Abstract:
A peritoneal dialysis machine includes: (i) a housing; (ii) an actuator carried by the housing so as to be able to interact with a peritoneal dialysis fluid carrying disposable; (iii) at least one heating element carried by the housing; (iv) a heater pan providing an upper surface of the housing, the heater pan cooperating with the at least one heater element to provide heat to a container of peritoneal dialysis fluid placed onto the heater pan, the container being part of or in communication with the peritoneal dialysis fluid carrying disposable; and (iv) a weight sensor cooperating with the heater pan to sense the weight of the peritoneal dialysis fluid located within the container.

Description:
PRIORITY CLAIM 
       [0001]    This application claims priority to and the benefit of U.S. patent application Ser. No. 11/420,608, filed May 26, 2006, the entire contents of which are expressly incorporated herein by reference and relied upon. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    In general, the present invention relates to medical fluid delivery systems that employ a disposable set with sterile fluid pathways. In particular, the present invention provides systems, methods and apparatuses for disposable set-based dialysis medical fluid therapies, including but not limited to those using peristaltic pumps, diaphragm pumps, pneumatic pumps and gravity. 
         [0003]    Due to various causes, a person&#39;s renal system can fail. Renal failure produces several physiological derangements. The balance of water, minerals and the excretion of daily metabolic load is no longer possible and toxic end products of nitrogen metabolism (urea, creatinine, uric acid, and others) can accumulate in blood and tissue. 
         [0004]    Kidney failure and reduced kidney function have been treated with dialysis. Dialysis removes waste, toxins and excess water from the body that would otherwise have been removed by normal functioning kidneys. Dialysis treatment for replacement of kidney functions is critical to many people because the treatment is life saving. 
         [0005]    Hemodialysis (“HD”) and peritoneal dialysis (“PD”) are two types of dialysis therapies used commonly to treat loss of kidney function. HD removes waste toxins and excess water from the patient&#39;s blood. The patient is connected to a hemodialysis machine via catheters into a patient&#39;s vein and artery. Blood is pumped from the patient and through the inside of hollow, porous tubes of a dialyzer connected to the machine. The machine produces dialysate, which is pumped outside the hollow, porous tubes. A pressure gradient causes excess water to be pulled from the blood, through the pours of the membrane, into the dialysate, where it is carried away. Diffusion and osmosis causes waste and toxins to move thought the pours into the dialysate to be carried away. Cleaned blood is returned to the patient. A large amount of dialysate, for example about 120 liters, is consumed to dialyze the blood during a single hemodialysis therapy. HD lasts several hours and is generally performed in a treatment center about three or four times per week. 
         [0006]    PD uses a dialysis solution, or “dialysate,” which is infused into a patient&#39;s peritoneal cavity via a catheter. The dialysate contacts the peritoneal membrane of the peritoneal cavity. Waste, toxins and excess water pass from the patient&#39;s bloodstream, through the peritoneal membrane and into the dialysate due to diffusion and osmosis, i.e., an osmotic gradient occurs across the membrane. The spent dialysate is drained from the patient, removing waste, toxins and excess water from the patient. This cycle is repeated. 
         [0007]    There are various types of PD therapies, including continuous ambulatory peritoneal dialysis (“CAPD”), automated peritoneal dialysis (“APD”), tidal flow APD and continuous flow peritoneal dialysis (“CFPD”). CAPD is a manual dialysis treatment. The patient manually connects an implanted catheter to a drain, allowing spent dialysate fluid to drain from the peritoneal cavity. The patient then connects the catheter to a bag of fresh dialysate, infusing fresh dialysate through the catheter and into the patient. The patient disconnects the catheter from the fresh dialysate bag and allows the dialysate to dwell within the peritoneal cavity, wherein the transfer of waste, toxins and excess water takes place. The introduction of twin bag sets reduced the number of connections and disconnections by “Y-ing” the drain line and the fresh dialysate bag. Nevertheless, manual PD requires a significant amount of time and effort from the patient, leaving ample room for improvement. After a dwell period, the patient repeats the manual dialysis procedure, for example, four times per day, each treatment lasting about an hour. 
         [0008]    APD is similar to CAPD in that the dialysis treatment includes drain, fill, and dwell cycles. APD machines, however, perform the cycles automatically, typically while the patient sleeps. APD machines free patients from having to manually perform the treatment cycles and from having to transport supplies during the day. APD machines connect fluidly to an implanted catheter, to a source or bag of fresh dialysate and to a fluid drain. APD machines pump fresh dialysate from a dialysate source, through the catheter, into the patient&#39;s peritoneal cavity, and allow the dialysate to dwell within the cavity, and allow the transfer of waste, toxins and excess water to take place. The source can be multiple sterile dialysate solution bags. 
         [0009]    APD machines pump spent dialysate from the peritoneal cavity, though the catheter, to the drain. As with the manual process, several drain, fill and dwell cycles occur during APD. A “last fill” occurs at the end of CAPD and APD, which remains in the peritoneal cavity of the patient until the next treatment. 
         [0010]    Both CAPD and APD are batch type systems that send spent dialysis fluid to a drain. Tidal flow systems are modified batch systems. With tidal flow, instead of removing all of the fluid from the patient over a longer period of time, a portion of the fluid is removed and replaced after smaller increments of time. 
         [0011]    Continuous flow, or CFPD, systems clean or regenerate spent dialysate and thereby consume a lesser volume dialysate when compared to CAPD or conventional APD. Regeneration systems pump fluid into and out of the patient, through a loop. Dialysate flows into the peritoneal cavity through one catheter lumen and out another catheter lumen. The fluid exiting the patient passes through a reconstitution device that removes waste from the dialysate, e.g., via a carbon filter and a urea removal column that employs urease to enzymatically convert urea into ammonia. The ammonia is then removed from the dialysate by adsorption prior to reintroduction of the dialysate into the peritoneal cavity. Additional sensors are employed to monitor the removal of ammonia. CFPD systems are typically more complicated than batch systems. 
         [0012]    Many PD systems use gravity to fill and drain. Patient data published by Brandes et al. shows that flow rates during fill cycle are relatively constant and related to the patient&#39;s position (supine&gt;sit) and the absolute head height of the supply bag. Drain cycles however normally take about twice as long as fill cycles and have an antilog relationship with time. Within the drain cycle, about 80% of intra-peritoneum volume is drained within the first 40% of the total drain time. Similar results are found from patient data by Amici et al., and from patient trials for Baxter&#39;s HomeChoice and Quantum PD cyclers. 
         [0013]    Flow rates of gravity fill and drain are functions of several physical parameters, including head heights to the patient&#39;s peritoneum, catheter type (resistances), tubing set type, etc. To overcome the fill and drain problems, some advanced APD machines use pumps to fill and drain. Pumps provide active fluid delivery but add complexity and cost. Accordingly, a need exists to provide a relatively low cost PD machine that combines desirable aspects of different types of APD systems. 
       SUMMARY OF THE INVENTION 
       [0014]    Described below is a peritoneal dialysis (“PD”) system that combines the advantages of gravity dialysate delivery and pumped dialysate delivery. In particular, gravity is used to fill the patient, while a vacuum source or pump is used to drain the patient in one preferred embodiment. The vacuum source can be variable, e.g., from zero to −1.5 psig. The vacuum source enables patients to sleep on the floor, underneath the drain bag or otherwise at an elevation that would not allow for adequate drain flow via gravity. 
         [0015]    In one primary embodiment, the system includes a stand. A heater plate is positioned at the top of the stand. The heater plate supports and heats one or more supply bag, such as one or more supply bag and a last-bag (holding an amount of dialysate that will be left in the patient between automated treatments). The stand is adjustable so that the supply bags are supported at an appropriate height above the patient, e.g., thirty-six inches. A line or tube extends from each supply bag to a valve, such as a multi-way pinch valve. The pinch valves are operated by the vacuum source. A control unit operates the vacuum source sequence. The control unit includes a microprocessor and memory in one embodiment, which control the vacuum source. The control unit also receives signals from a load cell or strain gauge, which is coupled to the drain container. This is done for the monitoring and the control of ultrafiltration which is generally considered to be the difference between the drained fluid volume and the filled fluid volume. 
         [0016]    A patient line extends from the multi-way valve. The patient line at its distal end includes a connector that connects to a transfer set and catheter implanted into the patient. A drain line also extends from the multi-way valve. The drain line is connected to a reusable drain container, such as a rigid container. A vacuum line extends from the rigid container to the vacuum source. In one embodiment, the vacuum line is located elevationally above the level that the spent fluid will rise to in the drain container. In this configuration, fluid cannot reach the vacuum line, precluding the spent fluid from the drain container from reaching and potentially damaging the vacuum source. A hydrophobic membrane can also be placed at the interface between the drain container and the drain line for this purpose. 
         [0017]    In this first embodiment, a priming cycle occurs as follows. The patient positions the end of the patient line so that its distal end is at substantially the same height as the supply bags. For example, the heater or its stand could include a hook onto which the patient hangs the patient line connector for priming. The control unit controls the vacuum source so that the valves to each of the supply bags, the patient line and the drain line are opened. The control unit is programmed to keep the valves open for a certain amount of time or until a certain volume (or weight) of fluid has flowed to ensure that each line is primed with fluid without dumping too much fresh fluid to drain. 
         [0018]    In the first embodiment, a drain cycle is performed, e.g., first to remove the spent last-bag volume of fluid residing in the patient&#39;s peritoneum from the night before. Here the control unit causes the vacuum source to open the drain valve and patient line valve, keeping all supply valves closed. The control unit also causes the vacuum source to pull a vacuum on the rigid drain container, which is connected to the drain line. The vacuum pulls spent dialysate from the patient&#39;s peritoneum, through the multi-way valve and into the drain container, which fills from the bottom up via gravity. The load cell and control unit measure the weight of the fluid in the drain container. Weight changes over time are also measured to determine flow rate. The flow rate is used as feedback to control the amount of vacuum applied to the drain container, which allows the flow rate of the drain cycle to be optimized. 
         [0019]    The control unit in one embodiment stores one or more patient profile, in which the variable vacuum source is modified to optimize flow and pressure with particular physiological characteristics of the patient. For example, when the patient&#39;s peritoneum is relatively full, the controller can be set to cause the vacuum source to remove fluid rapidly and relatively constantly from the patient. This can be done using a relatively low suction pressure because the source of spent fluid is relatively abundant and flows readily from the peritoneal cavity. As the patient&#39;s peritoneum becomes more and more empty, and the source of spent fluid becomes increasingly less abundant, the fluid flow starts to slow down. The suction pressure can be decreased to prevent the negative pressure in the patient&#39;s peritoneal cavity from causing pain to the patient. The suction pressure can be decreased from −1.5 to −1.2 psig for example. The profile is therefore adjusted to drain the patient as quickly, safely and comfortably as possible. 
         [0020]    Next, a fill cycle occurs as follows. The control unit causes the vacuum source to close the drain valve and each of the supply bag (last-bag) valves except for the initial supply bag valve. The control unit also causes the vacuum source to open the patient line valve. Gravity forces fluid from the initial supply bag to the patient&#39;s peritoneum. The head height from the supply bag to the patient will determine the flow rate. This fill flow through 6 mm outside diameter×4 mm inside diameter tubing can reach 200 ml/min under a twenty-four inch head height and 300 ml/min under a thirty-six inch head height. 
         [0021]    Afterwards, the control unit causes the vacuum source to close all valves for a dwell period in which the first supply of fluid resides in the patient&#39;s peritoneum, absorbing waste products. 
         [0022]    After the dwell, the next drain cycle occurs, and so on. In the next fill cycle, a different supply bag is used. In the last fill cycle, a last-bag is used, which can contain a lesser or greater amount of dialysate, and which is intended to dwell in the patient&#39;s peritoneum until the next therapy session. Each fill and last-bag has its own dedicated control valve in one embodiment. 
         [0023]    In a second primary embodiment, gravity is again used to fill the patient and vacuum is used to drain the patient. Here, the system includes a machine or control unit that is placed on a night stand for example above the patient, e.g., fifteen to forty inches above the patient. The top of the unit includes a load cell and a heater pan. A dual chamber bag is placed on the load cell/heater pan. The lower chamber, which resides directly on the heater pan, is a heating container or warmer pouch, which receives fresh fluid from a supply bag. The upper chamber is a temporary drain container, which receives spent fluid pumped from the patient&#39;s peritoneum via the vacuum source. The upper, temporary drain container of the dual chamber bag is connected fluidly to a house drain or final drain container, which is located elevationally below the dual chamber bag. Spent fluid is gravity fed from the dual chamber bag to house drain. 
         [0024]    A vacuum-tight cover is placed over the dual camber bag. Suitable gasketing and locking mechanisms are provided so that the cover can be sealed to the unit, around the load cell and heater pan. In this manner, a vacuum can be drawn inside the cover and on the outside the dual camber bag residing beneath the cover. The cover is configured to support one or more supply bag (including a last-bag). 
         [0025]    The dual chamber bag includes a valve portion in one embodiment. For example, the same sheets or plies used to form the fresh and spent containers can be used to form the valve chambers and fluid pathways of the valve portion. Or, the same sheets or plies can be used with a rigid path and valve forming member to form the valve portion. In another embodiment, the dual chamber bag is connected fluidly to a separate valve cassette. In any case, the valve portion or valve cassette is operable with a valve actuation portion of the control unit. The valve actuators in one embodiment are spring actuated closed and vacuum actuated open (against the spring). In this configuration, the valves close in a failsafe manner upon power loss or vacuum source failure. 
         [0026]    In this second embodiment, a priming cycle occurs as follows. The patient positions the end of the patient line so that its distal end is at substantially the same elevation as the one or more supply bag residing on top of the vacuum-tight cover. For example, the cover could include a hook onto which the patient hangs the patient line connector for priming. The control unit controls the vacuum source so that the valves to the fresh container of the dual chamber bag and to the patient line are opened. The control unit is programmed to keep these valves open for a certain amount of time or until a certain volume of fluid has gravity flowed to ensure that the fresh container and patient line are primed with fluid. The dual chamber bag weight is measured and recorded. 
         [0027]    Next, a drain from the patient&#39;s last-bag fill from night before occurs, while the fill volume in the fresh container of the dual chamber bag via the prime is heated. Here, the control unit causes the vacuum source to: (i) open a plurality of valves so that spent fluid can flow from the patient to the spent container of the dual chamber bag (for weighing); and (ii) pulls the last-bag spent fluid from the patient, e.g., at −1.5 psig under the vacuum-tight cover, against the head height difference between the temporary spent container of the dual chamber bag and the patient. The volume of fluid pulled from the patient is weighed and known. 
         [0028]    Once the fresh fluid is heated to a desired temperature and all spent last-bag fluid is pulled from the patient, the weigh scale and control unit record the combined weight of the fluid in the dual chamber bag. Then, the fill cycle starts and the heated fresh fluid is gravity fed to the patient, Here, the control unit causes the vacuum source to open one or more valve, enabling heated fluid from the fresh container of the dual chamber bag to be gravity fed to the patient&#39;s peritoneum. 
         [0029]    The line from the fresh container of the dual chamber bag to the patient is located at the bottom of the bag, such that air eggressing from the heated fluid floats to the top of the fresh container and only heated fresh fluid flows from the fresh container to the patient. In an alternative embodiment, an integral air separation chamber is provided in communication with the fresh container to collect air eggressing from the heated fluid. As fluid exits the heated supply bag, the weigh scale or load cell weighs and records the amount of fluid that has been delivered to the patient, which is seen as the loss in weight in the dual chamber bag from the total combined weight of the dual fills described previously. Once the programmed volume of fluid is delivered the patient or the scale no longer senses a drop in weight, the fill to the patient portion of the fill cycle is completed, one or more valve is closed, and the weight remaining in the dual chamber bag is recorded by the weigh scale and control unit. The control unit calculates the drain and fill volumes by subtracting the pre- and post-scale weights for both drain and fill cycles. 
         [0030]    After completion of the fill-to-patient portion of the fill cycle, the control unit causes the vacuum source to close at least the patient and drain valves for a dwell period in which the first supply of fluid is allowed to reside in the patient&#39;s peritoneum, absorbing waste products through diffusion and osmosis. During the dwell period, the control unit causes the vacuum source to open one or more valve, enabling fluid from the same or different dextrose supply bag to refill the fresh container of the dual chamber bag, so that it can be preheated for the next fill-to patient cycle. The increase in weight is again recorded. If it has not already happened, the control unit can also cause the vacuum source to open one or more valve, enabling the initial spent last-bag fluid to be gravity fed from the temporary drain chamber of the dual chamber bag to the final drain container or house drain. 
         [0031]    After the dwell, the next drain cycle occurs, wherein the vacuum source pulls spent fluid from the patient against the head height difference to the temporary spent container of the dual chamber bag. The incremental gain of weight due to the fluid reaching the temporary spent container is recorded. As soon as the first fill of spent fluid is pumped from the patient, the newly heated fresh fluid can be gravity fed from the fresh container of the dual chamber bag to the patient. The incremental loss in weight is recorded as the second fill volume. If the supply bags contain the prescribed fill volume, the recorded and prescribed volumes serve to double-check one another. 
         [0032]    Next, the second dwell period begins and the above-described process is repeated. Eventually a last-bag volume of fresh dialysate is delivered to the patient, which is allowed to dwell in the patient until a new therapy is begun the next day or evening. 
         [0033]    Either primary embodiment can be run to perform full fill, dwell and drain cycles or perform same partially, e.g., in a tidal mode type of modality. In the end a difference in the amount of fluid removed from the patient versus the amount of fluid delivered to the patient is calculated and represents ultrafiltrate or UF. The UF therapy prescription is set so that at the end of treatment the patient reaches his or her “dry weight”. The twenty-four hour UF calculation uses the last-bag volume from the night before and thus involves filling and draining from two treatments. 
         [0034]    It is therefore an advantage of the embodiments described herein to provide an improved dialysis system. 
         [0035]    It is another advantage of the embodiments described herein to provide a gravity fill dialysis system for patients who sleep on the floor or low to the ground. 
         [0036]    It is a further advantage of the embodiments described herein to provide a gravity fill dialysis system employing simplified pneumatics and/or hydraulics. 
         [0037]    It is yet another advantage of the embodiments described herein to provide a gravity fill dialysis system that employs a simplified disposable set or unit. 
         [0038]    It is yet a further advantage of the embodiments described herein to provide a gravity fill dialysis system that can be adapted for different therapy modalities. 
         [0039]    It is still another advantage of the embodiments described herein to provide a gravity fill dialysis system that is relatively gentle on the patient. 
         [0040]    It is still a further advantage of the embodiments described herein to provide a gravity fill dialysis system that achieves maximum flowrates, allowing for maximum dwell times and clearances. 
         [0041]    Moreover, it is an advantage of the embodiments described herein to provide gravity fill, vacuum drain dialysis system. 
         [0042]    Additional features and advantages of the present invention are described in, and will be apparent from, the following Detailed Description of the Invention and the figures. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0043]      FIG. 1  is a perspective view of one primary embodiment of an automated peritoneal dialysis system driven by gravity and vacuum. 
           [0044]      FIG. 2  is a schematic view of one embodiment for the disposable portion, valve, vacuum lines, electrical lines, control unit and control scheme of the system shown in  FIG. 1 . 
           [0045]      FIG. 3  is a perspective view of one embodiment for the heater and associated stand of the system shown in  FIG. 1 . 
           [0046]      FIG. 4  is a perspective view of one embodiment of a multi-tube valve actuator used with the automated peritoneal dialysis system driven by gravity and vacuum. 
           [0047]      FIG. 5  is a diagram showing the volume of fluid drained versus time of drain cycle for two patients. 
           [0048]      FIG. 6  is an elevation view of a second primary embodiment of an automated peritoneal dialysis system driven by gravity and vacuum. 
           [0049]      FIGS. 7A and 7B  are front elevation and top plan views, respectively, of one embodiment of a control unit with an integrated heater and load cell for the system of  FIG. 6 , wherein a vacuum-tight cover of the system is removed. 
           [0050]      FIGS. 8A and 8B  are front elevation and top plan views, respectively, of the apparatus of  FIGS. 7A and 7B  shown with the vacuum-tight cover in place. 
           [0051]      FIG. 9  is a top view of one embodiment for a disposable weigh/supply bag including a valve portion and associated tubes of the system shown in  FIG. 6 . 
           [0052]      FIG. 10  is a side view the disposable weigh/supply bag, valve and tubes of  FIG. 9 . 
           [0053]      FIGS. 11 to 14  illustrate one machine configuration for the second primary embodiment of the system of  FIG. 6 . 
           [0054]      FIG. 15  illustrates a disposable set that can be used with the second primary embodiment. 
           [0055]      FIGS. 16 through 19  illustrate various stages in the setup sequence for an alternative arrangement for the second primary embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0056]    Referring now to  FIGS. 1 to 3 , a first primary embodiment of an automated peritoneal dialysis (“APD”) system is illustrated by system  10 . System  10  includes an adjustable stand  12 , which in an embodiment is made of a relatively strong, lightweight and low cost metal or hard plastic. Stand  12  can for example be aluminum, steel or some combination of metal and plastic. Adjustable stand  12  includes an inner tube or stem  14 . Inner tube or stem  14  is sized to slide within an outer tube  16 . The patient or caregiver sets the overall height of stand  12  by moving inner tube  14  up or down with respect to outer tube  16  to a desirable position. Afterward, the patient or caregiver locks the inner tube in place relative to outer tube  16  via a suitable locking mechanism  18 . Outer tube  16  is fastened to, welded to or formed integrally with a set of legs  20 , which hold and balance tubes  14  and  16  and the apparatuses connected thereto. Casters or wheels  22  are coupled at the ends of legs  20 , so that system  10  can be maneuvered easily. One or more of casters  22  can have a locking mechanism to lock system  10  at a desired location. 
         [0057]    As seen more closely in  FIG. 3 , inner tube  14  is connected to and supports a medical fluid heater  30 . Medical fluid heater  30  can use any mode of heat transfer suitable to heat liquid within one or more medical fluid supply bag, such as resistance plate heating, radiant heating, convective heating, and any suitable combination thereof. Heater  30  in the illustrated embodiment includes a clam shell construction having a lid  32  and a base  34 . In an embodiment, the heater elements and associated heating are located in base  34 . Alternatively, the elements or heating pads are located in lid  32 . Further alternatively, the heating elements or pads are located in both lid  32  and base  34 . 
         [0058]    In the illustrated embodiment, heater  30  is sized and configured to hold a pair of supply bags  24   a  and  24   b , such that one supply bag  24   a  rests on top of the second supply bag  24   b . A single supply bag is provided alternatively. Further alternatively, three or more supply bags  24  (referring collectively to supply bags  24   a ,  24   b , etc.) are provided. One of supply bags  24  can be a last bag that holds a last-bag volume of fluid that remains at the end of treatment in the patient&#39;s peritoneum until the next treatment. Heater  30  can alternately hold two supply bags placed side by side with a third bag placed optionally on top of and between the bottom two bags. 
         [0059]    As illustrated, base  34  defines one or more opening and/or notch  36 . Openings  36  enable supply tubes  26   a  and  26   b  to extend from supply bags  24   a  and  24   b , respectively, while enabling lid  32  and base  34  to be closed together tightly around bags  24   a  and  24   b . This configuration helps to prevent supply tubes  26   a  and  26   b  from becoming crimped. 
         [0060]    As seen in  FIG. 2 , supply bags  24   a  and  24   b  can include or define one or more port  28 , which is configured to accept a temperature sensing device  38  in a sealed manner. Temperature sensing device  38  can be any suitable device, such as a thermistor, thermocouple or resistance temperature device (“RTD”) sensor. In the illustrated embodiment, temperature sensing devices  38  measure the temperature of heated dialysis directly. That is, temperature sensing devices  38 . actually contact the dialysate. In an alternative embodiment, the temperature sensing devices  38  are located for example on one or more of the inner surfaces of lid  32  and base  34  and contact the bag material instead. Here, the temperature of the bag material is assumed to reach the temperature of the dialysate over time. Alternatively, if a slight difference between bag and dialysate temperature is always present, that difference can be determined and compensated for. 
         [0061]      FIG. 1  shows that outer tube  16  supports a control unit  40 . Control  40  includes a video monitor  42 , such as a liquid crystal display (“LCD”), or other suitable type of display. Video monitor  42  in an embodiment operates with a touch screen overlay (not illustrated), which enables the operator to input commands into control until  40 . Alternatively, control unit  40  includes off-screen input devices  44 , which can be membrane switches, knobs, push-buttons or other types of electromechanical input devices. 
         [0062]    As seen in  FIG. 2 , video monitor  42  and input devices  44  are connected and controlled by one or more printed circuit board  46 , which includes among other components random access memory (“RAM”), read only memory (“ROM”)  46   b , a microprocessor  46   c  and a power supply  46   d . Code and data are stored on ROM  46   b  and RAM  46   a  as is known in the art. Processor  46   c  cooperates with RAM  46   a  and ROM  46   b  to control each of the functions of system  10 , such as control of heater  30 , the control of ultrafiltration removal and the control of the valves of system  10  via electrical solenoids  48   a  to  48   e . Alternatively or additionally, control unit  40  controls those functions using an application specific circuit (“ASIC”), solid state relay, MOSFET and the like. Power supply  46   d  provides the necessary power (amount and type) to solenoids  48   a  to  48   e  and heater  30 . To the extent that system  10  includes components requiring different types or ranges of power, a plurality of power supplies, such as power supply  46   d , can be provided. 
         [0063]    Solenoids  48   a  to  48   d  control valves  52   a  to  52   d , respectively of multi-way valve assembly  50  via vacuum lines  66   a  to  66   e , respectively. Valve assembly  50  in an embodiment includes a housing  54 , which defines or provides chambers for valves  52  (referring collectively to valves  52   a  to  52   d ). Housing  54  can be made of plastic or metal as desired. Valve assembly  50  can be attached to or integrated with the housing of control unit  40 . 
         [0064]      FIG. 4  illustrates one suitable configuration for multi-way valve assembly  50 . Here, valve assembly  50  is a custom manufactured assembly that is integral with the door of control unit  110  and allows the tubing set ( FIG. 15 ) to be loaded for treatment. Valve assembly  50  provides six pinch valves  52   a  to  52   d  (only four used in  FIG. 2 ). Springs  72  push valve heads to pinch a tube closed. A vacuum is applied to compress springs  76  and open a fluid pathway. In  FIG. 4 , solenoids  48   a  to  48   f  are mounted with multi-way valve assembly  50 . Solenoids  48   a  to  48   f  operate as described below in connection with  FIG. 2 . 
         [0065]    In  FIG. 2 , multi-way valve assembly  50  operates directly with supply lines  26   a  and  26   b , a patient line  56  (which is connected to a port coupled to the patient, the patient port coupled fluidly to a catheter that extends inside the patient to the patient&#39;s peritoneal cavity). A fourth drain line  58  runs from the multi-way connection within valve assembly  50  to a drain container  60 . 
         [0066]    Drain container  60  includes a spent fluid inlet  62   a , which is coupled to drain line  58 . Drain container  60  also includes a spent fluid outlet  62   b  which is coupled to a fifth vacuum line  66   e . A hydrophobic membrane  64  is placed in outlet  62   b  of drain container  60  in one embodiment to preclude spent fluid from entering vacuum line  66   e . Also, as seen in  FIG. 2 , inlet  62   a  and outlet  62   b  of drain container  60  are placed elevationally at the top of drain container  60 , such that spent fluid entering inlet  62   a  tends to fall via gravity to the bottom of drain container  60  and fill the drain container upwardly. Thus the configuration of drain container  60  itself tends to preclude spent dialysate from entering vacuum line  66   e.    
         [0067]    A vacuum source  70  is connected to the inlet ends of solenoids  48   a  to  48   e  via a vacuum manifold  72 . Vacuum source  70  and manifold  72  are configured to maintain a negative pressure on the inlet ends of solenoids  48   a  to  48   e  at all times while vacuum source  70  is powered. Vacuum source  70  in one embodiment includes a vacuum regulator and vacuum pump combining to provide a variable vacuum output, which can supply a negative pressure to valves  52   a  to  52   d  and drain container  60  from anywhere between zero psig up to −1.5 psig and beyond. One suitable vacuum regulator for vacuum source  70  is an ITV  209  model electronic vacuum regulator provided by SMC Corporation of America, Indianapolis, Ind. The regulator is placed upstream of the vacuum pump in one embodiment. 
         [0068]    In the embodiment illustrated in  FIG. 2 , valves  52   a  to  52   d  are spring loaded, failsafe valves. Valves  52   a  to  52   d  each include a plunger  74  which is compressed via a spring  76  to pinch or close off patient line  56 , drain line  58 , supply line  26   a  and supply line  26   b , respectively. To open one or more of those lines, a vacuum or negative pressure is applied to the valve source  70 , manifold  72 , the opening of one or more electrically operated solenoid  48   a  to  48   e , and the appropriate vacuum line  66   a  to  66   d . Valves  52   a  to  52   d  are said to be failsafe because upon a power loss or loss of vacuum, springs  76  cause each of the plungers  74  to close their respective tube or line, precluding any further flow of fresh or spent dialysate. 
         [0069]    PCB  46  controls electrically operated solenoids  48   a  to  48   e  in an embodiment by sending on/off electrical signals to the solenoids over electrical lines  78   a  to  78   e , respectively. The program stored on controller or PCB  46  causes electrical signals to open one or more of solenoid valves  48   a  to  48   e  at an appropriate time to establish a desired vacuum flow path and/or draw a vacuum on drain container  60 . 
         [0070]    As seen in  FIGS. 1 and 2 , drain container  60  is supported by a scale  80 . Scale  80  in turn is connected to mechanical ground  82  via a load cell or strain gauge  84 . Load cell or strain gauge  84  sends a signal to controller or PCB  46  via a signal line  86   a . The signal from strain gauge  84  can for be example a variable 4 to 20 milliamp or 0 to 10 VDC signal, which varies depending upon the amount of spent fluid that has been pulled by vacuum to drain container  60 . If the strain gage is bumped, an incorrect weight signed will be produced momentarily. Controller or PCB  46  can include averaging routines in its software that accommodates these anomalies. An accelerometer can be attached to the load cell, so that the controller will know when the load cell has been bumped. Anomalous readings are then excluded from the averaging routines. Similar variable signals are also sent from temperature measuring devices  38  along lines  86   b  and  86   c , respectively, to controller or PCB  46 . Controller  46  also receives inputs (e.g., on/off) from manually operated input devices  44  via input signal lines  86   d.    
         [0071]    On the output end, besides output lines  78   a  to  78   e  (e.g., on/off) to solenoids  48   a  to  48   e , respectively, controller  46  controls variable vacuum source  70  via a variable signal along output line  88   a . Controller  46  further controls the output to heater  30  via a variable signal along outlet line  88   b . In another embodiment, the outlet to heater  30  is an on/off type output, which is varied in frequency to control a duty cycle of heater  30 . 
         [0072]    Control unit  40  of System  10  is configured to optimize the rate at which fluid is removed from the patient&#39;s peritoneal cavity. Here, the rate at which the weight of fluid within drain container  60  changes over time is determined by dividing the difference in the signals sent by the strain gauge  82  along signal line  86   a  to controller  46  by a corresponding difference in time. The rate can be compared to an optimal rate stored in controller  46 . The signal from controller  46  along variable output line  88   a  to variable vacuum source  70  is then adjusted to adjust the amount of vacuum supplied along vacuum line  66   e  to drain container  60 . The vacuum is adjusted so that the actual rate of change of ultrafiltrate weight measured via strain gauge  84  meets the optimal drain or ultrafiltrate removal rate. 
         [0073]    In operation, system  10  initially performs a priming cycle. Here, the distill end  90  of patient line  56  is fixed at an elevational level that is at least substantially the same as supply bags  24   a  and  24   b .  FIG. 3  shows one embodiment for doing so, in which a clip or latch  92  is fixed to the base  34  of heater  30  and is configured to hold the end  90  of patient line  56  at a height that is at substantially the same as the height of supply bags  24   a  and  24   b . After the patient fixes patient line  56  as just described, the patient presses an input  44 . Control unit  40  causes each of valves  52   a  to  52   d  to be opened at an appropriate time to enable fresh dialysate to flow through each of supply lines  26   a  and  26   b , patient line  56  and drain line  58 , flushing air from those lines. 
         [0074]    Because fluid flow through patient line  56  is driven by gravity, the dialysate does not flow above end  90  positioned at the same elevation as supply bags  24   a  and  24   b . The prime cycle can be configured such that controller  46  of control unit  40  causes valves  52   a  to  52   d  to be opened for a preset amount of time or alternatively until a preset volume of fluid is sensed to have flowed through the tubes, after which all valves close in one embodiment. The closure of the lines at valve assembly  50  prevents fluid from flowing out the distal open end of the lines, e.g., at inlet  62   a  of drain container  60  of drain line  58 , due to the weight of the fluid column. The small inside diameter of the tubing used for the lines precludes air from flowing up into the tubing to relieve a vacuum that is created by the weight of the fluid column. Further, the closed valve assembly does not allow leakage of fluid. 
         [0075]    After prime, in one sequence of operation, system  10  performs an initial drain sequence in which spent dialysate leftover from the previous therapy is removed initially from the patient&#39;s peritoneal cavity. To do so, the patient removes the primed end  90  of patient line  56  from clip  92  of heater  30 . The patient connects the end  90  to a port stitched into the patient as is known in the art. The patient then presses an input  44  indicating that therapy can begin. For the initial drain, controller  46  of control unit  40  causes solenoids  48   a  and  48   b  to open. A corresponding vacuum is supplied via vacuum lines  66   a  and  66   b  to valves  52   a  and  52   b , respectively, to open those valves (pull them closed against the spring force). No vacuum is supplied to valves  52   c  and  52   d , so that the corresponding springs  76  cause the corresponding plungers  74  to pinch close both supply lines  26   a  and  26   b.    
         [0076]    Simultaneously, controller  46  causes solenoid  48   e  to open, which in turn allows a vacuum to be drawn along vacuum line  66   e , through hydrophobic membrane  64 , and into the chamber of drain container  60 . The vacuum in drain container  60  pulls fluid from the patient&#39;s peritoneal cavity, through patient line  56 , through drain line  58  and into container  60 , where it begins to fill to the container. As discussed above, feedback from strain gauge  84  cooperates with controller  46  and variable vacuum source  70  to optimize the rate at which fluid is pulled from the patient to drain container  60 . Because the patient drain is done via vacuum, the patient can be at a lower elevational level than drain container  60 , at the same level, or at a higher elevational level than drain container  60  that would nevertheless not be sufficient to drain the patient efficiently via gravity. 
         [0077]    The drain cycle in one embodiment is preformed using a profile, which optimizes the flow of fluid from the patient&#39;s peritoneum to drain container  60  to ensure that the patient is maintained in a comfortable state. To do so, drain flowrate is calculated from volume measurements in one embodiment to determine when the patient may be susceptible to discomfort. For example, the profile could divide the drain cycle into two phases, one which is a higher flow phase and another which is a lower flow phase. When the patient reaches the lower flow phase, the vacuum is adjusted to account for discomfort, which may occur at that lower flow. 
         [0078]    At the beginning of the drain cycle, the high flow phase can be performed using a relatively low suction pressure because the source of spent fluid is relatively abundant and flows readily and smoothly from the patient&#39;s peritoneal cavity. As the patient&#39;s peritoneum becomes more and more empty, and the source of spent fluid becomes increasingly less abundant, the drain flow starts to slow down.  FIG. 5  illustrates the “break point” concept that is understood in the art as a change in drain flow rate, which indicates that the peritoneum is relatively empty. System  10  then decreases the suction pressure to prevent it from causing pain to the patient. For example, the suction pressure is decreased from −1.5 psig to −1.2 psig. The profile is in this way adjusted to drain the patient as quickly, safely and comfortably as possible. 
         [0079]    Each patient can vary in terms of when the low flow phase occurs and how far the drain flowrate drops. For example, one patient may transition from the high flow phase to the low flow phase after 70% of their fill volume has been drained, whereas another patient may not transition until 90% of their fill volume has been drained. Also, the first patient&#39;s flow rate may drop to below 50 ml/min, while the second patient&#39;s flow rate may drop to below 25 ml/min when reaching the low flow phase. 
         [0080]    The chart of  FIG. 5  illustrates how patient drain rates can vary. Here, the initial drain rates for two patients are constant and track closely together for the first ten minutes of the drain cycle. At this time, and at a remaining volume of about 900 ml, the first patient&#39;s drain rate slows considerably over a “move-on” time of about eight minutes, at which point the drain cycle is stopped with approximately 550 ml of fluid remaining in the patient&#39;s peritoneum. The higher drain rate for the second patient on the other hand continues to about 13.5 minutes. At this time, and at a remaining volume of about 300 ml, the second patient&#39;s drain rate slows considerably over a “move-on” time of about five minutes, at which point the drain cycle is stopped with approximately 150 ml of fluid remaining in the patient&#39;s peritoneum. 
         [0081]    Based on the above-described physiological characteristics of the patient, the transition in suction pressure is made based upon a combination of flowrate and volume of fluid drained. Also, the “move-on” time needs to be adjusted so that the patient does not unduly waste therapy dwell time attempting to drain the last drop of spent fluid. 
         [0082]    The first fill cycle is then performed. In one embodiment, the fill cycle begins automatically after the initial drain, so that the patient can be asleep during this portion of the therapy if desired. In the fill cycle, controller  46  of control unit  40  causes either solenoid  48   c  or  48   d  to open, enabling a vacuum to open one of supply lines  26   a  or  26   b  via a respective valve  52   c  or  52   d . Also, controller  46  causes solenoid  48   a  to open, enabling a vacuum to open patient valve  52   a . Fresh dialysate is then enabled to flow from one of the supply bags  24   a  or  24   b , through the interface at multi-way valve assembly  50 , through patient line  56 , and into the peritoneal cavity of the patient. The flow of fluid in the patient fill is performed via gravity. Accordingly, supply bags  24   a  and  24   b  should be set via tubes  14  and  16  and locking device  18  to be at a minimum head height distance above the patient&#39;s peritoneal cavity, such as 3 ft. (0.9 m) above the peritoneal cavity. Assuming an inner diameter of 4 mm for supply lines  26   a  and  26   b  and patient line  56 , the gravity fed flow of dialysate will reach over 200 ml/min and could reach as high as 300 ml/min. 
         [0083]    After the known amount of fresh fluid is delivered to the patient, a dwell cycle occurs in which the fresh fluid is allowed to dwell within the patient&#39;s peritoneum, while diffusive and osmotic forces remove waste and excess water from the patient. The dwell period can be varied as needed but generally lasts for one to two hours depending upon the dialysis therapy prescription. After the dwell cycle occurs, the above, drain, fill and dwell cycles are repeated one or more times as prescribed by a physician. The final fill can be performed using a last-bag, which delivers a final amount of fluid to the patient. That final amount of fluid resides within the patient&#39;s peritoneal cavity until the next time therapy is performed. System  10  also includes one or more pressure and/or flow sensor used for alarm purposes, e.g., to detect a kinked or detached line. The pressure/flow sensor can be configured to sense the pressure/flow of at least one of the patient line, the drain line, the supply line and any one of the vacuum lines/manifold. 
         [0084]    At the end of therapy, the total amount of fluid collected in container  60  is known. Further, the total amount of fluid delivered from supply bags  24   a  and  24   b , assuming all fluid is delivered from the supply bags to the patient, is also known. The additional weight of spent fluid in container  60  over that delivered from supply bags  24  to the patient is known as ultrafiltrate, which is the excess fluid or water that is retained by the patient between treatments due to renal failure. Because a good portion of the fluid within container  60  is from the previous therapy&#39;s last-bag or last fill, the twenty-four hour ultrafiltrate volume takes into account the previous night&#39;s volume of last fill, which is typically close or equal to the last-bag fill of the instant therapy. 
         [0085]    In an embodiment, the connection of drain line  58  and vacuum line  66   e  to inlet and outlet  62   a  and  62   b , respectively, of drain container  60  is done via a quick disconnect or other readily assembled and disassembled connection. This is done so that the patient or caregiver in the morning or otherwise after therapy can disconnect drain container  60  readily from those lines to pour its contents into a house drain, such as a toilet. Scale  80  is accordingly configured such that drain container  60  can be removed from and reloaded into same readily. 
         [0086]    Referring now to  FIGS. 6 to 19 , a second primary embodiment of a system driven by gravity and vacuum is illustrated by system  100 . System  100  includes many of the same components as does system  10 . Where possible, these components are numbered the same. For example, system  100  includes a patient line  56  having a distill end  90 . System  100  also includes a drain line or tube  58 . System  100  further includes one or more supply bag  24  (referring generally to one of supply bags  24   a ,  24   b , etc.). Supply bag  24  communicates fluidly with a supply line  26 . System  100  differs in one respect from system  10  in that the load cell measures both the volume fluid that is delivered to the patient and the volume of fluid that is drained from the patient. 
         [0087]    System  100  also includes valves that allow fluid to flow to a desired destination during a particular cycle during therapy. The valves in one embodiment are failsafe, spring/vacuum actuated valves, such as valves  52   a  to  52   d  shown in connection with  FIG. 10 . Those valves are located inside of a control unit  110  of system  100 . The valves within control unit  110  include a spring actuator, such as spring  76  and plunger or pincher, such as plunger  74  of system  10 . The opening and closing of the valves of system  100  in one embodiment is the same as that described above in connection with system  10 . Accordingly, it is not necessary to re-illustrate show or re-describe such operation. 
         [0088]    Similarly, system  100  includes a heater  130  and load cell  184 . Heater  130  can be of any of the types of fluid bag warmers described above for heater  30 . Heater  130  in system  100  however is located on the top of control unit  110 . The heater pan is placed on or is incorporated with a load cell  184 . Load cell  184  performs the same function in system  100  as strain gauge  84  of system  10 . That is, load cell  184  measures the weight of fluid pulled by vacuum into a dual chamber bag  120 . Here additionally, load cell  184  measures the weight of fresh dialysate supplied to the patient. Load cell  184  in system  100  is configured to send a signal to a controller or PCB (configured with each of the alternatives described above for PCB  46 ) located within control unit  110  based on a compressive force due to the weight of fluid within dual chamber bag  120  (in the illustrated embodiment of system  10 , strain gauge  84  provides a signal based on a tensile force applied to scale  80  via the weight of fluid drawn into control container  60 ). Thus while heater  130  and load cell  184  provide similar functions as heater  30  and load cell  84 , their physical configuration and operation are different. 
         [0089]    As illustrated, control unit  110  includes input devices  44  and a video monitor  42  as described above in connection with control unit  40  of system  10 . The electrical layout of  FIG. 2  for system  10  is also largely applicable to the electrical layout of system  100 , which is housed inside control unit  110 . That is, a PCB including RAM, ROM, a microprocessor (ASIC or MOSFET) and one or more power supply receives varying amperage or voltage signals from load cell  184  and one or more temperature measuring device (not illustrated), which measures the temperature of fresh dialysate located within a fresh container  122  of dual chamber bag  120  directly or at the outer surface of bag  120  directly adjacent to the heated supply within fresh container  122 . 
         [0090]    The electrical scheme of system  100  also includes a variable electrical output to a variable vacuum source (similar to that provided along line  88   a  to variable vacuum source  70  of system  10  shown in  FIG. 2 ). Moreover, the controller or PCB of system  100  sends a variable or duty cycle output to heater  130  (as is done in connection with controller  46  and heater  30  of system  10 ). Control unit  110  in an embodiment housings electrically actuated solenoids (such as solenoids  48   a  to  48   e  of system  10 ), which allow or disallow a vacuum to be applied along vacuum lines (such as lines  66   c  to  66   e  of system  10 ) to the valves (described above) and to a vacuum chamber established beneath a vacuum tight cover  102  (shown in  FIGS. 8A ,  8 B,  18  and  19 ). System  100 , like system  10 , includes necessary vacuum lines, which in an embodiment are housed inside control unit  110 . 
         [0091]    Cover  102  is sealed via seal  104  located around the outside of load cell  184  and heater  130  to the top of control unit  110 . Seal  104  can be a soft rubber or sponge rubber seal, for example neoprene rubber or closed cell sponge silicone rubber. Seal  104  could also be constructed of an elastomer, which is extruded or molded in a geometric shape that seals well under a vacuum. A V-shaped gasket with its open side facing atmospheric pressure is one example of a suitable geometric vacuum seal. The weight of the cover may be sufficient to hold the cover in place. Clamping devices  106 , such as spring loaded twist clamps, can also be provided to hold cover  102  in a sealed relationship with the top of control unit  110 . In an embodiment, hinges  108  are provided such that cover  102  swings hingedly up from the top of control unit  110 . The weight of fluid within supply bag  24  also helps to seal cover  102  against the top of control unit  110 . That weight may be enough to maintain the seal under the relatively low negative pressures used in system  100 , e.g., on the order of between 0 and −1.5 psig. Also, the negative pressure itself would tend to pull lid  102  into the gasket  104 , precluding the need for clamping devices  106  and/or hinges  108 . 
         [0092]    System  100  can also include a reusable drain container or disposable drain bag (not illustrated and referred to hereafter as drain container for simplicity), which connects to and communicates fluidly with drain line  58 . In system  100  however the drain container is not weighted and is not used in the same way as in system  10  to determine and control ultrafiltration removal. The drain container of system  100  here is used to collect spent dialysate. It is configured to be located beneath control unit  110 , so that spent fluid from spent container  124  of dual chamber bag  120  can be gravity fed to the drain container. 
         [0093]    The control of fluid volume removed and flowrate is done using dual chamber bag  120 , load cell  184  and the switching of valves (which are spring closed and vacuum opened in one embodiment as described above in connection with valves  52   a  to  52   d  of  FIG. 10 ). As seen in  FIGS. 9 and 10 , dual chamber bag  120  includes a heated container  122  and a temporary spent container  124 . In an embodiment, flexible membranes used to form heating supply and temporary drain bag containers  122  ad  124 , respectively, of dual chamber bag  120  are also used to form at least a portion of valve portion  128 . Flow paths  126   a  to  126   d  for example can be thermal formed and one of the upper or lower plies of dual chamber bag  120 . In an alternative embodiment, two of the plies used to form containers  122  and  124  are sealed to a rigid member to form valve portion  128 . Further alternatively, valve portion  128  is separate from bag  120  and connected fluidly thereto via separate tubes forming part of flow paths  126   a  to  126   d.    
         [0094]    Flow paths  126   a  to  126   d  each communicate fluidly with a valve seat  136   a  to  136   d , respectively. An additional valve seat  136   e  is placed at the intersection of flow paths  126   b ,  126   c  and patient line  56  for reasons discussed below. Heated fresh container  122  communicates fluidly with supply line  26  and flow paths  126   a  and  126   b . Temporary spent container  124  communicates fluidly with drain line  58  and flow paths  126   c  and  126   d . Both containers  122  and  124  communicate fluidly with patient line  56 , necessitating fifth valve  136   e.    
         [0095]    As seen in  FIG. 6 , control unit  110  is placed on a nightstand or other location that is elevationally above the patient&#39;s peritoneum. Dual chamber bag  120 , resides above control unit  110 , and therefore resides above the patient&#39;s peritoneum. Further, supply bag  24  is placed elevationally above dual chamber bag  120  and can gravity fill dual chamber bag  120 . Dual chamber bag  120  in turn can gravity fill the patient&#39;s peritoneum. Furthermore, as discussed before spent dialysate stored temporarily spent container  124  of dual chamber bag  120  can be gravity filled into the drain container or drain bag located for example on the floor of the bedroom or other room in which therapy is taking place. 
         [0096]      FIGS. 11 to 19  illustrate one configuration and set-up sequence for system  100 .  FIG. 11  illustrates that load cell  184  is mounted to a base plate  186 . In one embodiment, load cell  184  is a dual load cell, which provides redundancy. Plate  186  can be hard plastic or metal, e.g., stainless steel, steel or aluminum.  FIG. 12  illustrates that a heated bag holder  130  is mounted to load cell  184 . Heated bag holder  130  includes heating elements (not illustrated) that heat a tapered bottom  132  and sides  134  forming the holder. Tapered bottom  132  tips the bags downwardly towards the open (line connection) end of heated bag holder  130 , which helps to direct fluid out of bags  122  and  124 . The transition from bottom  132  to sides  134  is chamfered or rounded to help support bags  122  and  124  and increase heater contact area. 
         [0097]      FIG. 13  illustrates that multi-way valve assembly  50  is also mounted to base plate  186 . Multi-way valve assembly  50  can be the six pinch valve unit shown and described in connection with  FIG. 4 .  FIG. 14  shows plate  186 , heated bag holder  130  and multi-way valve assembly  50  mounted into control unit  110 . Control unit  110  includes video monitor  42  and input devices  44  as described herein. Control unit also includes or defines a slot  112  for connecting patient line  56  and drain line  58  to heating bag  122  and drain bag  124 , respectively. Control unit also includes or defines a line holder  114 , e.g., a press-fit line holder, for fixing distal end  90  of patient line  56  for priming. 
         [0098]      FIG. 15  shows one configuration for a disposable set  190  of system  100 . Disposable set  190  includes patient line  56  and drain line  58 , which are connected fluidly to a cross  188 . Supply line  26  tees into patient line  56  at tee  192 . Patient line  56  is connected to cross  188  via elbow  194 , which orients the lines properly for the loading of the area of cross  188  of disposable set  190  into control unit  110 . The distal ends of lines  26 ,  56  and  58  are provided with connectors and clamps as needed. 
         [0099]      FIGS. 16 to 19  show a slightly different configuration for the second primary embodiment of system  100 . Here, a separate heating bag  122  and supply bag  124  are used instead of dual chamber bag  120  having separate containers  122  and  124 .  FIG. 16  shows that the area of cross  188  of disposable set  190  has been loaded into control unit  110 , and in particular behind the hinged door of multi-way valve assembly  50 . The lines are placed in operable position with selected pinch valves of multi-way valve assembly  50  so that they can be opened and closed selectively. Distal end  90  of patient line  56  is fitted into line holder  114  for priming. Heating bag  122  is placed in and supported by heated bag holder  130 . Patient line  56  is connected to the heating bag. 
         [0100]    In  FIG. 17 , empty, interim drain bag  124  is placed onto heating bag  122 . Drain line  58  is connected to the drain bag. As discussed above, in this configuration heating bag  122  and drain bag  124  are separate bags as opposed to being part of a single dual chamber bag  120 . Either configuration can be used. Here, the previous day&#39;s supply bag can be used as the current day&#39;s empty interim weigh bag to reduce cost and the volume of disposable waste. In  FIG. 18 , cover  102  is placed over bags  122  and  124 . In  FIG. 19 , supply bag  24  is placed onto cover  102 . Supply line  26  is connected to supply bag  24 . System  100  is now ready to be primed. 
         [0101]    Whether or not dual chamber bag  120  is used or separate bags  122  and  124  are used, in the priming cycle of system  100 , valve seats  136   a  to  136   e  are each opened allowing the fluid to flow throughout each of the lines. The priming purges all of the lines of air including the patient line  56 . The absence of air in the lines allows load cell  184  to accurately measure the volume of fluid delivered to the patient and drained from the patient and also prevents the delivery of air to the patient. The prime does not have to fully fill heater bag  122  or dual chamber bag  120  because gravity will prevent air from being delivered from heated fresh container or bag  122  to the patient. Heated fresh container or bag  122  may be provided with a vent (not illustrated), for example including a hydrophobic membrane, which allows air to be purged from container  122  as it is filled with fluid. 
         [0102]    The controller or PCB within control unit  110  causes the vacuum source to open the valves at valve seats  136   a  and  136   e , which enables fresh fluid to flow from supply bag  24 , through supply line  26 , through flow path  126   a , into and filling lower supply container  122  of dual chamber bag  120  (or separate bag  122 ), which contacts heater  130 , through flow path  126   b , through patient line  56  to distal end  90 . As above with system  10 , system  100  includes an apparatus that holds distal end  90  of patient line  56  at least substantially at the same elevational height as supply bag  24  during the prime cycle period. When prime is complete the patient connects distal end  90  of patient line  56  to the port stitched into the patient, which port communicates via an inserted catheter with the patient&#39;s peritoneum. During prime, the heating of fresh dialysate within supply container or bag  122  can begin. 
         [0103]    As with system  10 , the next step in the therapy in one embodiment is to remove the last-bag volume from the patient&#39;s last treatment. Before this is done, however, the weight of fresh fluid that has entered fresh container or bag  122  is noted. Afterwards, the vacuum source is allowed to: (i) open the valves at valve seats  136   c  and  136   e  and (ii) draw a vacuum within vacuum type cover  102  (valves at valve seats  126   a  and  126   b  opened previously for prime are now closed). This action causes spent fluid to be pulled from the patient&#39;s peritoneum, through line  56 , and into temporary spent container  124  of dual chamber bag  120 . Thus at the same time a batch of fresh dialysate from the prime is being heated, the previous last-bag volume can be pulled from the patient. The additional weight of spent fluid entering dual chamber bag  120  is noted. 
         [0104]    As soon as the volume of fluid in supply container  122  is heated to its desired temperature, it can be delivered to the patient (assuming this does not occur before the last-bag volume is removed completely from the patient). Assuming that the heating takes longer than the last-bag removal, the temporary spent container  124  can be drained to the drain bag while the fresh fluid in the fresh container  122  is being heated. Here, control unit  110  causes the valve operating with valve seat  136   d  to open path  126   d , enabling spent fluid to gravity drain from the temporary spent container  124  to the drain bag. If this portion of the drain occurs before the fill occurs, the drop in weight within dual chamber bag  120  can be noted via the load cell  184 , so that a double-checking of the amount of fluid delivered to and from each container  122  and  124  can be made. 
         [0105]    Once the fresh fluid in container  122  is heated to its desired temperature, the heated fresh dialysate is delivered through flow path  126   b , passed valve seats  136   b  and  136   e , through patient line  56  and into the patient&#39;s peritoneum. Gas eggressing from the dialysate as its being heated collects at the top of fresh container  122 . The interface between flow path  126   b  and fresh container  122  is therefore located at or near the bottom of fresh container  122 , such that only liquid flows from container  122  through patient line  56 . After the known amount of fresh fluid is delivered to the patient, a dwell cycle occurs in which the fresh fluid is allowed to dwell within the patient&#39;s peritoneum, while diffusive and osmotic forces remove waste and excess water from the patient. The dwell period can last for one to two hours for example depending upon the dialysis therapy prescription. 
         [0106]    Depending on the state of dual chamber bag  120  or separate bags during the dwell period, different fill, drain and valving sequences can occur. For example, if not already done, the controller of system  100  during the dwell cycle can cause the last-bag spent dialysate residing in temporary spent container or bag  124  to be gravity fed into the drain container. This second half fill can occur while a second fill of fresh dialysate into container  122  or bag occurs for heating. The drain of the interim spent container or bag  124  can occur simultaneously with the replenishing of the fresh container or bag  122  or sequentially since these weights are not required for the calculation. Once the first fill is removed form the patient and the second fill is heated to its desired fluid temperature, the second fill can be delivered to the patient for a second dwell period and so on. 
         [0107]    More than likely, the initial last-bag volume has been sent to the final spent container before the first dwell occurs, so a second batch of fresh dialysate can be delivered from supply bag  24  to fresh container or bag  122  of dual chamber bag  120  for heating. Because temporary spent container or bag  124  is empty when this happens, system  100  knows the weight of the second fill fluid is equal to the weight in container or bag  122  at the end of the second fill. When the first dwell period is over, spent fluid is vacuum driven to temporary spent container or bag  124 , while fluid is being heated within fresh container or bag  122 . Once the first fill is removed form the patient and the second fill is heated to its desired fluid temperature, the second fill can be delivered to the patient for a second dwell period and so on. System  100  can deliver a last-bag volume at the end of treatment, which operates as described above. 
         [0108]    Both systems  10  and  110  can perform a tital flow peritoneal dialysis treatment as an alternative to the batch type therapies just described. In tital flow systems, only a portion of the spent fluid is removed from the patient&#39;s peritoneum. The removed spent portion is back filled with fresh fluid. The partial exchanges occur more frequently than is done typically with batch type therapies. Tital flow therapies are accordingly more continuous. 
         [0109]    It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present invention and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims.