« PreviousContinue »
3,513,845 BYPASS HEART PUMP AND OXYGENATOR SYSTEM Merrill G. Chesnut, Arvada, Phillip B. Callaghan, Westminster, and Sven Gafvert, Boulder, Colo., assignors, by mesne assignments, to United Aircraft Corporation, a corporation of Delaware
Filed Sept. 15, 1966, Ser. No. 579,565 Int. CI. A61m 1/03 U.S. CI. 128—214 5 Claims
ABSTRACT OF THE DISCLOSURE
A cardiopulmonary bypass includes a reciprocating pump to deliver blood from a reservoir fed by an oxygenator to the femoral arteries. The oxygenator receives blood from either a venous roller pump or a reciprocable pump which draws the blood from a venous reservoir that in turn is fed by catheters placed into the superior and inferior vena cavae. The pumps are controlled by computer circuitry which provides the rate, the volume and the speed of blood flow under various controls. The system includes controls to permit utilization of an arterio-arterial assist device rather than as a complete cardiopulmonary bypass device. This includes the elimination of a check valve by utilizing differential flow crosssections. In one embodiment, a second roller pump delivers blood from a reservoir of the oxygenator to a bubble trap, the output of which is returned to the patient through a reciprocating pump.
This invention relates generally to heart pump systems for replacing the function of a patient's heart, and more particularly to a heart pumping system for complete cardiopulmonary bypass.
In complete or total cardiopulmonary bypass, the total blood flow from the venous side of the patient's circulatory system is withdrawn, oxygenated, and returned to the arterial side of the system under sufficient pressure to perfuse the peripheral arterial tree. In systems of this type, in contradistinction to partial veno-arterial bypass, bypass of the right heart, and bypass of the left heart, the entire oxygenating function is effected by an extra corporeal oxygenator rather than the patient's lungs.
A primary limitation in prior known cardiopulmonary bypass systems is that they have not had long-term capabilities due to the development of metabolic acidosis after extended perfusions. Metabolic acidosis may be defined as the acid products released in the circulatory system resulting from a lack of oxygen in the blood causing the incomplete combustion of carbohydrates, fats and proteins. The tissue hypoxia resulting from metabolic acidosis is most prevalent in the use of steady state heart pump systems, such as those employing roller pumps, but also appears to result from the use of known pulsatile systems.
The peripheral pooling of blood during long perfusions with resulting hypoxia has been relieved somewhat using presently known techniques of hemodilution. Further, operative respiration of the lungs with helium and drainage of the left ventricle during bypass have obviated some of the alveolar collapse and interstitial hemorrhage encountered with prior known systems and techniques. However, from the circulation standpoint the high rates of flow necessary in these prior systems have produced excessive damage to the blood and overloading of the reticuloendothelial system, plugging of the renal tubules and acute renal failure. In prior systems these high rates of flow have been necessary because low flow rates lead to the development of metabolic
acidosis, often times during fairly short time intervals of perfusion. However, as the length of perfusion has increased, three has been found to develop a paradoxical metabolic acidosis even when the perfusion rate matches
r the normal cardiac output. Many authors explain this development as due to a sludging of the blood in the peripheral arterial tree.
Attempts have been made by various investigators to avoid the metabolic acidosis by lowering the oxygen re
10 quirement of the tissues by hypothermia. However, hypothermia produces its own problems, e.g., at ten degrees centigrade (despite the great reduction in oxygen requirement) the temperature of the blood limits circulation profoundly.
15 It is therefore a primary object of the present invention to provide a new and improved total cardiopulmonary bypass system in which microcircultaion is better perfused without employing flow rate rates high enough to rupture coronary vessels, thus enabling the
20 system to maintain artificial circulation for longer periods of time and permitting more complicated surgical procedures to be attempted on the patient.
A further object of the present invention is to provide a new and improved pulsatile cardiopulmonary bypass
25 system which in general will eliminate the patient's tendency toward metabolic acidosis even over long-term perfusions.
A further object of the present invention is to provide a new and improved pulsatile cardiopulmonary by
30 pass system of the type described in which the arterial flow rate may be controlled by the surgeon as desired by simultaneously varying the speed and stroke length of a pulsatile pump in the system. A more specific object of the present invention is to
35 provide a new and improved bypass system of the type described above in which triggering signals from a variable rate pacemaker initiate each cycle of the pulsatile pump, and an automatic computer circuitry maintains coincidence between each pumping cycle and the period
40 of the triggering signals and also varies the flow rate by automatically varying the speed of stroking of the pump in response to changes in the selected volume by the surgeon.
Another object of the present invention is to provide
45 a new and improved cardiopulmonary bypass system of the type described above in which a roller pump is provided for withdrawing blood from the venous side of the patient's circulatory system and delivering it to an oxygenator, and including a reservoir for receiving blood
50 from the oxygenator prior to entry into a blood pumping chamber in the pulsatile pump.
A still further object of the present invention is to provide an improved cardiopulmonary bypass system, somewhat modified from that described immediately above, in
55 which two roller pumps are provided, one for pumping blood into the oxygenator and the other for withdrawing blood from the oxygenator and delivering it to the blood pumping chamber in the pulsatile pump.
Another object of the present invention is to provide
60 a cardiopulmonary bypass system of the type described generally above, but in somewhat modified form in that a second pusatile pump is provided for withdrawing blood from the venous side of the system and delivering it through the oxygenator in place of the roller pumps,
65 thereby more nearly simulating the physiological function of the human heart.
Still another object of the present invention is to provide a heart pumping system which may be used as a complete cardiopulmonary bypass during an operation and as a circulation assist postoperatively. In accordance with the present invention, a reciprocat3
ing piston pulsatile pump is provided in which each pumping cycle is initiated by triggering signals from a pacemaker in the form of an oscillator in an associated control circuit. A pumping cycle as defined herein is one complete reciprocation of the pumping piston within the pulsatile pump, i.e., a push and a withdraw stroke. The reciprocating piston defines an expanding and contracting fluid chamber within the pump connected to receive oxygenated blood and deliver it in pulsatile fashion to the arterial side of the patient's circulatory system. Several means are disclosed for withdrawing the blood from the patient's vena cavae, oxygenating the venous blood, and delivering it to the blood pumping chamber in the pulsatile pump.
While each pumping cycle is initiated by the pump triggering signal referred to above, a computerized control circuit is provided for varying the time base of each pumping cycle so that it coincides with the period of the triggering signal by normally maintaining the length of stroke selected by the surgeon and varying the rate of travel of the pumping piston to achieve this coincidence. However in complete cardiopulmonary bypass, as there is no essential relationship between pulsatile flow initiation and the patient's natural heart action, the pacemaker may be adjusted by the surgeon to the desired rate. The present computer circuitry does permit the surgeon to select the desired rate and volume and the computer circuitry automatically initially computes the proper pumping or stroke speed to eliminate dwell or overlap between the pumping cycles.
The regulation of arterial flow rate, which is one of the important aspects of the present invention, is effected in the present computerized control by the rate and volume control circuitry. The volume circuitry permits the surgeon to merely select the desired volume of blood to be pumped per cycle and the system automatically computes the correct pump speed and stroke length to achieve the selected volume without varying the time base for the pumping cycle dictated by the repetition rate of the triggering signal described above. It is this interrelationship between pumping speed, stroke length and cycle time that provides the capability of the present device of longterm perfusions and the elimination of metabolic acidosis produced by prior known systems.
The present system when used in complete bypass fashion provides adequate blood pressure profiles with low blood flow rates. These low flow rates are sufficient to avoid metabolic acidosis but are low enough not to rupture the coronary arteries.
Other objects and advantages will be readily apparent from the following detailed description taken in connection with the accompanying drawings in which:
FIG. 1 is a diagrammatic view of the present bypass system shown with its connections into the patient's circulatory system;
FIG. 2 is a sub-assembly view of a portion of the pump shown in FIG. 1;
FIG. 3 is a simplified diagrammatic view of the system shown in FIG. 1;
FIG. 4 is a diagrammatic view of a system similar to that in FIG. 1 employing two roller pumps in addition to a pressure pulse generator;
FIG. 5 is a diagrammatic view of a somewhat modified system employing two reciprocating piston pumps;
FIG. 6 is a schematic diagram of a portion of the control circuit including the pacemaker input circuitry and the reciprocating pump servo coils;
FIG. 7 is a schematic diagram of another portion of the control circuitry including a digital counter;
FIG. 8 is a schematic diagram of the computer portion of the control circuit which selects the volume, push and withdraw rates, and cycle time of the reciprocating pump of FIG. 1;
FIG. 9 is a schematic diagram of timing error sensors which determine the error in the pumping cycle time;
FIG. 10 is a schematic diagram of a reduced augmentation circuit which selects only certain heartbeats to initiate the pumping cycles; and
FIG. 11 is a partial schematic diagram of the power supply for the control circuits.
While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detail embodiments of the invention with the understanding that the present disclo
10 sure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the embodiments illustrated. The scope of the invention will be pointed out in the appended claims. Referring to the system shown in FIG. 1 of the draw
15 ings, a pressure pulse generator 10 is provided generally similar to the pump shown in our copending application, Ser. No. 406,722 filed Oct. 27, 1964, assigned to the assignee of the present invention. Reference should be made to this application for a more detailed description
20 of the pump 10. It will only briefly be described herein with particular reference to a combined on and off check valve 11 shown in FIG. 2 which permits both complete bypass operation and arterio-arterial circulation assist. The pump 10 includes a multi-member housing 13 hav
25 ing a cylinder formed therein which slidably receives a reciprocating piston 15 defining in the housing 13 a pumping chamber 16 and an actuating chamber 17.
A controller 20 described in more detail below delivers fluid in two directions through the fluid coupling 22 to
30 the actuating chamber 17 thereby reciprocating the piston 15 in forward and reverse strokes, sometimes referred to herein as push and withdraw phases, respectively.
As shown in FIGS. 1 and 3, the pump 10 is connected in complete cardiopulmonary bypass so that blood flow
35 from the heart and through the lungs is terminated and circulation and oxygenation is effected extracorporeally by the artificial system. Toward this end venous blood is drained by catheter assembly 27 from the superior and inferior vena cavae which normally drain into the right
40 atrim 25. This blood is drained by gravity into a venous collecting chamber 28. The chamber 28 should be placed below the level of the operating table for this gravity feed.
Venous blood in the reservoir 28 is pumped by a roller pump 30 through an oxygenator 32. The roller pump 30
45 may be any one of a number of commercially available units of this type. The oxygenator 32 may take several forms including the bubble type, disc, screen, or even membrane type.
Blood in the oxygenator drains by gravity into a res
50 ervoir 36. No bubble trap is required in this embodiment as any bubbles in the blood will rise to the top of the reservoir.
The reservoir 36 is connected to fitting 40 shown in FIG. 2 communicating through check valve 11 with the
55 pumping chamber 16 in the pump 10.
The valve 11 may be manually operated to either block flow from the reservoir 36 into the chamber 16, or to permit flow from the reservoir but prevent back flow from the chamber 16 into the reservoir. For this purpose a
60 manually rotatable valve member 42 is provided with a large diameter through passage 43 therein. When valve member 42 is rotated so that passage 43 is aligned with bore 44 in the fitting, fluid may flow from the reservoir 36 into the chamber 16. This is the valve open position, and
65 is so placed when the system is used in complete bypass. During postoperative circulation assist the valve 42 may be rotated 90 degrees from its valve open position closing bore 44. The function of this is described in more detail below.
70 A check valve assembly 47 is mounted within a passage 43 and permits flow from the reservoir 36 into the chamber 16, but prevents flow from the chamber into the reservoir. In this manner during the push stroke of the piston 15 blood will flow from chamber 16 into the patient's
75 arterial system rather than back into the reservoir 36.
The pumping chamber 16 is connected into the circulatory system through a catheter assembly 49 connected to fitting 50 (FIG. 2). The catheter assembly may be similar to that shown in our copending application, which includes branched catheters adapted for insertion into the femoral arteries up into the patient's descending aorta.
It should be noted that there are no check valves in the catheter assembly 49 preventing flow from the arterial side of the patient's circulatory system into the pumping chamber 16 as the piston 15 withdraws. To prevent any 1Q significant amount of blood from being removed from the arterial tree during this withdrawal action, the diameters of the bore 44 and passage 43 are large compared with the smallest diameter of the catheter assembly 49 so that the catheters offer much greater resistance to flow during 15 the withdrawal of piston 15 than the passages connected with the reservoir 36.
As the piston 15 moves in its push phase forcing blood into the arterial tree, the check valve 47 prevents reverse flow into the reservoir 36. 20
As the controller and actuator 20 delivers fluid through the coupling 22, piston 15 reciprocates drawing blood into chamber 16 through check valve 47 (with valve member 42 open), and in the opposite phase forcing blood from the chamber 16 through catheter assembly 49 into the 25 arterial tree. This action provides pulsatile perfusion of the blood in the arterial tree.
In FIG. 4 a cardiopulmonary bypass system is shown generally similar to that shown in FIGS. 1 to 3 except that the reservoir 36 is replaced by a combination of a 30 second roller pump 52 and a bubble trap 54. With this arrangement blood is forced into the pumping chamber 16' rather than being fed by gravity from a reservoir such as noted with respect to FIGS. 1 to 3. When piston 15' withdraws during the withdrawal phase, both the pressure 35 from roller pump 52 and the withdrawal action of the piston 15' cooperate in filling the chamber 16'. There is only minimal leakage through the valve 47' during the push phase of the pump 10' as the pressure in chamber 16' is above the output pressure from pump 52, although 40 the valve 47' closes somewhat slower in this embodiment than in the embodiment of FIGS. 1 to 3.
Since the system shown in FIG. 4 is essentially closed from the oxygenator to the arterial side of the patient's circulatory system, the bubble trap 54 is required to re- 4g moved gases entrained in the blood.
The minute flow in the system shown in FIG. 4 is somewhat higher than that shown in FIG. 3 due to the additional filling assist of chamber 16' by the pump 52.
In the FIG. 5 embodiment, a cardiopulmonary bypass 50 system is disclosed generally similar to those described above with reference to FIGS. 1 to 4 except that an additional pulsatile pump 56 is provided for withdrawing blood through valve 58 from the reservoir 28". Valve 58 is a check valve and may be similar in construction and op- 55 eration to the valve 11 shown in FIG. 2. Pump 56 during its withdraw phase draws fluid from reservoir 28", and during its push phase pumps blood into oxygenator 32". The withdrawal of blood from the oxygenator 32" is effected by the withdrawal action of piston 15" in pump 60 10". A bubble trap 54' is also necessary as the system is a closed one from the oxygenator 32". Suitable circuitry is provided (not shown) to balance the output of the pumps 56 and 10" so that they may operate under different load situations preventing the oxygenator 32" from being either 65 flooded with too much blood or being drained dry.
In all the above systems the intermittent infusion of blood into the arterial tree produces a pulsatile arterial pressure wave. The height or amplitude of this wave may be increased by increasing the travel of the piston 15 70 and for this purpose a suitable volume dial is provided on the controller 20 in FIG. 1 which permits the surgeon to select the desired volume per cycle of the pump. In addition, the relative time duration of the positive pressure wave in comparison to the total cycle time of the 75
pump may be altered by changing the relative time duration of the push and withdraw phases of the piston 15. Furthermore, the length of cycle is also governed from the controller 20 by changing the rate of pacemaker which provides triggering signals for each cycle of the pump. During complete cardiopulmonary bypass the phase relationships between the patient's natural heart action and the synthesized wave produced by the pump 10, important in assisted circulation, are of no importance.
The control circuitry described below, contained in the controller 20, exercises control over the pumping parameters of stroke length, speed of stroking during both push and withdraw phases, and pump cycle duration. It should be understood at this point that only portions of the described circuitry are operative during complete cardiopulmonary bpyass, the other portions being operative during arterio-arterial assist as a postoperative circulation aid.
Triggering and driving circuit
The triggering and driving circuit disclosed in FIG. 6 is generally adapted to develop triggering signals for initiating each cycle of the reciprocating pump 10. For complete cardiopulmonary bypass, a pacemaker 132, which may take the form of an astable multivibrator, provides triggering pulses for the pumping cycles. A suitable control 132a is provided for varying the repetition rate of the triggering signals from the pacemaker so that the surgeon may select the cyclical rate he desires. For arterio-arterial assist, which is employed as a postoperative measure in the present device, an EKG trigger level selector 125 is provided for initiating the pumping cycles in timed relationship with the patient's EKG waveform. It should be understood that the pacemaker 132 and the trigger level selector 125 are used selectively.
In the arterio-arterial mode, the triggering circuit is effective to develop triggering pulses and delay them from a selected trigger level portion of the QRS segment of the EKG wave at a predetermined trigger level, and derives and delays a triggering pulse therefrom. The triggering pulse derived initiates the push phase of the pumping cycle and effects delivery of fluid into the patient's aorta increasing intra-aorta pressure at a time when the workload of the heart is the lowest. As noted above, during postoperative arterio-arterial assist the valve 11 would be closed. The delay time for the triggering pulse determines the phase relationship of the pumping cycle to the arterial pulse wave, and is determined physiologically as the phase relationship, which reduces the intraventricular pressure to a minimum for a given volume pumped and increases the postsystolic arterial pressure to an extent which returns the intra-aortic pressure to its pre-pump level or better so that coronary and peripheral circulation may be assisted. The withdrawal phase begins immediately upon completion of the pumping phase and continues during aortic valve opening thereby aspirating the left ventricle into the aorta. The withdrawal phase continues until the peak of the next intraventricular waveform at which time another pumping or push phase begins in response to another triggering signal. This phase relationship is not of any significance in the complete cardiopulmonary bypass as there is no load on the patient's heart.
As shown in FIG. 6, an EKG trigger level selector 125 is connected to receive the patient's EKG waveform from a conventional electrocardiogram through line 126. Line 126 connected to line 127 is adapted to drive an oscilloscope so that the patient's EKG waveform may be viewed during the use of the heart pumping system in the arterio-arterial mode by the surgeon or technician. Reference should be made to the copending application Chesnut et al. for the details of construction of the trigger level selector 125.
A selector switch 131, which may be located on a convenient control panel, permits the alternate initiation of