Abstract:
A pump assembly for ambulatory peritoneal dialysis transfer procedures includes a portable power supply geared to drive a high-volume peristaltic pump. A cassette of the pump comprises an encasement; tubing including an inner portion positioned within the encasement, a patient-side portion for connection to an indwelling peritoneal dialysis catheter and an opposing portion connectable to a system for containment and communication of a peritoneal dialysis solution which may be one single-compartment bag assembly; a safety valve for selectively occluding and permitting the communication of the solution through the inner portion; and a filter preferably interposed along the patient-side portion which filters air and particles from peritoneal dialysate that is flowing toward a patient and which allows peritoneal dialysate to flow substantially freely and unfiltered away from the patient.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of application Ser. No. 08/961,757, filed Oct. 31, 1997, now U.S. Pat. No. 6,129,699, which will issue Oct. 10, 2000. The U.S. Pat. No. 6,129,699 claims priority pursuant to the provisions of 35 U.S.C. 119(e) to the filing date of provisional patent application Serial No. 60/030,176, filed Nov. 1, 1996, for “APPARATUS AND METHOD FOR MICRO-EVACUATION OF SECRETIONS.” 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field 
     This invention relates to means for evacuating undesired bodily secretions of medical patients. It is more particularly directed to medical pumps, notably peristaltic pumps in filtered conduit systems. It is specifically directed to improved procedures for the fluid transfer stage of kidney dialysis treatments. 
     2. State of the Art 
     The medical environment has numerous applications for fluid delivery and suction. During surgery, for example, entry sites must have blood or other fluids evacuated. Emergency care personnel must clean a wound properly during care and cleanup. For example, after-surgery complications can cause the endocrine system to overproduce, building pockets of fluid in and around the lungs, or within the peritoneal cavity. In each case, the excess fluid must be removed. This procedure must be accomplished in a mild, gentle manner to avoid tissue trauma or damage to the surrounding area. 
     Many fluid delivery systems, particularly in a hospital, outpatient, laboratory or home care environment, utilize pumps. Various types of such pumps are constructed with piston, diaphragm, or peristaltic mechanisms. Some such pumps are capable of bi-directional function. While the majority of medical pumps are relied upon for the infusion of fluids, some are applied to evacuation procedures. 
     Applications of various liquid handling and delivery systems include infusion of blood and blood products such as in hemodialysis; total perenteral nutrition; chemotherapy; hydration maintenance; transfer of samples from one container to another; and administration of medicaments to tissues, organs, the vascular system or other bodily sites. Other applications include pleural therapy, evacuation of wound weepage and other undesirable bodily secretions as well as transfer of peritoneal dialysate solutions. Such infusion and evacuation procedures typically utilize lower volume pumps. 
     Though some pumps for micro-volume applications are inexpensive enough to be disposable, as illustrated by U.S. Pat. Nos. 5,556,263 and 5,632,606 to Jacobsen et al., virtually all medical pumps, particularly those of higher-volume systems, notably, those used for peritoneal dialysis, are prohibitively expensive for patient acquisition. 
     The negative pressure necessary to evacuate fluids is typically generated by means of gravity, a bellows-type container, a resilient bladder or a mechanical pump. Representative such means devices disclosed by U.S. Pat. Nos. 3,875,941 to Adair; 3,982,539 to Muriot; and 3,742,822 to Talbert. The device disclosed in U.S. Pat. No. 5,029,580 to Radford et al. incorporates a multi-lumen endotracheal catheter for simultaneous introduction of therapeutic gases under positive pressure and aspiration of undesirable respiratory secretions and gases under negative pressure. Additional lumens may be incorporated for introduction of medication and lavage solutions. Provision may also be made for monitoring pressures, temperatures and catheter tube flow rates. The interaction of negative and positive pressures at the distal (patient) tip of such catheters combined with tip perforations and curvatures results in homogenization of localized secretions and gases, resulting in more efficient aspiration. 
     Screening at the distal tip of such devices may be accomplished by structure such as those disclosed in U.S. Pat. Nos. 3,308,825 to Cruse; 4,002,170 to Hansen et al.; and 4,068,664 to Sharp et al. 
     Existing evacuation devices suffer from various disadvantages. Flow rates tend to be either fixed or irregular, and are insufficiently regulated. Flows are typically uni-directional. Costs are prohibitively high for disposability, adversely impacting the ambulatory user. Operation is excessively complicated, unduly limiting the home care user. 
     There is a need for a low-volume, micro-evacuator device, wherein electronic circuitry enables regulated flow rates in alternate directions of flow in a selected, even adjustable, net-suctioning pattern. This mode of operation would prevent obstruction of the suction catheter and enhance the reliability of secretion flow. There is also a need for an inexpensive high-volume medical pump. 
     It would also be advantageous for a micro-evacuator device to be constructed (1) unobtrusively to enable ongoing suction of undesired bodily fluids throughout ambulation of a patient; (2) sufficiently inexpensive to be disposable; (3) sufficiently simple for use in a home care environment and/or (4) with a real-time monitor and indicator of catheter pressure and other important variables. 
     In low-volume applications it is necessary or desirable to provide pump portability to reduce health care costs and enhance patient comfort, convenience, ambulatory productivity and overall lifestyle. For identical reasons it would be desirable to achieve portability for high-volume pumping applications, such as peritoneal dialysis. Current high-volume pumps incorporate bulky, heavy and expensive features such as AC powered liquid warning chambers, alarms for obstruction, volumetric and pressure monitoring, programmable actuation schedules and bi-directional flow. Accordingly, they are generally stationary, and not portable. U.S. Pat. Nos. 4,381,003 and 4,498,900 to Buoncristiani and 5,438,510 to Bryant et al. disclose such elements. There remains a need for a small, light-weight and portable medical pump to support high-volume transfers. 
     During a typical peritoneal dialysis procedure involving a pump, known as continuous cyclical peritoneal dialysis or CCPD, the pump remains affixed to a power source, and the patient remains attached to the pump for several cycles of infusion and evacuation of dialysate solution throughout the night. The gravity feed/drain approach, known as continuous ambulatory peritoneal dialysis or CAPD, likewise requires patient immobility throughout approximately five such transfers every four to six waking hours involving roughly at least 10 minutes to infuse new dialysate and 20 minutes to drain used dialysate each transfer. There is a need for a medical pump capable of more rapidly transferring high-volumes of dialysate into and out of a patient who may remain ambulatory not only during dialysis but also throughout each transfer procedure. 
     Presently, both gravity feed and pump methods of performing peritoneal dialysis normally involve drainage of used solution from the peritoneum into an unused receptacle for later disposal. Clean, unused solution is then introduced into the peritoneum from a solution reservoir. These procedures, typical examples of which are illustrated by U.S. Pat. Nos. 3,620,215 to Tysk; 4,396,382 to Goldhaber and 4,412,917 to Ahjopalo, require the use of two separate solution containers. Such procedures presuppose a series of valve or clamp openings and closings in a defined sequence to ensure that solution is directed in accordance with protocol, illustrative of which is FIG. 4 of U.S. Pat. No. 4,239,041 to Popovich et al. 
     It is important that any pump transfer set provide for facile, clean connection and disconnection of the dialysate containment system to the indwelling catheter tube, whereby to minimize the potential for peritonitis. When an ambulatory patient completes a transfer of dialysis solution through a stationary pump, the patient is normally disconnected from the pump at the indwelling tube. The patient is thereby permitted to move about freely, until being reconnected to continue with the next transfer procedure. Each such exchange exposes a patient to potential contamination. Typical precautions against contamination involve wearing a face mask, closing windows and doors and turning off air conditioning in rooms or vehicles in which exchanges are to take place. These expedients are not entirely effective, and there thus remains a need for an improved arrangement, whereby to minimize this mode of patient exposure. 
     Though unused dialysis solution is sterile, organic particles and air bubbles are typically carried by the solution. Air bubbles introduced to the patient are known to cause severe muscle pains in the shoulders and chest, until the air diffuses into the surrounding body tissues. Some incidence of non-bacterial peritonitis is known to be associated with the organic materials carried by dialysis solution. An air and particle filter for use in a gravity-feed system is disclosed by U.S. Pat. No. 4,239,041 to Popovich et al. U.S. Pat. No. 4,311,587 to Nose et al. discloses a system in which a filter for use with a pressurized source of fresh dialysate solution is associated with a check valve constructed to permit flow only away from the filter. U.S. Pat. No. 4,488,961 to Spencer discloses a housing for maintaining a filter element in a filtering position during fluid infusion and in a free-flow position during fluid withdrawal. Filters preventing passage of bacteria prevent rapid gravity-flow and are only practical for use with pumps, not gravity flow CAPD. There remains a need for a practical system for screening out air bubbles and filtering particulate matter from fresh dialysate. There is a further need for such a filter to protect against microbial migration to the peritoneal cavity during an exchange of single- or multiple-bag dialysate containment systems. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention may be envisioned as either improved apparatus or improved procedures enabled by the apparatus. In particular, the invention provides a novel procedure, which may be termed “Ambulatory Transfer Peritoneal Dialysis” (ATPD). This procedure differs from known CAPD and CCPD procedures, in that the patient remains ambulatory during the transfer phase of a dialysis treatment. In general, the procedure is enabled by a special interface between the indwelling tube of the patient and the containers used for waste collection and dialysate supply. This interface couples with a mechanism capable of increasing the head pressure normally inherent in a gravity feed system. This increase in pressure facilitates more rapid exchange, but perhaps more importantly, makes the use of biofilters in the dialysate flow path practical. Volumetric flow rates suitable for peritoneal dialysate transfer of in excess of 100, typically 300 or more ml/minute through a biofilter capable of excluding bacterial fragments are practical. 
     Certain preferred embodiments provide for increased head pressure through an inexpensive high-volume, small-sized, light-weight, closed system peristaltic pump assembly. Such an assembly typically comprises a positive displacement pump of the type in which fluid is urged through a resilient, compressible tube by means of traveling compression rollers. Alternative designs incorporate a collapsible dialysate reservoir as a pumping chamber. The flexible plastic bags conventionally used for both fresh and spent dialysate are ideal such reservoirs. A filled such bag may be placed within a mechanism structured (e.g., as a “clam shell”) to apply squeezing action, thereby to force dialysate towards a patient at a selected rate and/or pressure. The same mechanism may be adapted to clasp (e.g., by means of adhesive) the walls of a collapsed or partially collapsed reservoir. The mechanism may operate to reconfigure, that is to increase, the internal volume of the container. In this fashion, spent dialysate may be withdrawn by suction, at a selected rate from a patient at the commencement of an exchange. 
     Some embodiments of the invention utilize an improved version of a positive displacement pump of the type in which a section of elastic tubing functions as a resilient pump chamber. This pump chamber is typically positioned within a housing comprising a support surface for the resilient chamber. Liquid is urged through the chamber by a traveling roller assembly associated with the housing. The roller assembly is structured and arranged to press a roller surface against a section of the resilient chamber towards the support surface, whereby to reduce the transverse cross section of the tubing between the roller surface and the support surface. The roller surface travels away from an inlet to the resilient chamber and towards an outlet from the resilient chamber. The improvement of this invention provides the resilient pump chamber and its support surface in a cassette. The roller assembly is provided in association with a drive mechanism organized such that the roller surface travels repetitively within an open sided housing from an inlet towards an outlet. The open sided housing is structured to receive the cassette in an installed condition. The housing and cassette are mutually adapted so that when the cassette is in its installed condition, the resilient chamber is functionally positioned with respect to the roller assembly. That is, these components are spatially arranged so that the roller surface urges fluid through the chamber. A normally biased-closed valve may be provided in association with the cassette, the valve being structured and arranged to open when the cassette is in its installed condition. 
     The pumps envisioned by this invention will ordinarily be powered by a small battery, ideally of the rechargeable type. Alternatively, the drive means may comprise a manually operated handle, a detachable power drill or power screwdriver or the like. Such a manual handle, drill or screwdriver may be engaged with a drive train. The drive train may include gear means for reducing the rate of rotation of a driven axle, preferably usable with the power implements; or the drive train may comprise a direct socket in association with the driven axle preferably usable with a manual handle. 
     A novel transfer set for the exchange of dialysate solution is also provided by this invention. This transfer set includes a length of medical tubing, constituting a bidirectional flow path for dialysate solution between an indwelling patient catheter tube and a dialysate containment system. A first coupling is carried at a first end of this length of medical tubing for connection to an indwelling patient catheter tube. Structure in fluid flow communication with the length of medical tubing constitutes means for directing fresh dialysate solution traveling through the tubing towards the first coupling through a first travel path and directing spent dialysate solution traveling through the tubing from the patient through a second travel path. A biofilter may be positioned in circuit with the first travel path. 
     In certain preferred embodiments, a check valve assembly in fluid flow communication with the length of medical tubing includes the biofilter and is structured and arranged to filter air and particles from fresh dialysate solution as it flows toward a patient and to allow free, unfiltered flow of spent dialysate solution away from a patient. The transfer may also include a safety valve for selectively permitting flow of a dialysate solution through the length of medical tubing. A segment of this medical tubing may function as the pump chamber of a positive displacement pump of the type described previously in this disclosure. 
     A high-volume peristaltic pump assembly for portable peritoneal dialysis procedures in accordance with this invention will typically include a portable power supply (typically a rechargeable battery pack). A motor, powered by this power supply generally includes a driven shaft capable of clockwise and counterclockwise rotation. A displacement impeller assembly may be mounted to turn within an impeller chamber in response to rotation of the driven shaft. This impeller assembly typically includes a plurality of roller elements carried through a circular travel path within the impeller chamber. The travel path is situated partially within a zone which presents a receptacle opening into the impeller chamber. A transfer set adapted for use with this assembly will include a cassette configured to install within this receptacle opening to occupy the zone. The cassette constitutes an encasement for a segment of the length of medical tubing, and includes a reaction (tube support) surface constructed and arranged closely to approach the travel path of the roller elements when the cassette is installed within the receptacle opening. The transfer set necessarily includes a length of medical tubing, including an intermediate segment positioned within the cassette adjacent the reaction surface. This length of medical tubing includes a patient end releasably connectable to an indwelling peritoneal dialysis tube and an opposite end releasably connectable to an assembly for containment of dialysate solution. 
     Most notably, this invention provides a method of performing a peritoneal dialysis procedure on a patient which permits that patient to remain ambulatory during infusion and evacuation of dialysate solution. The method comprises the steps of: 
     1. associating a detachable, disposable peritoneal dialysis transfer set with a portable pumping device. (The transfer set is of the form described in this disclosure to provide a directional flow path for dialysate solution between an indwelling patient catheter tube and a dialysate containment system. The portable pumping device may be any of those described in this disclosure.) 
     2. The transfer set, pumping device and dialysate containment system are all shaped and dimensioned so that they are suitable for attachment to a patient for ambulatory transport by the patient during infusion and exhaustion of dialysate solution. 
     3. operating the portable pumping device to infuse peritoneal dialysate solution from the dialysate containment system to the patient; 
     4. waiting for a period of time sufficient to allow dialysis within the patient; 
     5. operating the portable pumping device to evacuate the dialysate solution from the peritoneal cavity of the ambulatory patient to the dialysate containment system; and 
     6. disassociating the transfer set from the pumping device to enable disposal of the transfer set and the dialysate containment system. 
     Circuitry means for selectively governing actuation, direction and operation of the motor are preferably also included. The circuitry may comprise sensor means for detecting pressure changes based upon changes of rotational rate per time interval of the drive shaft or turn shaft. The circuitry may further comprise means for intermittent pump reversal in a selected pattern, said pattern based upon time intervals, external events such as pressure changes or changes in pump speed, or preselected programming. Certain embodiments utilize electronic circuitry to enable regulated flow rates in alternate directions of flow in a net-suctioning pattern. This mode of operation assists in the prevention of obstruction of a suction catheter, for example; particularly at its tip. 
     Accordingly, a novel method of performing a peritoneal dialysis procedure on a patient who may be ambulatory not only during dialysis but also during infusion and evacuation of a dialysate is disclosed. The novel method comprises the steps of associating a portable peristaltic pump with a detachable, disposable peritoneal dialysis transfer set, said transfer set including an encasement; a tube, a middle portion of which is locatable within the encasement, including check valve means in fluid communication with said tube for preventing passage of air bubbles and particles as a dialysate solution is pumped Through the check valve means toward the peritoneal cavity of the patient and for allowing free, at least largely unfiltered flow of the dialysate solution away from the patient; operating the portable pump to infuse peritoneal dialysate solution from the dialysate containment system through the patient end and releasably connected indwelling tube to the patient; optionally temporarily disassociating the portable pump from the transfer set without disconnection of the patient end from the indwelling peritoneal dialysis tube; waiting for a period of time sufficient to allow dialysis within the patient; reassociating the optionally disconnected portable pump to the transfer set; operating the portable pump to evacuate the dialysate solution from the peritoneal cavity of the ambulatory patient to the dialysate containment system; and disassociating the transfer set from the pump to enable disposal of the transfer set and containment system. 
     The containment system of this method may comprise one single-compartment dialysate container. The device remains unobtrusive while enabling ongoing suction of undesired bodily fluids of an ambulatory patient. The micro-evacuator system of the present invention is sufficiently inexpensive to be disposable and sufficiently simple for use in a home care environment and may be equipped with a real-time monitor and indicator of catheter pressure and other important variables. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     In the drawings, which illustrate what is currently regarded as the best mode for carrying out the invention: 
     FIG. 1 is a schematic of the circuitry for the central processing unit; 
     FIG. 2 is a schematic of an H-bridge motor driver circuit; 
     FIG. 3 is a schematic of the circuitry utilizing an infrared detector; 
     FIG. 4 schematically outlines network circuitry of temperature sensor electronics; 
     FIG. 5 is a schematic for battery recharging from an external power source; 
     FIG. 6 is a circuitry schematic of the battery monitoring function; 
     FIG. 7 is a top, partially open view of the peristaltic pump featuring the wheel and spindle assembly, portions of the circuit board and including the transfer cassette; 
     FIG. 8 is a side, partially transparent view of the peristaltic pump without the transfer cassette; 
     FIG. 9 is a top, partially open view of the peristaltic pump featuring the gear configuration; 
     FIG. 10 is a top view of the transfer cassette; 
     FIG. 11 is a top view of the particle and air filter; 
     FIG. 12 is a side, partially transparent view of the particle and air filter; 
     FIG. 13 includes five side views, designated FIG.  13 ( a ) through FIG.  13 ( e ), respectively, illustrating five sequential positions of piston, drive arm and linkage elements during operation; 
     FIG. 14 is a partial cut away view of the piston seal ring; 
     FIG. 15 includes five side views, designated FIG.  15 ( a ) through FIG.  15 ( e ), respectively, each partially cut away, illustrating piston positions relative to outlet and inlet valves in the five sequential piston positions of FIGS.  13 ( a )- 13 ( e ); 
     FIG. 16 a  is a side view of the cam relative to the lever when the fluid tubing is unobstructed; 
     FIG. 16 b  is a side view of the cam relative to the lever when the fluid tubing is obstructed; 
     FIG. 17 depicts the functional features of the pump system relative to the patient and waste container; 
     FIG. 18 a  and FIG. 18 b  comprise a schematic diagram of a suction control circuit; 
     FIG. 19 depicts the functional features of the pressure and other sensors relative to the patient and waste container; 
     FIGS. 20 a  and  20   b  compare a schematic diagram of a suction/pressure circuit; and 
     FIGS. 21 a  and  21   b  comprise a schematic diagram of a power supply. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The electronic circuitry of this invention has several functions, and may be organized as illustrated schematically by FIGS. 1 through 6. 
     FIG. 1 illustrates a central processing unit (CPU) U 4  and associated circuitry. The CPU obtains clock pulses from two sources. Crystal Y 1  provides the main clock pulses for CPU program step execution. An oscillator, formed by U 3 C, U 3 D and associated components, provides a stable 4 mS square wave to the CPU. This 4 mS square wave is used as a time base reference. 
     U 5  holds the CPU reset on power up, or if the incoming +5VDC supply drops too low. The MC34164 is a voltage measuring device that drops its output low if the input voltage drops below the internally preset voltage. This low output forces the CPU to reset. 
     The CPU data lines can be programmed for either input, output, or hi-impedance operation. In this application, the data lines RA 0  through RA 3  are programmed for output operation, while RB 0  to RB 7  are programmed for input operation. 
     The CPU itself contains internal memory which is programmed to execute commands that control the overall function of the pump  100 . (See generally, FIGS. 7-10.) When power is applied and the CPU reset line goes high, program execution begins. The CPU then monitors the input lines to see whether to drive the motor  110  forward (when a “Fill” command is detected on switch S 2 ) or reverse (when a “Drain” command is detected on switch S 2 ). 
     Respectiver input and output data lines are dedicated to the following respective functions: 
     RA 0 : Motor Reverse Command (REV) 
     RA 1 : Motor Forward Command (FWD) 
     RA 2 : Beeper On (BEEP) 
     RA 3 : Low Battery Warning LED (LOBAT) 
     RB 0 : Fill Command from Control Switch S 2  (FILL) 
     RB 1 : Drain Command from Control Switch S 2  (DRAIN) 
     RB 2 : Rotate data from Rotation Sensor (ROTATE) 
     RB 3 : Battery 3.0V Sensor input ( 3 _ 0 LO) 
     RB 4 : Battery 3.3V Sensor input ( 3 _ 3 LO) 
     RB 5 : Hi Speed Command from Control Switch S 1  (HI) 
     RB 6 : Medium Speed Command from Control Switch S 1  (MED) 
     RB 7 : Low Speed Command from Control Switch S 1  (LO) 
     Each of the switch and voltage monitoring inputs are pulled high by resistor network R 13 . This arrangement allows the CPU input line to be pulled to ground by the device connected to the CPU. The exception to this rule is the Rotate input. It is driven selectively low or high by inverter U 3 F (FIG.  3 ). 
     CPU outputs FWD and REV are connected to an H-bridge motor driver circuit, as shown by FIG.  2 . The H-bridge is formed by Q 2 , Q 3  and associated components. When the FWD output from the CPU goes high, the REV output will be forced low, and the N-channel mosfet inside Q 2  turns on, providing a ground to one side of the motor M 1 . This ground is also applied to one side of R 6  which pulls down the gate of the P-channel section within Q 3 . At this time the Q 3  P-channel section turns on and provides battery voltage to the other side of the motor M 1 . This action causes the pump motor M 1  to rotate in the clockwise direction. 
     If the CPU output FWD is forced low and the REV output is placed in a high state, the N-channel mosfet within Q 3  turns on and provides a ground to the motor terminal  110  formerly connected to the voltage of the battery  120 . This ground is also connected to one side of R 2 , pulling down the gate of the P-channel section within Q 2 . Q 2  is thereby allowed to place the battery 120 voltage on the other side of the motor M 1 . The motor M 1  will then turn counter-clockwise. 
     If the CPU forces both FWD and REV outputs low, transistors Q 2  and Q 3  turn off. The motor M 1 , having no driving voltages, will coast to a stop. To precisely limit the pump  100  to a single rotation, the motor M 1  must be stopped abruptly at the end of the rotation. Briefly changing motor direction, such as from clockwise to counterclockwise, will provide a braking function to the motor M 1 . 
     The H-bridge is protected from transient voltages by diodes D 2  through D 8  and D 10 . 
     FIG. 3 shows an infrared emitter (D 1 ) that is positioned on the circuit board appropriately to allow its emitted light to reflect from a mirror and back into a detector (Q 1 ). The rotating wheel/spoke assembly, generally  130 , passes through this light path as the pump  100  operates. Whenever the light is interrupted, a signal is sent to the CPU via the wire labeled ROTATE. The signal can be used by the CPU to determine how fast the pump  100  is turning by comparison to the 4 mS clock. It can also be used to determine whether the pump  100  has stopped turning for any reason, such as mechanical or electronic failure. 
     If, during operation, the tubing, generally  140 , on the intake side (either the bag side tube  150  or the patient side tube  160  in a reversible pump  100 ) becomes occluded, the pump  100  will begin to develop a vacuum within the tube. Because the central portion  165  of the tubing  140  has a thin wall, the vacuum will collapse the portion  165 , and the wheel/spoke assembly  130  will no longer have to push the fluid load. In this case, with less load on the entire motor M 1  and gear assembly  170 , the motor M 1  will speed up. The infrared detector/CPU combination can detect this increase in speed and signal the operator either with visual flashes on LED D 18  (FIGS. 1,  7  and  8 ) or by a series of beeps on BZ 1 . 
     The infrared signal is generated by applying a square wave, made by U 1  and its associated components, to the infrared LED, D 1 . The square wave turns the LED on and off at a frequency of approximately 2000 Hz. The pulsating light travels to the detector and is fed from that point to an AC amplifier formed by Q 5 , Q 6  and associated components. The reflected light is amplified, sent to an inverter U 3 F, and on to the CPU for processing. 
     The CPU filters out the 2000 Hz wave to obtain only the rotation component of the signal. The 2000 Hz wave is used to help reject interference from other infrared sources. 
     The battery  120  is charged when an external 12 volt DC power source is attached to connector J 1  (FIG.  5 ). This 12 volt supply energizes the “Battery Charged” network in FIG. 4 formed by U 2 , U 10 , U 11  and associated circuitry. U 2  and U 11  are temperature sensors that detect battery and ambient temperatures respectively. When both temperatures are the same, the battery charging circuitry is enabled by the output of comparator U 10 A. As the battery  120  nears its state of maximum charge, its temperature begins to climb. When the battery temperature is 10 deg. C above the ambient, the battery charging circuitry is disabled by the output of U 10 A and the LED D 19  is lit. 
     U 12  provides a regulated +5V to the “Battery Charged” detection circuitry. Battery charging is accomplished, as shown by FIG. 5 when U 9  and associated components are enabled by the “Battery Charged” circuit. This circuit forms a switching power supply  180  that provides enough current to fast-charge battery BT 1 . The circuit can be tailored to deliver more or less charging current to the battery  120 , depending on its specification, by adjusting the value of resistor R 35 . 
     When the charging circuit is disabled, a trickle charge continually keeps the battery  120  in a state of full charge. The trickle can be left on indefinitely because the trickle current is kept below the limit specified by the battery manufacturer. Trickle charge is provided through diode D 17  and limited by resistor R 38 . 
     The 12 volt source attached to connector J 1  can be obtained from a wall adapter or from an automobile cigarette lighter adapter (neither shown). 
     FIG. 6 illustrates monitoring of battery condition by U 6  and U 7  that detect voltages of 3.0 and 3.3 respectively. When the battery voltage, ideally 3.6V, drops below 3.3V the CPU is signaled and causes the LED D 18  to come on. When a battery voltage of 3.0V is detected by U 6  the CPU is again signaled and the motor M 1  is turned off, and cannot be enabled until the battery  120  is charged and the unit has been turned off and back on using S 2 . 
     The battery voltage is also applied to a switching power supply formed by U 8  and associated components. This supply provides 5 volts to the internal circuitry with the exception of the “Battery Charged” circuit. 
     The circuitry is integrated on a PC board, generally  190 , and associated with the battery  120 , motor M 1 , gear assembly  170  and wheel/spoke assembly  130 , all of which are enclosed within a body  200 . Adjacent the rotatable spindle  230  and appending plurality of wheels  210  and spokes  220  is an arched opening  240  on the body  200  into which may be releasably seated a transfer cassette  250 . The transfer cassette  250  is preferably made of a plastic material for economic disposability. 
     A safety valve  260 , which may be integral with the transfer cassette  250 , as depicted in FIG. 10, is structured and arranged to occlude the tubing  140  until released counter to its closed bias prior to operation of the pump. If the safety valve  260  is formed integral with the transfer cassette  250 , the valve  260  may be designed to release upon installation of the transfer cassette  250  within the arched opening  240 . Accordingly, the safety valve  260  prevents inadvertent and untimely back flow from a patient in the event the transfer cassette  250  is disassociated from the arched opening  240  of the pump  100  to relieve the patient of the pump  100  during dialysis. 
     A releaseable clip  270  holds the transfer cassette  250  within the arched opening  240 . The clip  270  is structured and arranged to preclude unintentional release of the transfer cassette  250 ; a user may manually unlatch a release pin  280  to disengage the clip  270  and detach the pump  100  from the transfer cassette  250 . 
     The transfer cassette  250  defines a wall  310  against which the central portion  165  of the tubing  140  is resiliently compressed by the plurality of wheels  210  as the turn shaft  300  in operation rotates the spindle  230  and appending wheel/spoke assembly  130  in either direction. 
     In operation, the battery  120  powers the motor M 1 , the motor M 1  drives a drive shaft  290  at a velocity of between 1,500 and 15,000 rotations per minute (“rpm&#39;s”) which in turn drives the gear assembly  170 . The gear assembly  170  reduces the rpm&#39;s from the drive shaft  290  to a turn shaft  300  in a ratio of approximately fifteen to one, enabling the pump  100  to drive volumetric flow rates in excess of 100 ml/minute for at least 20 minutes. 
     Alternatively, the electrical power drive of the motor M 1  and associated gear assembly  170  may be effectively replaced by use of a manual drive handle (not shown) structured and arranged to be attached to the spindle  230  at a manual drive socket  320  situateable at either end of the turn shaft  300 . It is also within contemplation that a powered chuck, such as that of a power drill or power screwdriver (not shown), may be coupled (at higher rpm&#39;s) to an alternative drive socket  330  or (at lower rpm&#39;s) directly to the manual drive socket  320 . 
     In the preferred embodiment of the invention, a check valve  340  is interposed along and in communication with the liquid flow channel comprising the tubing  140  and preferably located near the patient on the patient side  160  of the tubing  140 . The check valve  340  depicted in FIGS. 11 and 12 is structured and arranged to filter air and particles from the dialysate solution as it flows toward a patient and to allow free, unfiltered flow of dialysate solution away from a patient. 
     The check valve  340  comprises a supply port  350  into which flows unused dialysate solution; an air passage  360 ; a pre-flow chamber  365  where air bubbles and excess air entering the check valve  340  may be collected for exhaustion through the air passage  360 ; hydrophilic filter media  370  capable of screening air bubbles and particles of 0.2 micron size and larger from the dialysate; a disposal port  380  through which unused dialysate solution can continue to the peritoneal cavity of a patient or through which used dialysate can be evacuated from a patient; an after-flow chamber  390  in fluid communication with the disposal port  380 ; and a filter bypass  400  providing a route for used dialysate to at least partially circumvent the filter media  370 . Second valve means  410  may optionally be included to ensure that used dialysate substantially entirely circumvents the filter media. Such means  410  may beneficially be in communication with the disposal port  380  and after-flow chamber  390 . 
     The check valve  340  may desirably be structured in a wafer-like shape, as illustrated, to facilitate unobtrusive storage against the body of a patient. Such storage makes feasible patient comfort as well as inconspicuous association with the indwelling incubation apparatus for potential repeat use throughout a series of dialysate transfers. The indwelling tube and peritoneum are thereby protected significantly from microbial contamination throughout multiple transfers and during the interim when, for example, a dual bag system is detached during CAPD. 
     EXAMPLE 1 
     This example describes a low volume evacuation system constructed in accordance with FIGS. 13 through 21 b  of the drawings. 
     Views (a)-(e) of FIG. 13 illustrate five positions of a pump piston assembly  7  and three of its main components. FIG.  13 ( a ) illustrates a drive arm  10  linked to a motor shaft (not shown) at a rotation point  15 . The drive arm  10  is attached to a piston  20  by means of a linkage  25 . 
     As the drive arm  10  rotates counterclockwise to the position shown by FIG.  13 ( b ), the drive arm  10  and linkage  25  draw the piston  20  downward, in the direction indicated by the arrow A. As the drive arm  10  continues to the position of FIG.  13 ( c ), the piston  20  moves downward to full extension. Continuing the movement of the drive arm  10  counterclockwise to the position of FIG.  13 ( d ) reverses the direction of piston travel; i.e., the piston  20  is pushed upward, in the direction indicated by the arrow B, by the linkage  25  until it has reached it full upward movement, as shown by FIG.  13 ( e ), completing one complete travel cycle. If the drive arm  10  continues its counterclockwise movement, the cycle repeats. 
     If the piston  20  is placed within a cylinder  30  as shown in FIG. 14, such that there is a seal between the piston  20  and the walls  35  of the cylinder  30 , the action of the operating piston  20  will create either a vacuum [FIGS.  13 ( a )- 13 ( c )], within the cylinder  30 , or pressurize the cylinder  30  [FIGS.  13 ( c )- 13 ( e )]. The vacuum or pressurization can be sustained by a seal ring  40  or by a tight fit between piston  20  and cylinder  30 . 
     FIGS. 15 ( a )-( e ) illustrate the basic function of two valves  45 , 50  attached to the cylinder  30  and piston  20 . FIG.  15 ( a ) illustrates valves  45 , 50  closed. As the drive arm  10  begins to turn in a counterclockwise direction, an inlet valve  45  is opened allowing fluid  55  to enter the chamber  60  due to the vacuum created by the piston  20 , as shown by FIG.  15 ( b ). Fluid  55  continues to flow into the cylinder  30  until the piston  20  reaches its maximum downward stroke, as shown by FIG.  15 ( c ), at which time the inlet valve  45  is closed. As the drive arm  10  continues its counterclockwise travel, the piston  20  begins to move forward to create pressure in the cylinder  30  [FIG.  15 ( d )]. An outlet valve  50  is then opened to allow the movement of fluid  55  out of the cylinder  30  until the piston returns to its initial position [FIG.  15 ( e )]. 
     FIGS. 16 a  and  16   b  illustrate a gear mechanism  65  attached to the motor (not shown) which includes a cam  70  that rotates one time per complete piston cycle. This cam  70  is linked to the valves  45 , 50  by means of two levers  75 , 80 , one for each valve  45 , 50 , that ride upon the cam  70  as it rotates. Protrusions  85 , 90  are placed on the cam  70  such that they engage the levers  75 , 80  when the piston  20  is in the correct position. The levers  75 , 80  turn the valves  45 , 50  on and off as they encounter a protrusion  85 , 90  on the cam  70 . The levers  75 , 80  could include wheels or other friction-reducing components that ride upon the cam  70 . 
     The levers  75 , 80  each comprise a cam end  95 , 100  and a tube end  105 , 110 . As the cam end  95  of one of the levers  75 , 80  upwardly encounters one of the protrusions  85 , 90 , the lever  75  or  80  pivots around the particular one of the pivot points  115 , 120  associated with the one of the levers  75 , 80 . As the lever  75  or  80  thus pivots, its corresponding tube end  105 , 110  is pressed downward, crimping the tube  125  until the tube  125  is occluded. 
     Thus, the opposite end of each lever  75  or  80  is placed against the tube  125  attached to either the inlet valve  45  or the outlet valve  50  of the cylinder  60 . When the lever  75  or  80  is pressed against the tube  125 , and the tube  125  flattens, the internal cross-sectional area through which fluid normally passes is reduced to essentially zero, closing the particular valve  45  or  50 . When the lever  75  or  80  is not pressed against the tube  125 , the tube  125  resumes its original shape, and maximum cross-sectional area, and the given valve  45  or  50  is open. When all components are working together, a pumping action is produced that will move fluid from inlet to outlet. 
     Thus far, the drive arm  10  has been described as being rotated counterclockwise. If the motor (not shown) is reversed, the direction of the drive arm  10  changes to clockwise which reverses the sequence shown in FIG.  15 . Also, the valve-controlling cam  70  works in reverse. As a result, the functions of the valves  45 ,  50  are reversed. That is, fluid comes in through the outlet valve  50  and out through the inlet valve  45 . 
     The basic pump system is illustrated in FIG.  17 . The pump  7  can be attached to any patient  130  location such as into the peritoneal cavity  135 , the pleura  140  or within the bronchial tube  145  using existing entry devices and tubing couplers (not shown). The pump  7  can also be used to remove fluid  55  from external sites such as wounds in the Emergency Room (not shown). As illustrated, fluid  55  is removed by the pump  7  from the patient  130  and deposited into a waste container  150 . 
     Because the pump  7  can be reversed simply by reversing the motor (not shown), it is possible to pump inward (in the direction indicated by arrow C) two or more cycles and then back to the patient  130  one or more cycles. This action ensures that the end  124  of the tube  125  inserted into the patient  130  does not become occluded; pumping back to the patient  130  forces any debris or coagulated fluids  55  away from the end of the entry device or tubing  125 . The number of cycles pumped inward as opposed to the number of cycles pumped back to the patient  130  is determined by adjusting appropriate control devices (not shown). To achieve a removal of fluid  55 , the number of cycles inward must exceed the number of cycles outward (toward the patient). 
     A further variation is to change the speed of the motor and thereby the cycle repetition rate to remove either more or less fluid  55  from the patient  130  site per unit of time. Motor speed may also be determined by setting appropriate control devices. 
     Different pump mechanisms  7  can be manufactured to satisfy the demands of varying applications. For example, the diameter of the pump piston  20  and corresponding cylinder walls  35  can be modified to affect pressure or fluid displacement per cycle. 
     The pump mechanism  7  may be constructed of disposable materials that enable the parts that have been contaminated by fluids  55  to be discarded. The reusable pump motor and electronics are a separate assembly and are able to be reset and reused. The disposable pump assembly  7  can be sterilized and attaches either by snap fit or by mechanical fastener to the pump motor assembly. 
     Referring to the suction control schematic diagram of FIG. 18A, the microprocessor (U 1 ) and associated components perform all control and monitoring functions. It is coupled to the motor driving circuitry formed by Q 1 -Q 4  and its associated components. This electronic circuitry called an H-bridge, allows the motor to be driven bi-directionally and has the ability to quickly stop the motor. 
     When the microprocessor sends a low signal to resistors R 5  and R 6 , both Q 3  and Q 4  are turned off. Also, the emitter-base junctions of Q 1  and Q 2  are turned off by resistors R 28  and R 27 , respectively. If the microprocessor sends a high signal to R 5 , the emitter-base junction of Q 3  is forward biased and Q 3  turns on. This condition causes current to flow through R 3  and consequently forward biases the emitter-base junction of Q 2 . The action of these two “on” transistors is to provide a ground path from the motor through Q 3  and a power supply connection to the other side of the motor through Q 2 . The motor is thus energized. 
     If the microprocessor sends a high signal to R 6 , the emitter-base junction of Q 4  is forward biased and Q 4  turns on. This causes current to flow through R 2  and consequently forward biases the emitter-base junction of Q 1 . The action of these two “on” transistors is to provide a ground path from the motor through Q 4  and a power supply connection to the other side of the motor through Q 1 . The motor is thus energized, but in the reverse direction. The motor can in this way be controlled by the microprocessor. 
     If the motor is to be stopped, the microprocessor releases the high signal it had been sending to the H-bridge, which turns the power off to the motor as previously described. The microprocessor then sends a signal to the H-bridge to reverse the direction for a brief period of time. This action causes the motor to come to an immediate halt rather than coast to a stop. Using this technique, it is possible to get one and only one complete pump cycle without any overshoot. 
     The motor is linked to a rotation sensor (S 1 ) through a gear mechanism that engages the motor shaft. The rotation sensor signals the microprocessor when a single pump actuation has been completed. The rotation sensor can take the form of a mechanical switch, a hall effect device, or optical sensor. Further, the actuating gear could have a small metal plug embedded at one or more points around the circumference while a metal detecting sensor watches for the metal presence. This discussion focuses on a mechanical switch that is activated by a cam on the gear. 
     Switches SW 1  and SW 2  are accessible to the operator and allow the device to be controlled according to the needs of the patient. SW 1  controls the speed of the motor while SW 2  controls the number of cycles of inward pumping as opposed to outward pumping. The setting is expressed as a ratio and has a minimum of 2:1 and a maximum of 100:1. A DIP switch (S 2 ) can be configured by a service person to allow a greater ratio for either the minimum or maximum settings. 
     The microprocessor loads information from the control switches by means of activating U 3  and U 4  one at a time. These chips transfer the switch information onto a common data bus that is accessible by the microprocessor. Other selectable functions can be added to the pump simply by adding more switches and data transfer chips. Functions that can be added include, but are not limited to, a delay between pump cycles, or creating groups of pulses, either in an input or output direction, and separated by a time delay. 
     Power options for the pump unit are shown in power supply schematics of FIGS. 9 a  and  9   b.  AC power enters through J 1 , S 3  and fuses F 1  and F 2 . Power is fed from the fuses to transformer T 1  where the voltage is stepped down. Bridge rectifier D 5  converts the output AC wave into a DC voltage that is filtered by C 2 . Resister R 13  limits current through the “Power On” LED D 7 . Power from the bridge rectifier is also fed to resistor R 12  and onto voltage regulator U 5 . The output of the voltage regulator is +5VDC and is high frequency filtered by C 3 . R 12  reduces the power dissipation of the regulator. 
     The +5VDC regulator output is further reduced and regulated by the zener diode D 6  to +3VDC. This voltage is fed to the H-bridge for use in driving the pump motor. 
     The AC power option is equipped with battery back-up that is configured to provide battery power only if the power switch is on and the AC power is not present. Since the motor and circuitry used require minimal power, the battery backup does not need large capacity. 
     Normally, the voltage coming from the bridge rectifier is higher than the voltage from the backup battery. This reverse biases diode D 8 . In the event that AC power is interrupted, and the power switch is on, D 8  will forward bias and the battery BT 1  begins to supply power to the pump. 
     The “Battery Only” power supply shown in FIGS. 21 a  and  21   b  is essentially a duplicate of the AC power supply voltage regulator section with only a battery driving the input. Battery status can be monitored using commercially available integrated circuits. This option is for ambulatory versions that are used by a patient not able to stay in one place or by a patient in a location where AC power is not available. 
     The voltage regulators shown in the schematic have a relatively high power loss and are given as examples only. Other methods of voltage regulation with higher power efficiencies are available and could as easily be used. These are generally of higher cost, however. One example is the National Semiconductor Simple Switcher series. 
     To prevent damage to the pump mechanism and extreme pressures delivered to the patient, pressure sensors can be attached to the inlet and outlet tubes as shown in FIG.  19 . The electrical diagram of the sensor circuitry is shown in FIGS. 20 a  and  20   b.  The output of the circuit is fed back to the microprocessor. When an over-pressure situation is detected, the microprocessor can turn off the pump and notify the operator by means of a beeper, referenced in FIG.  18 A. 
     The pressure sensor U 9  is connected to an instrumentation amplifier U 7 . The pressure signal is amplified 100 times by U 7  and relayed to U 8 A. U 8 A is configured as a comparator and checks to see if the incoming pressure signal is over or under the specified limit created by potentiometer R 22 . If the pressure exceeds the limit, then the output sent to the microprocessor goes high and the microprocessor proceeds to shutdown the system. If the pressure is below the limit then the output signal is low and the microprocessor continues on with normal operation. 
     FIGS. 20 a  and  20   b  illustrate a pressure schematic showing two pressure sensor circuits. FIG. 20 a  is for detection of extreme vacuum or negative pressure. FIG. 20 b  is for detection of extreme positive pressure. In both cases the same pressure sensor is used. The manufacturer provides different attachment ports depending upon whether positive or negative pressure is being tested. 
     The pressure sensor manufacturer also offers devices capable of sensing different maximum pressures. A pump device may be manufactured for specific applications that requires higher pressures. In this case a pressure sensor with a higher pressure capability would be selected. 
     Other methods of detecting pressure problems are available and equally usable. If the pressurized tube is connected to a diaphragm that is attached to a mechanical switch, an extreme pressure will move the diaphragm and actuate the switch. The switch is the device that signals a pressure error to the microprocessor. This method requires no power and would be suitable to a battery powered device. 
     Reference in this disclosure to details of the illustrated or other preferred embodiments is not intended to limit the scope of the appended claims, which themselves recite those features regarded as important to the invention.