US3877843A - Pulsatile pumping system - Google Patents

Abstract

A portable pulsatile pumping system simulates the pumping mechanism of a human heart in pumping fluid for such applications as organ perfusion systems. The pumping system includes a regulated source of pressurized gas, a pulsatile pump having an aorta chamber providing a sustained minimum diastolic pressure and a ventricle chamber providing a higher systolic pressure during a selectively variable part (1 to 99 percent) of each cyclic pumping action, the periodicity of which may be varied from 5 to 150 cycles per minute. The gas source is connected to the pump by a first adjustable pressure regulator to maintain the chosen diastolic pressure in the aorta chamber. The ventricle chamber is alternately coupled to gas pressure taken through a second pressure regulator and vented by a solenoid mechanism operated by a digital electronic timing control circuit. The digital electronic control system employs digital counters and selector switches to generate square wave pulses of varying duration and periodicity in a manner which provides both conservation of electrical battery energy and high reliability. At the same time, an optimum pumping system is achieved because the elasticity of the gas and connecting tubing are employed to smooth the sharp signal transitions.

Description

United States Patent [191 Fischel 1451 Apr. 15, 1975 1 PULSATILE PUMPING SYSTEM [75] Inventor: Halbert Fischel, Sherman Oaks,

Calif.

[73] Assignee: Baxter Laboratories, Inc., Morton Grove, Ill.

22 Filed: May 21,1973

21 Appl. No.: 361,960

[56] References Cited UNITED STATES PATENTS 3,266,487 8/1966 Watkins et al 128/1 D 3,376,660 4/1968 McGinnis 128/1 D X 3,430,624 3/1969 Flanagan et a1.

3,516,331 6/1970 Oelrich et al. 91/459 X 3,545,221 12/1970 Swenson et al. 195/127 X 3,639,084 2/1972 Goldhaber 417/394 Primary ExaminerWilliam L. Freeh Assistant Examiner-Richard E. Gluck Attorney, Agent, or F irm-Garrettson Ellis [57] ABSTRACT A portable pulsatile pumping system simulates the pumping mechanism of a human heart in pumping fluid for such applications as organ perfusion systems. The pumping system includes a regulated source of pressurized gas, a pulsatile pump having an aorta chamber providing a sustained minimum diastolic pressure and a ventricle chamber providing a higher systolic pressure during a selectively variable part (1 to 99 percent) of each cyclic pumping action, the periodicity of which may be varied from 5 to 150 cycles per minute. The gas source is connected to the pump by a first adjustable pressure regulator to maintain the chosen diastolic pressure in the aorta chamber. The ventricle chamber is alternately coupled to gas pressure taken through a second pressure regulator and vented by a solenoid mechanism operated by a digital electronic timing control circuit. The digital electronic control system employs digital counters and selector switches to generate square wave pulses of varying duration and periodicity in a manner which provides both conservation of electrical battery energy and high reliability. At the same time, an optimum pumping system is achieved because the elasticity of the gas and connecting tubing are employed to smooth the sharp signal transitions.

10 Claims, 4 Drawing Figures II:- 140/80 m2 PERFUSION i SYSTEM H Uw M-L ,2 l-T'fli' l PATENTEBAPR 1 51975sum 1 95 3 TEMPERATURE CONTROL SYSTEM FROM CONTROL CIRCUIT 86 1 PRESSURIZEO AIR CONTROL CIRCUIT T0 SYSTEM No.2

P,-' .TENTEBAPR1 SL975 877. 843sum 3 5 3 30a 220 o 2.2m i

ONESHOT 306 2K IOOO/l/u -soo 90 f:

FlG.-4

PULSATILE PUMPING SYSTEM BACKGROUND OF THEINVENTION 1. Field of the Invention This invention relates to a system providing gentle, pulsatile pumping for life sustaining fluids, and more particularly to pulsatile pumping systems for organ perfusion systems whose cyclic characteristics may be varied within wide ranges.

2. History of the Prior-Art There are many biomedical systems in which it is desirable to pump life sustaining fluids in a pulsatile manner closely simulating cardiac action. One such application is in an organ perfusion system for preserving an organ such as a kidney from the time it is removed from a donor until it is feasible to transplant it in a recipient.

An organ perfusion system typically recirculates a perfusate containing oxygen and nutrients under control of a pump. Perfusate is drawn from a pool in which the kidney rests, passed through an oxygenator which adds oxygen and removes carbon dioxide, adjusted in temperature, typically by cooling to 510 C., and returned to the kidney. Incoming perfusate is connected to the renal artery of the kidney and passes through the kidney to the pool of perfusate in which the kidney rests, from which pool it is again recirculated. While the reasons are not fully understood at present, a pulsatile pumping action is preferred because it appears to aid the distribution of perfusate through an organ and the performance of life sustaining functions.

Because of the difficulty of getting donors and recipients at the same place at the same time it is desirable that an organ perfusion system be portable and be able to maintain the organ viable, for at least several days. At the same time it must provide smooth, gentle handling of the perfusate under controlled conditions so as not to shock the life sustaining fluid. An advantageous pulsatile pump that closely simulates cardiac pumping action when properly energized is described in U.S. Pat. No. 3,639,084 and incorporates distensible ventricle and aorta chambers connected in series by one-way valves. An atrium chamber collects perfusate under gravity flow and the adjacent ventricle chamber responds to applied periodic systolic pressures to pump perfusate into the aorta chamber which is under constant bias to provide a sustained minimum diastolic pressure. As described in the referenced patent. the systolic and diastolic pressures may be supplied by a regulated source of pressurized air and a fluid logic control circuit may control the periodic repetition of systolic pressure in the ventricle chamber. However, the fluid timing and logic control requires large amounts of compressed air, which militates against portability, and such controls do not adequately permit adjustability over wide operat on ranges.

SUMMARY OF THE INVENTION A pulsatile pumping system for life sustaining fluids in accordance with the invention is portable and economical but yet provides the high reliability, versatility and gentle handling needed for organ perfusion. A pulsatile pump is driven by a highly portable pressurized gas source under control of an accurate, low energy digital electronic circuit. The digital circuit provides accurate control of the pumping action over a wide range of pumping rates and pressure proportions while LII the elasticity of the gas and connecting tubing smooth sharp transitions resulting from digital control.

A particular example of the system includes a pump of the distensible chamber type having ventricle and aorta chambers responsive to applied fluid pressures, a source of pressurized fluid providing driving energy for the pump, a diastolic pressure regulator valve coupling the pressurized fluid to the aorta chamber to maintain a constant diastolic pressure therein, a systolic pressure regulator valve coupling the pressurized fluid to the ventricle chamber to provide alternate atmospheric and systolic pressures therein under control of an electronic control circuit, and an electronic digital control circuit connected to control the systolic pressure regulator valve. The control circuit includes a transducer which is responsive to square wave signals and a digital circuit providing square wave signals at a selected variable frequency with the systolic portion of each cycle having a selectively variable proportion. The elasticity of the driving fluid and connecting conduits smooth the sharp actuating signal transitions provided by the digital electronic control to attain a gentle but precise pumping action.

The control circuit includes a variable frequency square wave clock signal generator and two series connected stages of a binary coded decimal (BCD) counter which recycles after each cycles of the clock signal. BCD to decimal decoders are connected to provide a decimal output indicating the state of the units and tens portions of the counter respectively. A pair of two rotor multiple contact rotary switches is connected to the decimal outputs of each of the units and tens decoders so that the rotatable wiper arms are energized when the counters have counted to the decimal outputs which are connected to the contacts at which the rotors are set. A flip flop providing the systolic pressure control signal is connected to reset when the counters recycle and set when the advancing count causes the rotors of both the units and tens switches to become simultaneously activated. As the flip flop sets and resets it provides a square wave pump control signal demarcating alternate diastolic and systolic time intervals withadjustably selectable proportions and the frequency.

BRIEF DESCRIPTION OF THE DRAWINGS A better understanding of the invention may be had from a consideration of the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic diagram of an organ perfusion system utilizing a pulsatile pumping system in accordance with the invention;

FIG. 2 is a partly block diagram and partly schematic representation of a digital electronic control circuit controlling the operation of the pulsatile pumping system shown in FIG. 1;

FIG. 3 is a schematic diagram representation of a variable frequency square wave clock signal generator used in the electronic control circuit shown in FIG. 2; and

FIG. 4 is a schematic diagram representation of a square wave clock signal frequency indicator used in the electronic control circuit shown in FIG. 2.

DETAILED DESCRIPTION Referring to FIG. 1, there is shown a portable organ perfusion system for preserving living organs over an extended period of time. Thesystem 10 includes a container ororgan chamber 12, in which an organ is to be maintained, aperfusate conditioning system 14 and a pulsatile pumping system 16 which controls the recirculation of life substaining perfusate from a pool in thecontainer 12, through theconditioning system 14 and through anorgan 18 in thecontainer 12 back to the pool in thecontainer 12.

Perfusate moves under gravity flow from the pool in thecontainer 12 through aconduit 20 andT section 22 to anoxygenator 24 of conventional construction. TheT section 22 contains athermistor probe 26 which is in thermal communication with perfusate passing therethrough and generates an electrical temperature signal indicative of perfusate temperature on aconductor 28. Perfusate enters the oxygenator at aninlet 30 and passes through theoxygenator 24 under gravity flow to anoutlet 32. Theoxygenator 24 has anoxygen inlet 34 connected by aconduit 36 to apressure regulating valve 38 which is in turn connected to a source of pressurizedoxygen 40. Thepressure regulator valve 38 maintains the oxygen pressure within theoxygenator 24 at a proper level for dissolving a desired amount of oxygen in the perfusate as it passes through theoxygenator 24. An outlet42 is connected to aconduit 44 to vent carbon dioxide which is removed from the perfusate as it passes through the oxygenator. Thus, as perfusate reaches theoutlet 32 it has been resupplied with oxygen and unwanted carbon dioxide has been removed. Anaccess T coupling 46 is connected byconduits 48 and 50 between theoutlet 32 of theoxygenator 24 and aninlet 52 of apulsatile pump 54 within the pumping system 16.

Thepump 54, which is of the distensible chamber type described in US. Pat. No. 3,639,084, delivers the perfusate at anoutlet 56 from which it passes through aconduit 58 to aheat exchanger 60 havingperfusate inlet 62 connected to theconduit 58 and aperfusate outlet 64. Theheat exchanger 60 has aninlet 66 andoutlet 68 through which a heat carrying fluid passesto provide thermal compensation for the perfusate to tend to maintain it at a selected constant temperature. Atemperature control system 70 receives the heat carrying fluid through aconduit 72 which is connected to theoutlet 68 and delivers heat carrying fluid through aconduit 74 to theinlet 66.

Thetemperature control system 70 is connected to operate in response to the temperature control signal onconductor 28 to maintain the perfusate at a desired temperature. The temperature control system removes heat from the heat carrying fluid as it is recirculated through theheat exchanger 60 in a typical situation where a perfusate temperature of 5l0 C. is desired. As the heat carrying fluid is circulated through theheat exchanger 60 it is in thermal communication with-the perfusate, thereby tending to maintain perfusate leaving the heat exchanger atoutlet 64 at the same temperature as heat carrying fluid entering the heat exchanger throughinlet 66. In other arrangements it may be desirable to maintain the perfusate at or near normal body temperature control and in this case it may be necessary for thetemperature control system 70 to add heat to the heat carrying fluid as it is recirculated through theheat exchanger 60 in order to maintain the perfusate at the desired temperature.

As perfusate leaves theoutlet 64 ofheat exchanger 60 it flows throughconduit 76 to access T coupling 78 I and then throughconduit 80 back to thecontainer 12 where theconduit 80 is connected to anorgan 18 which is being preserved. For instance in the case of a kidney, theconduit 80 would be connected to the renal artery thereof. Theaccess T couplings 46 and'78 permitperfusate to be periodically. drawn off by hypoder- A mic needles for laboratory analysis. Similarly, substances can be added to the perfusate by injection through theaccess T couplings 48, 78.

In addition to thepump 54, the pumping system. 16

thepump 54, a solenoid transducer 84 controlling a systolic pressure valve in the pressure regulating and conduit system and a digitalelectronic control system 86 providing a periodic square wave pulse control signal for actuating solenoid 84. The source of pressurized fluid may alternatively be provided by a battery driven electric motor driving a compressor. The pulse control signal has a selectively variable frequency with systolic and diastolic time intervals of adjustably selectable duration within each cycle. The pump '54 is designed to provide a gentle pulsatile pumping action closely resembling the pumping action of a human heart which alternates a relatively low diastolic pressure with a relatively high systolic pressure during each pumping cycle. Thepump 54 contains three chambers which are con nected in series through one-way valves 88 and 94 which permit perfusate to flow only in a forward direction through thepump 54. Anatrium chamber 92 co]- lects perfusate as it passes under gravity flow through.

theinlet 52. A ventricle chamber is divided by aflexible membrane 96 intotwo portions. An interior orperfusate portion 98 ofthe ventricle chamber is interior to themembrane 96 and receives perfusate throughoneway valve 88 from theatrium 92 under gravity flow when the external ordriving fluid portion 100 of the ventricle is at atmospheric pressure. The external por tion 100 of the ventricle chamber is connected to the pressure regulating system through a small flexible, elastically expansible energy absorbing conduit 102 of a resilient material such as silicone rubber having an.

inside diameter of about A inch.

The pressure regulating system includes a high pressure regulating valve having aninlet orifice 112 connected to thehigh pressure source 82 and anoutlet orifice 114. Thepressure regulating valve 110 maintains a constant pressure of about 20 psi at theoutlet 114.A Y connection 116 has an inlet connected to theregulated pressure outlet 114 andseparate outlets 120, I22. A fourway diastolicpressure regulator valve 124 has aninlet orifice 126 connected tooutlet 120, anoutlet oriflce 128 and avent orifice 130. The diastolicpressure regulator valve 124 provides a selectable constant output pressure of 0-500 millimeters of mercury at theoutlet 128. This diastolic pressure is set at a desired level by varying the position of acontrol knob 132 which is typically set to provide a diastolic pressure of about 80 millimeters of mercury. Thevalve 124 can either supply theoutlet 128 with driving fluid from.

source 82 or vent driving fluid from theoutlet 128 to the atmosphere throughvent 130 as necessary to maintain the diastolic pressure constant.

Asystolic pressure regulator 136 similar todiastolic pressure regulator 124 has aninlet 137 connected to theoutlet 122 ofY connector 116, anoutlet 138, and avent 139. A four-way valve 140 has aninlet orifice 141 coupled tooutlet 138, anoutlet orifice 142, anatmospheric vent orifice 143 and is mechanically coupled to solenoid 84 to connect theoutlet 142 to atmospheric pressure throughvent 143 when solenoid 84 is inactive and to provide a desired systolic pressure atoutlet 142 when solenoid 84 is activated. A desired systolic pressure between 0 and 500 millimeters of mercury may be selected by rotating acontrol knob 144 oncontrol valve 136 to a desired position. Thecontrol knob 144 is typically set to provide a systolic pressure of 240 millimeters of mercury. The conduit 102 is connected to the regulating system at theoutlet 142 of solenoid actuatedvalve 140.

Anoptional aorta chamber 148 ofpump 54 provides a low diastolic pressure which may be greater than atmospheric pressure and has a construction very similar to that of the ventricle chamber. Theaorta chamber 148 has a flexible membrane ordiaphragm 150 which divides an interior portion of thechamber 152 from anexterior portion 154. Theexterior portion 154 is connected by aconduit 156 to theoutlet 128 of diastolicpressure regulator valve 124 which causes the predetermined diastolic pressure to be constantly maintained in theexternal portion 154 ofaorta chamber 148.

During a diastolic portion ofa pumping cycle, the solenoid 84 is inactive and the external portion 100 of ventricle chamber is vented to atmospheric pressure. This allowsmembrane 96 to expand as perfusate flows by reason of a gravity head through one-way valves 88 from theatrium 92 into theinterior portion 98 of ventricle chamber. Then, as solenoid 84 receives an activating signal fromcontrol circuits 86,systolic control valve 140 is driven to a systolic pressure condition to provide the systolic pressure throughoutlet 142 and conduit 102 to the exterior 100 of ventricle chamber. This relatively high systolic pressure drives perfusate from theinterior portion 98 of ventricle chamber through one-way valve 94 to theaorta chamber 148 which is somewhat smaller than ventricle chamber. As perfusate is forced through one-way valve 94 during this systolic portion of the cycle, theflexible membrane 96 collapses, theinterior portion 98 decreases in volume, and the exterior portion 100 increases in volume. At the beginning of a systole portion of a pumping cycle, thepump 54 continues to provide perfusate at the diastole pressure. However, theaorta membrane 150 rapidly expands to maximum capacity, permitting the systolic pressure to then be passed through the aorta chamber to thekidney 18. The cycle is then repeated as the solenoid 84 is deactivated, causingsystolic control valve 140 to again vent the exterior portion 100 of ventricle chamber to the atmosphere.

After the systolic portion of a pumping cycle is terminated bycontrol circuit 86 themembrane 150 begins to collapse under the constant pressure in theexternal portion 154 of theaorta chamber 148 to force perfusate out through theoutlet 56 at the constant, sustained, minimum diastolic pressure. Before themembrane 150 is completely collapsed a new systolic portion of a pumping cycle must be commenced to force more fluid into the aorta chamber. In this way thepulsatile pump 54 provides alternating diastolic and systolic pressures at theoutlet 56 with a pumping characteristic very closely following that of a human heart The small internal diameter of conduit 102 and the elastic energy absorbing properties of the driving fluid and conduit 102 combine to provide an energy absorbing fluid impedance which acts as a hydraulic filter to smooth sharp pressure transitions in the ventricle chamber. Some life sustaining fluids such as whole blood are easily damaged by shock and must therefore be treated extremely smoothly and gently. This hydraulic impedance or filtering characteristic permits the hydraulic control system to be controlled by a square wave pulse signal having sharp transitions (for example 5 millisecond rise 30 millisecond decay) without damaging the life sustaining fluid. By the time the digital pulse control signals reach the external portion of the ventricle chamber sharp transitions have been filtered out. Thus, thepulsatile pump 54 is able to handle a life sustaining fluid gently and without shock, whether it be whole blood, perfusate or some other fluid, even though control is provided by a digital electronic signal having sharp transitions.

A second organ perfusion system represented by ahollow rectangle 162 and labeled Perfusion System No. 2 is connected to receive perfusate at aninlet 164 through aconduit 166 from the pool incontainer 12 and provide perfusate through outlet 168 andconduit 170 to aconduit 172 which connects to a second organ to be preserved within thecontainer 12. Organ Perfusion System No. 2 shares thecontainer 12 and certain components in thecontrol circuit 82 with Perfusion System No. 1 and may be assumed to be substantially identical to Perfusion System No. 1 even though it is not described in detail.

The electronicdigital control circuit 86 includes a variable frequencysquare wave generator 200 which generates a digital square wave clock signal at a frequency selected by an operator, afrequency indicator circuit 202 which indicates to an operator the frequency of the square wave clock signal, aproportioning control circuit 204, agated flip flop 206, apower amplifier 208 and asolenoid coil 210 which controls the activation of solenoid 84 (FIG. 1).

Theproportion control circuit 204 includes a century counter having a BCD units counter 212, a BCD tens counter 214 connected to count cycles of the counter 21.2, a BCD todecimal converter 216 responsive to the outputs from theunit counter 212 and a BCD todecimal converter 218 responsive to outputs from the BCD tens counter 214. The BCD counters 212, 214 may be implemented with MC 7490P integrated circuits manufactured by Motorola and the BCD todecimal converters 216, 218 may be implemented with MC 7442P integrated circuits, also manufactured by Motorola. The decoded decimal units and decimal tens outputs of the century counter indicate the successive counts of the century counter as it counts clock pulses from 0 to 99 and then recycles back to 0 at count 100. For instance when the counter reaches the count of 55 thenumber 5 outputs of both theunits converter 216 andtens converter 218 will have a high voltage thereat and each of the other decoded decimal outputs will have a low or ground potential thereat. Thecounter 212 and converter216 together with thecounter 214 andconverter 218 form first and second decade counting systems providing discrete decimal outputs indicative of instantaneous counts therein.

Four switches are provided to permit operator control of the proportion of each pumping cycle during which systolic pressure is desired, two for systemNo. 1 and two for system No. 2. Each switch contains two completely insulated portions designated part A and part B having mechanically coupled rotors which are simultaneously and synchronously positioned by a single control knob. Switch U1 is a ten position rotary switch in which an A portion has the fixed contacts thereof connected to the ten decimal outputs of theunits converter 216 in sequence. Similarly, switch T1 is a 11 position rotary switch having ten of its ll contacts connected to the ten decimal outputs oftens converter 218 in sequence. The eleventh contact is not connected. The two switches U2 and T2 of the second perfusion system are connected in similar manner with the ten A contacts of switch U2 connected to the ten decimal outputs ofunits converter 216 and ten of the eleven A contacts of switch T2 connected to the ten decimal outputs oftens converter 218 with the elev' enth A contact left open. The BCD units counter 212 receives the variable frequency clock signal as an input onconductor 220 and BCD tens counter 214 receives its counting input from decimal output zero fromunits converter 216 onconductor 222. Theintegrated circuits 212, 214, 216 and 218 may otherwise be connected, biased and compensated in a conventional manner. Anisolator 224 which may be implemented with an MC 836P integrated circuit manufactured by Motorola is connected to receive inputs from the decimal zero output oftens converter 218, the decimal zero output ofunits converter 216, therotary wiper contact 226 of switch TIA, therotary wiper contact 227 of switch UlA, therotary wiper contact 228 of switch TZA and therotary wiper contact 229 of switch U2A and provide outputs designated OT, OU, TlAR, UlAR. T2, AR, and U2AR respectively in response thereto.

These six signals are used by systolic pulse generating circuits for both systems No. l and No. 2 to generate the systolic pulse signals which actually control the activation ofsolenoid coil 110. Since this portion of the system is identical for both system No. l and system No. 2, the systolic pulse generating circuits for system No. 2 is indicated merely by ahollow rectangle 132 and it will be understood that the same description applies as given hereafter for system No. 1.

As illustrated with respect to system No. 1, the wiper arm signals TLAR and ULAR for the digitand for the decimal and unit switches respectively are received by an ANDgate 234 controlling the .1 input to aJK flip flop 236 within an integrated circuit gatedflip flop 216. The TLAR and ULAR signals operate in combination with the clock signal to activate ANDgate 234 at the selected variable count, causing ANDgate 234 to generate an intermediate control signal which activates the .1 input to flipflop 236. An ANDgate 238 generates an intermediate control signal which activates the K input to flipflop 236 in response to the OT, OU and clock signals which occur as the century counter resets. The ANDgates 234 and 238 are connected to be enabled by the clock signal from thesquare wave generator 200. An inverting preset input to flipflop 236 is connected through a 10K resistor 240 to a 5 volt source. It is also connected to the number contact of the B portion of switch TL. Thenumber 10 contact of the A portion of switch TL is not implemented. A movable ode ofdiode 262 connected to the same +12volt rotor 244 of switch TLB is connected to ground. An inverting clear input to flipflop 236 is connected through a 10 K resistor 242 to a 5 volt source and to thenumber 0 contact of the B portion of the switch UL. The wiper I arm 245 of switch ULB is connected to thenumber 0 fixed contact of switch TLB. Thus, whenever both of the system No. 1 proportioning system switches are set to zero,flip flop 236 is constrained to the clear state.

Similarly, whenever switch TLB is set to the number 10 a position,flipflop 236 is constrained to remain in the one or true state. The Q output offlip flop 236 provides the square wave systolic pulse control signal on con-.ductor 250 which drives thecoil 210 throughpower switching amplifier 208.

Conductor 250 is connected through a 3.3K resistor 252 to the base of annpn transistor 254. The collector oftransistor 254 is connected through a 220 ohm resistor 256 to a +5 volt source and the emitter oftransistor 254 is connected through a 1K resistor 258 to ground and also to the base input of annpn transistor 260. The

emitter oftransistor 260 is connected to ground and the collector is connected both to the anode of adiode 262 and to a negative terminal ofsolenoid coil 210 in solenoid 84. Thesolenoid coil 210 anddiode 262 are connected in parallel with the positive terminal ofcoil 210 being connected to a +12 volt source and the cathsource.

Thepower switching amplifier 208 responds to a systolic pulse control signal onconductor 250 by activating thecoil 210 when the control signal is high or true and inactivating thecoil 210 when the control signal is at ground potential or false. Whenever the systolic pulse, control signal is true,transistor 254 is turned on permitting current to flow through the collector and emitter thereof to inturn cause transistor 260 to be turned on. Astransistor 260 is turned on activating current is permitted to flow from the +12 voltsource throughcoil 210 to the collector oftransistor 260 and then out through the emitter oftransistor 260 to ground. This activation ofcoil 210 causes solenoid 84 to switch four-waypressure regulator valve 136 to the systolic pressure state wherein systolic pressure is applied to external cavity 100. As the systolic pulse control signal returns to ground potential,transistors 254 and 260 are switched off and the continued flow of cur rent through thecoil 210 is blocked. Ascoil 210 is deactivated solenoid 84 causespressure regulator valve 136 to return to a state wherein atmospheric pressure is communicated to external chamber portion 100. En-

ergy which may be stored bysolenoid coil 210 at thetime transistor 260 is switched off may be dissipated throughdiode 262.

The variable frequencysquare wave generator 200 is illustrated in greater detail in FIG. 3. The generator.

200 includes a type 2N284Ovariable frequency oscillator 260 having a B2 terminal connected througha l K resistor 262 to a +5 volt source and a BL terminal connected through a 68ohm resistor 264 to ground. The

control terminal E ofoscillator 260 is connected through a 15p. farad capacitor 266 to ground and also through afrequency control circuit 268 to the +5 volt source. Thefrequency control circuit 268 includes a 20K potentiometer 270 having one terminal and the wiper contact connected to the +5 volt source and the other terminal connected to a 16.5K resistor 272. The other terminal ofresistor 272 is connected to one terminal of an 8.2megohm resistor 274 and one terminal of a 1megohm potentiometer 276 having a logarithmically varying resistance. The opposite terminal ofresistor 274, the wiper arm ofpotentiometer 276, and the opposite terminal ofpotentiometer 276 are connected to the gate or control input E tooscillator 260. The output from theoscillator 260 is taken from a BL terminal which is connected througha l K resistor 280 to the base of annpn amplifying transistor 282.Transistor 282 has its emitter connected to ground and its collector connected through a 3.3K resistor 284 to a +5 volt potential. The collector oftransistor 282 is connected to the base of asecond amplifying transistor 286 having its emitter connected to ground and its collector connected through a 1K resistor 288 to the +5 volt potential, The square wave clock signal is provided onconductor 220 which is connected to the collector of amplifyingtransistor 286.

The variablesquare wave generator 200 provides a square wave clock signal at a frequency variable between 8.33 and 250 hertzin accordance with the setting ofpotentiometer 276. This frequency range corresponds to a frequency range of 500 to 15,000 cycles per minute which is divided by 100 by thecentury counter 204 to provide a frequency range of 5 to 150 pulses per minute for the systolic pulse control signal onconductor 250.

Thefrequency indicator circuit 202 is illustrated in greater detail in FIG. 4. Thefrequency indicator 202 includes a oneshot 300 which receives the clock signal fromsquare wave generator 200 onconductor 220 and generates a positive output for a selected time interval in response to each positive going transition of the clock input. The one shot 300 may be a type MC 8601? integrated circuit manufactured by Motorola and has a 44.2K resistor 302 and a 0.22 p. farad capacitor 304 connected in a conventional manner to control the time interval of the output. The output is taken from the key terminal and connected through a 2.21K resistor 306 and a 2 Ktrim pot 308 to a positive terminal of amilliameter 310 which has its negative terminal connected to ground. A 90 ,u.farad filter capacitor 312 is connected in shunt across the terminals ofmilliameter 310 to smooth changes in voltage across the terminals of themeter 310. Theresistor 306 andpotentiometer 308 operate in conjunction with a fixed voltage at the Q output of one shot 300 to provide in effect a constant current source which providesmeter 310 with a fixed amount of charge for each fixed firing interval of oneshot 300. The total charge per unit oftime reaching milliameter 310 is thus directly proportional to the frequency at which the one shot is fired under control of clock signal onconductor 220. This charge must pass throughmilliameter 310 in the form of a current which drives the pointer to a rotational position directly proportional to the frequency of the clock signal.Milliameter 310 may be calibrated to indicate the frequency of the systolic pulse control signal directly.

The electronicdigital control circuit 86 provides precise, highly reliable, low cost control of the pulsatile pumping system with the consumption of very little electrical power. A highly portable, conventional 12 volt battery (not shown) easily provides the required source of electrical energy. A conventional voltage regulator such as a LM309K manufactured by National Semiconductor may be connected to the 12 volt battery to provide the +5 voltage source required at many points in thecontrol circuit 86. While an easily portable battery provides the electrical power, an easily portable bottle of pressurized air may be used to provide the pneumatic power. Since the pressurized air driving fluid is used only to drive thepulsatile pump 54, much less driving fluid is consumed by theperfusion system 10 than would be required if the driving fluid were also used to energize a pneumatic timing control system. Since a 25-pound bottle of pressurized air will operate theperfusion system 10 for 8-12 hours, the complete perfusion system including energy sources is relatively light in weight and highly portable. This arrangement makes optimum use of both electrical and pneumatic elements and energy sources to provide an economical, highly reliable,portable perfusion system 10 which can be used to preserve an organ for several days while transporting it from one place to another.

The electrical control system permits the systolic portion of each cycle of thepulsatile pump 54 to be varied under automatic control between 1 and 99 percent, fixed at 0 percent, fixed at percent or completely controlled by hand. For instance, by setting the units and tens control switches to number 55, diastolic pressure will be provided during the first 55 percent of each pumping cycle and systolic pressure will be provided during the last 45 percent of each pumping cycle. As the century counter recycles the 0 outputs of both the units and tens BCD todecimal converters 216, 218 will go true causing the OT and OU signals to go true to activate the K input to flipflop 236. The K input causesflip flop 236 to reset and produce a ground potential output signal which turns offpower amplifier 208 to deactivatesolenoid coil 210 and connect the exterior portion 100 ofventricle chamber 94 to atmospheric pressure. As soon as the century counter reaches the count of 55 the 5" outputs of the units and tens BCD todecimal converters 216, 218 go true causing the TLAR and ULAR signals to go true, thereby activating the J input to flipflop 236. As the J input is activatedflip flop 236 switches to the true state to provide a high voltage systolic signal which turns onpower switching amplifier 208 to activate thecoil 210 in solenoid 84 and connect the external portion 100 of ventricle chamber to the selected systolic pressure. This systolic pressure is maintained throughout the last 45 counts of the pumping cycle until thecentury counter 204 recycles to again switch the systolic pulse control signal to the low state. By setting the proportion switches TL and UL at any desired count between 99 and 1 the systolic or high pressure portion of each pumping cycle can be varied from 1 to 99 percent.

When both the units and tens proportioning switches are set to the zero position, the B portion of the switch causesflip flop 236 to be constrained to the zero state and the exterior portion 100 of ventricle chamber is continuously vented to atmospheric pressure. Similarly, when the tens switch is set to thenumber 10 position the preset input offlip flop 236 is continuously activated causing the flip flop to provide a continuous systole signal as a pulse control signal to cause a systole pressure to be continuously provided to the exterior portion 100 of ventricle chamber. Sincepulsatile pump 54 requires alternating systolic and atmospheric pressures in the ventricle chamber to maintain pumping action, no fluid will be pumped so long as the proportion switches are set to provide continuous systolic or diastolic pressures at the ventricle chamber. However, by

setting the tens unit switch in the zero position and manually alternating the ten switch between the zero and ten position, both the frequency of the pumping cycle and the relative proportions of systolic and dia stolic pressure can be controlled manually over any desired range.

Although there has been described above a particular arrangement of a pulsatile pumping system in accordance with the invention, it will be appreciated that the scope of the invention is not limited thereto. Accordl ingly, any modification, variation or equivalent arrangement within the scope of the appended claims should be considered to be within the scope of the invention.

What is claimed is:

l. A system for providing a selectively controllable pulsatile flow of a perfusate to simulate cardiac action comprising: a pulsatile perfusate pump which comprises flexible chamber means, said means being collapsible in response to applied fluid pressure, to pump perfusate in said chamber means through a flow line in pulsatile manner;

at least one fluid pressure means;

adjustable systolic pressure regulator means coupled to said fluid pressure means;

first conduit means including control signal respon sive valving means coupling said systolic pressure regulator means to said ventricle chamber means; and

electronic control means including adjustable means for generating square wave control signals of adjustable duration and repetition rate, the square waves having sharp rise and fall times, wherein said valving means comprises a two output valve having a venting output and an output communicating with said perfusate pump, wherein said fluid pressure means comprises a pressure storage vessel, and wherein said electronic control means comprises counter means adjustable to provide valving means controlling outputs at selected counts, said I counter means being adapted to count said square wave control signals.

2. The invention as set forth inclaim 1 above, wherein said first and second conduit means comprise small diameter resilient tubing, and wherein the applied fluid under pressure is air.

3. A combination electronic pneumatic pump control system for gently controlling a pulsatile pump maintaining a first output pressure and producing a periodically occurring systolic output pressure greater than the first pressure in response to a periodically occurring fluid drive pressure comprising:

a selectively venting pressure control valve having an input connectable to a drive fluid pressure source under control of a transducer;

a conduit connected to the outlet of the pressure control valve to a fluid operated pulsatile pump for providing operating fluid to said pump, said conduit restricting the flow of drive fluid therethrough;

a transducer connected to control said pressure control valve to selectively connect the outlet to said pressure source in response to first and second states respectively of an electronic digital control signal having sharp transitions between states; and

an electronic digital control circuit providing an electronic digital control signal to the transducer, said control circuit including a recycling counter,

means responsive to the counter for switching the electronic digital control signal to a first state when the counter reaches a first selected count, and means for switching the electronic digital control signal to a second state when the counterreaches a second selected count, each state being present during a selected variable proportion of each control signal.

4. The pump control system asset forthin claim 3 above, wherein the conduit includes at least one elasti cally expansible portion which absorbs energy as it expands in response to a pressurized drive fluid therein.

5. The pump control system as set forth inclaim 4 above, wherein the drive fluid is an expandable gas.

6. The pump control system as set forth inclaim 5 above, wherein the drive fluid is compressed air.

7. The pump control system as set forth inclaim 3 above, wherein at least one of said first and second counts isselectively variable under operator control.

8. The pump control system as set forth inclaim 5 above, wherein the electronic digital control circuit includes an oscillator generating a clock signal at a selectively variable frequency; a recycling counter connected to count cycles of the clock signal; means re-. sponsive to the counter for generating first and second intermediate control signals in response to first and second counts'of the counter respectively, said control signal generating means including means for selectively i varying the count at which at least the first intermediate control signal is generated; and means connected to switch the electronic digital control signal to the first and second states in response to the first and second intermediate control signals respectively.

9. A system for providing a selectively controllable pulsatile flow of a perfusate to simulate cardiac action, the flow having selectable diastolic and systolic intervals and pressures comprising:

a pulsatile perfusate pump having at least a pair of pump chamber means responsive to applied fluid pressures;

means providing diastolic and systolic fluid pressures;

conduit means providing substantial impedance to fluid flow and coupling each of said diastolic and systolic pressure means to a different chamber of said perfusate pump;

signal responsive valving means coupled into the conduit means coupling the systolic pressure means to the perfusate pump; and

electronic control signal generating means coupled to said valving means and including means for generating a systole control signal of controllable duration and repetition rates, to provide control signals to said signal responsive valving means, said systole control signal means comprising an electronic digital control circuit which includes an oscillator for generating a clock signal at a selectively variable frequencies; a recycling counter connected to count cycles of the clock signal; means responsive through the counter for generating first and second the first intermediate control signal is generated;

and

means for altering the signal responsive valving means in response to the first and second intermediate control signals respectively.

10. For use in an organ perfusion system circulating a perfusate through an organ, a pulsatile pumping system comprising:

a pump connected to receive perfusate in an inlet and means for connecting the first control fluid inlet to a high pressure control fluid source in response to a first electrical signal condition and disconnecting the first control fluid inlet in response to a second electrical signal condition;

timing control circuit coupled to said means for connecting for providing a bistate electrical signal of selectable periodicity having alternate first and second electrical signal conditions, the control circuit including means responsive to operator control for selecting the relative durations of the first and second electrical signal conditions during each period, in which said timing control circuit comprises an electronic digital control circuit including a recycling counter, means responsive to the counter for assuming the first electrical signal condition when the counter reaches a first selected count, and means responsive to the counter for assuming the second electronic signal condition when the counter reaches a second selected count.

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Claims (10)

1. A system for providing a selectively controllable pulsatile flow of a perfusate to simulate cardiac action comprising: a pulsatile perfusate pump which comprises flexible chamber means, said means being collapsible in response to applied fluid pressure, to pump perfusate in said chamber means through a flow line in pulsatile manner; at least one fluid pressure means; adjustable systolic pressure regulator means coupled to said fluid pressure means; first conduit means including control signal responsive valving means coupling said systolic pressure regulator means to said ventricle chamber means; and electronic control means including adjustable means for generating square wave control signals of adjustable duration and repetition rate, the square waves having sharp rise and fall times, wherein said valving means comprises a two output valve having a venting output and an output communicating with said perfusate pump, wherein said fluid pressure means comprises a pressure storage vessel, and wherein said electronic control means comprises counter means adjustable to provide valving means controlling outputs at selected counts, said counter means being adapted to count said square wave control signals.

2. The invention as set forth in claim 1 above, wherein said first and second conduit means comprise small diameter resilient tubing, and wherein the applied fluid under pressure is air.

3. A combination electronic pneumatic pump control system for gently controlling a pulsatile pump maintaining a first output pressure and producing a periodically occurring systolic output pressure greater than the first pressure in response to a periodically occurring fluid drive pressure comprising: a selectivelY venting pressure control valve having an input connectable to a drive fluid pressure source under control of a transducer; a conduit connected to the outlet of the pressure control valve to a fluid operated pulsatile pump for providing operating fluid to said pump, said conduit restricting the flow of drive fluid therethrough; a transducer connected to control said pressure control valve to selectively connect the outlet to said pressure source in response to first and second states respectively of an electronic digital control signal having sharp transitions between states; and an electronic digital control circuit providing an electronic digital control signal to the transducer, said control circuit including a recycling counter, means responsive to the counter for switching the electronic digital control signal to a first state when the counter reaches a first selected count, and means for switching the electronic digital control signal to a second state when the counter reaches a second selected count, each state being present during a selected variable proportion of each control signal.

4. The pump control system as set forth in claim 3 above, wherein the conduit includes at least one elastically expansible portion which absorbs energy as it expands in response to a pressurized drive fluid therein.

5. The pump control system as set forth in claim 4 above, wherein the drive fluid is an expandable gas.

6. The pump control system as set forth in claim 5 above, wherein the drive fluid is compressed air.

7. The pump control system as set forth in claim 3 above, wherein at least one of said first and second counts is selectively variable under operator control.

8. The pump control system as set forth in claim 5 above, wherein the electronic digital control circuit includes an oscillator generating a clock signal at a selectively variable frequency; a recycling counter connected to count cycles of the clock signal; means responsive to the counter for generating first and second intermediate control signals in response to first and second counts of the counter respectively, said control signal generating means including means for selectively varying the count at which at least the first intermediate control signal is generated; and means connected to switch the electronic digital control signal to the first and second states in response to the first and second intermediate control signals respectively.

9. A system for providing a selectively controllable pulsatile flow of a perfusate to simulate cardiac action, the flow having selectable diastolic and systolic intervals and pressures comprising: a pulsatile perfusate pump having at least a pair of pump chamber means responsive to applied fluid pressures; means providing diastolic and systolic fluid pressures; conduit means providing substantial impedance to fluid flow and coupling each of said diastolic and systolic pressure means to a different chamber of said perfusate pump; signal responsive valving means coupled into the conduit means coupling the systolic pressure means to the perfusate pump; and electronic control signal generating means coupled to said valving means and including means for generating a systole control signal of controllable duration and repetition rates, to provide control signals to said signal responsive valving means, said systole control signal means comprising an electronic digital control circuit which includes an oscillator for generating a clock signal at a selectively variable frequencies; a recycling counter connected to count cycles of the clock signal; means responsive through the counter for generating first and second intermediate control signals in response to the first and second counts of the counter respectively, said control signal generating means including means for selectively varying the count in which at least the first intermediate control signal is generated; and means for altering the signal responsiVe valving means in response to the first and second intermediate control signals respectively.

10. For use in an organ perfusion system circulating a perfusate through an organ, a pulsatile pumping system comprising: a pump connected to receive perfusate in an inlet and deliver perfusate in an outlet, said pump including first and second control fluid inlets and providing a first perfusate pressure at the outlet in response to a high control fluid pressure at the first control fluid inlet and a second perfusate pressure at the outlet in response to a low control fluid pressure at a second control fluid inlet in the absence of the high control fluid pressure at the first control fluid inlet; means for connecting the first control fluid inlet to a high pressure control fluid source in response to a first electrical signal condition and disconnecting the first control fluid inlet in response to a second electrical signal condition; a timing control circuit coupled to said means for connecting for providing a bistate electrical signal of selectable periodicity having alternate first and second electrical signal conditions, the control circuit including means responsive to operator control for selecting the relative durations of the first and second electrical signal conditions during each period, in which said timing control circuit comprises an electronic digital control circuit including a recycling counter, means responsive to the counter for assuming the first electrical signal condition when the counter reaches a first selected count, and means responsive to the counter for assuming the second electronic signal condition when the counter reaches a second selected count.

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