|Publication number||US3919722 A|
|Publication date||Nov 18, 1975|
|Filing date||Mar 6, 1973|
|Priority date||Mar 6, 1973|
|Also published as||CA1030703A, CA1030703A1, DE2449320A1|
|Publication number||US 3919722 A, US 3919722A, US-A-3919722, US3919722 A, US3919722A|
|Inventors||Lowell T Harmison|
|Original Assignee||Us Health|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (3), Referenced by (75), Classifications (16)|
|External Links: USPTO, USPTO Assignment, Espacenet|
United States Patent [191 Harmison TOTALLY IMPLANTABLE ARTIFICIAL REPLACEMENT HEART  Inventor: Lowell T. Harmison, Bethesda, Md.
 Assignee: The United States of America as represented by the Secretary of the Department of Health, Education and Welfare, Washington, DC.
 Filed: Mar. 6, 1973  Appl. No.1 338,611
 US. Cl 3/l.7; 3/1
 Int. Cl. A61F 1/24  Field of Search 3/1, DIG. 2, 1.7; 128/1 D, 128/DIG. 3
 References Cited UNlTED STATES PATENTS 3,668,708 6/1972 Tindal 3/1 3,771,173 11/1973 Lamb, Jr 3/1 3,783,453 1/1974 Bolie 3/1 Nov. 18, 1975 Primary Examiner-Ronald L. Frinks Attorney, Agent, or Firm-Browdy and Neimark ABSTRACT A totally implantable replacement heart system comprises a blood pump, energy converter, heart rate control computer and an energy storage unit. The blood pump is a four-chambered unit having two reservoirs or atria with two large valves forming the inflow to the pumping chambers or ventricles, and tricuspid pulmonary and aortic valves. The artificial heart has been designed to adapt to different types of internal power systems (electrical, nuclear, or pneumatic).
The heart rate control computer utilizes stroke volume as one of the principal control parameters. This control system is always seeking to converge on a rate that maintains stroke volume at full value or at a predetermined high percent of full stroke volume. A key part of the control logic is the automatic override of heart rate from the right heart thereby providing sensitivity to central venous conditions.
13 Claims, 15 Drawing Figures V atent' Nov. 18, 1975 Sheet10f9 3,919,722
mm JNOV.18,1975 Sheet2of9 3,919,722
ARTERIAL FLOW TO BODY VENOUS RETURN VENOUS FLOW FROM HEAD TO LUNGS ARTERIAL RETURN VENOUS RETURN FROM LUNGS FROM TRUNK 03. Patent N0v.l8,1975 Sheet3 0f9 Sheet 4 of 9 65. Patent Nov. 18, 1975 I U Patent Nbv.18,1975
Sheet 5 of 9 US. Patam N0v.18,1975 I Sheet6of9 3,919,722
@ atent Nov. 18, 1975 Sheet 7 of 9 3,919,722
VENOUS RETURN +20% STEP INCREASE FLOW STEADY STATE LEVEL I time T0 HEART FINAL STEADY RATE A STEADY STATE RATE time RESIDUAL ATRIAL MAY. RESIDUAL VOLUME VOLUME V I time I SKIN TRANSFORMER AC/AC I Q T Q I BATTERY I RECTIFIER I r "1 I L &1?! k CR TRL I H R .5. d- I CONTROL COMPUTER IRCU TS MECHANlCAL LEFT I 017 CONVERTER RIGHT l I20 VAC 1 6o L. a fi a w -J l ENERGY SUBSYSTEM OD P TOTALLY IMPLANTABLE ARTIFICIAL REPLACEMENT HEART FVIELD or HE INvENTIoN The present invention relates essentially to an artificial heartand, more pertinently, to a totally inplantable artificial heart designed-and constructed for disposition with a ,human or animal. body asa complete replacement for the natural human or animal heart.
BACKGROUND OF THE INvENT oN Of the vital organs, the heart'has the most elementary function since it acts simply as a pumpvThe heart is a four-chambered device made up of two pumps, called ventricles, and two reservoirs,-,-called atria. The right (120 mm Hg). The mean blood flow through the right and left heart is typically 6,liters/minute. The left ventricl'e does about four times the work of the right ventricle. The mechanical pumping power of the heart usually ranges between 1 .5 and 4 watts. (These power levels are over 10,000 times higher than those required for cardiac pacing) t 1 The heart is an extremely complicated pump that must adapt to a wide range of requirements to provide adequate blood flow to satisfy physiologic needs. To meet these requirements, fromsleepto peak exercise, the heart must provide the flow necessary through changes in rate and/or stroke volume, I
The value and importance of the instant invention can bereadily understood by considering a patient afflictcd with Americas number one killer, cardiovascular disease, who must be fully-or partially confined to a bed or wheelchair by virtue of his ailing heart. Such a patient may undergo ,surgeryin which the patients heart would be completely removed, and the instant invention mounted inside the patients body as a replacement or substitute for the removed heart. Thereafter that patient; whose span of life prior tothe surgery was highly questionable and in any event of relatively short duration. should assume a substantially normal as well as active life; not only of an ambulatory character but even to the extent of participating in physical sports and games, and maintain that active life for anindefinite period. In other'words, the instant invention is designed to indefinitely prolong the lives of patients. human or animal, which would otherwise be materially foreshortened by virtue of heart trouble.
In the past artificial hearts designed to provide an actual substitute for the'entire human or animal heart have derived their power from a source of energy carried by the user, externally of the body. In order to connect the external power source to the transplanted heart an orifice must be made in the bodyof the user. Thecreation of the orifice and the insertion of the connectingelement results in discomfort and possible irrita'tion or infection to the user.
It is well known that the natural-heart pumps less' blood during rest than during exercise and accomplishes this by changing its-frequency or number of beats, and the blood output per beat. The speed of operation of prior artificial hearts has been controlled, when a change in physical activity is contemplated, by the natural adjustment of a rheosta t or equivalent ele- 2 ment which varies only the pumping frequency while keeping the blood output per beat substantially constant. Thus the range of operation of prior artificial hearts is not quite as great or as flexible as that of the natural heart from complete rest to very violent exercise.
SUMMARY OF THE INVENTION The shortcomings of prior art artificial replacement hearts are satisfactorily overcome by the present invention. An object of the present invention is thus to overcome the defects of the prior art such as indicated above.
With the foregoing in mind, it is an important object of'the instant invention to provide a totally implantable artificial heart capable of being mounted in the chest cavity of a human or animal.
Also, a principal object of this invention is a totally implantable artificial heart capable of functioning as a complete replacement for a human or animal heart, and which may automatically vary the frequency of beats and the stroke volume or output per beat.
Another object of the present invention is an implantable energy system that would accept power from an internal storage unit and convert the energy into useful driving energy for squeezing the chambers of the total heart in a controlled fashion.
Another object is to provide a control system that would regulate the flow of energy from the implanted power system to the artificial heart and provide the controlled output energy into the blood with the proper physiologic waveforms.
Another object of the instant invention is a total artificial heart that would accept all returning venous and pulmonary blood with any fixed demands.
Another object of this invention is a completely implanted power unit that would provide the necessary I energy at the current, voltage and frequency necessary for operating the total heart without creating excessive heat.
A further object ofthe present invention is to provide a control system responsive to changing physiological needs and to instantaneous energy demands.
Yet another object is the dissipation of heat within the system and its transfer to the surrounding biological tissue and fluid.
A still further object is the provision of adequate flow to the pulmonary and systemic tissues without damage to the blood.
Another object of the instant invention is to provide an artificial heart capable of developing psuedoendothelial surfaces on all its blood contacting surfaces.
Yet another object is to provide a total heart which does not demand blood from either the lungs or the venous tree and would be fully responsive to the returning flow.
Another object is to provide a system which functions normally without creating undesirable noise. vibrations, or other side effects.
A still further object is to provide a complete heart designed to adapt to three types of internal power control systemselectrical, nuclear. or pneumatic.
ln furtherance of these and other objects, a principal feature of the present invention is a totally implantable replacement heart comprising four pumping chambers, two atria and two ventricles with an energy unit nested therebetween.
A still further feature of the instant invention is a to-.
tally implantable replacement heart comprising an energy recovery unit.
The artificial heart of the present invention is similar to the natural heart. It is a four-chambered pump having two atria with two large valves forming the inflow to the ventricles. and tricuspid pulmonary and aortic valves. Blood flows into the atria through surgical quick connects that are designed to conform to the size and shape of the natural vessels and the artificial heart. The atria are designed to accommodate wide changes in returning venous flow and to be responsive to intrathoracic pressure. Large atrioventricular valves were developed to provide large flow areas. to minimize pressure drop, to achieve rapid filling, and to minimize low flow regions within the atria and ventricles. The ventricles are designed to provide a uniform pumping action without causing damage to the blood or stagnant flow regions. Also. they are so arranged as not to permit the moving internal surfaces to contact each other during the pumping cycle. This is done in order to eliminate potential wear points and to permit living cellular surfaces to be put on the internal surface of the pump. All blood-contacting surfaces have been designed to permit 21 living surface to develop, i.e.. endothelial or pseudoe ndthelial surfaces. All components may well be fabricated from materials that do not require a living surface. The compression of the ventricles accomplished through a pressure plate bonded to the external surface of the ventricle.,The ventricular ejection volumes are approximately equal to the natural heart so as to achieve an operating heart beat range similar to the natural heart. The components of the total implanted heart are individually replaceable.
The energy converter is designed to nest within the blood pump assembly or. in the abdominal assembly and provide the controlled power for actuating both the left and right hearts. The system converts rotary motion into linear motion within the mechanical energy converter to actuate each ventricle. After the actuator has moved completely to the ejected position. it is free to return to its original position. It will not return unless there is sufficient blood available in the atria to flow into the ventricles. Hence. the degree of filling or return of the actuator is controlled entirely by the available supply of blood in the atria on a beat-by-beat basis. This automatically varies stroke volume from O to a completely full stroke. The power changesdue to filling variation are reflected back to the energy converter and to the motor control electronics. The motor control electronics provide variable electrical input power to satisfy the instantaneous load conditions and maintain a constant speed which in turn maintains the prescribed heart rate commanded by the heart control computer. A single implanted package contains the heart control computer. motor control circuits. batteries. battery charge control units and sensors that monitor the degree of left or right ventricular filling.
The artificial heart of the instant invention has been designed to adapt to electrical. nuclear. or pneumatic internal power systems.
The electrically powered, totally implantable. artificial heart comprises: (a) a blood pump and energy system which are placed in the thoracic cage; (b) a control system. power conditioning circuitry and energy storage unit which rest in the abdominal cavity under the diaphragm; and (c) an energy receiving coil, placed under the skin. that receives the energy from an external transmission unit.
The electrical power to operate this system is transmitted across intact skin to the implanted transformer. The energy is used directly to power the converter and- /or charge the implanted batteries. if the external power source is interrupted. the system will automatically switch to internal battery power (up to 4 hour discharge capacity). The complete heart system has the capacity to satisfy all cardiac output requirements from rest to peak exercise (15 L/min). It may be possible to consider the use of biological fuel cells that would make the electrical system completely implantable and self-contained.
The nuclear powered. totally implantable, artificial heart substitutes a thermal engine with a nuclear heat source for the energy storage unit of the electrically powered heart. Hydraulic pressure generated by the engine is conveyed by a tube to the blood pump and its control'unit located within the chest. The heat-energy source is about grams of plutonium-238 (Pu-238) in a 3-layer metal capsule designed and proven to withstand corrosion. high impact and crush pressures, and cremation to insure against leakage of the radio-isotope in an accident.
One of two nuclear thermal engines may be employed. One is a vapor cycle steam engine. the other a modified Stirling cycle engine.
In the vapor cycle engine system, the water alternates many times each second between the vapor and liquid phases. The fundamental problem of valve and sliding seal leakage associated with conventional Rankine engines is obviated by the vapor cycle engine which does not'use either valves or sliding seals. Linear motion is obtained by means of bellows.
The vapor cycle engine can be controlled electronically via any electromechanical actuator such as a solenoid torque motor or piezo-el cctric bimorph. Pressurization of the engine is achieved by vaporizing a single drop of water or transferring it from the condenser to the boiler. v
The modified Stirling engine is incorporated in a power source which produces hydraulic energy which powers an automatically controlled actuator. Heat is supplied by a radio-isotope and stored in a molten-salt reservoir. Liquid is pumped at a pressure difference of about 200 psig.
A displacer oscillates in a closed engine cylinder heated at one end and cooled at the other. The annular space between the cylinder and the displacer functions as the gas heater regenerator. and gas cooler, with a minimum of dead volume. In place of the more conventional power piston, the cold end of the engine is fitted with inlet and outlet check valves which allow pressure surges produced by the oscillating regenerator to generate a pumped gas or liquid output. The displacer is supported at the hot end by a flexure and driven from the cold end by a controllable displacer drive and sup- An analysis of the physiologic control me'chanisms of the natural heart was made. The physiologic cardiac control systems are various and complex; the end result nates the displacer gas seal problem and considerably simplifies this miniature engine.ln the displacer drive a metal bellows seal hermetically isolates all 'moving bearing and seal surfaces from the engine working gas, allowing latitude in choice of bearing lubrication. The displacer support at the hot end is a flexure which operates at a stress level sufficiently low to ensure long life.
Pneumatic power may be supplied by a thermocompressor engine which is a variant of the Stirling engine. The modified Stirling cycle system of the thermocompressor engine converts heat directly to pressurized gas by heating and cooling the working media in a closed cycle. The gas is expanded when hot and compressed when cold. and work is extracted since the expansion work exceeds the compression work. The implanted thermocompressor engine converts the heat from radiosotope source to usable energy through a working medium.
The pressure difference in the system accomplished through a single displacer piston chamber (the hot end temperature above 1200F and the cold end below 250F). The implanted engine utilizes a regeneration external to the driving piston. The displacer piston moves the gas from end to end of the cylinder through a regenerator and heater. When the displacer piston moves gas into the hot end of the cylinder, the gas is heated flowing through the regenerator and heated by the hot end of the engine, thus increasing the gas pressure.
The system employs the pneumatic power to modulate and actuate the operation of the artificial heart. A pneumatic pump actuator controller may be used in conjunction with the other artificial heart components.
The thermocompressor engine utilizes a thermodynamic cycle in which helium is alternately heated and cooled to provide pressure fluctuations which can be utilized to drivean artificial heart. The thermocompressor engine is coupled to the blood pump by means of a pneumatic logic unit.
In place of these internal power control systems which are implanted in the abdomen of the patient, the artificial replacement heart of the instant invention may be provided with a self-contained nuclear drive system.
into the pulmonary artery and aorta at normal pressures. If systemic and pul monary venous returns are transiently unequal, pulmonary and systemic outputs must also be appropriately unequal. In addition, the
control system must require no intravascular transducers or sensors, must maximize total system performance at any given power output level (for example, during sleep, rest or exercise), and must be insensitive to changes in system spatial orientation and attitude.
is that the natural heart can rapidly change its output to meet a wide range of physiologic needs. In basic terms, there are intrinsic and extrinsic mechanisms of cardiac v control. Intrinsic control results from the nature of the hearts pressure-volume or cardiac-muscle-fibers(tension-length) relationship. Therein lies the basis of the Frank-Starling law, which says that (in the absence of extrinsic influences) the heart will increase its output in response to increased input. Extrinsic cardiac control is the result ofa complex neurohumoral system which has the capacity to regulate heart rate, peripheral vascular tone (arteriolar and venous), and mechanical state of the heart muscle (e.g. position in the pressure-volume curve) in the interests of meeting physiologic needs. In
, total artificial heart also involves both intrinsic and extrinsic mechanisms. In this case the intrinsic control is the built in relationship among venous return (ventricular filling), stroke volume, and heart rate. As a result of this intrinsic control, the extrinsic physiologic control mechanisms can still influence recipient. Direct input to the total artificial heart from the central nervous system is of course absent. Cardiac output will, however, increase in response to the peripheral neurohumoral effects of the psychic stimulus: general adrenegic levels increase as the sympathetic nervous system and adrenal medulla are activated; arteriolar tone increases to increase systemic pressure; venous capacitance volume decreases, resulting in increased venous return. Cardiac output is increased as the total artificial heart responds by pumping all of the increased return (through automatic increase in stroke volume and heart rate) into a higher systemic pressure; more pressure-volume work is done, the additional power for which is instantly available.
In short, by being intrinsically controlled by venous return, and by having large amounts of power instanta' neously availableto it, the total artificial heart in effect is completely controlled by physiologic demands. This control theory has been demonstrated to be hemodynamically stable and completely responsive to physiological needs in multiday experiments and under a variety of induced cardiovascular conditions. Further experimental study is needed to establish, under chronic conditions, the physiological effectiveness of this the ory.
Two Heart Control Computers have been developed for controlling the complete heart. One is an analog system and the other a digital system. The control phi,-. losophy utilizes stroke volume as one of the principal control parameters. When blood flow requirements,
either pulmonary or systemic, increase and full stroke volumes are being used, the beat rate of the heart will automatically be increased until the stroke volume decreases to less than full stroke. When this condition is attained, the heart rate is decreased to establish a balance between the number of full and partially full stroke volumes. System convergence is achieved because the totally implanted heart is always seeking to restore and maintain full or near full stroke conditions Experimental studies confirmed the computencon trol approach in which the heart automatically;( a)-increases its rate if all the blood-returning to either the left or right heart cannot be pumped through increase,
of stroke volume to the limit; (-b) decreases its rateif the blood returning to either the left orright heart is low and requires only a very limited number of-full strokes to pump all of the returning blood; and (c) continues at a given rate if the number of full strokes isapproximately the same as the numberof non-full strokes.- This control logic operates on a convergency principle. The system is always seeking -to converge on a r-atethat maintains stroke volume at full value or at a predeterr. mined high percent of full strokevolume.
The principal input into the heart control computer is full stroke signals from both left and right ventricles. The computer continuously monitors beat rate and stroke volume for each-beat and performs an-analysis based on the-immediately preceeding series of heart beats, e.g. everyfive preceeding heartbeats. One of the following conditions will prevail and produce=the're-- sulting action based on a 5 heart beat analysis:
a. If either the left or right ventricle has taken a suffi= cient number of strokes, e.g.' four or five full strokes, the computer will increase heart rate, eg. by five beats per minute and automatically sample the next series of beats;
b. If the left ventricle has taken two or 'three'full strokes and the right ventricle has had no more than three full strokes, the computer will signal to hold the heart rate constant, e.g. for the next five or ten seconds;
c. If the left ventricle has taken none or one full stroke and the right ventricle had no more than three full strokes, the computersignals the he'art'to decrease its heart rate, e.g. by five beats per minute and hold for five or ten seconds; i
d. If the left ventricle has taken three or less full strokes but the right ventricle has had four or five full strokes, the computer increases the rate, etg. by five beats per minute. (A key part of the control logic is this automatic override of heat rate'from.
the right heart providing sensitivity 'to'cen t ral'venous conditions.) g
The Heart Control Computer (HCC) automatically regulates heart rate over a wide range, e.g. 'fro'm abproximately to 200 beats per minute in response to physiologic needs. Sensors located in the heart but not inside the ventricle provide an output signal'each time a ventricle (left or right) receives sufficient blood't'o achieve a full stroke. No sensors in the blood stream or tissue are required. The computer stores information on recent blood pump filling history and p'r ocies'se's'it every beat or multiple beats, e.g. every 2 to 5'second's (depending upon heart rate) to provide the cQptliQlgpl'jviously described. All numerical constants'can 'be altered to either increase or decrease sensitivity o f the Heart Control Computer. The above constants have proven to be very effective in achieving the appropriate degree of sensitivity and responsiveness to all normal and abnormal (drug'induced) physiological conditions.
8: The complete l-lCc,can be reduced to the sizeof a dime. i I
A number of possible .control. methods and approaches were considered inarriving at the control system. They arezw 1 i ,a, Continuous. tren d method aslthe stroke volume increased or. decreased, the. heart rate would increse or decrease on a percentage basis for each incrementalchangeg instroke volume on a beat-bybeat basis with both-right andleft ventricles being analyzed fonchangeg, 1 l v,
b. R ate offilling method -as changes occur in filling .rate and. in thepercentageofmestroke volume, r the heart rate would. be increasedor decreased; c. Complete stroke volume method-when either ventricle becomes. filled, the heart automatically goes into systole-ejecting all-.of the. blood in each ven-tricl,e,, or the ventricle that is filled ejects and theother ventricle does not eject until it is completely filled; however, theven tricle ejecting first .cann'ot eject-a second time until thesecond ventrilhcle has completedaits, ejection. Between these, two
limits, there are a variety of synchronous and async-h ronous conditions that can be established. :None of the aboveapproaches require any instrumentation .or sensors to be placed in the blood stream, they are not sensitive to movement orto any spatial arrangement. Thesezconcepts permit control of rate and stroke-volume with electrical, hydraulic-pr pneumatic logic circuitry. This permits the nuclear; heart systems to function without the generation of electrical energy for control. The totally implanted heartsystem under animal evaluationutilizesthe more simplifiedconcept of control that monitors the condition in each ventricle bas'edon percentage of full'stroke as previously discussed. When the system has the capacityto automatically'vary stroke volume and rate, it permits determination ofthe physiological trends and requirements very accurately and withthe'appropriate sensitivityso that the total heart'automaticallyincreases, decreases, or holds its rate constant based on. physiological demand to provide'a stable control system.
Satisfactory performance.physiologically is; dependent upon having surfaces that do not shed .emboli or 'thromboses, or cause damage to the blood during pumping. Toward this goal, all -blood"contacting surfaces have been designed to permit the development of living endothelial' or pseu'doendoth'elial type-surfaces. All surfaces of the pump develop a smooth glistening living interface surface-from the blood stream. Early in the development program, some difficulty existed with regard to flow andthrombosis formatiom-however, in later experiments involving changes in fabrication, these problems have been minimized. No significant adverse physiologic effectshave occurred, i.e., peripheral emboli and body damage. The leaflets of the valve, both'atrial'and tricus'pid,re'main very flexible and responsive to'dynamic flow conditionswithoutincreasing changes in pressure drop. Based upon the accumulated experience, prolonged total cardiac replacement may be "achieved.
I The report by the instant inventor, Lowell T. Harmlon ,entitle"Tota'lly Implantable Nuclear Heart Assist And Artificial'Heart, National Heart And Lung Insti- ,the present specification.
BRIEF DESCRIPTION OF'THE DRAWINGS FIG. 1a is a perspective view of an electrically powunit 205.
FIG. 2 is a perspective view'of a nuclear powered, to-
tally implantable artificial heart and its location within the human body. a a
FIG. 2a is a partial cutaway view .of the nuclear powered artificial heart of the presentinvention.
FIG. 3 is a perspective view oftheartificial heart of FIG. 3a implanted in a'human bodyn FIG 3a is a broken away view of a totally implantable artificial heart with a self-contained nuclear drive sys- FIG. 7 is a cross-sectional view of the artificial heart taken along hne B'TB of and l n A A of interior surface of the left A-V valve plate 7. The A-V FIG. 6.
FIG. 8 is an exploded view of the' total heart assembly.
FIG. 9' is a block schematic diaphragm of the electrically powered total heart system shown in FIG. 1.
FIG. 10 is a block schematic diagram oflthe. heart rate control computer for the totally implantable artificial heart. i
FIG. 11 is a schematic of the implantable battery power supply. 1
FIG. 12 is a series of graphs showing the relationship of venous return flow; heart rate, and residual atrial volume to time.
For a better understanding of the invention a possible embodiment thereof will now be described with reference. to the, attached drawing, it being understood that this embodiment is to be intended as merely exemplary and in no way limitative.
DETAILED DESCRIPTION Referring to FIG. 1, the totally implantable artificial heart 101 is shown in place in the thoracic cage of a human as a replacement for an ailing natural heart. The electrical storage unit 105 is located in the abdominal cavity under the diaphragm and is connected to the artificial heart by means of an electrical cable 102. Electrical energy from the outside of the body is transmitted :by an external transmission unit 103 across intact skin to an energy receiving coil 104 placed under the skin. The external transmission unit. 103 may be supplied with power from batteries carried in a vest or attached case (See also FIG. 9). Theneed for external recharging maybe eliminated through theuse of bio-fuel cells. FIG. la shows the artificial heart 101, the electrical storage unit 105 and the transmission unit 104 in more detail. l
FIG. 2 shows a nuclear gtem..The total artificial heart 201 is connected to a nuclear engine 203 located in the abdominal by a hydraulic cable 202. As shown in FIG. 2a. ,the nuclear engine 203 comprises a control housing 204 and a thermal energy storage unit 205. Contained-within the thermal energy storage unit 205 is aplutonium fuel capsule 206. Vacuum foil insulation 207 is disposed between the powered artificial heart syscontrol housing 204 and the thermal energystorage FIG. 3a shows a totally implantable artificial heart 301 with a self-contained nuclear drive system 302. As
can be seen, the approach eliminates the necessity of an energy source located in the abdominal cavity. FIG. 3 shows the artificial heart of FIG. 3a in place in the body of the recipient.
Referring now to FIGS. 4-8, the total artificial heart Ibasically comprises a left atrium 60, a left atroventricular (A-V) valve plate 7, a left ventricle 61, an energy converter 54, a right ventricle 51, a right A-V valve plate 55, and. a right atrium 50 (See FIG. 7).
The left atrium 60 comprises a flexible cup-shaped bladder and an open-ended branch-off 62 for receiving arterial return from the lungs. The open end of the bladder faces towards the center of the artificial heart 1 and forms a complete enclosure about the exterior surface of the left A-V valve plate 7.
The left A-\/ valve plate 7 is a rigid circular disk com- .prising a plurality of longitudinal openings 63 (See FIG.
8),. Each longitudinal opening 63 is overlaid with flexible flaps of A-V valves 64. Metal stays are embeded in the A-V valves 64 which are hingedly attached to the rior surface of the left A-V valve plate 7. Disposed within the open end of the branch-off 65 is a tricuspid valve 66. The tricuspid valve 66 is provided with three slits or channels in its upper surface to allow for the passage of blood therethrough (See FIG. 8). The left ventricle housing 3 is sleeve-shaped so as to receive the left ventricle 61 and includes an externally threaded outer end 67. The externally threaded outer end 67 mates with an internally threaded, O-shaped, left atrial clamp ring 5.
The left atrial clamp ring 5 fits over the left atrium 60 and when screwed onto the left ventricle housing 3 secures the left A-'V valve plate 7 between the left atrium 60 and the left ventricle 61. The union between the ventricle housing and the atrial clamp ring is seated by an atrium washer 4'.
The left ventricle housing 3, like the right ventricle housing 2, is provided with an aperture in its lower surface. A tubular CO puncture housing 43 is inserted into the aperture in the ventricle housing and a self sealing washer 53 is inserted therein. This arrangement permits a hyperdermic needle or similar device to communicate with the interior of the ventricles and thereby provides a means for the ingress or egress of fluids thereto. A washer 45 and top cover 44 are employed to cap the CO puncture housing 43 and the self-sealing washer 53. (See FIG. 7). I
Bonded to appropriately the lower $4 of the outer surface of the interior side of the left ventricle 61 and right ventri'cle51 are compression plate assemblies 70 and 10, respectively." ""An energy converter 54 is disposedin the center of the'artificial heart. The energy converter 54 which conturn moves the compression plates 70 and 10 outward.
The outward movement of the compression plates need not be simultaneous as shown in FIG. 7 where the right ventricle 2 is shown being compressed by the outward movement of the right compression plate 10 while the left ventricle 61 and the left compression plate 70 are shown in a non-compressing state. Once the compression plate assemblies have been driven outward and the ventricles compressed, a reset spring 52 or similar device is used to return the compression-plate assemblies to their original positions.
The energy converter 54 is enclosed within the left ventricle housing 3 and the right ventricle housing 2.
.The housings are secured together by means of a V clamp 11. The V-clamp comprises two jaws which are pivotally joined to a third connecting section by hinges 12,12 and 13,13 and dowel pins 16. The open ends of the jaws may be joined and tightened by means of angle brackets and nut 14 (See FIG. 5).
Electrical energy is supplied to the energy converter from either an electrical energy storage unit or a nuclear engine located in the abdominal cavity by a multistranded wire 23. The multi-stranded wire 23 which is enclosed within an insulated sleeve 17 communicates with the energy converter 54 through corresponding apertures in the V-clamp 11 and the bottom of the joined left ventricle housing 3 and the right ventricle housing 2 (See FIG. 7). A sliding bushing 22 is disposed in the aperture in the V-clamp l1 and acts as a sleeve for the multi-stranded wire 23 passing therethrough. Just prior to its entrance into the sliding bushing 22 the multi-stranded wire 23 passes through a dome-shaped clamp bushing 21 which caps the aperture in the V- clamp 11.
Of course, the use of a bio-fuel cell or an artificial heart with a self-contained nuclear power source would eliminate the necessity of the separate electrical energy storage unit of nuclear engine and the interconnecting cable.
The right side of the artificial heart 1 is similar to the left side except that, instead of having a single branchoff 62 like the left atrium 60, the right atrium has a dual branch-off. The dual branch-off comprises one branch 68 which receives venous return from the trunk and another branch 69 which receives venous return from the head. The right atrium may also have single inflow similar to that shown for the left atrium 60.
The right ventricle 51, like the left ventricle 61, has a simple branch-off 71. The branch-off7l which supplies venous flow to the lungs also comprises a three channeled tricuspid valve.
The tricuspid valves are housed in metallic cylindrical tricuspid valve housing 25,25 which are disposed at the ends of the branch-offs 65 and 71. The tricuspid valve housings 25,25 are secured to the branch-offs by a spacer ring 26 and clamp ring 27 (See FIG. 5). All of the valves in the artificial heart are interchangeable and may be of different types, e.g. tricuspid, disc, ball, and flap.
Metallic cylindrical coupling rings 33 are attached to the open ends of the branch-offs 62, 68 and 69. Disposed over the outer ends of the coupling rings 35 and the tricuspid valve housings 25,25 are cylindrical Dacron flocked metallic quick connects 30. The quick connects comprise multi-fingered retainer means 28 which secure the quick connects to the tricuspid valve housings 25,25 or the coupling rings 33. Tissue grabbing barbs 34 are disposed on the outer surface of the quick connects 30.
12 Tubular elbow adapts 31 may be disposed within the surgical quick connects 30, if necessary to enhance the tissue connection. A protecting ring 32 encircles the clamp assembly, surgical quick connects and tricuspid valve housings may be made of stainless steel or other similar material. The A-V valve plates may be manufactured out of any suitable metal. All blood contacting surfaces are flocked with Dacron or a like material to promote the development of a living surface, i.e. endohelilial or pseudo-endothelical surfaces.
The basic assembly procedure for the total heart comprises the following steps:
I. the tricuspid valve housings are clamped and bonded to the left and right ventricles;
2..surgical quick-connect adapter rings are bonded to the inlets of the left and right atria;
3. the right and left ventricles are positioned in their respective metal housings;
4. the right and left A-V valves are located onto their respective ventricles; and
5. the right and left atria are positioned and the atrial clamp rings are tightened down. The following is one example ofa heart rate control computer operative in the present invention.
The Heart Rate Control Computer illustrated diagramatically in FIG. 10 is contained within the implantable electronics package and is constructed on circuit board.
The Heart Rate Control Computer regulates heart rate over a range from 50 to 200 beats per minute in response to signals indicating ventricular filling. A sensor is arranged to provide an output signal each time a ventricle receives sufficient blood to fill it to percent or more of its capacity. The computer stores this information on recent blood pump filling history and processes it to derive one of the three following commands.
l. The computer commands a five beat per minute increase in rate ifleft or right side gets five full indications out of five.
2. The computer commands a five beat per minute decrease in rate if the rate has not changed for 10 seconds and left side has at most one full indication out of five.
3. The computer commands that there be no change in heart rate if neither increase or decrease criteria are satisfied.
Referring to the block diagram of FIG. 10 after the start of the computer cycle when a Fill Detector output exceeds the threshold of the corresponding Fill Pulse Generator, a pulse is transmitted to the Fill Counter. This will occur whenever the corresponding ventricle is at least 95 percent full.
The Count Detectors determine if either of the Fill Counters has reached a count of five, or if the left count is less than two. When the Reset Pulse occurs, the Rate Change Calculator logic circuits determine if a rate change is required. If either 5 Count Detector has an output, the Rate Change Calculator emits a rate increase pulse, which increases the value in the Computer Heart Rate Storageby an amount equivalent to tor has no output, the Rate Change Calculator emits a rate decrease pulse, which decreases the stored value of computerheart rate by five beats per minute. The l Second Delay Pulse Generator will have an output if either a rate increase or decrease pulse has been emitte'd within the last seconds. Therefore, after a heart rate change, the heart rate will not decrease for at least ten seconds.
The value in the Computer Heart Rate Storage determines the speed at which the Motor Drive Control Circuits will try to drive the motor in the Energy Converter. The actual heart rate is proportional to motor speed. The Rate Control Error Generator therefore compares the Motor Speed Calculator output to the Computer Heart Rate Storage to determine the error signal input to the Motor Drive Control Circuits.
The Motor Speed signal is also used to drive the Heart Rate Counter. When the Heart Rate Counter reaches a count of five beats, a Reset Pulse is emitted by the Reset Pulse Generator. This resets all the counters and triggers the Rate Change Calculator outputs. The computer cycle then begins again.
Since extremely low power operational amplifiers are now available, it was decided to use analog, rather than digital circuitry in the Rate Computer.
In the Fill Pulse Generators, linear amplifiers amplify the signals from the strain gage Fill Detectors. Their outputs are applied to threshold amplifiers. The gains of linear amplifiers must first be adjusted to compensate for differences in strain gage sensitivity. Then a right and left thresholds, as determined by the voltage divider, must be adjusted to produce Fill pulses at the point where the blood pump is 95 percent full. The two 150 ms one-shot multivibrators provide Fill Pulse Generator outputs of constant width to drive the'Fill Counters.
The Fill Counters are simply analog integrators. The integrators drive threshold circuits, which perform the Count Detector functions. The logical operations of the Rate Change Calculator are performed by diodes which drive two amplifiers. f
The lO-Second Delay Generator is a one-shot multivibrator circuit which is reset each time it receives an input, whether or not it has completed a count. The 10 ms delay multivibrator associated with this circuit eliminates a race condition in the logic circuit.
The Computer Heart Rate Storage is performed by .an analog integrator, which also includes limiting diodes to control the extremes of the heart rate. Provision has been made for manual adjustment of heart rate as determined by this circuit. The manual rate is obtained either by operation ofa toggle switch in the Test Point Box, or by operation of an internal magnetic switch by means of a large magnet outside of the electronics package. 7
The Rate Control Error Generation is performed by a differential amplifier, which compares the output of the Heart Rate Storage to the Motor Speed Signal, and drives the Drive Pulse Generator.
The Heart Rate Counter is an analog integrator operating on the Motor Speed signal. When the integrator indicates that the time of five heart beats has elapsed, a threshold amplifier fires and triggers the ms delay multivibrator. This multivibrator triggers the logic circuitry output and then fires the 60 ms one-shot multivibrator circuit which drives the reset transistors of the v about 5 beats per minute. If the 0 or l- Count Detector I has an output and the l0 Second Delay Pulse Generadesigned to free run if its input stays high, so that a lockup condition cannot occur in the HeartRate r 4 v v three integrating counters. The 15 ms multivibrator is Counter and Reset circuitry.
-' In the basic motor drive control loop the phase of the moving rotor is indicated by Hall effect device signals. These signals are converted to drive pulses of the appropriate phase by the Drive Pulse Generator, the drive pulse widths being controlled by the error signal from the Rate Computer. These pulses are then amplified in the Motor Drive Circuits and used to drive the two phase motor winding. A signal proportioned to motor speed is derived by circuits in the Drive Pulse Generator. This signal is compared to the desired motor speed signal in the Rate Computer to obtain the Rate Control Error signal.
In the circuitry associated with the generation of the motor drive pulses. Amplifiers produce amplified Hall signals of the desired amplitude and dc level. Common mode variations in the Hall device outputs, due to electrical noise, bias variations, and thermal variations, are cancelled out by the balanced input circuitry of these amplifiers.
Two further amplifiers are used as unity gain inverters. Since the Hall devices are located on the motor stator so as to produce rotor position signals which are 90 out of phase with each other,.the addition of the inverters produces signals at all four quadrature phases.
The phases of the four Hall signals produced do not in general coincide with the optimum phases for the motor drive pulses. However, since these signals are nearly sinusoidal, they can simply be combined in weighted resistive adders to produce four signals of the desired phases. The signals are again nearly sinusoidal and have the phases needed for the motor drive pulses.
The actual drive pulses are generated in threshold amplifiers. At the negative input of one of the threshold 1 amplifiers, for instance, three signals are'added:
l. The Hall signal which has a negative maximum at the' time when the phase A pulse should occur,
2. A positive going full-wave rectified signal formed from the phase B and E Hall signals, and
3. The dc Rate Control Error signal from the computer.
The resulting waveform has a negative triangular peak at the desired phase for the A drive pulse. A positive output pulse is produced during the time that this signal is below the amplifier threshold. The width of the pulse increases as the Rate Control Error signal is made more negative. Othe amplifiers operate in similar fashion to produce the A, B, and E drive pulses.
This technique provides a smooth, reasonably linear, variation of drive pulse width: with control error signal for drive pulse widths even up to so that the feedback gain of the control loop'is nearly constant over the range of drive pulse widths normally required.
The motor drive circuits consist of two parts: 7
l. The power amplifiers which drive the two phase motor winding; and
2. the analog circuits which calculate motor current and motor speed from the motor input signals.
The Driver amplifiers are conventional, except that the amount of drive current available is varied in proportion to the peak motor current required, as determined by the motor current calculation circuit. This drive level signal determines the output amplitude of the device level amplifiers. The power output stages which follow these amplifiers are simply switched on or v off by the amplifier output pulses,- thereby applying nearly the full battery voltage (+l4V nominal) across the drive motor winding for a period of time. equal-to the input pulse width from the Drive Pulse Generator.
The advantage of the current level drive control is that less current is drawn by transistors when low output currents are required, and therefore these amplifiers maintain a reasonable efficiency at low drivelevels;
The current calculating circuit simply amplifies the voltage drop across the 0.0300 resistors in series'with each motor winding in balanced differential amplifiers. These amplifier outputs are then inverted in further amplifiers, so that both positive and negativegoing'replicas of each current pulse are available. The outputs of these four amplifiers are applied to a four-phase fullwave peak detector, the output of which is smoothed in a filter-amplifier to give the dc current signal which controls the Driver amplifier output capability.
The voltage applied to the motor winding is also obtained through balanced differential amplifiers. These signals are combined in RC networks with the current waveforms and the result amplified to obtain a replica of the motor back-EMF voltage. Since motor'back- EMF voltage is proportional to motor speed, a signal with dc level properties to motor speed is obtained from the back-EMF signal in a four-phase detector, necessary waveform inversions being performed. The resulting signal is sent to the Rate Computer for comparison with the desired motor speed signal, and the resultant Rate Control Error signal is used to control drive pulse width.
The implantable battery power supply shown schematically in H6. 11 receives input power from 'the implanted secondary coil of an intact-skin transformer. A controllable rectifier circuit converts this ac power to clc at'a voltage suitable for both charging the battery pack and running motor control circuits. The battery pack as shown is wired in parallel with the load so that it takes both the ripple current from the charger and the ac fluctuations in load current.
The battery control circuits derive information from each cell of the battery pack to control thecharg er output.
If at any time the battery pack charge content declines below optimum, the control circuit provides maximum available power throughout to charge the pack in the shortest possible interval. When any one or more cells of the battery pack reaches a fullycharg'ed condition, the control circuit terminates the rapid charge and reverts to a normal trickle charge mode of operation. I
When the power output is unavailable, for instance, when the skin transformer is decoupled, power is supplied from the implanted battery pack to operate the heart. Sufficient capacity is provided to operate a total heart device forabout 3-4 hours. If ac power'is not restored before the battery becomes dischargedflhe bat tery control circuit terminates battery discharge when any one cell of the battery pack is discharged to a cell voltage of approximately 0.7 volts. This protects the battery pack from over discharge and possible cell damage. v
The battery output current supplies power direct l'y'to the Motor Drive Circuit output stages, and also pro-h vides power to the Low Power Voltage Supply which provides regulated voltages for the low power circuitry in the Motor Drive Control and Rate Computer.
;.,ln opeiratiomelectrical ehergyis supplied to an external transmission unit ;1Q3b y batteries carried in an attachecaseor vest-.(See:.FlG. ,1), The electrical energy is then transmitted from the external transmission unit .103across intact skin to an energy receiving coil .104
implanted just,. under. the skin. The.electrical energy then travels to an electricalenergy storage unit 105 where it is finally-transmitted to the energy converter of the artificial heart 5 The energy converter converts the electrical energy to mechanical energythrough anelectric motor which actuates any suitablemechanical driving means. In the preferred form, the electric motor through a series of reductiongears drives cam members.; As the cam mem- .bers are rotated to their high point, they forc e the compressionplate assembly 70, lq outward, thereby compressing the ven tricle lt is this compression ofithe ventricle which produces the actgalpumping of the blood. When the cam is rotated past itshigh; point, the cam surface losescontact with the compression plate assembl -y.7 0 10.which is now free to return to its original position means of-reset springs 52 or, like devices. However, the compression plate 70, 10 will not return unless there is blood available the atria to flow into the ventricles. Hence, the degree of filling or return of the compression plate is controlled entirely by the available supply of blood in the basis. g v ,lf a nuclear, power source, as shown in FIG. is utilized, energy in the form of heat is' converted to electrical' energy in thethermal energy storage unit 205. The electrical energy is then transmitted to' the artificial atria on a beat-by-beat hearts energy conve rter which converts the electrical energy to mechanical energy in the manner described above. The same basic process takes place if an artificial heart with a self-contained nuclear drive system. is employed. I i
In a typical cycle, blood carrying CO is supplied to I the right atrium. From the right atrium the blood passes through the right A-V valves into the right ventricle. As
the right ventricle is compressed byth e outward movement of the right compression plate assembly, the blood contained therein is forced out or pumped to the lungswhere theCO; is released and the blood oxygenated.
I The oxygenated blood is then transported to the left atrium. From the left atrium, the oxygenated blood passes through the left A-V valves. into the 'left ventricle. As the left ventricle is compressed by the outward movement of the left compression plate assembly the oxygenatedblood contained there'in is' forced out or pumpedto the arterial system. The 'cycle then begins again.
A-V valve blowthrou'gh arid the subsequent backflow of blood from the ventricles to the atria duringpumping is prevented the rnetalli c stays which are mebedded within the flexible flaps or A- V valves.
,Also, as the .ventricular blood volume changes during pumping the internal air volume between the ventricles must change' l' This is accomplished by a flexible bag, fabricated from Silastic or a, similar material, which is clarnped to theoiit side of the metallic ventriie housings. This bag "also forms a body fluid seal for 'th'e el'ec'tric motor.
As note fd earlier, the pumping of the left and right "vehtri'cle s'need n'ot'be'simultaneous and is, in fact, regulatedby'the heart rate control computer. In operation,
computer response to a decrease ininlet blood flow is 17 fully accommodated within a single beat interval by decreased ventricle filling, but increases ininlet flow must be accommodated by one or more of the following three mechanisms: I K
I. A l() percent increase in ventricle filling can occur within a single'beat (assuming the fill sensor trigger is set at 90 percent of ventricular volume). 2. The computer can increase heart rate but within the limiting rate of change of 4.25 bpm/beat. 3. When the capability of the above two mechanisms has been exceeded, or during a speed change transient, the excess of inflow-outflow must be accumulated in the atria. 7 if an increase occurs which finally exceeds atrial storage capacity, then the inevitable result will be an increase in atrial pressure which implies an increase in vena caval or pulmonary vein pressure =either of which should be avoided. The most critical situation therefore arises from a step increase in blood inflow that exceeds the percent excess ventricle'capacity. The atria should be designed to accommodate reasonable changes in inflow that would frequently occur. The following analysis results in a method of predicting the required atrial capacity necessary to accommodate a given step change in venous return without causing excessive atrial pressure. If blood return to the heart incrcases'at a rate faste than the computer can accommodate by increasing heart rate (such as a step increase in venous return), then blood must accumulate in the atria until such time that the rate increases to pump the new inlet flow. This situation is illustrated in FIG. 12.
The maximum rate of change of the computer-controlled heart rate, ignoring fine-grain variations within a beat, is given by the expression:
where K is the fraction of heart beats in which a fill.-
,pulse occurs. lfa fill pulse occurs on every beat, K 1',
and the maximum positive change of heartrateoccurs. If there are no fill pulses, K =0, and the maximum negofR bythe heartis ideally: (4)
where V is the ventricle volume. The accumulated volume of blood in the atrium when the input flow rate. Q exceeds the output is:
assuming that the initial value of v is zero.
Consider a large step increase in Q, at F(). For r 0: QI QII(I+X) (6) Where Q R V is the maximum initial output flowrate possible, without any accumulation in the atrium and X is the fraction by which the step increase exceeds 0 When this step increase occurs, fill-pulses will occur every beat, K=l until some point after the time, t,,.. when the heart rate reaches the value necessary to make Q Q During this time excess blood will accumulate in the atrium, so that the residual atrial volume, diastolic atrial volume, V, will reach a maximum when Q Q After time, t,,,, fill-pulses will continue to occur on each beat until the accumulation in the atria is pumped out and the ventricle filling drops back to the fill threshold level, percent. Therefore, R will continue toincrease until the fill-pulses begin to disappear, after which time R will decrease until it reaches the required steady-state value. The heart rate when The maximum value of V, which occurs at t t,,, is the volume which the atrium must be able to accommodate if venous pressure buildup is to be avoided. The maximum value is:
Ill III (Ql o For 0 t l,,, m (9) since K l.
at t 2 R R so that 1 R. I Q, l 1,,, 8 in R0 a In Q 5 ln(l+x). (11) since Q VR From Eqs. (8), (9), and (10):
Since Evaluatingthse quantities we seethat 0.0224 min e 1346 seconds and f(x) 0.00440 therefore llO v 100044) =o.u39
so the maximum required atrial residual volume is l 1.4 percent of ventricle volume.
Symbols t Time variable R Instantaneous heart rate R,, Initial value of R R Heart rate for 0 Q. 8 Maximum change in R pcr beat 4.25 beats/min/beat) K Fraction of time that fill pulses are occurring 0. Blood flow rate into the heart atrium Q Blood flow rate out of the heart ventricle Q Value of maximum ventricle output when R R V Effective ventricle volume v Residual volume of blood accumulated in the atrium with time I i x l I x fix) n(l+x) H As one example, the artificial heart operating at a steady state under computer control is presented with a 10 percent increase in venous return. This will be fully accommodated by an immediate increase in ventricle filling followed by a 10 percent increase in rate. No atrial expansion is required.
As a second example, assume that the artificial heart is operating at steady state at a nominal I00 bpm and is presented with an abrupt percent increase in venous return. This will require transient blood storage in the atria and therefore increase the atrial residue volume. The final heart rate that results in this example will be a 20 percent increase or 120 bpm. The rate at which output flow equals input flow is R 1 l0 bpm. During the transient, the maximum atrial residual volume ratio will be and will occur at a response time Mock loop data tell us that the artificial heart under.
computer comtrol at 90 percent filling e'xpells about 80 ml per stroke. Thus we may assume that the ventricle capacity with complete filling is about 89 ml. Using V= 89 ml we get v,, =0.l 14(89) l0.l ml of residual atrial volume.
Given the cycle timing used in the present face cam systems, the atrial capacityvariation during each heart beat is 0.36 V= 32 cc. From tests of A-V valve regurgitation during systole, we determined that the atria must also accommodate about l7 ml from this source bringing the atrial capacity variation during the heart cycle to 32 =17 =49 ml.
To accommodate the 20 percent step increase in venous return would require an additional 10 ml bringing the required total atrial capacity to 59 ml. Measure-
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|International Classification||A61M1/10, F02G1/043, A61M1/12|
|Cooperative Classification||A61M1/1037, F02G1/043, A61M1/1046, A61M1/1086, A61M2001/1049, A61M1/106, A61M2001/1096, F02G2280/005, A61M1/12|
|European Classification||A61M1/10E, F02G1/043, A61M1/10R|