U.S. patent number 3,890,969 [Application Number 05/435,223] was granted by the patent office on 1975-06-24 for cardiopulmonary bypass system.
This patent grant is currently assigned to Baxter Laboratories, Inc.. Invention is credited to Halbert Fischel.
United States Patent |
3,890,969 |
Fischel |
June 24, 1975 |
Cardiopulmonary bypass system
Abstract
An emergency alertable gravity feed cardiopulmonary bypass
system is disclosed in which a blood volume responsive 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.
Inventors: |
Fischel; Halbert (Santa Ana,
CA) |
Assignee: |
Baxter Laboratories, Inc.
(Morton Grove, IL)
|
Family
ID: |
23727540 |
Appl.
No.: |
05/435,223 |
Filed: |
January 21, 1974 |
Current U.S.
Class: |
604/6.14;
128/DIG.3; 422/48; 422/46; 604/67 |
Current CPC
Class: |
A61M
1/3666 (20130101); A61M 1/3624 (20130101); A61M
1/3603 (20140204); Y10S 128/03 (20130101) |
Current International
Class: |
A61M
1/36 (20060101); A61M 001/03 () |
Field of
Search: |
;128/214R,214B,214E,214F,214.2,230 ;23/258.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Lewis et al., Jour. Thoracic Surg.; Vol. 43, No. 3, Mar. 1962, pp.
392-396..
|
Primary Examiner: Truluck; Dalton L.
Attorney, Agent or Firm: Altman; Louis
Claims
What is claimed is:
1. A cardiopulmonary bypass system for receiving a variable rate
gravity fed venous blood flow from a human circulatory 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 transducer 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 subsequent 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 in which said blood volume
transducer means is coupled to the first container by a vertically
extending standpipe having a small interior volume in comparison
with the interior volume of said first container, said standpipe
being positioned to prevent blood from the first container from
coming into contact with said transducer.
4. The invention as set forth in claim 2 and in which the
transducer means, the gas containment means and the collapsible 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.
5. 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.
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 including means responsive
to the flow rate of the main pump for maintaining 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. 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 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.
8. The invention as set forth in claim 7 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 container for
communicating a flow from the reservoir to a said container;
and
valve means for selectively admitting a fluid from the reservoir to
the first container.
Description
BACKGROUND 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 surgical recovery
that is coupled to a human body to revitalize and pump blood,
thereby performing certain functions of the heart and lungs and
often partially or fully bypassing a portion of the circulatory
system. The cardiopulmonary bypass system receives a venous blood
feed (oxygen deficient blood) from the human circulatory system,
oxygenates and warms the blood and returns the blood to the
circulatory system at a flow rate corresponding to the venous
drainage, thus reducing the load on the lungs and heart.
A cardiopulmonary bypass system in a partial support capacity is
used, for example, during cardiac intensive care of patients who
have suffered a cardiac infarction where a portion of the heart
muscle has died from an insufficient blood supply. The dead muscle
is soft and difficult to suture since it will tear easily. The
muscle may heal if the patient is kept quiet and heart chambers are
subject to a minimum amount of pressure. Failing such care, an
aneurysm may result in which the softened muscle swells up and
stagnates pools of blood which tend to clot. The tendency toward
development of an aneurysm is minimized by reducing the pumping
load on the heart with the partial support system. Typically the
infarcted tissue scars over and thereby regains its tensile
integrity in several weeks during which time the cardiopulmonary
bypass system must operate continuously. Recent developments in
pump oxygenation equipment, such as membrane oxygenators having
limited long term blood degradation effects, have made possible
long term partial support of this duration. In the past,
technicians have monitored the flow of blood in pump oxygenation
systems for a relatively short period of time, such as less than
four hours, during heart surgery. However, the costs and
availability of technicians generally preclude their usage on a
long term basis, and even where they are used human error can be a
significant problem.
Conflicts between safety, costs and flexibility must be reduced to
provide a satisfactory cardiopulmonary bypass system. Such
desirable features include responsiveness to a gravity feed rate,
minimal blood degradation and long term reliability. In addition,
the exposure of the blood to air should be minimized, while the
buildup of excess gases should be avoided or at least
indicated.
Many specific requirements must be met in a practical partial
support system. For example, the cardiopulmonary bypass system
experiences a load as the blood is returned to the human body. The
load is variable and the flow impedance seen by the cardiopulmonary
bypass system may increase if for example the arteries are
constricting or decrease when hemorrhaging is occurring. Yet the
cardiopulmonary bypass system should generally maintain a constant
flow rate to the human body, equal to the venous drainage. In the
past, the return flow rate has been controlled in response to
central venous pressure or return flow pressure. See, for example,
Turina, et al., "An Automatic Cardiopulmonary Bypass Unit for Use
In Infants", The Journal of Thoracic and Cardiovascular Surgery 63
(February 1972), p. 263, 264. However, venous pressure is an
inaccurate measure of blood flow and may vary considerably for a
constant blood flow depending on the physical state of the
patient.
Blood removal from the human circulatory system by a
cardiopulmonary bypass system should not cause an excessive vacuum
or suction so as to collapse the veins, yet provide a substantial
and generally uniform blood flow to effectively unload the
patient's cardiopulmonary system. A system utilizing a negative
pressure in a caval cannula is described in an article by Turina et
al., "Servo-controlled Perfusion Unit With Membrane Oxygenator for
Extended Cardiopulmonary Bypass", Biomedical Engineering (March
1963) pp. 102-107. The Turina system however, is rather
sophisticated and complex and utilizing sensors and servos for a
number of controls, and thus is both unduly costly and subject to
greater tendency to failure.
The rate and changes in rate of blood flow indicate the physical
state of the patient, and thus it would be desirable to monitor the
blood flow rate. The physician may find it necessary to increase or
decrease the return flow rate of the blood. Increasing the blood
flow rate in excess of the drainage rate often requires the
addition of blood to the system. It would be advantageous to have a
cardiopulmonary bypass system which could introduce quantities of
blood to the blood flow in addition to the blood supplied by the
patient's circulatory system.
The quantity of blood flowing in the circulatory system of a
neonate or young infant is extremely critical. For example, hyaline
membrane disease attacks the alveolar sacks of infants. When this
occurs, the lining of the lungs is impervious to oxygen and
CO.sub.2. Since the infant having this disease receives
insufficient oxygen, the treatment in the past has been to
increase, in concentration and pressure, the oxygen provided to the
infant. Although the disease is often cured by this technique,
other serious conditions may set in which are caused by the toxic
effects of oxygen such as retrolental fibroplasia, in which the
retina is destroyed. By using a cardiopulmonary bypass system, the
lungs are allowed to heal. The control of blood volume is extremely
important since the hyaline disease typically occurs with
underweight 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.
SUMMARY OF THE INVENTION
In broad terms, 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 is also flexible so as to
inhibit air suction when empty and thereby prevent an air embolism
to the circulatory system.
A standpipe extending from the bag is coupled to a gas pressure
responsive transducer. The standpipe provides a confined 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 fractional changes in the confined gas volume
and subsequent pressure changes that are much amplified with
respect to the fractional blood volume changes of the bag. A second
collapsible bag is provided that functions generally in a buffer
capacity and supplies revitalized blood to the patient.
Revitalization means generally comprising a pump, a membrane
oxygenator and a heat exchanger is coupled between the first and
second bags. A recirculation path communicating between the second
bag and the first bag provides a positive recirculation of a part
of the blood flow, relieving excess pressure in the second bag and
insuring equilibrium in the flow rates. A main variable speed pump
coupled to the second bag delivers a controlled blood flow from the
second bag to a human circulatory system. To regulate pump speed, a
rate setting control responsive to the transducer signal drives the
main pump at a rate which tends to maintain the blood volume of the
first bag at a predetermined point for a particular blood drainage
rate such that the return blood flow rate is held at substantially
the rate of the venous blood flow. The rate setting control may be
manually varied by a supervising physician to directly change the
rate of flow without shutting off the automatic system.
In accordance with another feature a reservoir is included for
storing blood. The blood in the reservoir may be selectively
admitted into the first drainage bag for increasing the total blood
volume of the combined circulatory and cardiopulmonary bypass
system. A valve coupled tube may be used to tap off an excess
quantity of blood if the flow exceeds predetermined levels.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a combined block and simplified broken away schematic
diagram of an example of a blood flow controller in accordance with
the invention.
DETAILED DESCRIPTION
Referring to FIG. 1, in a preferred embodiment of cardiopulmonary
bypass system 10 in accordance with the invention, a collector
means 12 is disposable below a blood withdrawal point on a patient
for receiving a gravity fed venous blood flow from a human
patient's circulatory system. A gas containment means or standpipe
14 coupled into the interior of the collector means extends
vertically to a pressure responsive transducer 16 which is in
operative relation to the interior at the upper end of the
standpipe 14. The collector means 12 generally comprises a first
collapsible bag 18 and a venous feed tube 20 coupled at an inlet of
the collapsible bag 18. While the collapsible bag 18 and the venous
feed tube 20 may be of various materials they here are of a
surgical quality neoprene and are typically disposable units. The
thickness of the collapsible bag 18, which is preferably
transparent or translucent, is sufficient for it to accept a
substantial volume of blood without danger of rupture or
susceptibility to puncture from contact with foreign objects. The
bag 18 is also, however, sufficiently pliable for its walls to
readily conform to the interior blood volume, thereby substantially
eliminating an interior blood-gas interface and 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 air has been
exhausted from the bag interior.
The standpipe 14 is preferably a rigid and transparent or
translucent shaped tubular element of surgical quality. The
standpipe 14 having a small interior volume in comparison with the
interior volume of the first collapsible bag and having nominal
blood levels therein, defines a confined gas volume 22 within a
cylindrical chamber 23 and exerting a pressure through a sterility
barrier 24 within the chamber 23 on the transducer 16. An increase
of blood flow into the first collapsible bag 18 causes a distention
of the bag 18 and thereby causes the blood level in the standpipe
14 to increase, reducing the confined gas volume 22. A reduction of
the confined gas volume 22 causes an increase in the pressure
applied through the sterility barrier 24 to the transducer 16.
Small fractional changes in the blood flow rate into the
collapsible bag 18, manifested by small fractional volume changes
of blood in the collapsible bag 18 causes large fractional changes
in the pressure of the confined gas volume 22. Thus the combination
of the collection means 12, the standpipe 14 and the transducer 16
provide a highly sensitive means of measuring and indicating
changes in the venous flow rate.
While the transducer 16 provides a signal related to a blood flow
rate from the patient into the collapsible bag 18, this signal is
not necessarily related to the signal which would be obtained if,
for example, a patient's central venous pressure were monitored.
The applicant's invention tends to provide a more accurate
indication of venous flow rate since a patient's blood pressure may
vary with changes in blood volume in the patient's circulatory
system and with other parameters.
Revitalization or oxygenation means 28 is provided for continuous
revitalization of the blood including the oxygen transfer to oxygen
deficient blood and the warming of blood which has been partially
cooled since removal from the patient. The oxygenation means 28
generally comprises an oxygenation pump 30 driven by a pump motor
32 coupled thereto. The oxygenation pump 30 is coupled to a
membrane oxygenator and heat exchanger 34 in series fashion, with
the oxygenation pump 30 forcing blood through the membrane
oxygenator and heat exchanger 34. The pump motor 32 for the
oxygenation pump 30 may be a roller blood pump in which blood is
carried between a membrane and a surface defining a cylindrical
chamber by rollers rotating and bearing on the membrane and against
the surface.
A second collapsible bag 36 comparable to the first bag 18 is air
evacuable and is preferably translucent or transparent. Flow
through the oxygenation means 28 is transported to the collapsible
bag 36 via a conduit 37 to provide generally a continuous supply of
freshly revitalized (i.e., oxygenated and warmed) blood to the
second collapsible bag 36. The second collapsible bag 36 also helps
to dampen or buffer uneven or pulsating flows of blood returned to
the patient by way of a main pump 38. For positive circulation
under all conditions, the main pump 38 is constantly driven at a
slightly slower rate than the oxygenation pump 30 so that the main
pump 38 does not operate without a blood flow supply.
Although two collapsible bags 18, 36 are described, it should be
noted that a single partitioned bag may be used in accordance with
this invention. The collapsible nature of the bags, besides
limiting blood-gas interfaces, helps prevent a massive air
embolism. Should blood in either bag 18 or 36, for some reason, be
emptied and collapse occur, air which could enter through leaks in
the cardiopulmonary bypass system 10 are prevented from being
pumped into the patient's circulatory system.
A recirculation path is defined by a tube 39 coupling blood from
the second bag 36 to the first bag 18, providing pressure relief to
equalize pressure between the two bags 18, 36. Excess pressure
would tend to be present in the second collapsible bag 36 in the
absence of the recirculation path, because of the faster pump rate
of the oxygenation pump 30 with respect to the main pump 38.
The main pump 38 is preferably a roller blood pump coupled to the
second collapsible bag 36 for returning the oxygenated and warmed
blood to the patient's circulatory system. The main pump 38
maintains a blood flow rate invariant with respect to a varying
impedance or load of the human circulatory system as experienced by
the pump 38, despite the fact that the impedance or load provided
by the patient's circulatory system varies with the patient's
physical state. For example, a constricion in the patient's
circulatory system causes an increased impedance, yet blood is
returned to the patient at a rate independent of that physical
state.
A variable speed main pump motor 40 coupled to the main pump 38
drive the pump 38 at a desired controllable blood flow rate in
response to a signal fed from controller means or a rate setting
control 42. The rate setting control 42 may simply be an amplifier
circuit providing an error signal tending to drive the variable
speed pump motors at a rate equal to the venous blood flow. A
preferred embodiment given by way of example provides a rate
setting control 42 comprising an amplifier circuit 44, a servo
motor 46, a speed reducer 48 coupled to the servo motor, a variable
impedance or a potentiometer 50 mechanically coupled to the speed
reducer 48 and a control knob 52 on the potentiometer shaft. Rate
setting control 42 is responsive to a signal from the transducer 16
to provide the variable speed pump motor 40 with a signal from the
potentiometer 50, which adjusts the signal from a voltage source 51
to drive the main pump 38 at a flow rate corresponding to the blood
volume in the collapsible bag 18. The blood volume in the
collapsible bag 18 is maintained at a predetermined level such that
the return blood flow rate is held substantially equal to the
venous blood flow. The control knob 52 coupled to the potentiometer
50 can be used to manually override the rate setting control 42 to
exercise supervisory control of the flow rate of the main pump
38.
The amplifier circuit 44 amplifies a bipolar null referenced signal
from the transducer 16 to provide a signal sufficient to drive the
servo motor 46. This signal is bipolar in that it may represent
deviations from a null in either of two directions corresponding to
either an increase in pressure exerted on the transducer 16 by the
confined gas volume 22 or a decrease in pressure exerted by the
confined gas volume 22. In setting up the system the pressure
within the confined gas volume 22 may be equalized at ambient by a
closeable output (not shown) in the cylinder 23, the outlet being
shut when a desired blood level is reached in the standpipe 14. The
servo motor 46 rotates in accordance with the polarity of the
transducer signal tending to rotate the potentiometer 50 in
accordance with the blood volume in the collapsible bag 18, as
sensed by the transducer 16.
The speed reducer 48 may be a gear reduction system coupled between
the servo motor 46 and the potentiometer 50, reducing the angular
rotation of the potentiometer 50 with respect to the angular
rotation of the servo motor 46 thereby providing an adjustable gain
in the system. Gain is adjusted to allow time for changes in the
pump rate of the main pump 38 to influence blood volume changes
sensed by the transducer and further rotation of the servo motor
without excessive overtravel of the potentiometer 50.
The setting of the potentiometer 50 determines the speed of the
variable speed pump motor 40 which in turn determines the flow rate
of the main pump 38. An adjustable resistance 54 in the motor 40
energizing circuit permits further adjustment to maintain a pump
rate through the oxygenation pump 30 in excess of that through the
main pump 38, such that a flow is recirculated back from the second
collapsible bag 36 to the first bag 18 and the main pump 38 does
not operate without a blood supply.
Dial indicia 53 juxtaposed adjacent the control knob 52 indicates
the instantaneous rate at which the main pump 38 is being driven.
The knob 52 may be manually rotated by overcoming the torque
supplied by the servo motor 46 through the speed reducer 48. A slip
clutch or a friction coupling between the speed reducer 48 and the
potentiometer 50 is suitable for a motor 46 of greater torque, but
this arrangement would not comparably restore the knob 52 to the
proper setting when released.
An outlet tube 56 whose exterior surface is hermetically joined to
the bag 36 can be closed by a clamp 57 to permit exhaustion of
interior air in the same fashion as the first bag 18.
A reservoir 58 is provided for receiving and storing an excess
quantity of blood from the cardiopulmonary bypass system 10 and for
increasing the volume of the blood in the cardiopulmonary bypass
system 10 by releasing such blood to the second bag 36 through a
valve 59. A valve 60 in the conduit from the main pump 38 may be
used to tap off blood from the cardiopulmonary bypass system 10.
The valves 59, 60 are used to add blood to the reservoir 58 and to
release blood to the cardiopulmonary bypass system 10 may be
manually actuable or may be of a type actuable by an electrical
signal. For example, a perfusion flow servo system is described in
the Turina et al. article in the March 1973 issue of Biomedical
Enginerring, previously cited. A cardiotomy tube (not shown) may
also be coupled into the reservoir 58 to provide a blood source to
the reservoir 58. The cardiotomy line is used to remove blood which
collects adjacent severed veins and arteries resulting from
incisions during an operation. The blood, having been suctioned off
from the patient, is in a frothy condition and a debubbler (not
shown) is typically used to reduce the frothy condition of the
blood before it enters the reservoir 58.
To review the operation of the cardiopulmonary bypass system 10,
the first collapsible bag 18 is generally disposed at a level
beneath that of the patient so as to promote a gravity blood feed.
Initially, blood is added to the first collapsible bag 18 with the
bag clamps 21, 57 released. Ambient air pressure is established in
the interior volume 22 and the transducer 16 by opening a valve
(not shown) or disconnecting the standpipe 14 from the cylinder 23.
Blood is added until the blood level in the standpipe 14 reaches a
reference of priming level 62, after which the standpipe 22 is then
reconnected to the sterility barrier 24 and the transducer 16. Thus
the pressure in the confined volume 22 is initially equalized with
respect to ambient.
Air that is present in the first and second collapsible bags 18, 36
is forced out, either manually or by filling the bags 18, 36, and
the outlets 19, 56 are then closed by the clamps 21, 57. The blood
air interfaces within the bags 18, 36 are thus minimized.
Venous blood flows under gravity into the first collapsible bag 18,
whose volume then varies in accordance with the rate of blood flow
therethrough. This volume establishes the blood level in the
standpipe 14, and as previously described fractional changes in the
blood volume within the bag 18 cause much larger variations in the
pressure exerted on the transducer 16. Though the transducer 16
signal is generally referenced to ambient pressure, an inverted
U-tube arrangement (not shown) may be used to provide a negative
pressure head so that the transducer may be arbitrarily oriented
where the level of the collector means 12 varies from the position
depicted in the embodiment of FIG. 1 and is, for example, disposed
closer to the level of the patient.
The transducer 16 signal is applied to the amplifier circuit 44,
providing an energizing signal to the servo motor 46, which rotates
at a rate determined by signal amplitude and in a direction
determined by polarity. Through the speed reducer 48, motor
rotation turns the potentiometer 50 in a corresponding direction at
a slower speed, also rotating the control knob 52 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 potentiometer 50
setting, the blood level is returned toward the null position 62,
slowing down or reversing the servo motor 46. Note that the pump
motor 40 can continue to operate at or near a substantially
constant speed and that the system is stabilized by gain adjustment
at the speed reducer 48 although other means might also be
used.
Blood from the first collapsible bag 18 is pumped through the
revitalization or oxygenation means 28, by the oxygenation pump 30,
which provides sufficient pressure to drive the blood through the
membrane oxygenator and heat exchanger 34 and to the second
collapsible bag 36. Because the oxygenation pump motor 32 speed is
also determined by the potentiometer 50 setting, the oxygenation
pump 30 pumps blood at a flow rate in excess of the flow rate of
the main pump 38 as determined by the setting of the adjustable
resistor 54. Excess pressure developed by the oxygenation pump 30
within the second collapsible bag 36 is relieved via the tube 39
which serves as a recirculation path. Blood from the second
collapsible bag 36 is then pumped by the main pump 38 to the
patient's circulatory system.
It is important to alert a physician to the existence of a low
blood volume condition in a patient. This condition may represent
internal hemorrhaging and may require that an additional quantity
of blood be introduced into the total system. A physician or
assistant, alerted to such a condition may now increase the
circulating blood volume by opening the reservoir valve 59, thereby
allowing blood to flow into the second collapsible bag 36. Also, or
alternatively, the physician may manually override the knob 52,
thereby increasing the flow rate of the main pump 38 to the human
circulatory system. It should be recognized that such an increase
in the return flow rate without replenishment can only be carried
on for a limited period of time without collapse of the bags 18 and
36.
Thus, a simple, accurate and sensitive cardiopulmonary bypass
system for receiving a variable rate gravity fed venous flow from a
human circulatory system, revitalizing the blood and returning it
to the circulatory system at a rate substantially equal to the
venous flow rate has been described which is volume alterable and
provides means for reducing degrading blood gas interfaces.
While the invention has been particularly shown and described and
with reference to a preferred embodiment thereof, it will be
understood by those skilled in the art that various changes in form
and details may be made therein without departing from the spirit
and scope of the invention.
* * * * *