Abstract:
A peritoneal dialysis machine including: a housing; a mechanically actuated piston head extending from a pump actuator housed by the housing, the mechanically actuated piston head positioned to extend towards and away from a fluid pumping cassette, the fluid pumping cassette coupled operably to the housing such that a flexible membrane of the fluid pumping cassette faces the piston head; a pressure sensor positioned by the housing adjacent to the mechanically actuated piston head so as to sense a pressure of a medical fluid moved by the mechanically actuated piston head within the fluid pumping cassette; and a vacuum chamber formed about the mechanically actuated piston head, the vacuum chamber holding a vacuum that sucks the flexible membrane of the fluid pumping cassette onto the mechanically actuated piston head as the mechanically actuated piston head extends away from the fluid pumping cassette.

Description:
PRIORITY CLAIM 
     This application claims the benefit of U.S. patent application Ser. No. 10/975,733, filed Oct. 27, 2004, entitled “Improved Priming, Integrity and Head Height Methods and Apparatuses For Medical Fluid Systems” which claims the benefit of U.S. Provisional Patent Application No. 60/515,815, filed Oct. 28, 2003, entitled “Improved Priming, Integrity and Head Height Methods and Apparatuses for Medical Fluid Systems”, the entire contents of which are hereby incorporated by reference and relied upon. 
    
    
     BACKGROUND 
     The present invention relates generally to medical fluid systems and more particularly to the testing and priming of such systems. 
     It is known in peritoneal dialysis systems to perform integrity tests that attempt to verify that the numerous fluid valves in a disposable cassette do not leak, that leaks do not occur between multiple pump chambers in the cassette, that leaks do not occur across fluid pathways, and that an isolation occluder, which is intended to stop liquid flow in fluid lines connected to the cassette in the event of a system malfunction, is performing that procedure properly. In one known wet leak test described in U.S. Pat. No. 5,350,357, a disposable cassette is loaded into a peritoneal dialysis cycler and the solution bags are connected. The test consists of the following steps: 
     (i) a negative pressure decay test of the fluid valve diaphragms is performed; 
     (ii) a positive pressure decay test of the fluid valve diaphragms is performed; 
     (iii) a positive pressure decay test is performed on the first pump chamber, while a negative pressure decay test is performed on the second pump chamber; 
     (iv) a negative pressure decay test is performed on the first pump chamber, while a positive pressure decay test is performed on the second pump chamber; after which 
     (v) both pump chambers are filled with a measured volume of fluid, all fluid valves are opened and the occluder is closed, positive pressure is applied to both pump chambers for a period of time, after which the volume of fluid in each pump chamber is measured again to determine if any fluid has leaked across the occluder. 
     As indicated, the above testing procedure is performed after solution bags are connected to the peritoneal dialysis system. If integrity of the cassette or tubing is faulty, the sterility of the solution bags becomes compromised. In such a case, both the disposable cassette and solution bags have to be discarded. Additionally, it is possible that liquid from the solution bags can be sucked into the machine&#39;s pneumatic system, causing the pneumatic system of the machine to malfunction. 
     Wet tests are also susceptible to false triggers. In particular, cold solution used in the test causes many false disposable integrity test alarms each year because the tests fail when an occluder, which is supposed to clamp off all fluid lines, does not properly crimp or seal the tubing lines. When the solution is cold, it cools the set tubing to a lower temperature than the tubing would be if placed only in room air. Colder tubing is harder to occlude, allowing fluid in some cases to leak past the occluder and cause the test to fail. Once a dialysis therapy starts, the fluid passing through the tubing is warmed to about 37° C., enabling the occluder to perform satisfactorily. 
     It is therefore desirable to have an integrity test that is performed before the solution bags are attached to the therapy machine and to eliminate the use of cold solution to prevent false triggers. 
     A “dry” test is described briefly in U.S. Pat. No. 6,302,653. The description is based in part upon the “dry test” implemented in the Baxter HomeChoice® cycler in December of 1998. The actual test implemented in the HomeChoice® cycler consists of four steps, the first of which occurs before the solution bags are connected. The next three steps require the solution bags to be connected but do not require fluid to be pulled from the bags into the machine.  FIGS. 1  to  4  illustrate the areas of a fluid cassette tested by the individual steps of the known “dry” test. While the above “dry” test eliminates the problem of fluid potentially leaking into the pneumatics of the machine, the test does not prevent the sterility of the bags from being compromised potentially upon a leak and thus from being discarded if the integrity of the disposable cassette is compromised. 
     Moreover, dry testing with air is believed to be more sensitive than the wet test, which uses dialysis fluid. It is therefore also desirable to have an integrity test that uses air for sensitivity reasons as well as for the reasons stated above. 
     While integrity testing poses one problem to manufacturers of medical fluid machines, another common problem is the priming of the fluid system within those machines. In many instances, air must be purged from one or more tubes for safety purposes. For example, in the realm of dialysis, it is imperative to purge air from the system, so that the patient&#39;s peritoneum or veins and arteries receive dialysis fluid that is free of air. Consequently, automated dialysis machines have been provided heretofore with priming systems. In peritoneal dialysis, the object of priming is to push fluid to the very end of the line, where the patient connector that connects to the patient&#39;s transfer set is located, while not priming fluid past the connector, allowing fluid to spill out of the system. 
     Typically, dialysis machines have used gravity to prime. Known gravity primed systems have a number of drawbacks. First, some priming systems are designed for specifically sized bags. If other sized bags are used, the priming system does not work properly. Second, it happens in many systems that at the beginning of priming, a mixture of air and fluid can be present in the patient line near its proximal end close to a disposable cartridge or cassette. Fluid sometimes collects in the cassette due to the installation and/or integrity testing of same. Such fluid collection can cause air gaps between that fluid and the incoming priming solution. The air gaps can impede and sometimes prevent gravity priming. Indeed, many procedural guides include a step of tapping a portion of the patient line when the line does not appear to be priming properly. That tapping is meant to dislodge any air bubbles that are trapped in the fluid line. 
     A third problem that occurs relatively often in priming is that the patient forgets to remove the clamp on the patient line prior to priming that line. That clamped line will not allow the line to prime properly. An alarm is needed to inform the patient specifically that the patient needs to remove the clamp from the patient line before proceeding with the remainder of therapy. Fourth, if vented tip protectors are provided at the end of the patient line, the vented tip protectors may not vent properly and impede priming. An alarm is again needed to inform the patient that the line has not primed properly. Fifth, cost is always a factor. Besides providing a priming apparatus and method that overcomes the above problems, it is also desirable to use existing components to perform the priming, if possible, to avoid having to add additional components and additional costs. 
     Another concern for medical fluid systems and in particular automated peritoneal dialysis (“APD”) systems is ensuring that solution bags are placed at a height relative to the machine that is suitable for the machine to operate within designated parameters. The height of solution bags, such as dialysate bags, lactate bags and/or dextrose bags, needs to be monitored to ensure that the proper amount of fluid will be pumped to the patient during therapy and that the correct amount and proportion of additives are infused. Two patents discussing bag position determination are U.S. Pat. Nos. 6,497,676 and 6,503,062. 
     SUMMARY 
     The present invention in one primary embodiment performs an integrity test on both the cassette sheeting and the molded cassette features of a disposable cassette. The methodology of the invention is applicable to many cassette based pumping and liquid distribution systems and is particularly suited for dialysis treatment, such as automated peritoneal dialysis. The steps of the integrity test are performed almost exclusively before solution bags, such as peritoneal dialysis solution bags, are connected to a dialysis therapy machine, such as a peritoneal dialysis machine. Such a test is advantageous because if an integrity problem arises, the patient only has to discard the disposable cassette and associated tubing, not the solution. Also, because fluid is not connected to the machine to perform the test, there is no opportunity for fluid, due to a leak, to be sucked into the machine&#39;s pneumatics, potentially causing malfunction. 
     The dry testing of the present invention is performed with all fluid lines capped except for the drain line, which is covered with a tip protector and/or membrane that allows air but not liquid to escape. Because the lines remain capped, they are not connected to the solution bags. Consequently, no solution bags become contaminated if the cassette has a leak. 
     The testing steps are able to be performed with capped lines for a number of reasons. In some steps, the tip protectors, or caps, connected to all lines except the drain line are left in place because the cassette sheeting and fluid pathways are tested with valves in the open position rather than the closed position. When the valves are open, all of the fluid channels in the cassette are in direct communication with both pump chambers and the drain line, which has a bacteria retentive tip protector that allows air to pass through it. Air from a failed test can therefore pass through the drain line from cassette, changing the pressure in the system so that a leak can be detected. 
     In other test steps, the tip protectors can be left in place because one part of the system is pressurized, while the other is evacuated. Air leaking from the positively pressurized part of the cassette leaks to the evacuated part and is readily detectable as is air escaping from or leaking into the cassette. Further, because air flows more readily than does water or solution through a leak, the air test is more expedient and sensitive than a fluid based test, increasing accuracy and repeatability and decreasing test time. 
     The present invention in another primary embodiment provides an apparatus and method for priming a medical fluid delivery system. The priming method and apparatus is described herein for an automated peritoneal dialysis machine, however, the test is applicable to any fluid delivery system, which requires the purging of air for safety or operational reasons. The method and apparatus operates with a system having a fluid container or fluid bag, at least one fluid pump and at least one tubing line, such as a patient line extending from that fluid pump. In a first step of the priming method, valves surrounding the fluid pump are configured so that fluid flows via gravity or via the pump into the pump chamber and fills such pump chamber but does not exit the chamber. In a second step, the valves are switched so that the fluid in the supply bag is no longer able to fill the pump chambers, and so that the pump chambers can be pressurized and thereby pump the fluid from the pump chambers downstream and partially into the patient line. The machine processor is configured to expect a pressure drop in the pump chamber when the pump chamber expels fluid therefrom. If such pressure drop is not seen, the patient has likely forgotten to remove the clamp in the patient line and an error message is generated. In a final step, the valves surrounding the pump are opened so that fluid from the container or bag can continue to flow through and prime the patient line until fluid reaches the end of the patient line, which is positioned at the same elevational height as the top of the fluid in the fluid container. 
     As indicated above, if the patient line is inadvertently clamped during priming, the pressure in the pump chamber during the pushing step would not fall to an expected level, prompting a suitable alarm. Further, the initial pushing of fluid through the proximal part of the patient line, nearer to the cassette, in many instances will overcome the resistance to fluid flow caused by air trapped in that portion of the line, and allow priming to thereafter take place in a proper manner. 
     Another primary aspect of the present invention is an apparatus and method for determining the vertical position or head height of one or more solution bags as well as a drain bag. The method and apparatus use atmospheric pressure to establish a zero position relative to the therapy machine, such as an APD machine. The bag height determination can determine whether a solution bag is in the proper position to achieve a desired pumped flowrate, whether the solution bag is properly located on a heater plate, whether the relative position between two or more bags is proper, whether the drain bag is located in a proper position or whether one or more of the bags is empty, etc. 
     It is therefore an advantage of the present invention to provide an integrity test that consumes less time than previous practices. 
     It is another advantage of the present invention to provide an integrity test that is more effective at detecting leaks than previous practices. 
     It is a further advantage of the present invention to provide an integrity test that is more convenient for the patient if a leak is detected. 
     It is another advantage of the present invention to provide an integrity test that minimizes the supplies that must be discarded if a leak is detected. 
     It is yet another advantage of the present invention to provide an integrity test that is immune to failure of other machine components, such as a flow line occluder. 
     It is still another advantage of the present invention to provide an integrity test that does not require warm solution. 
     It is still a further advantage of the present invention to provide an integrity test from which it is possible for a user to distinguish between a failure of the disposable set and a leak in the pneumatic system of the machine or cycler. 
     Moreover, it is an advantage of the present invention to eliminate false triggering due to cold solution used in integrity testing. 
     Still further, it is an advantage of the present invention to provide a priming method and apparatus that operates to automatically dislodge air pockets located initially in the priming line, which would otherwise tend to slow or completely stop priming. 
     Yet another advantage of the present invention is to provide a priming method and apparatus that detects when the patient or operator has inadvertently left a clamp on the priming line, so that the therapy machine can generate a suitable alarm. 
     Further still, an advantage of the present invention is to be able to determine the elevational location and head height of one or more solution and drain bags. 
     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 
         FIGS. 1 to 4  are opposite views of a cassette showing different areas of the cassette that are integrity tested during a known integrity test. 
         FIG. 5  is a plan view of one embodiment of a disposable set operable with the integrity test of the present invention. 
         FIG. 6  is a perspective view of one embodiment of a machine that can accept the cassette of the disposable set shown in  FIG. 5 . 
         FIG. 7  is a perspective view of the cassette of the disposable set shown in  FIG. 5 , wherein flexible membranes of the cassette are exploded to show various inner components of the cassette. 
         FIG. 8  is a portion of a cross section taken along line VIII-VIII in  FIG. 7 . 
         FIG. 9  is a schematic view of one embodiment of a pneumatic operating system for the machine and cassette shown in  FIG. 6 . 
         FIGS. 10 to 15  are elevation views of opposite sides of the cassette shown in  FIG. 5  illustrating the different components or areas of the cassette that are integrity tested in the various steps of one embodiment of the integrity test of the present invention. 
         FIG. 16  is a schematic illustration of an alternative medical fluid machine that employs mechanical positive pressure actuation versus pneumatic pressure. 
         FIGS. 17 to 22  are schematic views illustrating one apparatus and method of the present invention for priming a medical fluid system. 
         FIGS. 23 and 24  are schematic views illustrating a method and apparatus of the present invention that evaluates solution and drain bag head heights. 
     
    
    
     DETAILED DESCRIPTION 
     One primary aspect of the present invention is an improved leak detection system for any type of cassette-based medical fluid therapy that exerts mechanical or pneumatic positive or negative pressure on a disposable fluid cassette. Another primary aspect of the present invention is an improved priming technique for a medical fluid therapy machine, such as an automated peritoneal dialysis (“APD”) system. While APD is one preferred use for the present invention, any cassette-based medical fluid system or system using a sterile, disposable fluid cartridge can employ the apparatuses and methods of the present invention. A further primary aspect of the present invention is to provide an apparatus and method for determining the head weight of the solution. 
     Improved Cassette-Based Leak Test 
     The following method is a “dry” method, which is more sensitive to leaks and other defects when compared to fluid based integrity testing. The method also eliminates some problems associated with older tests, such as having to discard solution bags or potentially harming the mechanical components of the machine upon a leak. 
     Referring now to the figures and in particular to  FIGS. 5 to 9 ,  FIG. 5  illustrates a disposable set  50  that includes a disposable cassette  100  as well as a set of tubes. As shown in the exploded segment  52 , the tubing set includes a heater line  54 , drain line  56 , first proportioning line  58 , day/first bag line  60 , second proportioning line  62 , last fill line  64  and patient line  66 . Each of those lines is used with the HomeChoice® machine in one embodiment. It should be appreciated however that other lines associated with other dialysis or medical fluid systems can be used alternatively with the present invention. Automated peritoneal dialysis (“APD”) machines, dialysis machines generally or medical fluid machines besides dialysis machines are collectively referred to herein as medical fluid machine  150 , which is shown in  FIG. 6 . More or less lines may also be used without departing from the scope of the invention. 
     Each of the lines  54  to  66  terminates at a first end at cassette  100  and at a second end at an organizer  42 . In operation, machine  150  holds organizer  42  initially at a height that enables a gravity prime to fill fluid at least substantially to the end of at least some of the lines  54  to  66  without filling fluid past connectors located at the end of these lines. Priming is discussed in more detail below. 
       FIG. 6  illustrates that the cassette  100  and tubes  54  to  66  of set  50  are loaded vertically in one embodiment into machine  150  and held firmly in place between door gasket  152  and diaphragm  154 . Door gasket  152  is attached to door  156 , which swings open and closed to removably lock cassette  100  in place. Diaphragm  154  provides an interface between the valve and pump actuators, located inside machine  150  behind diaphragm  154 , and the valve and pump fluid receiving chambers located in cassette  100 . 
       FIG. 7  is a perspective view of cassette  100  showing that the cassette  100  includes a housing  102 , which is sealed on both sides by flexible membranes  104  and  106 . The housing defines a plurality of pump chambers P 1  and P 2 , valves V 1  to V 10  (which are located on the opposite side of housing  102  from the side shown in  FIG. 7 ), a plurality of flow paths F 1  to F 9  and a plurality of ports  108  that extend through an interior divider  110  that divides housing  102  and cassette  100  into two separate fluid flow manifolds. 
       FIG. 8  illustrates a cross-section taken through line VIII-VIII shown in  FIG. 7 . The cross-section shows membrane  106 , divider  110  and a port  108  described above. Additionally, external valve chamber walls  112  and internal valve chamber wall  114  are illustrated, which cooperate to produce one of the valves V 1  to V 10  on one side of divider  110  of cassette  100 . Further, internal chamber wall  114  cooperates with a back  116  (which can also be a flexible membrane) to create various ones of the flow paths F 1  to F 11  on the other side of divider  110  of cassette  100 . Flexible membrane  106  seals to external chamber walls  112  and upon application of a force f to internal chamber walls  114  (to close a fluid connection between a first one of the paths F 1  to F 11  and a second one of those paths). Upon the release of force f or the application of a vacuum or negative force to membrane  106 , membrane  106  is pulled away from internal wall  114 , reestablishing the communication between the fluid paths. 
       FIG. 9  illustrates a schematic view of a pneumatic control system  10  for a dialysis machine, such as an automated peritoneal dialysis machine is illustrated.  FIG. 9  is a schematic of the pneumatic control system employed in the HomeChoice® Automated Peritoneal Dialysis system and is useful for describing the operation of the present invention. It should be appreciated however that the teachings of the present invention are not limited to the HomeChoice® machine nor to only those machines having the same or analogous components. Instead, the present invention describes a test and methodology that is applicable to many different medical fluid systems. 
     In a set-up portion of the integrity test of the present invention, disposable cassette  100  is loaded into dialysis machine  150 . To do so, an air pump (not illustrated) is turned on. That air pump communicates with various pneumatic components illustrated in  FIG. 9 , including emergency vent valve A 5 , occluder valve C 6 , and actuators C 0 , C 1 , C 2 , C 3 , C 4 , D 1 , D 2 , D 3 , D 4  and D 5  for the fluid valves, which causes an occluder  158  (see also  FIG. 6 ) to retract to enable the disposable set  50  and cassette  100  to be loaded into machine  150 . Once the set  50  has been loaded, emergency vent valve A 5  is closed, so that high positive bladder  128  can be inflated, which seals cassette  100  between the door  156  and diaphragm  154 , while maintaining the occluder  158  in an open position ( FIG. 6 ). The remainder of the test is illustrated by  FIGS. 10 to 14 . 
     Referring now to  FIG. 10 , a first step of the test tests the pump chambers P 1  and P 2  using positive pressure and tests valves V 1  to V 10  using negative pressure. In particular, the cassette sheeting of cassette  100  over pump chambers P 1  and P 2  is pressurized to +5 psig using the low positive pressure tank  220  and valves A 3  and B 1  shown in  FIG. 9 . A −5 psig vacuum is pulled on the cassette sheeting of cassette  100  over the fluid valves V 1  to V 10  using negative tank  214  and valves A 0  and B 4  shown in  FIG. 1 . 
     Simultaneous pressure decay tests are then conducted on the: (i) air volume in the low positive tank  220  and pump chambers P 1  and P 2 ; and (ii) the air volume in the negative tank  214  and fluid valves V 1  to V 10 . If the pressure decay in the positive pressure system exceeds, e.g., one psig, an alarm is sent displaying a pump chamber sheeting damaged error or code therefore. If the difference in pressure in the negative pressure system exceeds, e.g., one psig, an alarm is sent displaying a fluid valve sheeting damaged error or code therefore. Positive pressure tested areas for this first step are shown in double hatch and negative pressure tested areas are shown in single hatch in  FIG. 10 . 
     Importantly, test step one tests cassette  100  from the outside. That is, the pressure is applied to the outside of the sheeting over pump chambers P 1  and P 2  and negative pressure is applied to the outside of the sheeting over valves V 1  to V 10 . As described below, the remaining test steps apply positive pressure and negative pressure to the sheeting from inside the cassette. The designation of the Figures however is the same, namely, positive pressure tested areas (internal and external) are shown using a double hatch. Negative pressure tested areas (internal and external) are shown using a single hatch. The ports  108  tested in each step are darkened and labeled either “positive pressure tested” or “negative pressure tested”. 
     Referring now to  FIG. 11 , a second step of the test of the present invention tests the pump chambers P 1  and P 2 , certain fluid pathways and certain valves using positive pressure and negative pressure. The second step begins by evacuating negative tank  214  to −5 psig and opening valve B 4  to fill pump chamber P 2  in the cassette with air through open fluid valve V 7 . Next, low positive pressure tank  220  is pressurized to +5 psig and valve A 3  is opened to empty pump chamber P 1  through open fluid valve V 10 . Fluid valves V 7  and V 10  are then closed. Occluder valve C 6  is de-energized so that occluder  158  closes, pinching/sealing all fluid lines  54  to  66  exiting cassette  100 . Valves A 3  and B 4  are then closed. Actuator valve B 1  is opened with fluid valves V 4 , V 6  and V 7  open to pressurize the air in cassette pump chamber P 2  and to test the fluid pathways downstream of V 4 , V 6  and V 7  for leakage across the occluder  158  and/or across the fluid channels within the cassette. Actuator valve A 0  is then opened with fluid valves V 1 , V 2  and V 9  open to create a vacuum in cassette pump chamber P 1  and to test the fluid pathways downstream of V 1 , V 2  and V 9  for leakage across occluder  158  and/or across the fluid channels within the cassette. 
     Next, a first set of simultaneous pressure decay/rise tests is conducted on low positive pressure tank  222  and negative pressure tank  214 . The difference in pressure in both positive pressure tank  220  and negative pressure tank  214  is recorded as well as the final pressure in positive pressure tank  220  and negative pressure tank  214 . Valve V 3  is opened and a second set of simultaneous pressure decay/rise tests is conducted on low positive pressure tank  220  and negative pressure tank  214  as the contents of pump chamber P 2  flow freely into pump chamber P 1  through open valves V 1  and V 3 . If the sum of difference in pressures from the first set of pressure decay tests exceeds, for example, two psig, and the sum of the difference in pressure from the second set of tests is less than one psig, an alarm is issued for a cross-talk leakage error. Positive pressure tested areas for the second step are shown in double hatch and with ports  108  so marked and negative pressure tested areas are shown in single hatch and with ports  108  so labeled in  FIG. 11 . 
     Referring now to  FIG. 12 , a third step of the test tests the pump chambers P 1  and P 2 , certain fluid pathways and certain valves using positive pressure and negative pressure. The third step begins by evacuating negative pressure tank  214  to −5 psig and opening valve B 4  to fill pump chamber P 2  in the cassette with air through open fluid valve V 7 . Low positive pressure tank  220  is then pressurized to +5 psig and valve A 3  is opened to empty pump chamber P 1  through open fluid valve V 10 . Valves V 7  and V 10  are then closed. Occluder valve C 6  is de-energized so that the occluder  158  closes, pinching/sealing all fluid lines exiting cassette  100 . Valves A 3  and B 4  are closed. Pump actuator valve B 1  is opened with fluid valves V 3 , V 4  and V 6  open to pressurize the air in pump chamber P 2  and to test fluid pathways downstream of V 3 , V 4  and V 6  for leakage across occluder  158  and/or across the fluid channels within cassette  100 . Pump actuator valve A 0  is then opened with fluid valves V 2 , V 9  and V 10  open to create a vacuum in pump chamber P 1  and to test the fluid pathways downstream of V 2 , V 9  and V 10  for leakage across the occluder  158  and/or across the fluid channels within cassette  100 . 
     Next, a first set of simultaneous pressure decay/rise tests is conducted on low positive pressure tank  222  and negative pressure tank  214 . The difference in pressure in both positive tank  220  and negative tank  214  is recorded as well as the final pressure in positive pressure tank  220  and negative pressure tank  214 . Valve V 1  is opened and a second set of simultaneous pressure decay/rise tests is conducted on low positive pressure tank  220  and negative pressure tank  214  as the contents of pump chamber P 2  flow freely into pump chamber P 1  through open valves V 1  and V 3 . If the sum of the difference in pressure from the first set of pressure decay tests exceeds, for example, 2 psig, and the sum of the difference in pressure from the second set of tests is less than one psig, a cross-talk leakage error alarm or code therefore is sent. Positive pressure tested areas for the third step are shown in double hatch and with ports  108  so marked and negative pressure tested areas are shown in single hatch and with ports  108  so marked in  FIG. 12 . 
     Referring now to  FIG. 13 , a fourth step of the test tests the pump chambers P 1  and P 2 , certain fluid pathways and certain valves using positive pressure and negative pressure. The fourth step begins by evacuating negative pressure tank  214  to −5 psig and opening valve B 4  to fill pump chamber P 2  in cassette  100  with air through open fluid valve V 7 . Low positive pressure tank  220  is pressurized to +5 psig and valve A 3  is opened to empty pump chamber P 1  through open fluid valve V 10 . Fluid valves V 7  and V 10  are closed. Occluder valve C 6  is de-energized so that the occluder  158  closes, pinching/sealing fluid lines  54  to  66  exiting cassette  100 . Valves A 3  and B 4  are closed. Pump actuator valve B 1  is opened with fluid valve V 5  open to pressurize the air in pump chamber P 2  and to test the fluid pathways downstream of V 5  for leakage across the occluder  158  and/or across the fluid channels within cassette  100 . Pump actuator valve A 0  is opened with fluid valves V 1 , V 2 , V 9  and V 10  open to create a vacuum in pump chamber P 1  and to test the fluid pathways downstream of V 1 , V 2 , V 9  and V 10  for leakage across the occluder  158  and/or across the fluid channels within the cassette. 
     Next, a first set of simultaneous pressure decay/rise tests is conducted on low positive pressure tank  222  and negative pressure tank  214 . A difference in pressure in both positive tank  220  and negative tank  214  is recorded as well as the final pressure in positive pressure tank  220  and negative pressure tank  214 . Valve V 3  is opened and a second set of simultaneous pressure decay/rise tests is conducted on low positive pressure tank  220  and negative pressure tank  214  as the contents of pump chamber P 2  flow freely into pump chamber P 1  through open valves V 1  and V 3 . If the sum of the difference in pressure from the first set of pressure decay tests exceeds, for example, 1.5 psig, and the sum of the difference in pressure from the second set of tests is less than 0.75 psig, a cross talk leakage error alarm or code is sent and displayed. Positive pressure tested areas for the forth step are shown in double hatch and with ports  108  so marked and negative pressure tested areas are shown in single hatch and with ports so marked  108  in  FIG. 13 . 
     Referring now to  FIG. 14 , a fifth step of the test tests the pump chambers P 1  and P 2 , certain fluid pathways and certain valves using positive pressure and negative pressure. The fifth step begins by evacuating negative pressure tank  214  to −5 psig and opening valve B 4  to fill pump chamber P 2  in cassette  100  with air through open fluid valve V 7 . Low positive pressure tank  220  is pressurized to +5 psig and valve A 3  is opened to empty pump chamber P 1  through open fluid valve V 8 . Fluid valves V 7  and V 10  are closed. Occluder valve C 6  is de-energized so that the occluder  158  closes, pinching/sealing fluid lines  54  to  66  exiting cassette  100 . Valves A 3  and B 4  are closed. Pump actuator valve B 1  is opened with fluid valves V 3 , V 4 , V 6  and V 7  open to pressurize the air in pump chamber P 2  and to test the fluid pathways downstream of V 3 , V 4 , V 6  and V 7  for leakage across the occluder  158  and/or across the fluid channels within cassette  100 . Pump actuator valve A 0  is opened with fluid valve V 8  open to create a vacuum in pump chamber P 1  and to test the fluid pathways downstream of V 8  for leakage across the occluder  158  and/or across the fluid channels within the cassette. 
     Next, a first set of simultaneous pressure decay/rise tests is conducted on low positive pressure tank  222  and negative pressure tank  214 . A difference in pressure in both positive tank  220  and negative tank  214  is recorded as well as the final pressure in positive pressure tank  220  and negative pressure tank  214 . Valve V 1  is opened and a second set of simultaneous pressure decay/rise tests is conducted on low positive pressure tank  220  and negative pressure tank  214  as the contents of pump chamber P 2  flow freely into pump chamber P 1  through open valves V 1  and V 3 . If the sum of the difference in pressure from the first set of pressure decay tests exceeds, for example, 1.5 psig, and the sum of the difference in pressure from the second set of tests is less than 0.75 psig, for example, a cross talk leakage error alarm or code is sent and displayed. Positive pressure tested areas for the fifth step are shown in double hatch and with ports  108  so marked and negative pressure tested areas are shown in single hatch and with ports  108  so marked in  FIG. 14 . 
     In each of test steps two through five of  FIGS. 11 to 14  described above, pump chamber P 2  is filled with air and pump chamber P 1  is evacuated before the pressure decay/vacuum rise tests are performed. Those tests are improved when chamber P 2  is pressurized above atmospheric pressure as opposed to merely maintaining the chamber at atmospheric pressure. For one reason, maintaining chamber P 2  at a positive compensates for the slight compressibility of air in the chamber when the test steps are commenced. To pressurize chamber P 2 , air can be pushed from chamber P 1  to P 2  with the occluder  158  closed. When P 2  is pressurized, occluder  158  is opened, enabling chamber P 1  to be evacuated. Pressurized chamber P 2  should show very little pressure drop unless a leak in one of the tested pathways is detected. 
     Referring now to  FIG. 15 , a sixth step of the test of the present invention tests the pump chambers P 1  and P 2 , certain fluid pathways and certain valve ports  108  using positive pressure. To begin the sixth step, a −5 psig vacuum is pulled on the cassette sheeting over the two pump chambers P 1  and P 2  with all fluid valves except for drain valves V 7  and V 10  de-energized (closed), so that pump chambers P 1  and P 2  fill with air. Valves V 7  and V 10  are closed and the sheeting over pump chambers P 1  and P 2  of cassette  100  is pressurized to +5 psig using low positive tank  220  and valves A 3  and B 1 . A first pressure decay test is then conducted on the pump chambers P 1  and P 2 , fluid flow paths F 6 , F 7 , F 8  and F 9  and the darkened fluid ports  108  so marked within cassette  100  by monitoring the pressure in the low positive tank  220 . If the difference in pressure in the low positive tank  220  exceeds, e.g., one psig, an alarm is sent displaying a fluid valve leaking error or code therefore. 
     Occluder valve C 6  is de-energized so that occluder  158  closes, pinching/sealing all fluid lines  54  to  66  exiting cassette  100 . All of valves V 1  through V 10  except for V 5  and V 8  are opened and a second pressure decay test is conducted by monitoring the pressure in low positive tank  220 . If the difference in pressure in the low positive tank  220  exceeds, e.g., one psig, the sixth series of tests must be repeated. If the difference in pressure in the low positive tank  220  exceeds, e.g., one psig a second time, a an alarm is sent displaying occluder failed. Finally, the occluder is opened and a third pressure decay test is conducted by monitoring the pressure in low positive tank  220 . Test step six verifies that tests one and two have not failed if the difference in pressure exceeds, e.g., one psig. Positive pressure tested areas for the sixth step are shown in double hatch and with ports  108  so marked in  FIG. 15 . 
     The previous six test steps complete one embodiment of the dry integrity test of the present invention. Viewing the outcome of steps  1  to  4  of the prior art test in  FIGS. 1 to 4 , it should be appreciated that step  1 , shown in  FIG. 10  of the dry disposable integrity test of the present invention, tests the equivalent components of all four steps of the original dry integrity test. 
     Importantly, test steps two to six test the cassette from the inside. That is, positive pressure is applied inside the cassette to the inside of the cassette sheeting and negative pressure is applied inside the cassette to the inside of the cassette sheeting. The positive and negative pressure applied inside the cassette to the inside of the cassette sheeting is created by initially applying pressure (positive or negative) to the outside of the cassette and switching the valves to create the desired pressure distribution inside the cassette as described above. 
     The first five of the test steps ( FIGS. 10 to 14 ) can be performed with the tip protectors placed on lines  54  through  66  and with the clamps closed on all of the lines except for drain line  56 . The tip protectors, shown figuratively as caps  118  on the respective ports of cassette  100 , are actually at the ends of tubes  54 ,  58 ,  60 ,  62 ,  64  and  66 . The drain line  56  has a bacteria retentive tip protector that passes to atmosphere air that leaks through the membranes  104  and  106  ( FIGS. 7 and 8 ) or from housing  102 , lowering the pressure in the system so that a leak can be detected. The tip protectors are removed when solution bags are connected to the tubes prior to test step six in the series of six test steps. As seen in the prior steps  2  to  4  of  FIGS. 2 to 4 , all tip protectors have to be removed for those test steps. In the prior art therefore, when a cassette fails during any of the tests illustrated  FIGS. 2 to 4 , non-sterile air is introduced into the solution bags, causing the solution bags and the cassette to be discarded. 
     Test steps two through five of the present invention ( FIGS. 11 to 14 , respectively) test, using air within cassette  100 , the same areas of the cassette as does the prior art wet leak test described above. Because steps (i) through (v) of the prior art wet leak test require fluid, solution bags must be attached to obtain such fluid. The present invention eliminates that necessity. 
     Test step one of the present invention is able to leave the tip protectors connected to all lines except the drain line because the valves are tested in the open position rather than the closed position. When valves V 1  to V 10  are open, all of the fluid channels F 1  to F 11  in cassette  100  are in direct communication with both pump chambers P 1  and P 2  and the drain line. The drain line has a bacteria retentive tip protector that allows air to pass through it, e.g., is fitted with a hydrophobic membrane. Air from a failed test can therefore pass through the drain line from cassette  100 , changing the pressure in the system so that a leak can be detected. 
     Test steps two through five of the disposable integrity test of the present invention are able to leave the tip protectors in place because one part of the system is pressurized while the other is evacuated. Air leaking from the positively pressurized part of cassette  100  to the evacuated part is readily detectable as is air escaping from or leaking into cassette  100 . Because air flows more readily than does water or solution through a leak, the air test is more expedient and sensitive than a fluid based test, increasing accuracy and repeatability and decreasing test time. 
     Test steps two through five of the present invention include a redundant pressure decay test that verifies the results of the first pressure decay test. All four test steps two through five look for leaking flow from a pressurized section of cassette  100  to an evacuated section of the cassette  100 . If a leak arises between the two sections of the cassette, the pressure in the two sections should tend towards equilibrium when air flows from the high pressure section to the evacuated section. The redundant test opens valves between the positive and negative sections at the completion of the first pressure decay test to verify that there is a larger pressure change if no leaks exist or a minimal pressure change if a leaks exists. 
     A failure of occluder  158  to properly crimp tubing lines  54  to  66  does not materially affect the results for test steps two to five because the tip protectors are in place and would otherwise seal all of the lines that are being tested. Additionally, the users/patients are instructed to close the line clamps on all but the drain line when loading set  50  into machine  150 . Test step six, which tests the cassette valves V 1  through V 10  and the occluder  158 , can be conducted dry or wet since the solution bags have been connected. The dry test would have to be pressure based, whereas the fluid test could be either pressure or volume based. 
     The user can clamp the drain line on the disposable set when instructed to do so after an integrity test failure when using the method of the present invention and run the disposable integrity tests again. If the tests do not show a failure a second time (for many of the failure modes), the disposable set can be held responsible for the leak and not the machine  150 , e.g., the machine&#39;s pneumatic system and/or cassette/machine interface. That feature is useful when a patient seeks troubleshooting assistance. Determining that the machine  150  is working properly and that the cassette  100  is causing the failure precludes swapping a patient&#39;s machine needlessly after an integrity failure because of uncertainty about whether the cassette  100  or machine  150  is responsible for the test failure. Conversely, if the tests show a failure a second time, the machine  150  and/or the cassette/machine interface can be held responsible for the leak. 
     While cassette  100  is illustrated with pump chambers P 1  and P 2 , valve chambers V 1  to V 10 , associated ports  108 , and fluid paths F 1  to F 11 , it should be appreciated that the method of the invention is equally applicable to cassettes and actuating systems that have different pump and valve geometries than the ones shown as well as additional features, such as heaters, pressure sensors, temperature sensors, concentration sensors, blood detectors, filters, air separators, bubble detectors, etc. The cassettes can be rigid with a single side of sheeting, be rigid with dual sided sheeting, have dual sheets forming fluid pathways, have a rigid portion connected to a flexible portion, etc. The cassettes are useable in any medical fluid delivery application, such as peritoneal dialysis, hemodialysis, hemofiltration, hemodiafiltration, continuous renal replacement therapy, medication delivery, plasma pherisis, etc., and any combination thereof. 
       FIG. 16  shows one alternative embodiment of the present invention via system  200 , wherein the pneumatic source of positive pressure used above is replaced by a mechanical actuator  202  that pushes a flexible membrane film  203 . Film  203  is attached to a cassette  210  with sheeting  204  on one side of thereof. System  200  uses a vacuum to force the membrane  203  to follow a piston head  206  when head  206  retracts from or moves toward cassette  210 . While no external source of positive pressure is provided, air can be drawn into pumping chamber  208 , while fluid valve  212  is closed and actuator  202  and head  206  are moved forward to generate an internal pressure that is used to perform the disposable integrity tests described herein. A pressure sensor  214  is provided in one embodiment to perform the pressure decay tests. The position of actuator  202  and head  206  can also be used to perform a leak test by applying a constant force. The actuator and head should remain stationary when a constant force is applied if no leak is present. Forward motion would indicate that there is a leak in the system being tested. 
     Appendix A shows data from step one of the integrity test of the present disclosure. Appendix B also shows data from step one of the integrity test of the present disclosure. In Appendix B, the bolded, larger font size data shows when defects were detected. It is noteworthy that for fifty different cassettes tested and known to be defective, all fifty defects were detected. When the drain line was clamped after the software instructed the operator to do so, forty-seven of the fifty tests no longer failed indicating that the leak was in the cassette and not the therapy machine. The other three of the fifty clamped tests were inconclusive. Those three are marked in bolded italics. It is also noteworthy that one cassette appears to have two defects and is highlighted in bold italics as well. 
     For the test, ten defects were created in the pump chamber sheeting and forty defects were created in the valve sheeting. All pump chamber tests were run with positive pressure and all valve sheeting tests were run with negative pressure. The defects were punctures and slits made by a 0.035 inch (0.89 mm) outside diameter hot needle or an Exacto knife with a stop positioned to create consistent slits of 0.125 inch (3.2 mm). 
     Appendix C shows data from the integrity test step two of the present disclosure. The positive pressures represent pressures inside pump chamber P 2 , as measured by pressure sensors monitoring positive tank  220  ( FIG. 9 ). The negative pressures are for pressures inside pump chamber P 1 , as measured by the pressure sensors monitoring negative tank  214  ( FIG. 9 ). Cassettes predisposed with a number of defects were tested as well as some cassettes without known defects. Some of the defects were not detected by test step two. Test steps three, four and five did however reveal the defects that test step two did not. 
     Improved Priming Method and Apparatus 
     Turning to the priming method and apparatus of the present invention, the method and apparatus are advantageous in a number of respects. First, the method employs the pumps of the medical fluid machine  150  shown above in  FIG. 6  to pump priming fluid for an initial portion of the prime to dislodge air bubbles that typically become trapped, for example, in the patient line  66 , near cassette  100 . Second, the method uses software contained within the controller of machine  150  that expects to see a particular pressure drop when the medical fluid pump (or pumps) pushes the initial priming fluid. If the expected pressure drop is not seen, machine  150  assumes there is a clamp on the priming or patient line, responds accordingly and sends a suitable error message or code. 
     Referring now to  FIG. 17 , an initial schematic of an apparatus  250  for performing the priming method of the present invention is shown. The apparatus includes a supply bag  252  filled with a volume of fluid  254 . A line from solution bag  252  to pumps P 1  and P 2  is provided. In most instances, that line is the heater bag line  54  shown in  FIGS. 5 and 17 , which enters cassette  100  that houses pump chambers P 1  and P 2 . Valves  256  and  258  selectably allow fluid  254  to pass via line  54  to pump chambers P 1  and P 2 , respectively. A priming line is provided from pump chambers P 1  to P 2  to a distal end of the line, which is provided with a vented distal end connector  260 . Normally, the primed line is the patient line shown as line  66  in  FIGS. 5 and 17 . It should be appreciated, however, that the priming line may be a different line than the patient line. Moreover, the priming apparatus  250  and associated method is applicable to systems that prime multiple lines sequentially or simultaneously. 
     Connector  260  as illustrated is positioned in organizer  42  discussed above in connection with  FIG. 5 . The positioning of connector  260  is set so that the prime stops at a desired point at the beginning of or in the interior of connector  260 . That level as shown by line  262  is the same level as the height of fluid  254  in container  252 . Valves  266  to  268  are provided between pumps P 1  and P 2  and connector  260  to selectively allow fluid to enter patient line or priming line  66 . 
     The first step of the priming method shown in  FIG. 17  is to close valves  266  and  268  (black) and open valves  256  and  258  (white). Such valve arrangement enables fluid  254  to gravity feed or be drawn in by pumps P 1  and P 2  (the −1.5 psig shown in  FIG. 17  symbolizes the suction being applied to the flexible pump film as fluid is drawn into the pump chamber) from container  252  and fill pump chambers P 1  and P 2 . Because valves  266  and  268  are closed, no fluid enters priming line  66 . 
       FIG. 18  illustrates a second step of the priming method of the present invention. In  FIG. 18 , valves  256  and  258  are closed (black), so that no additional fluid can flow via heater bag line  54  from container  252  to pump chambers P 1  and P 2 . Next, a 1.0 psig pressure is applied to the flexible pump film, pressing the film against the fluid in pump chambers P 1  and P 2 . Valves  266  and  268  are then opened (white) so that fluid communication exists between pump chambers P 1  and P 2 , priming or patient line  66  and connector  260 . 
       FIG. 19  illustrates that after pressurizing the pump chambers P 1  and P 2 , fluid flows from those chambers through an initial portion of patient or priming line  66 . The pressure inside pump chambers P 1  and P 2  falls accordingly, e.g., to about 0.1 psig, as this fluid is displaced from the pump chambers and the volume of air pushing against the pump film expands. The fluid pumped from chambers P 1  and P 2  is not meant to extend all the way to connector  260 , rather, the pumped fluid is intended to flow through any trapped air at the proximal end of patient line  66 , so that such air is not an impediment to priming. Therefore, the fluid volume drawn into pump chambers P 1  and P 2  should be less than the volume inside patient line  66  extending from cassette  100  to connector  260 . 
     The volume of liquid that does fill patient line  66  via the pump stroke of chambers P 1  and P 2  does, however, push some air through vented connector  260 , leaving the line partially filled with solution and partially filled with air, wherein the air is collected at the distal end and the solution resides at the proximal end of line  66 . This method of dislodgement works regardless of how many extensions are added to patient line  66 . Older priming sequences had varied results depending upon whether a standard or non-standard length of patient line was used. The present method is independent of patient line length and can be used with a heater bag containing as little as 1000 ml of solution as seen in Table 1. 
     
       
         
               
             
               
               
               
               
             
               
               
             
               
               
               
               
             
               
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Patient Line Priming Height 
               
             
          
           
               
                   
                 1000 ml heater 
                 6000 ml heater 
                 1000 ml heater 
               
               
                   
                 bag volume 
                 bag volume 
                 bag volume 
               
               
                   
                   
               
             
          
           
               
                   
                 Average Primed Height Above Table 
               
             
          
           
               
                 Set with no patient 
                 7.17 
                 7.8 
                 6.28 
               
               
                 extension line 
               
               
                 Set with 1 patient 
                 6.8 
                 7.95 
                 6.34 
               
               
                 extension line 
               
               
                 Set with 2 patient 
                 6.5 
                 7.88 
                 6.23 
               
               
                 extension lines 
               
             
          
           
               
                   
                 Standard Deviation in Primed Height Above Table 
               
             
          
           
               
                 Set with no patient 
                 0.52 
                 0.16 
                 0.27 
               
               
                 extension line 
               
               
                 Set with 1 patient 
                 1.35 
                 0.16 
                 0.11 
               
               
                 extension line 
               
               
                 Set with 2 patient 
                 0.5 
                 0.13 
                 0.23 
               
               
                 extension lines 
               
               
                   
               
             
          
         
       
     
       FIGS. 20 and 21  illustrate the final step in the priming method associated with apparatus  250 . Here, inlet valves  256  and  258  are opened, while outlet valves  266  and  268  are left open. 
     In  FIG. 20 , any fluid in pump chambers P 1  and P 2  not pumped in  FIG. 19  is allowed to flow via gravity from such pump chambers into patient line  66 . Additionally, fluid  254  is enabled to gravity flow from container  252  to complete the patient line prime. In  FIG. 20 , the pressure in chambers P 1  and P 2  can drop to near zero psig as any remaining pressure from the pump stroke in  FIG. 19  is dissipated. FIG.  21  shows that the patient or priming line  66  is fully primed, with the level of fluid  254  reaching the elevational height  262  of the fluid  254  remaining in bag  252 . The level of fluid inside pump chambers P 1  and P 2  will also reach some equilibrium which may be at a slight positive pressure within those chambers. That is, the pressure in the pump chamber will equalize with the head pressure of patient line  66  and fill bag  252 . 
     If the patient line  66  is inadvertently clamped during priming, the pressure in pump chambers P 1  and P 2  in the step illustrated by  FIG. 19  does not fall below an expected level, e.g., from the one psig shown in  FIG. 18  to 0.1 psig shown in  FIG. 19 . The pressure instead remains at a higher level, such as 0.5 psig. The controller inside machine  150  senses that discrepancy and prompts the patient via a visual, audio or audiovisual message to unclamp the patient or priming line  66 . 
       FIG. 22  illustrates another advantage of the priming method of the present invention. A mixture of air and fluid can sometimes appear in the proximal part of the patient line  66 , near cassette  100 , at the beginning of prime. The mixture is usually near the cassette  100  because fluid may have entered into the line due to procedural errors during the setup procedure. For example, the patient may improperly connect the solution bags and open the clamps when the set is loaded. The mixture of air and fluid  254  can sometimes slow and sometimes prevent proper priming. The pressurized assist beginning in  FIG. 18  and ending in  FIG. 19  of patient line  66  will typically dislodge or overcome the problems caused by the air/fluid mixture, enabling proper priming. 
       FIG. 16  discussed above shows one alternative embodiment of the priming method of present invention, wherein system  200  replaces pneumatic pumps P 1  and P 2  in  FIGS. 17 through 21 . The pneumatic source of positive pressure used in  FIG. 19  is replaced by a mechanical actuator  202 , which pushes on a flexible membrane film  203 , which in turn is attached to a cassette  210  having sheeting  204  on one side of thereof. System  200  uses a vacuum to force membrane  203  to follow a piston head  206  when head  206  retracts and moves toward cassette  210 , drawing fluid into pumping chamber  208  when fluid valve  212  is open. Actuator  202  and head  206  are moved forward when another fluid valve (not shown) is opened, pushing fluid down the patient line. A pressure sensor  214  detects a pressure rise if the patient line is clamped. The position of actuator  202  and head  206  can be used to determine when to open valve  212  so that gravity can complete the priming of the patient line. 
     Appendix D shows data from the priming method of the present invention. Additionally, the data in Appendix E, Tables 3 and 4, was obtained from a software program that opened valves  256  and  258  when the pressure in pump chambers P 1  and P 2  fell below 0.2 psig. If the pressure did not fall to below 0.2 psig, the pressure was recorded and a message was logged that stated, “Timeout before PosP reached 0.20 psig”. A number of normal primes were performed as well as a number of primes wherein the patient line was clamped near the patient connector at the distal end of the line. 
     Solution Bag Head Height Determination 
     Dialysis, such as peritoneal dialysis or hemodialysis or other renal therapies such as hemofiltration or hemodiafiltration can performed using multiple solution bags, such as dialysate bags, lactate bags and/or dextrose bags. In such a case, it is advantageous to determine that the required solution bags are: (i) present and (ii) located at a vertical height suitable to enable the particular therapy to be performed, for example, an automated peritoneal dialysis performed by a machine. Such determinations should be made at the beginning of therapy, e.g., during the priming and cassette integrity tests, so that the machine can alert the patient of any problems before treatment begins and/or before the patient falls asleep. 
     Referring now to  FIGS. 23 and 24 , a system  300  illustrating one embodiment for determining solution bag head height is illustrated. System  300  of  FIG. 23  includes solution bags  302  and  304 , which are connected fluidly to pump chambers  306  and  308  via fluid lines  310  and  312 , respectively. Pump chambers  306  and  308  house flexible diaphragms  314  and  316 , respectively. Dialysate or therapy fluid can flow from pump chambers  306  and  308  when fluid valves  318  and  320  are opened, through fluid pathway  322 , to drain bag  324 . 
     System  300  includes valves  326  and  328  connected fluidly to chamber  306  and valves  330  and  332  connected fluidly to chamber  308 . Air/vacuum chambers  338  and  340  are placed between valves  326  and  328  and  330  and  332 , respectively. Differential pressure sensors  334  and  336  sense differential pressure within chambers  338  and  340 , respectively. It should be appreciated that if valves  326 ,  328 ,  330  and  332  are open, while pump chambers  306  and  308  are empty, differential pressure sensor  334  (placed between valves  326  and  328 ) and differential pressure sensor  336  (placed between valves  330  and  332 ) and are zeroed because the pressures in air/vacuum chambers  338  and  340  are equal to atmospheric pressure. 
     As seen in  FIG. 24 , when valves  318 ,  320 ,  328  and  332  are closed and fluid valves  326 ,  330 ,  342  and  344  are opened, fluid from solution bags  302  and  304  flows vertically down fluid pathways  310  and  312 , respectively, into pump chambers  306  and  308 . Respective flexible diaphragms  314  and  316  move when fluid flows into pump chambers  306  and  308 , causing a pressure rise in the air trapped in air/vacuum chambers  338  and  340 . Fluid flows into chambers  306  and  308 , through open valves  342  and  344 , until the pressure in respective air/vacuum chambers  338  and  340 , as measured by pressure sensors  334  and  336 , is equal to the pressure exerted by the solution (approximately water for purposes of density) in columns that are equal in height to vertical distances Y 1  and Y 2 . 
     If the pressure equivalent to that exerted by columns of solution of heights Y 1  and Y 2  is within a predetermined operating parameter for the medical fluid therapy system  300  (e.g., an APD system), the therapy is allowed to continue. If not, a suitable alarm is posted informing the patient or operator that one or both solution bags  302  or  304  is positioned outside the operating parameters of system  300 . 
     A pressure difference caused by differences in the vertical positions (pressure head heights) of solution bags  302  and  304  also has to be within set limits for system  300  to operate within specification in one embodiment. An inlet side of a pump subjected to a negative head height results in less fluid being pumped for each stroke of chambers  306  and  308 , as compared to strokes made when positive head height pressure is seen on the inlet side of a pump. Therefore when equal volumes of different solutions are being pumped by chambers  306  and  308  and mixed at a desired ratio, e.g., 1:1, it is advantageous for the vertical positions and corresponding pressure head heights of the two solutions to be the same or substantially the same. 
     The previous description of system  300  in  FIGS. 23 and 24  illustrates how sensors  334  and  336  can be zeroed and then used to test solution bag height in the context of a filling sequence, i.e., pump chambers  306  and  308  moving from empty towards full. It should be appreciated that conversely, sensors  334  and  336  can be zeroed and then used to test drain bag height in the context of a drain sequence, i.e., pump chambers  306  and  308  moving full or partially full towards empty. 
     In the drain test, pump chambers  306  and  308  are first filled with fluid from solution bags  302  and  304 , respectively, by opening valves  342  and  344 , so that therapy fluid flows through fluid pathways  310  and  312 , respectively, and into pump chambers  306  and  308  as shown in  FIG. 24 . Valves  326 ,  328 ,  330  and  332  are then opened, allowing the pressure in air/vacuum chambers  334  and  336  to be zeroed with respect to atmospheric pressure and enabling the differential pressure sensor readings of sensors  334  and  336  to be set or reset to zero. 
     Valves  342 ,  344 ,  328  and  332  are then closed and valves  318 ,  320 ,  326  and  330  are opened. Fluid flows then from pump chambers  306  and  308 , through fluid pathway  322 , to drain bag  324 . Diaphragms  314  and  316  within pump chambers  306  and  308  move accordingly, creating vacuums respectively inside air/vacuum chambers  338  and  340 . Fluid flow stops when the vacuum in air/vacuum chambers  338  and  340 , measured by pressure sensors  334  and  336 , respectively, is equal to a column of solution (negative pressure head height) of height Y 3  shown in  FIG. 23 . 
     The drain test ensures that the drain bag/drain line discharge is located below pump chambers  306  and  308 , so that no backflow occurs due to gravity. The drain test also ensures that the drain is not located too far below the pumps and valves, wherein the location causes an adverse effect on the operation of the valves. If the pressure equivalent to a column of solution of height Y 3  is within a predetermined operating parameter for the medical fluid therapy system  300 , the therapy is allowed to continue. If not, a suitable alarm is posted informing the patient or operator that the drain bag  324  is positioned outside the operating parameters of system  300 . 
     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 intended that such changes and modifications be covered by the appended claims.