Abstract:
A renal therapy blood cleaning system includes: a blood filtering device in communication with an extracorporeal circuit; a first pump configured to pump fluid to the blood filtering device; a second pump configured to pump fluid from the blood filtering device; a balance chamber in fluid communication with first and second lines, the first and second lines in fluid communication with the first and second pumps, respectively, the balance chamber configured to exchange like volumes of fresh and spent fluid; a plurality of valves; and a control scheme programmed to operate the plurality of valves to enable spent fluid taken from the balancing chamber through one of the first and second lines to be recirculated to the balance chamber through the other of the first and second lines to compensate for a volume of fresh fluid delivered to the blood filtering device.

Description:
PRIORITY 
       [0001]    This application claims priority to and the benefit as a divisional application of U.S. patent application entitled, “MEDICAL FLUID THERAPY FLOW CONTROL SYSTEMS AND METHODS”, Ser. No. 10/738,446, filed Dec. 16, 2003. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to medical systems and more particularly to medical fluid treatment therapies. 
         [0003]    Due to disease, injury or other causes, a person&#39;s renal system can fail. In renal failure of any cause, there are several physiological derangements. The balance of water, minerals and the excretion of daily metabolic load are reduced or no longer possible in renal failure. During renal failure, toxic end products of nitrogen metabolism (e.g., urea, creatinine, uric acid, and others) can accumulate in blood and tissues. 
         [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 sustaining. One who has failed kidneys could not continue to live without replacing at least the filtration functions of the kidneys. 
         [0005]    Hemodialysis (“HD”), hemofiltration (“HF”), hemodiafiltration (“HDF”) and peritoneal dialysis (“PD”) are types of dialysis therapies generally used to treat loss of kidney function. Peritoneal dialysis utilizes a sterile dialysis solution, or “dialysate”, which is infused into a patient&#39;s peritoneal cavity and into contact with the patient&#39;s peritoneal membrane. Waste, toxins and excess water pass from the patient&#39;s bloodstream through the peritoneal membrane and into the dialysate. The transfer of waste, toxins, and excess water from the bloodstream into the dialysate occurs due to diffusion and osmosis during a dwell period as an osmotic agent in the dialysate creates an osmotic gradient across the membrane. The spent dialysate is later drained from the patient&#39;s peritoneal cavity to remove the waste, toxins and excess water from the patient. 
         [0006]    Hemodialysis treatment removes waste, toxins and excess water directly from the patient&#39;s blood. The patient is connected to a hemodialysis machine and the patient&#39;s blood is pumped through the machine. Needles or catheters are inserted into the patient&#39;s veins and arteries to create a blood flow path to and from the hemodialysis machine. As blood passes through a dialyzer in the hemodialysis machine, the dialyzer removes the waste, toxins and excess water from the patient&#39;s blood and returns the cleansed blood back to the patient. A large amount of dialysate, for example about ninety to one hundred twenty liters, is used by most hemodialysis machines to dialyze the blood during a single hemodialysis therapy. Spent dialysate is discarded. Hemodialysis treatment lasts several hours and is generally performed in a treatment center about three times per week. 
         [0007]    Hemofiltration is an effective convection-based blood cleansing technique. Blood access can be venovenous or arteriovenous. As blood flows through the hemofilter, a transmembrane pressure gradient between the blood compartment and the ultrafiltrate compartment causes plasma water to be filtered across the highly permeable membrane. As the water crosses the membrane, it convects small and large molecules across the membrane and thus cleanses the blood. A large amount of plasma water is eliminated by filtration. Therefore, in order to keep the body water balanced, fluid must be substituted continuously by a balanced electrolyte solution (replacement or substitution fluid) infused intravenously. This substitution fluid can be infused either into the arterial blood line leading to the hemofilter (predilution), into the venous blood line leaving the hemofilter (postdilution) or both. Another type of therapy, hemodiafiltration, combines the diffusion and convective cleansing modes of hemodialysis and hemofiltration. 
         [0008]    A patient&#39;s hematocrit, which is the percentage of red blood cells in the blood, is about thirty-two to thirty-six percent by volume, leaving the amount of fluid in the blood to range from about sixty-four to sixty-eight percent. In a typical HDF and HF therapy, blood flow can be about 300 ml/min, wherein about 100 ml/min of the fluid is being removed through the filter, leaving a relatively smaller percentage of the blood as fluid to exit the hemofilter and to thereafter receive an amount of dialysate. 
         [0009]    Postdilution is a more efficient blood clearance mode than predilution HF or HDF. In some instances, postdilution HF or HDF can be fifty percent more efficient than predilution HF or HDF. With postdilution clearance, however, blood exits the body and enters the filter before the extracorporeal circuit receives therapy fluid or dialysate. Because the hemodialyzer or hemofilter can remove a good portion of the liquid from the patient&#39;s blood, postdilution clearance can hemoconcentrate or clot the blood filter. Predilution clearance, on the other hand, infuses fresh therapy fluid into the extracorporeal circuit before the filter and therefore at least substantially reduces the possibility that blood will clot in the hemofilter or hemodialyzer. 
         [0010]    With predilution HF or HDF, the dialysate is fed into the extracorporeal circuit prior to the hemofilter. Some of that fluid is then immediately removed by the filter, rendering the therapy less effective than postdilution therapy. Blood leaving the filter, however, has the same percentage liquid, e.g., sixty-four to sixty-eight percent, as the blood leaving the patient, reducing the chances of clotting or aggregating blood platelets because the blood has too high a percentage of solids. 
         [0011]    It is therefore desirable to provide a hemofiltration and/or a hemodiafiltration system that can perform both predilution or postdilution clearance modes. 
         [0012]    It is also desirable to provide an HF and/or an HDF system that provides a priming function, bolus infusion function and/or a blood rinseback function. System priming occurs at the beginning of therapy to remove air from the line, which would be harmful if delivered to the patient. The prime purges the air with a sterile or substantially sterile electrolyte solution. 
         [0013]    At certain times during HF or HDF therapy it is necessary to deliver a bolus or relatively large volume of fluid to the patient. It may happen during therapy that too much blood is removed from the patient too quickly. The patient&#39;s vascular space contains only five to six liters of blood. Removing too much blood too quickly can possibly lower the pressure in the vascular space. The patient&#39;s heart rate will quicken and the vascular system will contract in an attempt to compensate for the loss in blood pressure, however, such measures may not be enough to prevent the patient from becoming hypotensive. In such a case, providing a bolus or volume of fluid to the patient is one effective procedure for increasing the blood pressure in the vascular system. 
         [0014]    It is further desirable to have an HF or HDF system that can provide a blood rinseback at the end of therapy. At the end of therapy there is typically blood that remains in the extracorporeal circuit. It is desirable to return as much of that blood as possible to the patient. To do so, the blood therapy system needs to have the ability to pass a volume of fluid through the blood circuit sufficient to push the blood remaining therein back to the patient. 
         [0015]    Both the bolus feature and the rinseback feature present challenges to the machine manufacturer. For instance, if the machine uses a fluid balancing system or match flow equalizer that removes an equal amount of fluid from the patient for each amount of fluid delivered to the patient, that balancing system must be accounted for to enable a positive net fluid volume to be delivered to the patient. Second, since the fluid is delivered directly to the extracorporeal circuit, the bolus or rinseback fluid needs to be sterile or of an injectable quality. 
         [0016]    Removing ultrafiltrate (“UF”) from the patient is a precise operation in which a specific amount of fluid needs to be removed from the patient over the course of therapy. The amount of fluid removed from the patient therefore needs to be carefully monitored. In that regard, problems arise if the device or devices controlling the UF rate or volume output fails, e.g., if a valve fails. In such a case, uncontrolled flow from the patient can occur causing an overfiltration of the patient. It is therefore desirable to have an ultrafiltration flow control device that fails in such a way that fluid flow is blocked and uncontrolled UF removal does not occur. 
         [0017]    Certain HF and HDF machines generate the fluid used during therapy at the time and place that the therapy takes place. Those machines are referred to as “on-line” machines because they make and provide the solution on-line. On-line machines use micro or ultrafilters to sterilize the solution or make it of an injectable quality before the solution is delivered to the patient&#39;s extracorporeal circuit. The filters over time accumulate bacteria and endotoxin along the outer filtering surfaces of the membranes located inside the filters. It is therefore desirable to have a method and apparatus that cleans or at least reduces the amount of bacteria and endotoxin that accumulate and reside along the membranes of the filters used to create dialysate on-line. 
       SUMMARY OF THE INVENTION 
       [0018]    The present invention provides systems and methods for improving medical fluid delivery systems, such as hemodialysis (“HD”), hemofiltration (“HF”) and hemodiafiltration (“HDF”) systems. The present invention includes a multitude of aspects relating to medical fluid flow. In one aspect, systems and methods for selectively performing pre- and postdilution HF and HDF clearance modes are provided. In another aspect, systems and methods for providing priming, bolus and rinseback fluid volumes during/after HF and HDF therapies are provided. In a further primary aspect, improved systems and methods for removing ultrafiltrate from the patient are provided. In still a further aspect, the present invention provides an improved filtration configuration and method. 
         [0019]    In one aspect of the present invention, an HF or HDF system is provided that performs pre- and/or postdilution clearance modes, e.g., concurrently or simultaneously. The system efficiently uses flow components to perform both pre- and postdilution clearance modes. For example, the system does not require an extra pump or an additional pump segment to be located in the substitution fluid line, wherein such additional components would have to be integrated into the machine to react appropriately to alarms and operator settings, etc. 
         [0020]    The pre/postdilution feature of the present invention instead uses a “Y” connector located at the output of the system&#39;s substitution line. A first leg of the “Y” connector extends to the postdilution drip chamber. A first check valve is placed on the first leg to prevent blood from backing into the first leg or substitution fluid infusion line. The second leg of the “Y” can be used for multiple purposes, such as for a connection to the predilution drip chamber or the arterial line to prime the extracorporeal circuit. In the present invention, the second leg is used to deliver dialysate, prefilter, to the blood line. A second check valve is accordingly placed on the second leg to prevent blood from backing into the substitution line. 
         [0021]    Two substitution line pinch clamps are provided, one for each leg output of the “Y” connector. In one embodiment, when pre- and postdilution are desired during the same therapy, the arterial line is primed. When the patient or nurse is ready to connect the dialysate lines to the dialyzer, the second leg of the “Y” connector is connected fluidly to an arterial drip chamber located upstream from the blood pump. The first leg of the “Y” connector is connected fluidly to the venous drip chamber. The electrically or pneumatically actuated substitution line pinch clamps placed on each of the first and second legs extending from the “Y” connector control the amount of substitution fluid used for predilution and postdilution infusion. 
         [0022]    In one embodiment, the operator sets a total target substitution fluid volume that the patient is to receive. In addition, the operator inputs a percentage pre-versus postdilution setting, for example, by setting a specific predilution volume or flowrate or postdilution volume or flowrate or enters a percent predilution versus a percent postdilution. Upon starting therapy, the single substitution pump runs continuously, while the clamps alternate to achieve the desired pre- and postdilution percentage. For example, if the total substitution flowrate is 150 milliliters/minute (“ml/min”) and a fifty ml/min substitution predilution flowrate is desired, the postdilution clamp could be closed while the predilution clamp is opened for, e.g., five seconds, followed by the predilution clamp being closed and the postdilution clamp being opened for ten seconds. The result is a continuously running flow of fluid into one of the arterial or venous drip chambers, for example, to perform postdilution therapy a majority of the time for its improved clearance ability, while performing predilution therapy enough of the time to prevent blood clotting and hypotension. 
         [0023]    The system is provided with suitable alarms and assurances, such as a sensor that senses if one or both the clamps is in the wrong position, e.g., both clamps being closed at the same time. In such a case, the machine sends an appropriate alarm and takes an appropriate evasive action. There are many alternative technologies to sense clamp position, such as via a microswitch, Reed switch, Hall effect switch, optical sensing, ultrasonic sensing, pressure transducer and the like. 
         [0024]    In another aspect of the present invention, an HF/HDF system is provided that performs special fluid delivery functions, such as a prime, a bolus function and a blood rinseback using fluid components in an efficient arrangement. Those function can be commenced manually or automatically, e.g., upon receipt of a signal from a suitable biosensor. In one embodiment, a two-way isolate valve is placed in the post dialyzer therapy fluid or dialysate circuit. The isolate valve is electrically or pneumatically controlled by the machine controller to perform one of a plurality of functions at a desired time in therapy. 
         [0025]    In one implementation, the isolate valve is used to perform a bolus infusion, e.g., to stabilize the patient who has low blood pressure or is hypotensive. The bolus amount can be predetermined or entered at the time it is needed. Upon an operator input or suitable signal from a sensor, a bypass valve in the upstream dialysate line is closed or de-energized so that normal flow to the dialyzer is stopped and so that an ultrafiltrate flowmeter is turned off. The isolate valve located downstream of the dialyzer is also closed, so that the dialyzer is isolated between the bypass and isolate valves. Transmembrane pressure (“TMP”) alarm limits, operable during normal therapy, are disabled while the dialyzer is isolated. A purge valve located upstream from the bypass valve is opened, allowing post dialyzer fluid sent previously to drain to be drawn through the purge valve to match the flow of fluid to the patient that flows through the balancing chambers or flow equalizer. The volume of fluid flowing to the patient flows through at least one filter, out of a substitution port, is pumped via the substitution pump to the venous drip chamber and through the venous access line to the patient. After the bolus amount is delivered, the purge valve is closed and the patient&#39;s blood pressure is allowed to stabilize. Next, the isolate valve is opened, the TMP limits are reset and normal therapy is resumed. 
         [0026]    The above apparatus is also suitable to perform a substitution fluid rinseback at the end of therapy to rinse blood remaining in the extracorporeal circuit back to the patient. Here, the operator begins the procedure by pressing a “Rinseback” button and perhaps a “Verify” confirmation input. The rinseback feature, like the bolus volume, can be initiated automatically. An amount of rinseback solution can be preset or set at the time of the procedure. The valve configuration and operation described above is repeated using the bypass valve, isolate valve, TMP alarm limits and purge valve. The substitution pump delivers the programmed rinseback amount to the patient. Again, previously discarded solution is pulled back through the system to balance the fluid flowing to the patient through the match flow equalizer. Here, instead of delivering the amount to the venous dialyzer, as with the bolus solution, the amount is delivered to the arterial access line prior to the arterial drip chamber, so that as much of the extracorporeal circuit as possible is rinsed. 
         [0027]    To communicate the substitution pump with the arterial access line, the operator can connect the access line to the second leg of the “Y” connector described above. Or, if the system is used in combination with the pinch clamps described above, the post-dilution clamp is closed and the predilution clamp is opened, allowing for automatic operation. 
         [0028]    The machine is set to alert the operator when the rinseback is complete. After the fluid pressures have stabilized, the purge valve is closed, the isolate valve and bypass valve are opened, the TMP limits are activated and treatment is ended per the normal procedure. 
         [0029]    In a further aspect of the present invention, the machine uses a ceramic piston rotating reciprocating pump for ultrafiltration (“UF”) instead of a more complicated, more accident prone and more expensive diaphragm pump type UF flowmeter assembly. The location of the ceramic pump is predialyzer, immediately downstream of the purge valves. The rotating, reciprocating piston pump is capable of running at a suitable high rate of speed, such as four to eight liters per hour, for rinse and disinfect modes. During therapy, the pump runs at a flowrate equivalent to the desired patient UF rate. 
         [0030]    The substitution fluid flow and a volumetric equivalent to the patient&#39;s UF is taken from the flow path pre-dialyzer, that is, fresh solution is removed from the system. In one embodiment, the ceramic pump operates with balancing chambers that add and remove an equal volume of fluid to and from the system. Any fluid taken from the system by the ceramic piston pump and any substitution fluid given to the patient as an HDF or an HF infusion is automatically removed from the patient by the post-flow balancing chamber. The fresh solution is removed from the dialysate flow path, therefore, downstream from the balancing chambers so as not upset the balance of same. 
         [0031]    There are many advantages to using the ceramic pump and associated flow configuration. The rotating reciprocating ceramic piston pump does not allow flow directly from the input to the output, in contrast to the balancing chamber type UF flowmeter. If the balancing chamber type of UF device fails, there is an uncontrolled flow during half of the cycle, resulting possibly in an overfiltration of the patient. The piston pump of the present invention, on the other hand, is not subject to that type of failure, because its input port does not communicate fluidly with the pump&#39;s outlet port. If the pump fails, it fails closed, stopping fluid flow. The piston also prevents purge valve errors from causing a UF error. 
         [0032]    The rotations of the pump are monitored using a Reed Switch, optical sensor, flowmeter, tachometer or other type of feedback device, so the pump rotations and the corresponding ultrafiltration volume removed can be checked by an independent mechanism. The pump is placed before the dialyzer, preventing the pump from becoming clogged with organic substances removed from the dialyzer. The pump is, however, placed downstream from at least one membrane filter used to help purify the fresh dialysate. That arrangement provides a continual rinse along the surface of the membranes of the filters. The rinse removes at least a portion of the build-up of bacteria and endotoxin along the membrane surfaces. As a further advantage, the arrangement also removes air from the membrane filters during treatment. The removal of the balancing chamber type UF meter and addition of the rotating, reciprocating pump makes the flow path of the dialysis system simpler, while improving the safety and performance of the equipment. The ceramic piston pump in one embodiment is used to perform the rinseback and bolus infusion features that have been described previously. The pump in those applications operates in the opposite direction so that flow travels to the patient. 
         [0033]    In a further aspect, an improved filter configuration and filtration method are provided. The configuration includes at least two filters placed in series between pumps or other hydraulically complicated flow mechanisms. The filter portion of the dialysate flow path is simplified to reduce the accumulation of bacteria and endotoxin. Also, a pump located upstream of the filters is operated to create a higher flowrate than a pump located downstream from the filters. The flow differential also helps to strip accumulated bacteria and endotoxins from membrane surfaces located within the filters as well as tubing connecting the filters. 
         [0034]    Each of the above aspects can be employed alone or in any combination with one another. 
         [0035]    It is therefore an advantage of the present invention to provide a hemofiltration (“HF”) or hemodiafiltration (“HDF”) system that can perform both pre- and postdilution clearance modes with a single substitution pump. 
         [0036]    It is another advantage of the present invention to provide an HF or HDF system that performs certain net positive fluid flow functions, such as a prime, a bolus function and a rinseback function. 
         [0037]    It is a further advantage of the present invention to provide an improved ultrafiltrate flow metering system. 
         [0038]    It is yet another advantage of the present invention to provide an HF or HDF system with safety improvement features. 
         [0039]    Moreover, it is an advantage of the present invention to provide an HF or HDF system with a simplified flow regime. 
         [0040]    Still further, it is an advantage of the present invention to provide an HF or HDF system with performance improvement features. 
         [0041]    Yet an additional advantage of the present invention is to provide a HF or HDF system with an improved filtration system and method. 
         [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  illustrates systems and methods of the present invention for providing pre- and/or postdilution HF/HDF clearance modes, a bolus volume to the patient, a prime to the patient and/or a blood rinseback volume to the patient. 
           [0044]      FIG. 2  illustrates one embodiment of a therapy fluid delivery manifold used in the systems and methods shown in  FIG. 1 . 
           [0045]      FIGS. 3 and 4  illustrate systems and methods of the present invention for removing ultrafiltrate from the patient and for filtering medical therapy fluid. 
           [0046]      FIGS. 5 to 7  illustrate one embodiment of an ultrafiltrate pump used in the systems and methods shown in  FIGS. 3 and 4 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0047]    The present invention provides systems and methods for improving medical fluid delivery systems, such as hemodialysis (“HD”), hemofiltration (“HF”) and hemodiafiltration (“HDF”) systems. In various embodiments, systems and methods for selectively performing pre- and postdilution HF and HDF clearance modes are provided. In other embodiments, systems and methods for providing bolus, prime and rinseback fluid volumes during/after HD, HF and HDF therapies are provided. In further embodiments, improved systems and methods for removing ultrafiltrate from the patient are provided. Still further, the present invention provides an improved filtration configuration and method. 
       Pre/Postdilution HDF and HF 
       [0048]    Referring now to the drawings and in particular to  FIG. 1 , an HF and/or HDF system  10  is illustrated. System  10  in one embodiment is part of a machine that can perform HD, HF or HDF as selected by a doctor or nurse. The machine is typically used in a treatment center and in one embodiment generates dialysis solution via generation unit  12 . One suitable dialysate generation unit  12  for system  10  is described in the maintenance manual for Baxter&#39;s System 1000® therapy machine. It should be appreciated from the disclosure herein, however, that the present invention is not limited to dialysate delivery systems or in-center systems but instead applies to any suitable medical fluid therapy treatment. 
         [0049]    Whether system  10  operates in an HF or HDF mode, system  10  includes a dialysate flow path  20  and an extracorporeal or blood circuit  70 . In dialysate flow path  20 , fluid generated via generation unit  12  is pumped via a supply pump  14  through a supply regulator  16 , which sets the maximum pressure of the dialysate in the flow path. Dialysate path  20  employs a number of flow control devices that ensure that the desired amount of fluid is delivered to and removed from the patient (described in commonly owned U.S. Pat. No. 5,486,286, the teachings of which are incorporated herein by reference). In particular, dialysate flow path  20  includes a flow equalizer or balancing chamber  30  and an ultrafiltrate flowmeter  50 . Flow equalizer  30  includes a pair of fixed volume chambers  32  and  34  that each have a flexible membrane within, creating four variable volume cavities C 1 , C 2 , C 3  and C 4 . For fixed chamber  32 , the volume in variable cavity C 1  is inversely proportional to the volume in variable cavity C 2 . Likewise, for fixed chamber  34 , the volume in variable cavity C 3  is inversely proportional to the volume in variable cavity C 4 . 
         [0050]    The two chamber pairs  32  and  34  are provided so that one fixed volume chamber  32  or  34  pumps fluid to the filter/dialyzer, while at the same time, a second fixed volume chamber  32  or  34  pumps an equal amount of fluid from the filter/dialyzer. Match flow equalizer or balancing chamber  30  therefore ensures that any fluid going through equalizer  30  is in turn removed from equalizer  30 , resulting in a net fluid gain or loss to the patient of zero. Cavities  32  and  34  also alternate so that in each stroke fluid is pumped to and from the patient, resulting in a steady or non-pulsitile flow profile. 
         [0051]    Cavities  32  and  34  operate with inlet valves  36  and outlet valves  38 , which are alternated to achieve the above-described flow equalization. In particular, those valves are configured to enable one of the chamber pairs  32  or  34  to receive dialysate flowing through line  18  from regulator  16  to fill one of the cavities C 2  or C 4 . That filling action causes a corresponding one of the cavities C 1  or C 3  to decrease in volume and thereby push used or spent dialysate that filled cavity C 1  or C 3  in the previous stroke out line  22 , through an output pressure equalizer  24 , through a blood leak detector  26  and flow restrictor  28  to drain line  40 . While that action is happening, a dialysate pressure pump  42  is pulling spent dialysate from filter/dialyzer  44  and pushing that spent dialysate through a pressure regulating recirculation loop  46  to the other flow chamber pair  32  or  34 . Pump  42  pushes fluid into one of the variable spent dialysate cavities C 1  or C 3 . 
         [0052]    The increasing volume of spent dialysate in the variable chamber necessarily decreases a like volume of fresh dialysate that filled variable cavity C 2  or C 4  in the previous stroke, pushing same toward the patient. Fresh dialysate is pushed out line  48 , through output pressure equalizer  24 , through a first ultrafilter  52 , through a portion of filtration line  88 , through a second ultrafilter  54  and through a dialysate monitoring manifold  56 . Suitable ultrafilter brands are discussed below. From manifold  56 , fresh filtered fluid flows either through a three-way bypass valve  58 , out bypass valve through line  60  into filter/dialyzer  44  or out through substitution port  86 , through the remainder of filtration line  88  and to blood circuit  70 . 
         [0053]    As illustrated, a second outlet or bypass line  62  extends from bypass valve  58  and extends either into post-dialyzer line  64 , leading to pressure regulating recirculation loop  46 , or alternatively extends into rinse line  66  and through rinse valve  68  to drain  40 . Bypass line  62 , rinse line  66  and rinse valve  68  enable various system components to be rinsed or cleaned prior to the beginning of therapy. 
         [0054]    Blood circuit  70  includes an arterial access line  72  and a venous access line  74 . Arterial access line  72  includes a Y-connection  76  that connects to a dialysate input line described below. Arterial line  72  carries blood from patient  78  to an arterial drip chamber  80 . Blood is transferred through extracorporeal circuit  70  via a peristaltic blood pump  82 . Pump  82  pumps blood from arterial line  72 , through drip chamber  80 , to the blood inlet of dialyzer  44 . The blood is pumped through the inside of membranes contained within the dialyzer, wherein diffusive transport of toxins and waste products from the blood takes place, and from the output of dialyzer  44  into a venous drip chamber  84 , through venous access line  74 , and back to patient  78 . 
         [0055]    Predialyzer dialysate line  60 , dialyzer  44 , postdialyzer line  64  and the remainder of dialysate flow path  20  are maintained at a pressure lower than that of the blood within circuit  70 , resulting in the convective transport of waste out of the membranes within dialyzer  44  and a transport of waste and other undesirable substances from the patient&#39;s blood. System  10  is additionally or alternatively capable of performing hemofiltration, in which solution flows along filtration line  88 , through substitution port  86 , through microfilter/ultrafilter  90 , through postfilter line  92 , through substitution fluid pump  94  and through a pre/postdilution fluid manifold  100 , directly to blood circuit  70 . 
         [0056]    Referring additionally to  FIG. 2  in combination with  FIG. 1 , pre/postdilution manifold  100  is illustrated in greater detail. Filter  90  in one embodiment is a microfilter. One suitable microfilter is a Pall™ Gelman™ single use 0.22 micron filter. In another embodiment, filter  90  is an ultrafilter. One suitable reusable ultrafilter is a Medica™ Diapure™ 28 filter. One suitable single use ultrafilter is a Medica™ 150u filter. In general, microfilters differ from ultrafilters in the capability of the different filters in removing small particles. In general, ultrafilters can remove smaller particles than can microfilters. For purposes of the present invention, the term “microfilter” includes filters having a membrane pore or membrane opening size of about 1000 to about 105 Angstroms (“Å”), which effectively filters particles, such as red blood cells, yeast, fungi, bacteria and some proteins. The term “ultrafilter” as used herein includes filters having a membrane pore or membrane opening diameter or length of about 10 to about 1000 Å, which effectively filters particles such as endotoxins (pyrogen), viruses and proteins. In one preferred embodiment, the ultrafilters used in the present invention have a range of pore sizes of about 10 to about 40 Å. 
         [0057]    Filter  90  operates with ultrafilters  52  and  54  to ensure that a sterile or injectable quality fluid is pumped via substitution pump  94  into the substitution fluid manifold  100 . Fluid is pumped via pump  94 , through Y-connection  102  into either postdilution line  104  or predilution line  106 . A cap  108  is shown removed from a union  109  located at the end of pigtail  126  in line  106 . Manifold  100  in an alternative embodiment provides only postdilution line  104  and pigtail  126 , wherein remainder of line  106  is removed and the corresponding output from Y-connector  102  is capped off via cap  108 . The remainder of line  106  can then be selectively added to pigtail  126  by removing cap  108 . When predilution line  106  is fully connected, system  10  can perform either pre- and/or postdilution HF and HDF as desired. 
         [0058]    As seen in  FIG. 1 , postdilution line  104  extends to the venous drip chamber  84 . Predilution line  106  extends in one embodiment to a Y-connector or T-connector  76  positioned in a line  73 , which is located between pump  82  and drip chamber  80 . In an alternative embodiment, line  106  (shown in phantom) extends via a solenoid valve  77  (in phantom) to a second Y-connector or T-connector  79  located in arterial access line  72 , which feeds into post-pump line  73 . The alternative embodiment is used with a rinseback feature described below. As described in more detail below, it is advantageous to connect predilution line  106  to arterial access line  72  via connector  79  when system  10  is combined with the bolus, prime and rinseback features described below. It should be appreciated however that the predilution therapy operates equally as well with line  106  connected to arterial access line  72  via connector  79  or to line  73  via connector  76 . 
         [0059]    A check valve  110  is placed in postdilution line  104 , which allows fluid to flow only in the direction from pump  94  to blood circuit  70 , preventing blood from backing up through lines  92  and  88  into filters  52  and  54  or other parts of dialysate flow path  20 . Likewise, a check valve  112  is placed in predilution line  106  to prevent blood from backing into dialysate flow path  20  from predilution line  106 . 
         [0060]    Postdilution line  104  includes a pinch clamp  114 . Predilution line  106  likewise includes a pinch clamp  116 . Suitable pinch clamps for system  10  are provided for example by Medica™, Model M03122. Clamps  114  and  116  are electrically operated, pneumatically operated or are otherwise controlled via a microprocessor of system  10  to be opened and closed selectively as specified by the therapy. Manifold  100  of system  10  enables HF or HDF therapy to occur: (i) via postdilution clearance only by opening valve  114  and closing valve  116  throughout therapy; (ii) via predilution clearance only by opening valve  116  and closing valve  114  throughout therapy; (iii) via pre- and postdilution clearance modes by sequentially opening valve  114 , while valve  116  is closed and then reversing that state and opening valve  116 , while valve  114  is closed; or (iv) via pre- and postdilution clearance modes simultaneously by opening valves  114  and  116  simultaneously. 
         [0061]    Although not illustrated, when pre- and postdilution therapy is performed simultaneously, a variable flow restrictor can be placed in either one or both pre- and/or postdilution lines  106  and  104 , respectively, to partition the percentage flow of dialysate through lines  104  and  106  as desired (e.g., 80% of flow flows through postdilution line  104 , while the remaining 20% flows through predilution line  106 ). To that end, valves  114  and  116  could instead be needling-type valves that selectively allow a desired percentage flow to pass through lines  104  and  106 . Or, such needling valves can be placed in combination with on/off valves  114  and  116 , so that there are valved flow restriction settings and on/off control for both pre- and/or postdilution clearance modes. 
         [0062]    In one embodiment, the operator sets the overall target substitution volume into the machine employing system  10 . The operator then enters a percentage rate or percentage volume of pre-versus postdilution fluid flow. The single substitution pump  94  runs continuously. The clamps  114  and  116  alternate to achieve the desired pre- and postdilution clearance rates. In one example, if the desired percentage breakdown is two-thirds postdilution and one-third predilution and the total flowrate is 150 ml/min, the postdilution clamp could be closed for five seconds, while the predilution clamp  116  is open. Afterward, that state is reversed so that the predilution clamp  116  is closed, while the postdilution clamp  114  is open for the next ten seconds. That sequence is repeated throughout therapy, or at least the portion of therapy that includes convective clearance. Alternatively, flow restrictions are placed in lines  104  and  106  and set to produce the desired two-thirds postdilution of one-third predilution profile, while valves  114  and  116  are opened throughout the convective clearance portion of the therapy. 
         [0063]    The goal of diverting some of the convective flow from postdilution to predilution is to prevent hemoconcentration while providing a predominantly postdilution treatment. To that end, it is desirable not to cycle the valves over too long a period so that such a condition could occur. On the other hand, it is also desirable not to cycle the valves too frequently for wear and maintenance purposes. The desired cycle time for the valves is therefore chosen to accommodate both of those factors. 
       Bolus and Rinseback Functions 
       [0064]    Referring still to  FIG. 1 , a second primary embodiment of the present invention involves the ability of system  10  to perform not only a priming sequence, but to also provide a bolus of fluid to the patient as needed and to perform blood rinseback at the end of therapy. The bolus feature and blood rinseback feature are described hereafter in turn. 
       Bolus Infusion 
       [0065]    To provide a bolus or volume of fluid to the patient, for example, when the patient has lost too much liquid from the patient&#39;s vascular system, the bypass valve  58  is set so that dialysate flow no longer flows through predialyzer line  60  but instead bypasses the filter/dialyzer  44  and line  60  and flows alternatively through bypass line  62 . Rinse valve  68  is closed so that dialysate flowing through line  62  tees into dialysate return line  64 , which shunts the fluid through match flow equalizer  30  to drain  40 . The bypass valve  58  configuration has the effect of modifying the dialysate flow path  20  so that dialysate flow bypasses filter/dialyzer  44 . As described above, dialysate returning through line  64  is cycled through pressure regulating recirculation loop  46  via dialysate pump  42 . Recirculation loop  46  helps to control pressure at the inlet of the flow equalizer  30 . In particular, recirculation loop  46  operates with input pressure equalizer  118  and supply regulator  16 . Supply pump  14  sets a pressure along line  18 . That pressure in line  18  moves a diaphragm within input pressure equalizer  118  back and forth, which either restricts an orifice that builds pressure in loop  46  or opens the orifice lowering the pressure in the loop, which in turn allows more or less fluid to circulate within loop  46 . 
         [0066]    Besides de-energizing bypass valve  58  so that dialysate flows through bypass line  62 , shutting off flowmeter  50 , an isolate valve  120  placed in postdialyzer line  64  is closed. Valves  58  and  120  completely isolate filter/dialyzer  44  from the remainder of dialysate flow path  20 . To create the bolus volume, with filter/dialyzer  44  isolated, purge valve  122  is opened to drain. At the same time, a portion of the fluid flowing from flow equalizer  30  to bypass valve  58  flows through filtration line  88 , out of substitution port  86 , through filter  90 , through postfilter line  92  and is pumped via substitution pump  94  and postdilution line  104  (or predilution line  106 ) through venous drip chamber  84 , which purges any air from the solution, allowing an injectable quality bolus or volume of fluid to flow into patient  78  via venous access line  74 . Since valve  122  is connected to an open source of fluid, namely, from fluid pumped via flow equalizer cavities C 1  and C 3 , through blood leak detector  26 , through flow restrictor  28 , through line  125  and though line  126  (shown with dual directionally pointed arrows), a volumetric equivalent to the fluid pumped to the extracorporeal circuit  70  via pump  94  can be infused into the system between the pre and post flow equalizers of equalizer  30 . After the fluid flows goes through valve  122 , the fluid flows through filters  52 ,  54  and  90  and is monitored for proper conductivity and temperature. Pump  94  will shut down if any of those measurements is outside of a correct range. 
         [0067]    The control scheme of system  10  is operable to manually or automatically initiate the bolus volume. In one embodiment, the control scheme automatically commences the bolus feature upon receiving an appropriate signal from a biosensor, such as a hemoconcentration sensor, a blood volume sensor, an electrolyte sensor, an oxygen sensor and any combination thereof. 
         [0068]    It is important to note that the transmembrane pressure (“TMP”) alarm limits should be disabled or opened during the time that the isolate valve is closed. The TMP alarms in normal operation ensure that there is a positive pressure differential from the blood circuit  70  to the dialysate flow path  20  through dialyzer  44 , so that the net flow of liquid is from the blood stream to the dialysate flow path  20 . In addition, the TMP is monitored to detect pressure changes that may indicate a problem. When isolate valve  120  is closed, the TMP in dialyzer  44  isolated between valve  120  and bypass valve  58  may tend to equalize. However, because dialysis is not being performed at this moment, such equalization is not a concern and thus the alarms are not necessary. 
         [0069]    Flow equalizer  30  requires an equal volume of fluid to flow from line  18  to the equalizer as the volume flowing to equalizer  30  from recirculation loop  46 . It should be appreciated that because there is a volume of fluid being delivered to the patient and no fluid can be pulled from the patient with dialyzer  44  isolated, less fluid would return to flow equalizer  30  through line  62 , compared to the amount of fresh fluid delivered to flow equalizer  30  from source  12 . Accordingly, a makeup source of fluid is needed. For example, if supply pump  14  delivers 300 ml/min to flow equalizer  30  and 100 ml/min is pulled through substitution port  86  to the patient, only 200 ml/min will return through bypass line  62 , postdialyzer line  64 , recirculation loop  46  to flow equalizer  30 . The fluid return is deficient by 100 ml/min with respect to the 300 ml/min global supplied via source  12 , and such deficiency will cause flow equalizer  30  to operate improperly. 
         [0070]    To provide the additional fluid, purge valve  122 , which operates with ultrafilter  52 , is opened during the bolus infusion as discussed above. Purge valves  122  and  124  operate normally with ultrafilters  52  and  54 , respectively, to enable the filters to be rinsed prior to therapy. Opening purge valve  122  enables the additional needed fluid, e.g., the additional 100 ml/min, to be pulled through lines  125  and  126  and into the dialysate flow path  20 . Liquid pulled through drain line  126  has previously flowed through dialyzer  44  and been pumped to drain  40  after passing through flow equalizer  30 . Accordingly, the additional fluid pulled through line  126  needs to be sterilized to be of an injectable quality. The filters  52  and  54  and additional disposable filter  90  in filtration line  88  achieve that requirement. That is, fluid entering system  20  through purge valve  122  flows through ultrafilters  52  and  54 , out substitution port  86 , through a third ultrafilter or microfilter  90  and ultimately to patient  78 . Filters  52  and  54  in one embodiment are large surface area, reusable filters. Disposable filter  90  can be an ultrafilter or a microfilter. Placing three filters in series enables system  10  to have triple redundancy during normal operation and for the bolus infusion. 
         [0071]    As an extra safety measure, if for some reason the makeup fluid pulled from drain line  126  and passing through both filters  52  and  54  does not produce an injectable quality solution, dialysate monitoring manifold  56 , which includes a dialysate conductivity probe, temperature sensor, a flow sensor and a dialysate pressure transducer will trip an alarm upon which substitution pump  94  is shut down. In the event that an alarm is tripped and substitution pump  94  is shut down, the configuration of the peristaltic pump  94  is such that the rotating head clamps the tubing off at a point along the tubing wrapped around the pump head, effectively stopping flow of fluid at that point. 
         [0072]    To deliver the bolus volume, the substitution pump  94  pumps the volume through a check valve, such as check valve  110  of post dilution line  104 , into venous drip chamber  84 . It should be appreciated that pre- and postdilution manifold  100  is not necessary to practice the bolus solution feature of the present invention. However, the bolus solution volume can be implemented via pre- and postdilution manifold  100  discussed above. To do so, pinch clamp  114  is opened to allow the bolus volume to pass through check valve  110 , pass by clamp  114  and travel via line  104  to drip chamber  84  or, pinch clamp  116  is opened to allow the bolus volume to pass through check valve  112 , pass by clamp  116  via line  106  and travel to drip chamber  80 . From drip chamber  80  or  84  the bolus volume travels via venous access line  74  to patient  78 . 
         [0073]    The amount of the bolus volume is either predetermined or set by the operator upon initiating the bolus function, for example, via a touch screen controller. In one embodiment, the bolus amount is set into the machine employing system  10  via a keypad on the touch screen. The amount of bolus can be controlled, for example, by monitoring the number of rotations of substitution pump  94  or by pumping until a desired setting is achieved on one of the biosensors described above. After the bolus volume is delivered to the patient, isolate valve  120  is opened, purge valve  122  is closed, and bypass valve  58  is energized to allow dialysate to flow through predialyzer line  60 , and not to line  62 . Opening valves  120  and  58  re-establishes fluid communication with dialyzer  44 . The TMP limits are accordingly reset or reopened. Prior to opening isolate valve  120 , one stroke can be taken of the UF flowmeter  50  to help create a positive transmembrane pressure when isolate valve  120  is opened. That procedure may be helpful in achieving a set UF target for the patient. 
       Blood Rinseback 
       [0074]    The blood rinseback feature of the present invention operates in a similar manner to the bolus infusion feature described above. The blood rinseback amount can be set at the time the procedure is started or preset according to a prescription or therapy protocol. Again, a touch screen having a keypad can be used to set the rinseback amount. While the rinseback function can be initiated manually in one embodiment, the present invention also contemplates automatically starting the rinseback function at the end of treatment. Further, while the blood rinseback procedure can be controlled by inputting a set amount of fluid, it is also possible to control the feature via a blood detector placed near the patient end of venous access line  74 , which detects when no more blood is present in blood circuit  70  and stops substitution pump  94  accordingly and automatically. 
         [0075]    Each of the major steps described above for performing the bolus infusion procedure is also performed for the blood rinseback procedure. Obviously, the procedures are performed at different times during therapy because the different procedures are for different purposes. The bolus function as described above is initiated manually or automatically when the patient appears to have become or is becoming hypotensive. Blood rinseback is performed at the end of treatment to push any blood remaining in the system back to patient  78 . Nevertheless, both procedures involve the use of isolate valve  120  and bypass valve  58  to isolate dialyzer  44  from the remainder of dialysate flow path  20 . Also, purge valve  122  is opened to enable an equal amount of fluid delivered to patient  78  to be drawn via drain line  126 , through filters  52 ,  54  and  90  into dialysate flow path  20 , so that flow equalizer  30  operates properly. 
         [0076]    One difference between the bolus function and the blood rinseback procedure is the location at which the blood rinseback volume is delivered to extracorporeal circuit  70 . As discussed above, the bolus volume can be delivered to venous drip chamber  84 . The rinseback amount is delivered on the other hand to the end of or to a point of arterial access line  72  marked by Y-connector or T-connector  79 , which is appropriate to clean blood in arterial line  72  through pump  82 , through arterial drip chamber  80 , through dialyzer  44 , through venous drip chamber  84  and finally through venous access line  74  to patient  78 . Connector  79  is connected to predilution line  106  via solenoid valve  77  to enable automatic control of the rinseback feature. It is contemplated therefore to use the pre- and postdilution manifold  100  in combination with the rinseback feature of system  10  and to deliver the rinseback volume from substitution pump  94 , through Y-connector  102 , through predilution line  106 , including check valve  112  and pinch valve  116 , through line  106  and solenoid  77 , to the arterial access line  72  at connector  79 . 
         [0077]    It should be appreciated, however, that manifold  100  is not necessary to deliver the rinseback volume of the present invention. For instance, the fluid connection can be made manually by the operator or nurse.  FIGS. 1 and 2  show a cap  108  that connects to a union  109  located at the end of pigtail  126 . It is possible that instead of using the already existing predilution line  106  when the rinseback volume is needed, cap  108  is removed from the union  109  of pigtail  126  and a substitution line (not illustrated) is manually coupled to the end of pigtail  126  and to either connector  79  of line  72  after being uncoupled from the patient or to connector  76  located in line  73 , for example, by removing a cap from connection  76 . In a preferred embodiment, that substitution line would include at its end a one-way valve or check valve, such as check valve  112 . 
         [0078]    To couple the substitution line manually to connectors  76  or  79 , blood pump  82  is shut down and either a cap is removed from connector  79  or the arterial access line  72  is disconnected from an arterial needle of the catheter that is inserted into patient  78 . A clamp is closed at the end of the arterial needle so that no blood is lost from the patient. Connector  76  or  79  is then connected to the substitution line, which is also connected to the end of pigtail  126 . In a further alternative embodiment, a luer connector with a rotating hub is provided in one embodiment at the end of arterial access line  72  to couple the line directly to the substitution line extending from pigtail  126 . After that connection is made, the rinseback volume is delivered as described above. 
         [0079]    The known way to provide a rinseback is to connect a saline bag to the arterial access line  72  after disconnecting such line from the arterial needle. Thereafter, saline flows from the saline bag through the arterial access line  72  to provide the saline rinseback or flush. Both the manual and automatically operating embodiments described above enable system  10  to eliminate the need for a separate saline or injectable solution supply to provide the blood rinseback. 
       Prime 
       [0080]    The prime feature of the present invention operates using the apparatus described above in connection with  FIG. 1  for the bolus and rinseback features to prime the extracorporeal circuit  70  prior to therapy. The prime includes a volume of fluid, such as dialysate, that is delivered at the beginning of the therapy to remove air from the extracorporeal circuit. The prime feature is used within a system or with a controller that is operable to receive an operator input to commence delivery of the prime. Alternatively, the system or controller is operable to commence delivery of the prime automatically at the beginning of therapy. In one embodiment, the amount or volume of the prime is entered by an operator when commencing delivery of the prime. The amount or volume can be predetermined prior to commencement of therapy. Alternatively, the amount or volume is delivered until air is no longer sensed in the extracorporeal circuit. 
       UF Flowmeter 
       [0081]    Referring now to  FIGS. 3 to 7 , another primary embodiment of the present invention is illustrated.  FIGS. 3 and 4  illustrate systems  150  and  160 , respectively, which include many of the same components described above in connection with  FIGS. 1 and 2 . Those components are marked with the same element numbers as used in  FIGS. 1 and 2 . The description of those elements including each of the alternatives discussed above in connection with  FIGS. 1 and 2  apply equally to like element numbers in  FIGS. 3 and 4 . 
         [0082]    One primary difference between the embodiments described in  FIGS. 1 and 2  compared with the systems  150  and  160  of  FIGS. 3 and 4  is that the UF flowmeter  50  is removed in  FIGS. 3 and 4 . The function of the UF flowmeter so shown in  FIGS. 1 and 2  is to remove fluid from the patient  78  that has accumulated in the patient&#39;s body over the time between the patient&#39;s last therapy and the current therapy. One of the problems that occurs with kidney failure is that the patient in many instances loses some or all of the ability to urinate. The fluid that would otherwise be removed from the patient via urination becomes stored in the patient&#39;s blood and surrounding tissues. Thus, while the dialyzer and the infusion of clean solution into patient  78  operate to clear waste products and other undesirable products from patient  78 , UF flowmeter  50  operates to remove an additional amount of fluid from the patient, which is equivalent to the amount of fluid gained by the patient between treatments. 
         [0083]    UF flowmeter  50  operates in a similar manner to one of the chamber pairs  32  and  34  of flow equalizer  30 . UF flowmeter  50  defines a fixed volume chamber  132  that is separated by a diaphragm into two alternating variable volume cavities C 5  and C 6 . Fixed volume chamber  132  is sized in a desired relation to the matched volume chambers  32  and  34 . Inlet valves  136  and  138  of UF flowmeter  50  can be cycled with inlet valves  36  and outlet valves  38  of flow equalizer  30 . In that manner, a known volume of fluid is removed with each stroke or valve cycle. The valves  136  and  138  alternate so that cavity C 6  fills and pushes fluid previously drawn into cavity C 5  through one of the outlet valves  138 , whereafter the valves switch so that cavity C 5  fills and pushes the previously filled volume in cavity C 6  through the other outlet valve  138 . 
         [0084]    UF flowmeter  50  is an effective but relatively complicated device. Also, the failure of one of the valves  136  or  138  can cause an uncontrolled flow during half of a cycle of the diaphragm, resulting in an overfiltration of the patient. 
         [0085]    Another potential problem with system  10  illustrated in  FIG. 1  is that air can become trapped in ultrafilters  52  and  54 . It is possible for air to also become trapped in disposable filter  90 , however, it is more likely that air enters reusable filters  52  and  54 . Another possible problem with system  10  is that dialysate pump  42  is placed directly in front of a UF removal line  134 , which leads to UF flowmeter  50 . That configuration can lead to the clogging of UF meter  50 . Also, the purge valves  122  and  124  are closed during normal therapy in system  10 , so that there is no flow across the outside the membranes of those filters (operational flow through filters is from the inlet of the filters to outside the membranes inside the ultrafilters, through the walls of the membranes, and through the inside of the membranes out the outlet of the ultrafilters). The material that is filtered in filters  52  and  54  remains inside the filters until a rinse cycle is performed after therapy, when purge valves  122  and  124  are opened. That is, bacteria and endotoxin that are filtered by the membranes inside ultrafilters  52  and  54  remain inside those filters throughout the duration of therapy. 
         [0086]    Another potential problem in system  10  of  FIG. 1  is that the only way to detect if one of the purge valves  122  and  124  is not functioning properly is to detect an increase or decrease in TMP. A TMP error that is not examined and diagnosed properly by an operator could result in a UF error for the patient. 
         [0087]    Referring now to  FIGS. 3 and 4 , the above-described problems are solved by removing UF flowmeter  50  and replacing same with a ceramic UF pump  140  in dialysate flow path  20 . Ultra pure dialysate for online HF and online HDF treatments is enabled by locating ceramic pump  140  downstream from the single purge valve  122  in system  150  of  FIG. 3  and downstream of dual purge valves  122  and  124  in system  160  of  FIG. 4 . In both cases, the purge valves are located downstream from the rinse outlet  142  of one of the ultrafilters  52  or  54 . Fluid that reaches pump  140  is therefore fluid that is to be removed along drain line  126 . As discussed below, pump  140  is a ceramic rotating, reciprocating piston pump in one embodiment, which is advantageous because it does not establish fluid communication between the inlet and outlet of the pump. That pump configuration enables the pump to fail safe, where uncontrolled fluid flow does not occur. 
         [0088]    Locating ceramic pump  140  downstream of purge valves  122  and  124  provides additional advantages. That is, besides isolating the inlet and outlet of the pump and thereby eliminating the potential for UF error due to component failure, locating pump  140  predialyzer reduces the possibility of the UF pump becoming clogged or corrupted with organic substances. That is, UF removed to drain from pump  140  is clean or sterile solution from generation unit  12 . The likelihood of a UF occurring error due to endotoxin and bacteria building up in the UF removal device is therefore substantially decreased in systems  150  and  160  of the present invention. 
         [0089]    Also, because pump  140  pulls fluid from the rinse outlet  142  of filters  52  and  54 , systems  150  and  160  provide a continual rinse along the outside of the membranes within those filters. In system  160  of  FIG. 4 , the purge valves  122  and  124  are cycled. e.g., at fifty percent for each valve, so that both filters  52  and  54  are rinsed and cleaned as therapy takes place. The rinse along the outer surface of the membranes of filters  52  and  54  also removes air from the filters continuously or semi-continuously during treatment. Even though pump  140  removes fresh dialysate as UF, dialyzer  44  functions as described above to diffuse waste products from the patient&#39;s blood. Waste is also removed through convective transport caused by the direct infusion of blood into the extracorporeal circuit  70 . That waste is then pumped through balancing chambers  30 , via dialysate pump  42 , to drain. The UF pumping of fresh dialysate via pump  140  does not alter the effectiveness of the therapies of systems  150  and  160 . 
         [0090]    As discussed above, one major advantage with using the ceramic rotating reciprocating piston pump  140  of the present invention is that fluid communication does not exist between the inlet and outlet of UF pump  140 .  FIGS. 5 to 7  illustrate one embodiment of UF pump  140 , which is a rotating and reciprocating piston pump.  FIGS. 5 to 7  illustrate the rotating reciprocating piston pump  140  in three states, namely, a fluid-in state in  FIG. 5 , a dwell state in  FIG. 6  and a fluid-out state in  FIG. 7 . One suitable rotating reciprocating piston pump is supplied by Diener Precision Pumps, Embrach, Switzerland. 
         [0091]    In  FIGS. 5 to 7 , valve  140  includes a rotating chamber  142  defining an opening  144  that receives an end of a rotating and reciprocating piston  146 . The end of the piston  146  includes an arm  148  with a ball bearing type head  152  that is received slidingly inside a coupling aperture  154 , which is in fluid communication with opening  144 . As chamber  142  is rotated via a shaft  156  having a substantially vertical axis, head  152  is carried by the outer wall of coupler opening  154 , which in turn rotates arm  148  and shaft  146 . Due to the angle of shaft  146  relative to substantially vertical shaft  156 , head  152 , arm  148  and shaft  146  are also translated in a direction of the angle of shall  146  back and forth depending on the rotational location of coupler opening  154  during rotation of chamber  142 . As illustrated in  FIG. 5 , during the fluid-in state, piston head  152  is pulled a further distance away from a pump body  158  than the vertical distance between piston head  152  and body  158  in the fluid-out state of pump  140  in  FIG. 7 . Piston head  152  is accordingly at an intermediate relative distance away from body  158  in the dwell state of pump  140  shown in  FIG. 6 . It should be appreciated, therefore, that the rotation of drive shaft  156  causes both a rotational motion and translational motion of shaft  146  relative to fixed body  158 . 
         [0092]    Body  158  defines port openings  162  that enable a lubricant such as water to lubricate the sliding engagement between shaft  146  and the inner bore of body  158 . Body  158  also defines inlet and outlet ports  164  and  166 , respectively. The lower end of shaft  146  defines a notch  168 . Notch  168  in the fluid-in state of pump  140  enables fluid to enter via inlet port  164  into a pump chamber  170 . Importantly, in the fluid-in state, no fluid communication exists between pump chamber  170  and outlet port  166 . In the dwell state of pump  140  in  FIG. 6 , shaft  146  has rotated to a position wherein notch  168  does not face or communicate with either port  164  or  166 , so that no fluid communication takes place between pump chamber  170  and the openings of ports  164  and  166 . In the fluid-out state of pump  140  in  FIG. 7 , shaft  146  has rotated to a position wherein notch  168  enables fluid communication to exist between pump chamber  170  and outlet port  166 . Importantly, in the fluid-out state, no fluid communication exists between pump chamber  170  and inlet port  164 . 
         [0093]    In operation, as the shaft moves from the fluid-out state ( FIG. 7 ) to the fluid-in state ( FIG. 5 ), the volume in pump chamber  170  increases, creating a vacuum and drawing fluid into chamber  170 . In the dwell state ( FIG. 6 ), the volume in pump chamber  170  has decreased from the volume in the fluid-in state ( FIG. 5 ), creating a positive pressure inside chamber  170 . As the shaft  146  moves from the dwell state ( FIG. 6 ) to the fluid-out state ( FIG. 7 ), the volume in chamber  170  further decreases and pushes fluid out of outlet port  166 . 
         [0094]    Because inlet port  164  never communicates fluidly with outlet port  166 , pump  140  even upon a failure or loss of power cannot allow an uncontrolled UF flow, decreasing significantly the inherent error potential in comparison to the error inherent in the valves  136  and  138  of prior flowmeter  50  and with the flowmeter  50  itself, as well as potential UF errors that could occur from a failure of one of the purge valves  122  and  124 . 
         [0095]    As alluded to above, the amount of ultrafiltrate removed from the patient is controlled in one embodiment by monitoring the number of rotations of shaft  146 . Rotating, reciprocating piston pump  140  is inherently accurate. If needed, however, a flow measuring device can be placed in drain line  126  to monitor the output of pump  140 . 
         [0096]    Pump  140  may also be used with each of the embodiments described above in connection with  FIGS. 1 and 2 , including the pre- and postdilution features, the bolus feature and the rinseback purge. In particular,  FIGS. 3 and 4  can employ the manifold  100  discussed above in connection with  FIG. 1  however same is not shown for the sake of clarity. To infuse the bolus and rinseback volumes, pump  140  rotates in the opposite direction to pull fluid from line  126  shown with dual directional arrows in  FIGS. 3 and 4  in the same manner as discussed above. 
       Filtration Configuration 
       [0097]    The present invention in  FIGS. 1 and 4  shows an improved filtration configuration. To produce a suitable replacement fluid for patient  78 , an electrolyte solution such as dialysate is filtered by ultrafilters and/or microfilters to achieve an injectable quality output. The present invention employs three filters in series without an intervening pump placed between the filters. The filters each add successive log reduction of bacteria and endotoxin. When a pump is placed between the filters, the pump becomes a place where bacteria and endotoxin accumulate during quiescent times, such as when the system is off. Accordingly, the present invention eliminates the need for placing a pump between the in-series filters. It should be appreciated however that sensors and other flow components besides pumps are contemplated to be placed between the in-series filters. 
         [0098]    In an attempt to remove as much bacteria and endotoxin as possible, the present systems shown in  FIGS. 1 and 4  uses three filters in series, namely, filters  52 ,  54  and  90 . Those filters help to ensure the quality of the solution by providing successive log reductions of bacteria and endotoxin. Filters  52 ,  54  and  90  can be any combination of single use or reusable ultrafilters, microfilters or other endotoxin/bacteria reducing devices, such as a clarigen dialguard column. In one embodiment, filters  52  and  54  are reusable and the hydraulics path  88  is constructed without complex hydraulic features, such as a pump, after the first filter in the system, thereby reducing risk of microbial and biofilm growth after the solution is first filtered. In one embodiment, filter  90  is a single use microfilter. 
         [0099]    For proper log reduction, it is important to lower the potential for bacteria growth and subsequent endotoxin production. To that end, the filtration configuration of  FIGS. 1 and 4  employs no pumps between filters  52 ,  54  or  90 . The flow of medical fluid from filters  52  and  54  passes through sterile tubing (and possibly other flow components) to the inlet of the next filter. Because more complex lumen surfaces of flow components have a greater the chance of forming biofilm, only tubing is provided in one embodiment between filters  52  and  54  and only a single dialysate monitoring manifold  56  is placed between filters  54  and  90 . Limiting the components between filters to only simple tubing (and possibly sensor components) helps to prevent the proliferation of bacteria on complex surfaces and to ensure the efficacy of the disinfection. 
         [0100]    The purging function during the preparation phase of the medical fluid systems of the present invention also helps to remove bacteria or endotoxin that may have grown since the machine was last used. With the simplified flow path between filters  52 ,  54  and  90 , however, very little growth occurs. 
         [0101]    Placing pumps before and after the filters  52 ,  54  and  90  enables the flowrate of fluid pumped, e.g., via dialysate pump  42 , through the filters to be higher than the flowrate pumped, e.g., via infusion pump  94 , to the patient  78 . The systems of  FIGS. 1 and 4  can therefore be set so that that the medical fluid flow to patient  78  is only a portion (albeit a potentially large portion) of the total flow out of the filters, which can be reusable filters. For instance, if the systems are used for hemofiltration and are set to flow 250 ml/min of replacement fluid to patient  78 , the flow out of filters  52 ,  54  and  90  can be 300 ml/min. The purpose for that excess flow is to prevent stagnant areas in the reusable filters at the connections of the filters to filtration line  88 , which helps to ensure that during quiescent times bacteria does not proliferate between filters  52  and  54  or after filter  54  in device  56  or filtration line  88 . 
         [0102]    Due to the use of filters in the above-described manner, the quality of the replacement fluid can be ensured through the combined log reduction of the filters and because the filters to a large extent only have to filter contamination from the incoming medical solution. In addition if one of the filters fails, the resulting log reduction of the remaining filters in most instances is still sufficient to provide a medical grade solution. In addition, the smooth clean surfaces in between the filters are easily and effectively disinfected, preventing growth during quiescent periods. It should be appreciated that while the filtration configuration described herein is particularly well suited for the systems of  FIGS. 1 and 4 , the configuration is expressly not limited to being used with the other features and inventions described in those figures and indeed is applicable to many different types of injection fluid flow regimes and configurations. 
         [0103]    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.