CA1042747A

CA1042747A - Cardiopulmonary bypass system

Info

Publication number: CA1042747A
Application number: CA217,828A
Authority: CA
Inventors: Halbert Fischel
Original assignee: Baxter Travenol Laboratories Inc
Current assignee: Baxter International Inc
Priority date: 1974-01-21
Filing date: 1975-01-13
Publication date: 1978-11-21
Also published as: US3890969A; AU474712B2; NL7500327A; GB1485300A; DE2501552A1; BE824319A; AU7628674A; JPS50103199A; LU71627A1; SE7500593L; IL46174A0; IL46174A; ZA747871B; FR2258191A1; IT1028478B

Abstract

Abstract of the Disclosure An emergency alertable gravity feed cardiopulmonary bypass system is disclosed in which a blood volume res-ponsive transducer is utilized in returning oxygenated blood to a human circulatory system at a pumping rate corresponding to venous drainage or selected norms. The transducer is coupled to a standpipe and is responsive to a confined gas volume therein related to the blood volume in a first air evacuable, gravity fed, collapsible bag and is coupled to a rate setting control. Blood flow from the first bag is directed by a control responsive oxygenation pump through a membrane oxygenator and heat exchanger and air evacuable collapsible bag and a main pump before return to the patient.
The oxygenation pump rate slaved to the main pump is greater than the gravity feed rate, and a pressure relieving conduit recirculates excess blood flow from the second bag to the first bag. Supervisory control of the flow rate of the main pump may be exercised by manual adjustment of the flow rate.

Description

Bac~ground of the Invention 1. Field of the Invention This invention pertains to blood flow rate controllers for pump oxygenation systems and, more particularly, to venous blood feed responsive, oxygenation systems for use in cardiovascular surgery and for cardiopulmonary partial support.

2. Description of the Prior Art Generally, a cardiopulmonary bypass system is a medical system used in cardiovascular surgery, intensive care and , ' .

:. ~k mb/ - 1 -'' ' . , ~ ~ .

1 surgical recovery that is coupled to a human body to revitalize 2 snd pump blood, thereby performing certain functions of the heart

3 and lungs and often partially or fully bypassing a portion of the

4 c~rculatory system. The cardiopulmonary bypass system receives a venous blood feed (oxygen deficient blood) from the human cir-6 culatory system, oxygenates and warms the blood and returns the 7 blood to the circulatory system at a flow rate corresponding to 8 the ~enous drainage, thus reducing the load on the lungs and 9 heart.
A cardiopulmonary bypass system in a partial support 11 capacity is used, for example, during cardiac intensive care 12 of patients who have suffered a cardiac infarction where a 13 portion of the heart muscle has died from an insufficient blood 14 supply. The dead muscle is soft and difficult to suture sinçe it will tear easily. The muscle may heal if the patient is kept 16 quiet and heart chambers are subject to a minimum amount of 17 pressure. Failing such care, an aneurysm may result in which 18 the softened muscle swells up and stagnates pools of blood which 19 tend to clot. The tendency toward development of an aneurysm is minimized by reducing the pumping load on the heart with the 21 partial support system. Typically the infarcted tissue scars 22 over and thereby regains its tensile integrity in several weeks 23 during which time the cardiopulmonary bypass system must operate 24 continuously. Recent developments in pump oxygenation equipment, such as mernbrane oxygenators having limited long term blood 26 degradation effects, have made possible long term partial 27 support of this duration. In the past, technicians have monitored 28 the flow of blood in pump oxygenation systems for a relatively 29 short period of time, such as less than four hours, during heart ~0 surgery. However, the costs and availability of technicians , .

~ 7 ~7 1 generally preclude their usage on a long term basis, and 2 even where they are used human error can be a significant 3 problem.
4 Conflicts between safety, costs and flexibility must be reduced to provide a satisfactory cardiopulmonary 6 bypass system. Such desirable features include responsive-7 ness to a gravity feed rate, minimal blood degradation and 8 long term reliability. In addition, the exposure of the 9 blood to air should be minimized, while the buildup of excess gases should be avoided or at least indicated.
11 Many specific requirements must be met in a practical 12 partial support system. For example, the cardi~pulmonary 13 bypass system experiences a load as the blood is returned to 14 the human body. The load is variable and the flow impedance seen by the cardiopulmonary bypass system may increase if 16 for example the arteries are constricting or decrease when 17 hemorrhaging is occurring. Yet the cardiopulmonary bypass 18 system should generally maintain a constant flow rate to the 19 human body, equal to the venous drainage. In the past, the return flow rate has been controlled in response to central 21 venous pressure or return flow pressure. See, for example, 22 Turina, et al., "An Automatic Cardiopulmonary Bypass Unit 23 for Use In Infants", The Journal of Thoracic and Cardio-24 vascular Sur~erv 63 (February 1972), p. 263, 264. However, venous pressure is an inaccurate measure of blood flow and 26 may vary considerably for a constant blood flow depending 27 on the physical state of the patient.
28 Blood removal from the human circulatory system by a 29 cardiopulmonary bypass system should not cause an excessive vacuum or suction so as to collapse the veins, yet provide a substantial .. . : . ~

~ 7 l and generally uniform blood f]ow to effectively unload the 2 patient's cardiopulmonary system. A system utilizing a negative 3 pressure in a caval cannula is described in an article by 4 Turina et al., "Servo-controlled Perfusion Unit With Membrane Oxygenator for Extended Cardioyulmonary Bypass", Biomedical 6 En~ineerin~ (March 1963) pp. 102-107. The Turina system however, 7 i9 rather sophisticated and complex in utilizing sensors and 8 servos for a number of controls, and thus is both undul~ costly 9 and subject to greater tendency to failure.
The rate and changes in rate of blood flow indicate ll the physical state of the patient, and thus it would be desirable 12 to monitor the blood flow rate. The physician may find it 13 necessary to increase or decrease the return flow rate of the 14 blood. Increasing the blood flow rate in excess of the drainage rate often requires the addition of blood to the system. It 16 would be advantageous to have a cardiopulmonary bypass system 17 which could introduce quantities of blood to the blood flow in 18 addition to the blood supplied by the patient's circulatory system.
19 The quantity of blood flowing in the circulatory system of a neonate or young infant is extremely critical. For 21 example, hyaline membrane disease attacks the alveolar sacks of 22 infants. When this occurs, the lining of the lungs is impervious 23 to oxygen and CO2. Since the infant having this disease receives 24 insufficient oxygen, the treatment in the past has been to increase, in concentration and pressure, the oxygen provided to 26 the infant. Although the disease is often cured by this technique, 27 other serious conditions may set in which are caused by the 28 toxic effects of oxygen such as retrolental fibroplasia, in which 29 the retina is destroyed. By using a cardiopulmonary bypass system, the lungs are allowed to heal. The control of blood volume '~

lS extremely important since the nyaline disease typically occurs with underweiyht infants, typically less than 2500 grams and having a total blood volume of only 150-300 cc, Thus it would be desirable to have a cardiopulmonary bypass system that is safe, reliable, gravity feed responsive, and volume alterable.

Summar of the Invention Y
In broad terms the present invention provides a system for providing a controlled blood flow to a human circulatory system comprising: collector means for receiving a blood feed from a patient; means coupled to the collector means and responsive to the volume of the blood therein for providing an indication related thereto; oxygenation means coupled to the collector means for revitalizing the blood;
and variable rate pump means coupled to the collector means for providing a return flow of blood to the patient at a flow rate responsive to the indication.
Accordingly, a cardiopulmonary bypass system for use with a human circulatory system in accordance with this invention comprises variable volume, air-free means for collecting a gravity feed blood flow from a patient and transducer means - coupled to the collector means for providing a blood volume responsive signal related to the feed rate of the blood. After oxygenating and warming the blood from the collector means, pump means coupled to the collector means returns the blood to the patient at a flow rate controlled by the signal from the transducer means such that the blood flow returning to the patient is substantially the same as the drainage rate from the patient.
In a preferred embodiment of the invention, a first collapsible bag is coupled to receive a gravity fed flow of blood. The bag is collapsible and air evacuable so that any blood-gas interface may be substantially eliminated, The bag ~, .
mb/ ~ - 5 -~ ~J~'~7~7 is also flexible so as to inhibit air suction when empty and thereby prevent an air embolism to the eirculatory system, A standpipe extending from the bag is eoupled to a gas pressure responsive transducer. The standpipe provides a eonfined gas volume, the pressure within which acts on the transducer. Blood flow rate changes into the bag manifested by blood volume changes of the bag result in fractianal ehanges in the confined gas volume and subse~uent pressure ehanges that are mueh Sa -, ~ 7l~7 l amplified with respect to the fractional blood volume changes 2 of the bag. A second collapsible bag is provided that functions 3 generally in a buffer capacity and supplies revitalized blood to 4 the patient. Revitalization means generally comprising a pump, a membrane oxygenator and a heat exchanger is coupled between 6 the first and second bags. A recirculation path communicating 7 between the second bag and the first bag provides a positive 8 recirculation of a part of the blood flow, relieving excess 9 pressure in the second bag and insuring equilibrium in the flow rates. A main variable speed pump coupled to the second bag 11 delivers a controlled blood flow from the second bag to a human - 12 circulatory system. To regulate pump speed, a rate setting control 13 responsive to the transducer signal drives the main pump at a 14 rate which tends to maintain the blood volume of the first bag , .
at a predetermined point for a particular blood drainage rate ~ 16 such that the return blood flow rate is held at substantially the ; 17 rate of the venous blood flow. The rate setting control may 18 be manually varied by a supervising physician to directly l9 change the rate of flow without shutting off the automatic system.
21 In accordance with another feature a reservoir is 22 included for storing blood. The blood in the reservoir may be 23 selectively admitted into the first drainage bag for increasing 24 the total blood volume of the combined circulatory and cardio-pulmonary bypass system. A valve coupled tube may be used 26 to tap off an excess quantity of blood if the flow exceeds 27 predetermined levels.
28 Description of the Drawin~s 29 Fig. 1 is a combined block and simplified broken away ' . ~ . ' ' .

1~4;~7~7 1 schematic diagram of an example of a blood flow controller in 2 accordance with the invention.
3 Detailed ~escription 4 Referring to Fig. 1, in a preferred embodiment of cardio-pulmonary bypass system 10 in accordance with the invention, a 6 collector means 12 is disposable below a blood withdrawal point 7 on a patient for receiving a gravity fed venous blood flow from 8 a human patient's circulatory system. A gas containment means or 9 standpipe 14 coupled into the interior of the collector means extends vertically to a pressure responsive transducer 16 which 11 is in operative relation to the interior at the upper end of 12 the standpipe 14. The collector means 12 generally comprises a 13 first collapsible bag 18 and a venous feed tube 20 coupled at 14 an inlet of the collapsible bag 18. While the collapsible bag 18 and the venous feed tube 20 may be of various material~ they here 16 are of a surgical quality neoprene and are typically disposable 17 units. The thickness of the collapsible bag 18, which is 18 preferably transparent or translucent, is sufficient for it ~.o 19 accept a substantial volume of blood without danger of rupture or susceptibility to puncture from contact with foreign objects.
21 The bag 18 is also, however, sufficiently pliable for its walls 22 to readily conform to the interior blood volume, thereby sub-23 stantially eliminating an interior blood-gas interface and 24 completely collapsing when all blood is removed. An outlet tube 19 at the top of the bag 18 can be closed by a clamp 21 when all 26 air has been exhausted from the bag interior.
27 The standpipe 14 is preferably a rigid and transparent 28 or trsnslucent shaped tubular element of surgical quality. The 29 standpipe 14 having a small interior volume in comparison with the interior volume of the first collapsible bag and having 1~427~7 1 nominal blood levels therein, defines a confined gas volume 22 2 within a cylindrical chamber 23 and exerting a pressure through 3 a sterility barrier 24 within the chamber 23 on the transducer 4 16. An increase of blood flow into the first collapsible bag 18 causes a distention of the bag 18 and thereby causes the blood 6 level in the standpipe 14 to increase, reducin~ the confined gas 7 volume 22. A reduction of the confined gas volume 22 causes an 8 increase in the pressure applied through the sterility barrier 24 9 to the transducer 16. Small fractional changes in the blood flow rate into the collapsible bag 18, manifested by small fractional 11 volume changes of blood in the collapsible bag 18 causes large 12 fractional changes in the pressure of the confined gas volume 22.
13 Thus the combination of the collection means 12, the standpipe 14 14 and the transducer 16 provide a highly sensitive means of measuring and indicating changes in the venous flow rate.
16 While the transducer 16 provides a signal related to 17 a blood flow rate from the patient into the collapsible bag 18, 18 this signal is not necessarily related to the signal which would 19 be obtained if, for example, a patient's central venous pressure were monitored. The applicant's invention tends to provide a 21 more accurate indication of venous flow rate since a patient's 22 blood pressure may vary with changes in blood volume in the 23 patient's circulatory system and with other parameters.
24 Revitalization or oxygenation means 28 is provided for continuous revitalization of the blood including the oxygen - 26 transfer to oxygen deficient blood and the warming of blood which 27 has been partially cooled since removal from the patient. The 28 oxygenation means 28 generally comprises an oxygenation pump 30 29 driven by a pump motor 32 coupled thereto. The oxygenation pump 30 is coupled to a membrane oxygenator and heat exchanger 34 in '' ;
i -8-~ 7 ~'7 1 series fashion, with the oxygenation pump 30 forcing blood through 2 the membrane oxygenator and heat exchanger 34. The pump motor 3 32 for the oxygenation pump 30 may be a roller blood pump in which 4 blood is carried between a membrane and a surface defining a cylindrical chamber by rollers rotating and bearing on the mem-6 brane and against the surface.
7 A second collapsible bag 36 comparable to the first 8 bag 18 is air evacuable and is preferably translucent or trans-9 parent. Flow through the oxygenation means 28 is transported to the collapsible bag 36 via a conduit 37 to provide generally a con-11 tinuous supply of freshly revitalized (i.e. oxygenated and warmed) 12 blood to the second collapsible bag 36. The second collapsible 13 bag 36 also helps to dampen or buffer uneven or pulsating flows 14 of blood returned to the patient by way of a main pump 38. For positive circulation under all conditions, the main pump 38 is 16 constantly driven at a slightly slower rate than the oxygenation 17 pump 30 so that the main pump 38 does not operate without a blood 18 flow supply.
19 Although two collapsible bags 18, 36 are described, lt should be noted that a single partitioned bag may be used in 21 accordance with this invention. The collapsible nature of the 22 bags, besides limiting blood-gas interfaces, helps prevent a 23 massive air embolism. Should blood in either bag 18 or 36, 24 for some reason, be emptied and collapse occur, air which could enter through leaks in the cardiopulmonary bypass system 10 are 26 prevented from being pumped in~o the patient's circulatory 27 system.
28 A recirculation path is defined by a tube 39 coupling 29 blood from the second bag 36 to the first bag 18, providing pressure relief to equalize pressure between the two bags 18, _~ _ 1~4~ 7 1 36. Excess pressure would tend to be present in the second 2 collapsible bag 36 in the absence o the recirculation path, 3 because of the faster pump rate of the oxygenation pump 30 with 4 respect to the main pump 38.
S The main pump 38 is preferably a roller blood pump 6 coupled to the second collapsible bag 36 for returning the 7 oxygenated and warmed blood to the patient's circulatory system.
8 The main pump 38 maintains a blood flow rate invariant with 9 respect to a varying impedance or load of the human circulatory system as experienced by the pump 38, despite the fact that the 11 impedance or load provided by the patient's circulatory system 12 varies with the patient's physical state. For example, a 13 constriction in the patient's circulatory system causes an 14 increased impedance, yet blood is returned to the patient at a rate independent of that physical state.
16 A variable speed main pump motor 40 coupled to the 17 main pump 38 drives the pump 38 at a desired controllable 18 blood flow rate in response to a signal fed from controller 19 means or a rate setting control 42. The rate setting control 42 may simply be an amplifier circuit providing an 21 error signal tending to drive the variable speed pump motors 22 at a rate equal to the venous blood flow. A preferred embodi-23 ment given by way of example provides a rate setting control 24 42 comprising an amplifier circuit 44, a servo motor 46, a speed reducer 48 coupled to the servo motor, a variable 26 impedance or a potentiometer 50 mechanically coupled to the 27 speed reducer 48 and a control knob 52 on ~he potentiometer 28 shaft. Rate setting control 42 is responsive to a signal 29 from the transducer 16 to provide the variable speed pump motor 40 with a signal from the potentiometer 50, which 31 adjusts the signal from a voltage source 51 to drive the main 1~ 4 ~ 7 1 pump 38 at a flow rate corresponding to the blood volume in the 2 collapsible bag 18. The blood volume in the collapsible bag 18 3 is maintained at a predetermined level such that the return 4 blood flow rate is held substantially equal to the venous blood S flow. The control knob 52 coupled to the potentiometer 50 can 6 be used to manually override the rate setting control 42 to 7 exercise supervisory control of the flow rate of the main pump 38.
8 The amplifier circuit 44 amplifies a bipolar null 9 referenced signal from the transducer 16 to provide a signal sufficient to drive the servo motor 46. This signal is bipolar 11 in that it may represent deviations from a null in either of two ~, 12 directions corresponding to either an increase in pressure 13 exerted on the transducer 16 by the confined gas volume 22 or a ~'~ 14 decrease in pressure exerted by the confined gas volume 22. In setting up the system the pressure within the confine~ gas , 16 volume 22 may be equalized at ambient by a closeable outlet (not ~,~; 17 shown) in the cylinder 23, the outlet being shut when a desired 18 blood level is reached in the standpipe 14. The servo motor 46 ::, 19 rotates in accordance with the polarity of the transducer signal t'i 20 tending to rotate the potentiometer 50 in accordance with the 21 blood volume in the collapsible bag 18, as sensed-by the 22 transducer 16.
23 The speed reducer 48 may be a gear reduction system 24 coupled between the servo motor 46 and the potentiometer 50, ` 25 reducing the angular rotation of the potentiometer 50 with 26 respect to the angular rotation of the servo motor 46 thereby 27 providing an adjustable gain in the system. Gain is adjusted 28 to allow time for ehanges in the pump rate of the main pump 38 29 to influence blood volume changes sensed by the transducer and further rotation of the servo motor without excessive overtravel 31 of the potentiometer 50.
32 The setting of the potentiometer 50 determines the :

1'~4;~7~'7 1 speed of the variable speed pump motor 40 which in turn deter-2 mines the flow rate of the main pump 38. An adjustable re-3 sistance 54 in the motor 40 energizing circuit permits further 4 adjustment to maintain a pump rate through the oxygenation pump 30 in excess of that through the main pump 38, such that 6 a flow is recirculated back from the second collapsible bag 36 7 to the first bag 18 and the main pump 38 does not operate 8 without a blood supply.
9 Dial indicia 53 juxtaposed adjacent the control knob 52 indicates the instantaneous rate at which the main pump 38 is ll being driven. The knob 52 may be manually rotated by overcoming 12 the torque supplied by the servo motor 46 through the speed 13 reducer 48. A slip clutch or a friction coupling between the 14 speed reducer 48 and the potentiometer 50 is suitable for a motor 46 of greater torque, but this arrangement would not comparably 16 restore the knob 52 to the proper setting when released.
17 An outlet tube 56 whose exterior surface is hermetically 18 joined to the bag 36 can be closed by a clamp 57 to permit ex-19 haustion of interior air in the same fashion as the first bag 18.
A reservoir 58 is provided for receiving and storing an 21 excess quantity of blood from the cardiopulmonary bypass system 22 10 and for increasing the volume ~f the blood in the cardio-23 pulmonary bypass system 10 by releasing such blood to the second 24 bag 36 through a valve 59. A valve 60 in the conduit from the - 25 main pump 38 may be used to tap off blood from the cardiopulmonary 26 bypass system 10. The valves 59, 60 used to add blood to the 27 reservoir 58 and to release blood to the cardiopulmonary bypass 28 system 10 may be manually actuable or may be of a type actuable 29 by an electrical signal. For example, a perfusion flow servo system is described in the Turina et al. article in the March 31 1973 issue of Biomedical En~ineerin~, previously cited. A
.:' 1 cardiotomy tube (not shown) may also be coupled into the reservoir 2 58 to provide a blood source to the reservoir 58. The cardio~omy 3 line is used to remove blood which collects adjacent severed 4 veins and arteries resulting from incisions during an operation.
The blood, having been suctioned off from the patient, is in 6 a frothy condition and a debubbler (not shown) is typically used 7 to reduce the frothy condition of the blood before it enters the 8 reservoir 58.
9 To review the operation of the cardiopulmonary bypass system 10, the first collapsible bag 18 is generally di~posed at a 11 level beneath that of the patient so as to promote a gravity 12 blood feed. Initially, blood is added to the first collapsible ~ .
13 bag 18 with the bag clamps 21, 57 released. Ambient air pres$ure 14 is established in the interior volume 22 and the transducer 16 by opening a valve (not shown) or disconnecting the standpipe 14 from 16 the cylinder 23. Blood is added until the blood level in the 17 standpipe 14 reaches a reference or priming level 62, aft~r which 18 the standpipe 22 is then reconnected to the sterility barrier 24 19 and the transducer 16. Thus the pressure in the confined volume 22 is initially equalized with respect to ambient.
21 Air that is present in the first and second collapsible 22 bags 18, 36 is forced out, either manually or by filling the bags 23 18, 36, and the outlets 19, 56 are then closed by the clamps 24 21, 57. The blood air interfaces within the bags 18, 36 are thus minimized.
26 Venous blood flows under gravity into the first 27 collapsible bag 18, whose volume then varies in accordance with 28 the rate of blood flow therethrough. This volume establishes 29 the blood level in the standpipe 14, and as previously described fractional changes in the blood volume within the bag 18 cause 7~L7 1 much larger variations in the pressure exerted on the transducer 2 16. Though the transducer 16 signal is generally referenced to 3 ambient pressure, an inverted U-tube arrangement (not shown) may 4 be used to provide a negative pressure head so that the transducer may be arbitrarily oriented where the level of the collector means 6 12 varies from the position depicted in the embodiment of Fig. 1 7 and is, for example, disposed closer to the level of the patient.
8 The transducer 16 signal is applied to the amplifier 9 circuit 44, providing an energizing signal to the servo motor 46, which rotates at a rate determined by signal amplitude and in a 11 direction determined by polarity. Through the speed reducer 48, 12 motor rotation turns the potentiometer 50 in a corresponding 13 direction at a slower speed, also rotating the control knob 52 14 so that the blood flow rate may be read off the dial 53. As main pump 38 speed is adjusted by the motor 40 controlled by the 16 po~entiometer 50 setting, the blood level is returned toward the 17 null position 62, slowing down or reversing the servo motor 45.
18 Note that the pump motor 40 can continue to operate at or near 19 a substantially constant speed and that the system is stablized ~; 20 by gain adjustment at the speed reducer 48 although other means 21 might also be used.
22 Blood from the firs~ collapsible bag 18 is pumped - 23 through the revitalization or oxygenation means 28, by the 24 oxygenation pump 30, which provides sufficient pressure to drive the blood through the membrane oxygenator and heat exchanger 34 26 and to the second collapsible bag 36. Because the oxygenation 27 pump motor 32 speed is also determined by the potentiometer 50 28 8etting, the oxygenation pump 30 pumps blood at a flow rate in 29 excess of the flow rate of the main pump 38 as determined by the setting of the adjustable resistor 54. Excess pressure ~ -14-:
,;''"

1~4Z7~L~7 1 developed by the oxygenation pump 30 withln the second 2 collapsible bag 36 is relieved via the tube 39 which serves 3 as a recirculation path. Blood from the second collapsible 4 bag 36 is then pumped by the main pump 38 to the patient's circulatory system.
6 It is important to alert a physician to the existence 7 of a low blood volume condition in a patient. This condition 8 may represent internal hemorrhaging and may require that an 9 additional quantity of blood be introduced into the total system. A physician or assistant, alerted to such a condition 11 may now increase the circulating blood volume by opening the 12 reservoir valve 59, thereby allowing blood to flow into the 13 second collaps;ble bag 36. Also, or alternatively, the 14 physician may manually override the knob 52, thereby in-creasing the flow rate of the main pump 38 to the human cir-16 culatory system. It should be recognized that such an increase 17 in the return flow rate without replenishment can only be carried 18 on for a limited period of time without collapse of the bags 19 18 and 36.
Thus, a simple, accurate and sensitive cardiopulmonary 21 bypass system for receiving a variable rate gravity fed venous 22 flow from a human circulatory system, revitalizing the blood and 23 returning it to the circulatory system at a rate substantially 24 equal to the venous flow rate has been described which is volume alterable and provides means for reducing degrading 26 blood gas interfaces.
27 While the invention has been particularly shown and 28 described and with reference to a preferred embodiment thereof, 29 it will be understood by those skilled in the art that various changes in form anddetails may be made therein without departing 31 from the spirit and scope of the invention.

Claims

WHAT IS CLAIMED IS:

1. A cardiopulmonary bypass system for receiving a variable rate gravity fed venous blood flow from a human circu-latory system, revitalizing the blood and returning the blood to the circulatory system at a flow rate substantially equal to the gravity fed blood flow comprising:
a first collapsible bag disposable below a withdrawal point coupled to receive a gravity fed flow of blood at an inlet, the collapsible bag being at least partially filled with blood and substantially without a blood-gas interface, the collapsible bag having a sufficient flexibility such that a collapse of the bag resulting from an emptying of blood therein inhibits a suction from occurring at the inlet;
a second collapsible bag;
recirculation path means for communicating blood from the second collapsible bag to the first collapsible bag;
revitalization means coupled between the first and second collapsible bags for continuously oxygenating and warming blood from the first bag and transporting the oxygenated and warmed blood to the second bag;
main pump means coupled to the second bag for delivering a blood flow from the second bag to a human circulatory system at a rate controlled by a control signal applied thereto;
blood volume transducer means coupled to the first bag for providing a signal related to the blood volume in the first bag; and controller means responsive to the blood volume indication for supplying a control signal to the main pump means to drive the main pump means at a rate which tends to maintain the blood volume of the first bag at a predetermined level such that the return blood flow rate is held substantially equal to the venous blood flow.

2. The invention as set forth in claim 1 and in which the first collapsible bag volume is determined by the blood therein and including gas containment means coupled to said first bag and said transducer means and having nominal blood levels and an interior volume small in comparison with the interior volume of the first collapsible bag, said gas containment means defining a confined gas volume, the pressure within which acts on the trans-ducer means such that blood flow rate changes into the first collapsible bag manifested by blood volume changes of the bag result in fractional changes in the confined gas volume and sub-sequent pressure changes that are much amplified with respect to the fractional blood volume changes of the bag.

3. The invention as set forth in claim 2 and in which the transducer means, the gas containment means and the collapsi-ble bag define a closed system such that when the gas containment means is exposed to ambient air pressure and the system is brought to a reference level, the closing of the system thereby defines a transducer reference with respect to subsequent blood flow changes.

4. The invention as set forth in claim 1 and further comprising rate setting control means tending to maintain a return blood flow rate equal to a venous feed rate and means for manually overriding the rate setting control.

5. The invention as set forth in claim 1 and further including a recirculation path between the second collapsible bag and the first collapsible bag for equalizing pressures between the first and second collapsible bags.

6. The invention as set forth in claim 1, and in which the revitalization means comprises:
a membrane oxygenator, oxygenator pump and heat exchanger coupled in series fashion, said oxygenator pump includ-ing means responsive to the flow rate of the main pump for main-taining the flow rate of the oxygenator pump at a rate greater than that of the main pump, such that a flow is recirculated back from said second bag to said first bag and the main pump does not operate without a blood flow supply.

7. A system for providing a controlled blood flow to a human circulatory system comprising:
collector means for receiving a blood feed from a patient;
means coupled to the collector means and responsive to the volume of the blood therein for providing an indication related thereto;
oxygenation means coupled to the collector means for revitalizing the blood; and variable rate pump means coupled to the collector means for providing a return flow of blood to the patient at a flow rate responsive to the indication.

8, The invention as set forth in claim 7, and in which the collector means comprises at least one flexible con-tainer including means for minimizing an areal blood-air inter-face therein.

9. In a cardiopulmonary bypass system of the type having a first container for receiving a blood drainage, a second container for receiving a revitalized blood flow from the first container, blood treatment apparatus, including oxygenation means, and an auxiliary pump coupled between the first and second containers; a recirculation path for coupling blood from the second container to the first container and a main pump coupled to the second container for providing a blood flow to a human cardiovascular system, the combination therewith of:
transducer means responsive to a blood volume in the first container;
means coupled between the main pump and the auxiliary pump for driving the auxiliary pump at a rate greater than that of the main pump; and means for driving the main pump at a rate related to blood volume responsive signals received from said transducer means.

10. The invention as set forth in claim 9 and further comprising:
a reservoir for storing a fluid at a level greater than that of a fluid level in the first container;
means coupled between the reservoir and the first con-tainer for communicating a flow from the reservoir to the first container; and valve means for selectively admitting a fluid from the reservoir to the first container.