130is kinked or pinched. The PD machine102is configured to determine a location of the occlusion relative to the position of the pressure sensor151A. The particular location of the occlusion can be considered by the PD machine102to determine the appropriate response. In the example shown inFIG.10, an occlusion1008is present in the patient line130at a distance x from the patient line port and/or the pressure sensor151A, which may be indicative of a kink or a pinch in the patient line130.

During the treatment, solution is exchanged (e.g., transferred, conveyed, etc.) through the patient line130. When the PD solution (e.g., the dialysate) being provided to or withdrawn from the patient line130encounters an occlusion, the patient line130may develop a deformity. For example, in the case of the solution being pumped toward the patient (e.g., solution being injected), the elastic material of the patient line130may expand in response to the solution encountering the occlusion, thereby resulting in an increase in volume and pressure within the patient line130. In the case of the solution being pumped from the patient (e.g., solution being withdrawn), the elastic material of the patient line130may contract, thereby resulting in a decrease in volume and pressure within the patient line130. The distensibility of the non-occluded portion of the conduit (e.g., the portion of the conduit between the patient line port and the occlusion1008, sometimes referred to as the first portion) can be measured, and the location of the occlusion1008can be inferred from the measured value. The occlusion1008may define a boundary between the first portion of the conduit and a second portion of the conduit (e.g., the rest of the conduit). It is possible to infer the location of the occlusion1008because the distensibility itself arises from, among other things, the length of the non-occluded portion of the conduit1008(e.g., the distance x between the patient line port and the occlusion1008).

The portion of the conduit between the patient line port and the occlusion1008is sometimes referred to as the non-occluded portion of the conduit or the pressurized portion of the conduit. The length of the pressurized portion of the conduit—the distance x between the patient line port and the occlusion1008—can be determined by approximating the conduit as a thin-walled cylindrical pressure vessel. According to such an approximation, the normal stresses in the wall of the conduit are given according to Equations 1 and 2:

σθ=Pg⁢D2⁢w(1)σz=Pg⁢D4⁢w(2)
where σθis the azimuthal (e.g., “hoop”) stress, σzis the longitudinal stress, Pgis the transmural pressure experienced by the conduit (e.g., the gauge pressure of the fluid inside the conduit when the conduit's exterior is exposed to atmospheric pressure), D is the conduit's inner diameter, and w is the conduit's wall thickness. In some implementations (e.g. in implementations in which the conduit has a relatively thick wall), determining the stress state in the conduit may require other consideration in addition to the biaxial stress shown in Equations 1 and 2.

When a closed volume of tubing of the patient line130that is initially filled with a solution has an incremental volume ΔVfof solution added while the occlusion1008is present, a change in pressure ΔP (e.g., a pressure rise) results. The magnitude of the change in pressure ΔP depends on the dimensions and the distensibility of the non-occluded portion of the patient line130. If the change in pressure ΔP, the incremental volume ΔVf, the properties related to the distensibility of the patient line130, and some of the dimensions of the patient line130are known, the location of the occlusion1008(e.g., the distance x between the patient line port and the occlusion1008) can be inferred. The incremental volume ΔVfof added solution as a function of the change in pressure ΔP is given according to Equation 3:

Δ⁢VfVf,i=2⁢a+1.3⁢1⁢3⁢a2+0.2⁢8⁢1⁢a3(3)
where Vf,iis the initial volume of the non-occluded portion of the patient line130

a=D⁢Δ⁢PEy⁢w′,
and Eyis the Young's modulus of the material of the patient line130(e.g., the Young's modulus of the elastomer). Equation 3 may assume that the Poisson ratio of the elastomer is 0.5, which may be a typical value for a rubber material. Equation 3 is derived from the stress tensor given by Equations 1 and 2, and may assume that the tubing material is isotropic with linear elastic properties.

Equation 3 implies that for a given incremental volume ΔVfof injected solution, the resulting rise in pressure ΔP depends upon the initial volume of the pressurized region Vf,i. For conditions where a<<1 (e.g., small strain approximation), ΔP is proportional to

Δ⁢V⁢fΔ⁢Vf,i.
Such a condition is expect to be maintained. In a conservative example (e.g., for soft rubber having Ey≈0.01 gigapascals), a relatively high ΔP of 600 mbar and representative tubing dimensions of D=4 mm and w=1 mm may yield a=0.024. Thus, under the expected conditions, Equation 3 can be approximated by Equation 4:

Δ⁢VfVf,i=2⁢D⁢Δ⁢PEy⁢w(4)
and Equation 4 can be rearranged to yield Equation 5:

Δ⁢P=Δ⁢VfCf(5)
where the fluidic capacitance Cfof the pressurized region of the patient line130is given by Equation 6:

Cf=2⁢Vf,i⁢DEy⁢w≈0.5⁢πEy⁢D3w⁢x(6)

In Equation 6, as inFIG.10, x represents the distance (e.g., the length of tubing) between the patient line port and the occlusion1008. The occlusion1008may be a complete or nearly-complete occlusion. The other factors of Equation 6 are relatively constant for a given sample of uniform tubing. Equation 6 illustrates that a measure of the fluidic capacitance Cfcan be translated into a measurement of the distance x between the patient line port and the occlusion1008. The fluidic capacitance Cfcan be measured according to Equation 5 using existing components (e.g., the pressure sensor151A) of the PD machine102, and the distance x can then be determined according to Equation 6. In this way, the methods and techniques described herein can easily be implemented in existing systems. In some implementations, the relationship between the fluidic capacitance Cfand the distance x between the patient line port and the occlusion1008can be evaluated empirically (e.g., rather than by direct use of Equation 6).

To help illustrate the method of measuring the fluidic capacitance Cfof the pressurized region of the patient line130,FIG.11shows a representation of a lumped-element electrical circuit that may be analogous to the fluidic system shown inFIG.10for the case of complete flow blockage. For the case of a partial flow blockage, the lumped-element electrical circuit may look similar to the representation shown inFIG.19, with the second resistor representing Rblockage+Rdownstream(e.g., rather than Rcatheter). The measurement of capacitance in the illustrated circuit may be performed by adding a known charge to the capacitor and measuring the resultant change in potential at the patient line port (e.g., position “1”). As described above, the equivalent fluidic measurement to adding a known charge is to inject a known incremental volume of solution, ΔVf; into the patient line130and measure the change in pressure ΔP.

In reality, the illustrated resistance and capacitance of the patient line130are distributed throughout the length of the patient line130(e.g., rather than lumped into discrete elements). This fact in addition to other effects (e.g., such as elastic waves and strain-rate-sensitive elastic properties of the patient line130) may give rise to transient behavior in the pressure in the patient line130after injecting the incremental volume of solution ΔVf. In some examples, measuring the change in pressure ΔP after such transients have subsided may lead to a more accurate measurement of the fluidic capacitance Cf.

Experiment 1

FIG.12shows an example experimental system1200in which the fluidic capacitance Cfof a pressurized region of a conduit can be determined. The system1200includes a syringe pump1210that is configured to inject a known incremental volume of fluid ΔVfinto the conduit that includes a tube1230(e.g., which mimics a patient line) and a catheter1202connected to the tube1230via a port1204. In this example, the tube1230had a length of approximately ten feet and the syringe pump1210was driven by a programmable stepper motor. The catheter1202is submerged in a reservoir of fluid1212(e.g., in place of a patient). An occlusion1208is present in the tube1230at various distances x from a pressure sensor1206that is positioned at a proximal end of the tube1230. In this example, the occlusion was created by hemostat clamping the tube1230at various distances x. The clamping of the tube1230represents a complete occlusion.

A relatively small known volume of distilled water (e.g., ΔVfof approximately 0.33 cubic centimeters) was injected by the syringe pump1210. The pressure sensor1206was configured to measure the pressure in the tube1230at the proximal end of the tube1230over time. The pressure measurements were made before, during, and after the injection. In some implementations, the pressure measurements occurred at a frequency in the order of hundreds of hertz or thousands of hertz (e.g., 1-2 kHz).

FIG.13shows a representative graph of the pressure measurements P (in mbar) obtained by the pressure sensor1206over time (in seconds) when the occlusion1208was positioned at x=339 cm. The change in pressure ΔP was measured as the net change in pressure after the transient behavior had subsided. In this example, the change in pressure ΔP was approximately 75 mbar. With the incremental volume of injected fluid ΔVfand the change in pressure ΔP being known, the fluidic capacitance Cfwas then determined according to Equation 5. In this example, the fluidic capacitance Cfwas determined to be approximately 4.4 cc/bar.

The experiment was then repeated for each of the tested distances x of the occlusion1208.FIG.14shows a representative graph of the calculated fluidic capacitances Cf(in cc/bar) versus the various distances x of the clampings (in centimeters). The data shown inFIG.14represents a “calibration curve” for fluidic capacitance Cfversus the distance x to the occlusion in the particular system. The data show that fluidic capacitance Cfcorrelates linearly with the distance x. The information can be used to refine the determination of the location of the occlusion. That is, using the fluidic capacitances Cfdetermined according to Equation 5, Equation 6 may indicate that the corresponding occlusions are present at a particular distances x. But in this example, we know the actual distance x to the occlusions. Thus, errors between the calculated distances x and the actual distances x can be noted and considered for future determinations (e.g., for experiments in which the actual distance x of the occlusion is unknown.

While Experiment 1 has largely been described in terms of a “fill direction” implementation in which an incremental volume ΔVfof solution is provided to (e.g., dispensed into) the conduit, thereby resulting in a pressure increase, the same principles and equations apply to “drain direction” implementations in which solution is withdrawn from the conduit, thereby resulting in a pressure decrease in the conduit.

Experiment 2

Experiment 1 was used to corroborate the validity of Equations 1-6 and to determine a calibration curve for the experimental system1200ofFIG.12testing for complete occlusions. Experiment 2 studies a similar technique implemented in an actual dialysis machine (e.g., the PD machine102ofFIGS.1-10) using the built-in pressure sensor151A to test for partial occlusions. The advanced testing described below was performed to achieve results that are more relevant to real PD treatment.

The experiment primarily focused on flow in the drain direction. The choice to focus on flow in the drain direction was made for the following reasons: i) a majority of problematic blockages typically occur in the drain direction; ii) a greater potential for difficulty was predicted in the drain direction due to possible pull-off of cassette film from the pump; and iii) initial tests in the fill direction suggested that the same patterns of pressure versus flow should be obtainable—albeit with different calibration curves that would need to be empirically determined.

FIG.15shows a schematic of a dialysis system1500in which the fluidic capacitance Cfof a pressurized region of a conduit can be determined. The dialysis system1500includes added components for flow control and pressure measurement used in the validation experiments described herein. For example, the dialysis system1500includes additional components that may not typically be included in a dialysis system for ordinary use with a patient.

The dialysis system1500includes the PD machine102, the PD cassette112housed in the PD machine102, a patient line1530, and the pressure sensor151A located at a proximal end of the patient line1530. The patient line1530may be substantially similar to the patient line130described above with respect toFIGS.1and10. In some implementations, the patient line1530may be a 10-foot patient line with dual patient connectors. In this example, the PD machine102is controlled by a computing device1534and a microcontroller1536such as a Mega 2650 microcontroller manufactured by Arduino LLC. In some implementations, the PD machine102may be controlled by a control unit (e.g., a processor) of the PD machine102, such as the control unit139shown inFIG.1. The microcontroller1536is operatively coupled to driver modules1538a,1538b. The driver modules1538a,1538bmay be DRV8825 stepper motor driver modules manufactured by Pololu Corporation.

The microcontroller1536, at the direction of code executed by the computing device1534, is configured to control the driver modules1538a,1538bto cause the driver modules1538a,1538bto operate pumps of the PD machine102(e.g., the pistons133A,133B ofFIG.2) in order to impose specified flow patterns. The microcontroller1536and the driver modules1538a,1538bprovided pulse streams to the pumps to accomplish the following types of motion: i) return to the “home” position as defined by an onboard limit switch; ii) move forward by a specified number of steps, in a user-defined stepping mode from full stepping to various increments of microstepping; and iii) move backward by a specified number of steps in a user-defined stepping mode. Some flow patterns were determined to be more desirable than others for the purpose of occlusion detection. Such desirable flow patterns were programmed in a sequence that is described below.

The ability to detect a partial occlusion (e.g., as compared to detecting a complete occlusion) presents challenges that do not manifest when detecting a complete occlusion. Typically, the less restrictive an occlusion is, the greater is the challenge for sensitivity and specificity of a method for determining its location. A relevant standard for quantifying partial occlusions in the PD machine102comes from the Drain Complication and Fill Complication conditions. Drain Complication and Fill Complication conditions occur when there is a flow restriction sufficient to depress the flow below a threshold value for a particular period of time. In a model case of a steady-state flow restriction, the threshold value of restriction that would generate a Drain Complication is one that would require a pressure of approximately −200 mbar (as measured at the pressure sensor151A) to drive a flow of approximately 30 milliliters per minute.

The pumps are configured to cause fluid to be pumped through a patient line-catheter conduit that includes the patient line1530, a catheter1502, and a port1504that connects the patient line1530to the catheter1502. The catheter1502may be a Flex Neck Classic catheter. The catheter1502, the port1504, and a portion of the patient line1530is submerged in a basin of water1512(e.g., in place of a patient). The water was held at room temperature (e.g., 20-25° C.). The free surface of the water was kept at the same height (e.g., ±2 centimeters) with respect to the direction of gravity as that of the pressure sensor151A of the PD cycler102. An occlusion1508was provided in the patient line1530at various distances x from the pressure sensor151A, with the occlusion1508defining a boundary between a first portion of the conduit (e.g., the pressured portion) and a second portion of the conduit (e.g., the rest of the conduit). The occlusions1508represented partial occlusions.

The distance x to the occlusions1508can be inferred from a measurement of the fluidic capacitance Cfof the pressurized region of a conduit (e.g., the segment of the patient line1530between the PD cycler102and the occlusion1508). For a patient line1530with tubing of uniform mechanical properties and cross-sectional dimensions (e.g., which is largely true in practice), the fluidic capacitance Cfis related proportionately to the length of tubing comprising the “capacitor.” The so-called capacitor can be “charged” by adding or withdrawing fluid at a fixed rate of flow, in a time interval short compared to the characteristic time of fluidic “leakage” through the partial occlusion. The fluidic capacitance Cfmay then be measured by its definition as the slope of distended volume versus pressure. In other words, two or more pressure measurements can be made during the withdrawing or dispensing stroke, the slope of the pressure versus time plot can be determined, and the distance x to the occlusions1508can be determined.

Equation 6 presents the theoretical basis by which the fluidic capacitance Cfis expected to be proportional to the distance x to the occlusion, with the constant of proportionality being a function only of tubing properties and cross-sectional dimensions. Equation 5 can be rearranged to present the differential definition of the fluid capacitance Cf, as shown in Equation 7:

Cf=dVdP(7)
During “charging” of a capacitor by the action of a fixed rate dV/dt of fluid injection or removal, the fluidic capacitance Cfcan be determined according to Equation 8:

Cf=dVdtdPdt(8)

As was the case in Experiment 1, once the fluidic capacitance Cfof the pressurized region of the patient line130is calculated, the distance x to the occlusion can be determined according to Equation 6.

Experiment 2 included the following general steps, which were performed for occlusions at various different distances:i. use the pump to add (for Fill Direction testing) or withdraw (for Drain Direction testing) a short burst (e.g., a “short stroke”) of flow at a fixed and known volumetric flow rate;ii. detect and measure the rate of change of pressure versus time at the pressure sensor151A; the time interval of data producing the slope estimate may be short compared to the characteristic decay time of the pressure;iii. calculate the effective fluidic capacitance Cfusing Equations 6-8; andiv. empirically determine a calibration curve between fluidic capacitance Cfand distance x to the occlusion.

The experiment was performed at various distances x and across a large number of cassettes, with different types, degrees, and locations of flow restriction (e.g., occlusions), in order to investigate the potential sensitivity and specificity of the detection method. Sensitivity and specificity are statistical measures of the performance of the detection method. The sensitivity, also referred to as the true positive rate, measures the proportion of positives that are correctly identified as such. In this context, the sensitivity may correspond to the ability of the system to correctly identify occlusions (e.g., for distances x within a particular range). The specificity, also referred to as the true negative rate, measures the proportion of negatives that are correctly identified as such. In this context, the specificity may correspond to the accuracy of the detection method (e.g., the margin of error of determined distances x).

A small volume (e.g., approximately 0.33 cubic centimeters) of water was moved through the patient line1530in the drain direction by a first pump of the PD machine102(e.g., a pump controlled by a first one of the driver modules1538a) at a fixed rate (e.g., 4.4 cubic centimeters per second). During this stroke, the pressure sensor151A, which is built into the PD machine102and located at the proximal end of the patient line1530, was used to measure two or more pressure values and detect the slope of pressure versus time for use in Equation 8.

The pressures were initially measured using both the pressure sensor151A of the PD machine102and a reference pressure transducer1540positioned downstream from the pressure sensor151A. The separate pressure measurements were taken to ensure that the pressure sensor151A built into the PD machine102was capable of achieving the necessary. For example, the pressure sensor151A is configured to detect the pressure in the patient line1530through a membrane of the cassette112, and various fluidic elements are positioned between the pressure sensor151A and the proximal end of the patient line1530. It was considered that these elements may have the potential to diminish and/or distort the accuracy of the pressure measurements. Thus, measurements made by the reference pressure transducer1540were used to verify the fidelity of the measurements made by the pressure sensor151A. A high degree of fidelity was observed, and the reference pressure transducer1540was removed to avoid possible artifacts.

FIG.16shows a pressure waveform1602that includes pressure measurements over time made by the pressure sensor151A during the short-stroke test. The pressure measurements were sampled at a frequency of 1 kHz. In this example, the occlusion1508of drain-critical value was positioned at a distance x=220 centimeters along the patient line1530. The measured pressure, relatively steady in the absence of pump motion, is seen to drop rapidly during a pump stroke having a duration of approximately 75 milliseconds that commences at approximately t=1 second. After abrupt cessation of pump motion, the pressure in the patient line1530slowly returns to its steady-state value (e.g., due to the leakage of the partial occlusion). The slope of the pressure versus time curve during the short-stroke can be evaluated to determine the fluidic capacitance Cfaccording to Equation 8. Once the fluidic capacitance Cfis known, locations x of occlusions (e.g., at unknown positions of the conduit) can then be determined by evaluating the slope of the pressure versus time curve during subsequent short-stroke tests.

The data shown inFIG.16correspond to the short-stroke test performed with a dispensed water volume of 0.33 cubic centimeters at a fixed rate of 4.4 milliliters per second for an occlusion1508positioned at a distance x=220 centimeters along the patient line1530. Data was also obtained for various other cassette112/occlusion1508configurations at various different distances x for the occlusion1508. For each test, the slope of the pressure versus time curve during the main downward event of the short-stroke was evaluated to determine the fluidic capacitance Cf, and the fluidic capacitances Cfwere correlated to the various different distances x of the occlusions1508. The correlated data can be used to create a calibration curve for refining future determinations of occlusion1508locations. In this way, errors between calculated distances x according to Equation 6 and the actual distances x of the occlusions1508during testing can be considered for calibrating future distance x calculations.

Experiment 3

Another way to determine the fluidic capacitance Cfof a pressurized region of a conduit is to measure the amount of time required for pressure measurements to decay below a predetermined threshold after fluid is provided to or withdrawn from the conduit in a long, steady-state stroke at a known volumetric flow rate. Like Experiment 2, which studied a technique for determining the fluidic capacitance Cfof a pressurized region of a conduit by measuring a change in pressure during a short dispensing or withdrawing stroke, Experiment 3 was also implemented in an actual dialysis machine (e.g., the PD machine102ofFIGS.1-10) using the built-in pressure sensor151A to test for partial blockages. The test setup was substantially similar to that described above with respect to Experiment 2 and as shown inFIG.15.

The distance x to the occlusions1508can be inferred from a measurement of the fluidic capacitance Cfof a pressurized region of a conduit (e.g., the segment of the patient line1530between the PD cycler102and the occlusion1508, sometimes referred to as the first portion). The occlusion1508may define a boundary between the first portion of the conduit and a second portion of the conduit (e.g., the rest of the conduit). For a patient line1530with tubing of uniform mechanical properties and cross-sectional dimensions (e.g., which is largely true in practice), the fluidic capacitance Cfis related proportionately to the length of tubing comprising the “capacitor.” As described above, the so-called capacitor can be “charged” by adding or withdrawing fluid. The capacitor may then be discharged by cessation of pump flow and thus passively communicating fluid to or from the patient (e.g., the patient's peritoneal cavity). The fluidic capacitance Cfmay be inferred from a characteristic time of the pressure decay that occurs during the discharge.

In general, a characteristic time is an estimate of the order of magnitude of the reaction time scale of a system. In the context of RC circuits and its fluidic analogy to Ohm's Law, the characteristic time is the time required for the capacitor to discharge by 1−1/e (e.g., by approximately 63.2%) from the initial value to the final (e.g., asymptotic) value. Thus, in focusing on the fluidic analogy to RC circuits explored herein, the characteristic time is the time required for the pressure inside the patient line1530to change from the initial pressure value to 36.8% of the difference between the initial pressure value and the final pressure value. The characteristic time can be expressed as a time constant, τ. Once the characteristic time constant r is known, the fluidic capacitance Cf—and in turn, distance x to the occlusion—can be determined.

Equation 6 presents the theoretical basis by which the fluidic capacitance Cfis expected to be proportional to the distance x to the occlusion, with the constant of proportionality being a function only of tubing properties and cross-sectional dimensions. The relationship between the fluidic capacitance Cfand the characteristic time constant r is expressed in Equation 9:
τ=RfCf(9)
where Rfis the fluidic resistance representing the partial occlusion itself. The fluidic resistance Rfmay be estimated from the fluidic analogy to Ohm's Law, as shown in Equation 10:
Rf=ΔP/Q(10)
where Q is an imposed volumetric flow rate and ΔP is the change in pressure in response to the imposed volumetric flow rate Q (e.g., the pressure drop across the occlusion).

Experiment 3 included the following general steps, which were performed for occlusions at various different distances:i. use the pump to add (for Fill Direction testing) or withdraw (for Drain Direction testing) flow at a fixed and known volumetric flow rate Q, measuring steady-state pressure achieved during this initial flow event;ii. determine the fluidic resistance Rfusing Equation 10;iii. abruptly stop the flow to allow passive decay of the pressure within the conduit, measuring the pressure versus time during the decay of pressure;iv. determine the characteristic time constant r using the pressure measurements;v. calculate the fluidic capacitance Cfusing Equation 9; andvi. empirically determine a calibration curve between fluidic capacitance Cfand distance x to the occlusion using Equation 6.

The experiment was performed at various distances x and across a large number of cassettes, with different types, degrees, and locations of flow restriction (e.g., occlusions), in order to investigate the potential sensitivity and specificity of the detection method.

In this example, fill direction testing will be discussed. A volume of fluid is provided to the patient line1530in a long, steady-state stroke at a known volumetric flow rate Q (e.g., sometimes referred to as a “long stroke”). During the pump stroke, an initial steady-state pressure P1is reached within the patient line1530, as measured by the pressure sensor151A. The initial steady-state pressure P1represents the pressure that results from the fixed volumetric flow rate Q and the characteristics of the occlusion1508. The initial steady-state pressure P1is used to calculate the fluidic resistance Rfusing Equation 10, where ΔP is the difference between the initial pressure in the patient line1530(e.g., before the pump stroke begins) and the initial steady-state pressure P1achieved during the pump stroke. In some implementations, the initial steady-state pressure P1is measured right before the long stroke is stopped, or when the long stroke is stopped.

At the end of the pump stroke, the flow is abruptly stopped to allow passive decay of the pressure within the patient line1530. The pressure sensor151A makes pressure measurements during the decay of pressure until a final steady-state pressure Pfis achieved (e.g., until the decay is complete and the pressure is not changing anymore). In some implementations, the pump stroke can be abruptly ceased as soon as it is determined that an initial steady-state pressure P1has been reached. Once the initial steady-state pressure P1and the final steady-state pressure Pfare known, the characteristic time constant τ is determined. The characteristic time constant τ is an elapsed time between the occurrence of the initial steady-state pressure P1and the occurrence of one of the plurality of pressure measurements taken during the decay of pressure.

FIGS.17A-Cshow examples of pressure versus time plots that illustrate how the characteristic time constant τ for a pressurized region of the patient line1530(e.g., acting as a capacitor) can be determined. The plot shown inFIG.17Ashows pressure measurements that are made during and after a dispensing (e.g., “fill”) stroke. For example, “charging” of the capacitor occurs when fluid is provided to the patient line1530, which corresponds to t=0 to t=t1in the plot. The pressure reaches an initial steady-state value P1. At t=t1, the flow is abruptly ceased and the pressure begins to decrease (e.g., the capacitor begins to discharge). The pressure eventually reaches a final steady-state value Pf. In this example, the final steady-state value is at or near zero. Knowing the initial P1and final Pfsteady-state values, the pressure P2that represents 36.8% of the difference between the initial P1and final Pfsteady-state values can be determined. This pressure P2has a value of 1/e*(P1−Pf). The characteristic time constant τ can then be determined by identifying the time at which the pressure inside the patient line1530is equal to P2and determining the elapsed time between t1and t2.

In some implementations, the final steady-state pressure Pfmay not be zero.FIG.17Bshows a plot of pressure measurements that approach a non-zero final steady-state value Pf. For example, the patient may be at an elevation that is different than that of the pressure sensor151A, and thus there exists a non-zero hydrostatic pressure in the case of zero flow in the patient line1530. In such cases, the pressure P2that represents 36.8% of the difference between the initial P1and final Pfsteady-state values has a value of 1/e*(P1−Pf)+Pf. The characteristic time constant τ can then be determined by identifying the time at which the pressure inside the patient line1530is equal to P2and determining the elapsed time between t1and t2.

In some implementations, a time-averaged pre-stroke zero-flow value may be subtracted from the pressure measurements as an initial step before determining the characteristic time constant r. In this way, one or both of the starting pressure (e.g., at t=0) and the final steady-state pressure Pfcan be adjusted to have a value of 0 mbar, thereby simplifying the characteristic time constant τ determination.

A similar method can be used for determining the characteristic time constant τ when withdrawing fluid from the patient line1530. The plot shown inFIG.17Cshows pressure measurements that are made during and after a withdrawing (e.g., “drain”) stroke. For example, “charging” of the capacitor occurs when fluid is withdrawn from the patient line1530, which corresponds to t=0 to t=t1in the plot. The pressure reaches an initial steady-state value P1. At t=t1, the flow is ceased and the pressure begins to increase (e.g., the capacitor begins to discharge). The pressure eventually reaches a final steady-state value PfIn this example, the final steady-state value is at or near zero. Knowing the initial P1and final Pfsteady-state values, the pressure P2that represents 36.8% of the difference between the initial P1and final Pfsteady-state values can be determined. This pressure P2has a value of 1/e*(P1−Pf). The characteristic time constant τ can then be determined by identifying the time at which the pressure inside the patient line1530is equal to P2and determining the elapsed time between t1and t2. In implementations in which the final steady-state pressure Pfis not zero, the characteristic time constant τ can be determined in a manner similar to that described above with respect toFIG.17B.

Once the characteristic time constant τ is determined, the fluid capacitance Cfis calculated according to Equation 9. The distance x to the occlusion1508is then determined according to Equation 6.

Similar tests can be performed for various other cassette112/occlusion1508configurations at various different distances x for the occlusion1508. For each test, the calculated fluidic capacitances Cfcan be correlated to the various different distances x of the occlusions1508. The correlated data can be used to create a calibration curve for refining future determinations of occlusion1508locations. In this way, errors between calculated distances x according to Equation 6 and the actual distances x of the occlusions1508during testing can be considered for calibrating future distance x calculations.

Experiment 4

In some implementations, instead of or in addition to determining the exact distance x to the occlusion, the relative location and/or the general location of the occlusion may be determined. For example, characteristics of a plurality of pressure measurements within the conduit can be analyzed to determine whether the occlusion is present in a region of particular interest, such as in a patient line region (e.g., outside the patient) or a catheter region (e.g., inside the patient) of the conduit. The conduit may include a fluid capacitive element that is strategically positioned between the patient line region and the catheter region such that the generated information can localize the occlusion to one region or the other. Based on the determined region of the occlusion, the type of the occlusion (e.g., a pinch in the patient line, an occlusion of the catheter, etc.) can be determined. The determination may be made using existing components (e.g., the pressure sensor151A) of the PD machine (102ofFIG.1), and without requiring backward flow in the detection procedure.

FIG.18shows a schematic diagram of the PD machine102connected to a patient. A proximal end of a patient line1830is connected to the PD machine102at a port (e.g., an inlet/outlet), and a distal end of the patient line1830is connected to the patient's abdomen via a catheter1802. The catheter1002is connected to the patient line via a port1804. A fluid capacitive element1810is positioned at the distal end of the patient line1830adjacent the port1804. In some examples, the fluid capacitive element1810may be positioned elsewhere. The patient line1830may be a tube made of a distensible and/or flexible material that is at least partially distended by operating pressures in the PD machine102. For example, the patient line1830may be made of an elastomeric material such as a polymer that develops a swell in response to positive operating pressures in the PD machine102. The pressure sensor151A is configured to measure the pressure in the patient line1830. The patient line1830, the fluid capacitive element1810, the port1804, and the catheter1802are sometimes referred to herein as the patient line-catheter conduit, or simply the conduit. The conduit may be substantially similar to that described above with respect toFIG.10, except in this example, the conduit also includes the fluid capacitive element1810.

Like the patient line1830, the fluid capacitive element1810may also be made of a distensible and/or flexible material that is at least partially distended by operating pressures in the PD machine102. For example, the fluid capacitive element1810may be made of an elastomeric material such as a polymer that develops a swell in response to positive operating pressures in the PD machine102. In some implementations, the fluid capacitive element1810may be part of the patient line1830(e.g., an elastomeric segment integrated into the patient line1830). The fluid capacitive element1810may have a distensibility that is substantially greater than that of the patient line1830itself. For example, the fluid capacitive element1810may have the capability to store additional fluid volume with a concomitant increase in local liquid pressure produced by a restoring force. Accordingly, occlusions that occur between the patient line port of the PD machine102and the fluid capacitive element1810do not cause the pressure sensor151A to experience the effects of the fluid capacitive element1810, and occlusions that occur between the fluid capacitive element1810and the tip of the catheter1802do cause the pressure sensor151A to experience the effects of the fluid capacitive element1810.

During a PD treatment cycle, an occlusion can occur at different locations in the conduit. For example, the patient line1830may become kinked or pinched, holes in the catheter1802may become occluded (e.g., with omental fat), or the patient line1830may develop an internal blockage at some location (e.g., from a deposit of omental fat). The PD machine102is configured to adjust its operation in response to an occlusion being detected, as described above with respect toFIG.10. An appropriate response by the PD machine102may depend on the type of the occlusion, and the type of the occlusion may be ascertained based on whether the occlusion occurs in the patient line region (e.g., between the patient line port and the fluid capacitive element1810) or the catheter region (e.g., between the fluid capacitive element1810and the tip of the catheter1802) of the conduit.

To help illustrate the method of analyzing the effect achieved by the addition of the fluid capacitive element1810to the conduit,FIG.19shows a representation of a lumped-element electrical circuit that is analogous to the fluidic system shown inFIG.18, in which P refers to pressures at various portions of the conduit, Q refers to the volumetric flow rate at various portions of the conduit, R refers to the fluidic resistance (e.g., including a patient line fluidic resistance component Rime and a catheter fluidic resistance component Rcatheter, collectively Rf), Vfrefers to the fluid volume, and Cfrefers to the fluid capacitance. Fluid mechanical analysis can be performed by drawing mathematical similarity to the analogous electrical circuit. A lumped element analysis can be performed in which fluid mechanical effects occurring over a distributed region of the conduit are represented by a discrete analytical elements (e.g., resistor or capacitor).

The electrical circuit analogies for the fluid mechanic lumped element analysis are shown in Table 1, and the physical and mathematical analogies consistent with the equations in Table 1 are shown in Table 2:

TABLE 1RepresentativeElectricalFluidExpression forCircuitConstitutiveConstitutiveFluid LumpedElementLawFluid EffectLawParameterResistorΔV = IRViscous pressure  lossΔP = QRfRf=8⁢μ⁢lπ⁢r4CapacitorΔ⁢V=Δ⁢qCFluid storage with  restoring forceΔ⁢P=Δ⁢VfCfCf≡A⁢Δ⁢VfΔ⁢FInductorΔ⁢V=L⁢dldtFluid inertiaΔ⁢P=Lf⁢d⁢Qd⁢tLf=ρ⁢lπ⁢r2

TABLE 2Electrical QuantityAnalogous Fluid QuantityPotential drop or change, ΔVPressure drop or change, ΔPCharge, qFluid volume, VfCurrent, IVolumetric flow rate, QResistance, RFluidic resistance, RfCapacitance, CFluidic capacitance, CfInductance, LFluidic inductance, Lf

Various assumptions may be made to simplify the mathematical analysis of the equations of Table 1, although such assumptions may not be required in all cases. For example, it may be assumed that the capacitive effects are linear (e.g., pressure increases proportional to fluid volume stored). The fluidic resistance Rfmay apply to the case of fully developed laminar flow in a rigid duct of circular cross-section (e.g., constant radius r, length l); for other internal flow situations, other expressions for the fluidic resistance Rfmay apply. In the general case (e.g., including turbulent or separating flow), the fluidic resistance Rfitself is a function of the volumetric flow rate Q. The dynamic viscosity is μ. As with the fluidic capacitance Cf, the analysis may be simplified by the linearity resulting from constant values of the fluidic resistance Rf, but such linearity is not required.

The fluidic capacitance Cfis the change in stored volume ΔVfof fluid divided by the quantity: change in restoring force ΔF divided by the area A over which the latter acts. The form of an expression for the fluidic capacitance Cfincorporating material properties and dimensions may depend upon the design of the fluid capacitive element1810and its mechanism of restoring force (e.g., elastomeric, pneumatic, spring, etc.). The fluidic inductance Lf applies to fluid having a fluid density p in a circular duct segment of constant radius r and length l.

The circuit ofFIG.19is shown without an inductor for the case in which inductive effects may be neglected, but inductive effects may be incorporated into the mathematical model if appropriate. The ordinary differential equation governing the circuit behavior can be written in terms of the time-varying volume of fluid stored in the fluid capacitive element1810, Vf,2(t), as expressed in Equation 11:

Q1(t)=Vf,2(t)Rc⁢a⁢t⁢h⁢e⁢t⁢e⁢r⁢Cf+dVf,2dt(11)

The object of Experiment 4 is to distinguish an increase in the fluidic resistance of the patient line region of the conduit Rlinefrom an increase in the fluidic resistance of the catheter region of the conduit Rcatheter, by measuring the pressure in the patient line region P1(e.g., near the patient line port) over time. The pressure in the patient line region over time P1(t) is affected differently by the fluidic resistance Rfincrease depending upon the location of such an increase. The placement of the fluid capacitive element1810between the patient line region and the catheter region makes it possible to make such a distinction, as shown in the analysis below.

A specified flow waveform Q1(t) is provided to the patient line1830. In this example, the flow waveform Q1(t) is known and is periodic such that it may be represented by a full Fourier transform as shown in Equation 12:

Q1(t)=Ao2+∑n=1NAn⁢cos⁡(ωn⁢t)+Bn⁢sin⁡(ωn⁢t)(12)

Equation 11 can be solved by superposition assuming that the fluidic resistance Rfand the fluidic capacitance Cfvalues are constant. In some examples, if the fluidic resistance Rfand the fluidic capacitance Cfvalues are not constant but are repeatable functions of flow and volume, respectively, a different method may be used to determine the expected characteristics of the pressures P versus the flow waveform Q1(t), such as numerical or experimental analysis. The result of the superposition provides a prediction of the pressure measured at the cycler P1(t), as shown in Equation 13:

P1(t)=Ao2⁢(Rline+Rcatheter)+∑n=1N{[⁠Rline⁢An+ωo⁢An-ωn⁢BnCf(ωo2+ωn2)]⁢cos⁡(ωn⁢t)+⁠[⁠Rline⁢Bn+ωn⁢An+ωo⁢BnCf(ωo2+ωn2)]⁢sin⁡(ωn⁢t)}(13)

In Equation 13, the characteristic frequency of the circuit ω0is given by Equation 14:

ωo=1Rcatheter⁢Cf(14)

Equation 13 expresses the pressure at the cycler P1(t) (e.g., the pressure in the patient line region of the conduit as measured by the pressure sensor151A) as the sum of a time-averaged and a transient (e.g., fluctuating) component. The time-averaged component is a function of the total fluidic resistance Rfof the conduit:

P1¯=Ao2⁢(Rline+Rcatheter).
Hence, an equivalent increase in either the fluidic resistance of the patient line region Rlineor the fluidic resistance of the catheter region Rcatheterwill affect P1equally. Thus, the time-averaged value of the pressure P1(t) cannot be used to identify the location of a sudden increase in flow resistance.

On the other hand, inspection of the transient component of the pressure P1(t) reveals a separation of the effects of the fluidic resistance of the patient line region Rime versus the fluidic resistance of the catheter region Rcatheter. A change in the fluidic resistance of the catheter region Rcatheteraffects the characteristic frequency ω0, while a change in the fluidic resistance of the patient line region Rlinedoes not. Conversely, a change in the fluidic resistance of the patient line region Rlinealone affects the transient component of the pressure P1(t) through the terms RlineAnand RlineBn. Thus, if the transient component of the pressure P1(t) is measured and compared to expected characteristics, the location of an increase in flow resistance may be determined.

Because the values of Anand Bndepend upon the shape of Q1(t), and the latter is to be imposed by design of the pump head operational protocol, it is advantageous to determine which waveform(s) Q1(t) will most specifically and sensitively reveal the location of resistance increase. Laplace transform analysis and experimental data provide the recommendations to follow.

An ordinary differential equation (e.g., such as Equation 11) with constant coefficients and a periodic forcing function, including one of impulsive character, is a good candidate for solution by the method of Laplace transforms. The solution may proceed as follows according to Equations 15-25, and its result complements that obtained by Fourier analysis in the previous section:

ℒ[Q1(t)]=ℒ[Vf,2(t)Rcatheter⁢Cf]+ℒ⁡(dVf,2dt)(15)ℒ[Q1(t)]=1Rcatheter⁢Cf⁢ℒ[Vf,2(t)]+s⁢ℒ[Vf,2(t)]-Vf,2(0)(16)(s)=(1Rcatheter⁢Cf+s)(s)-Vf,2(0)(17)
where(s) and(s) are the Laplace transforms of Q1(t) and Vf,2(t), respectively. Thus,

(s)=(1s+1Rcatheter⁢Cf)[(s)+Vf,2,(0)](18)
where Vf,2(t) is found by performing the inverse Laplace transform of Equation 18:

(s)=Vf,2(0)⁢(1s+1Rcatheter⁢Cf)+(1s+1Rcatheter⁢Cf)(s)(19)(s)=Vf,2(0)(s)+(s)(s)(20)
where

(s)=1s+1Rcatheter⁢Cf,
the inverse Laplace transform of which is g(t)=e−w0t(see Equation 14).

Proceeding to invert Equation 20 according to the linearity properties of the transform and the convolution rule,
Vf,2=Vf,2(0)g(t)+∫0tg(t−τ)Q1(τ)dτ(21)
Vf,2(t)=Vf,2(0)e−ω0t+∫0te−ω0(t−τ)Q1(τ)dτ(22)

Equation 22 provides input for Equation 24, an equation for the measured pressure P1(t), derived according to the circuit equations:

P2(t)=Vf,2(t)Cf(23)P1(t)=P2(t)+Q1(t)⁢Rline=Vf,2(t)Cf+Q1(t)⁢Rline(24)

Similarly to the Fourier result above but in a different mathematical form, Equation 24 demonstrates how the capacitive element creates a separation of the effects of a change in the fluidic resistance of the patient line region Rime versus a change in the fluidic resistance of the catheter region Rcatheter.

Depending upon the form of the flow waveform Q1(t), the integral in Equation 22 may be evaluated either analytically or numerically. In some implementations, the flow may be programmed to simplify the expected pressure waveform and to isolate the measurement of response time. Because the flow waveform Q1(t) is to be imposed by programmed pump head motion in this example, it may be appropriate to investigate the most advantageous achievable flow waveform Q1(t) (e.g., a flow waveform Q1(t) that results in the greatest sensitivity and specificity). In some examples, a simplifying case of the flow waveform Q1(t) may be a quasi-square wave with a frequency that is much less than the nominal value of the characteristic frequency ω0. That is, if the flow waveform Q1(t) entails a single dispensing step, with flow abruptly stopped, a period may follow in which Equation 24 is approximated by Equation 25:

P1(t)≈Vf,2(0)Cf⁢e-ωo⁢t(25)

Equation 25 shows how the measured time response of the pressure P1may be used to measure the characteristic frequency ω0. Once the characteristic frequency ω0is known, Equation 24 can be used to infer a change (e.g., or lack thereof) in the fluidic resistance of the catheter region Rcatheter. If the change in the fluidic resistance of the catheter region Rcatheterequals a combined increase in the fluidic resistance of the patient line region Rime and the fluidic resistance of the catheter region Rcatheterdetected by steady-state measurement, then the occlusion is likely positioned in the catheter region of the conduit (e.g., an occlusion of the catheter1802). Conversely, if a combined increase in the fluidic resistance of the patient line region Rlineand the fluidic resistance of the catheter region Rcatheterhas occurred without a change in the fluidic resistance of the catheter region Rcatheter, then the occlusion is likely positioned in the patient line region of the conduit (e.g., a pinch of the patient line1830).

In some implementations, the volumetric flow rate Q may be imposed in other ways; that is, the flow waveform Q1(t) may take on other forms. For example, in some implementations, the flow waveform Q1(t) can include a steady-state introduction of fluid, a ramped introduction of fluid, a parabolic introduction of fluid, and/or a cyclical introduction of fluid.

While the detection methods described herein have sometimes been described as being implemented in a testing environment, similar techniques can be employed for detecting occlusions in the conduit when the patient line is attached to a patient receiving a dialysis treatment (e.g., as shown inFIGS.10and18). For example, a determination of: i) the distance x of the occlusion, and/or ii) whether the occlusion is located in the patient line region or the catheter region of the conduit, may be made using the detection methods described herein. The type of the occlusion can then be inferred based on the determined distance and/or location.

While the dialysis system has been largely described as being a peritoneal dialysis (PD) system, other medical treatment systems can employ the techniques described herein. Examples of other medical treatment systems include hemodialysis systems, hemofiltration systems, hemodiafiltration systems, apheresis systems, and cardiopulmonary bypass systems.

While a number of equations for determining various parameters have been described above, in some implementations, such equations are used to illustrate a theoretical basis for the systems and techniques described herein and associated measurements and/or calculations. In some implementations, one or more elements of an equation may be different than those shown above. In some implementations, one or more values may be determined by empirical evaluation. For example, as described above with respect to Equation 6, in practice the relationship between the fluidic capacitance Cfand the distance x between the patient line port and the occlusion can be evaluated by empirical means.

FIG.20is a block diagram of an example computer system2000. For example, the control unit (139ofFIG.1), the computing device (1534ofFIG.15), and/or the microcontroller (1536ofFIG.15) could be examples of the system2000described here. The system2000includes a processor2010, a memory2020, a storage device2030, and an input/output device2040. Each of the components2010,2020,2030, and2040can be interconnected, for example, using a system bus2050. The processor2010is capable of processing instructions for execution within the system2000. The processor2010can be a single-threaded processor, a multi-threaded processor, or a quantum computer. The processor2010is capable of processing instructions stored in the memory2020or on the storage device2030. The processor2010may execute operations such as causing the dialysis system to carry out dialysis functions.

The memory2020stores information within the system2000. In some implementations, the memory2020is a computer-readable medium. The memory2020can, for example, be a volatile memory unit or a non-volatile memory unit. In some implementations, the memory2020stores information for causing the pumps of the dialysis system to operate as described herein.

The storage device2030is capable of providing mass storage for the system2000. In some implementations, the storage device2030is a non-transitory computer-readable medium. The storage device2030can include, for example, a hard disk device, an optical disk device, a solid-date drive, a flash drive, magnetic tape, or some other large capacity storage device. The storage device2030may alternatively be a cloud storage device, e.g., a logical storage device including multiple physical storage devices distributed on a network and accessed using a network.

The input/output device2040provides input/output operations for the system2000. In some implementations, the input/output device2040includes one or more of network interface devices (e.g., an Ethernet card), a serial communication device (e.g., an RS-232 10 port), and/or a wireless interface device (e.g., an 802.11 card, a 3G wireless modem, or a 4G wireless modem). In some implementations, the input/output device2040may include short-range wireless transmission and receiving components, such as Wi-Fi, Bluetooth, and/or near field communication (NFC) components, among others. In some implementations, the input/output device includes driver devices configured to receive input data and send output data to other input/output devices, e.g., keyboard, printer and display devices (such as the touch screen display118). In some implementations, mobile computing devices, mobile communication devices, and other devices are used.

In some implementations, the system2000is a microcontroller (e.g., the microcontroller1536ofFIG.15). A microcontroller is a device that contains multiple elements of a computer system in a single electronics package. For example, the single electronics package could contain the processor2010, the memory2020, the storage device2030, and input/output devices2040.

Although an example processing system has been described inFIG.20, implementations of the subject matter and the functional operations described above can be implemented in other types of digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this specification and their structural equivalents, or in combinations of one or more of them. Implementations of the subject matter described in this specification can be implemented as one or more computer program products, i.e., one or more modules of computer program instructions encoded on a tangible program carrier, for example a computer-readable medium, for execution by, or to control the operation of, a processing system. The computer readable medium can be a machine readable storage device, a machine readable storage substrate, a memory device, a composition of matter effecting a machine readable propagated signal, or a combination of one or more of them.

The term “computer system” may encompass all apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, or multiple processors or computers. A processing system can include, in addition to hardware, code that creates an execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of them.

A computer program (also known as a program, software, software application, script, executable logic, or code) can be written in any form of programming language, including compiled or interpreted languages, or declarative or procedural languages, and it can be deployed in any form, including as a standalone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file in a file system. A program can be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub programs, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network.

Computer readable media suitable for storing computer program instructions and data include all forms of non-volatile or volatile memory, media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks or magnetic tapes; magneto optical disks; and CD-ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry. The components of the system can be interconnected by any form or medium of digital data communication, e.g., a communication network. Examples of communication networks include a local area network (“LAN”) and a wide area network (“WAN”), e.g., the Internet.

A number of implementations of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other implementations are within the scope of the following claims.