U.S. patent number 3,881,483 [Application Number 05/396,603] was granted by the patent office on 1975-05-06 for extracorporeal blood circuit.
This patent grant is currently assigned to Rhone-Poulenc, S.A.. Invention is credited to Andre Sausse.
United States Patent |
3,881,483 |
Sausse |
May 6, 1975 |
Extracorporeal blood circuit
Abstract
An extracorporeal blood circuit in which a blood oxygenator is
placed in series between a first and second pump, the pumps being
of the peristaltic or ventricular type, the inlet to the first pump
being connected to patient's vein and the outlet of a second pump
to a patient's artery. The useful internal volume of the body of
the first and second pumps varies substantially proportional to the
pressure of the blood at the inlet, between minimum and maximum
values, the maximum useful volume of the first pump and the minimum
useful volume of the second pump being reached at a pressure of the
blood at the inlet of the respective pump within a range of
atmospheric pressure .+-. 20 mm mercury.
Inventors: |
Sausse; Andre (Sceaux,
FR) |
Assignee: |
Rhone-Poulenc, S.A. (Paris,
FR)
|
Family
ID: |
9104158 |
Appl.
No.: |
05/396,603 |
Filed: |
September 12, 1973 |
Foreign Application Priority Data
|
|
|
|
|
Sep 12, 1972 [FR] |
|
|
72.32286 |
|
Current U.S.
Class: |
604/6.14;
210/110; 210/137; 422/45; 604/118; 210/111; 417/244; 604/114 |
Current CPC
Class: |
A61M
1/3621 (20130101); A61M 1/1698 (20130101) |
Current International
Class: |
A61M
1/36 (20060101); A61M 1/16 (20060101); A61m
001/03 () |
Field of
Search: |
;128/214R,214B,214.2,DIG.3 ;23/258.5 ;210/321,416 ;417/244 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Truluck; Dalton L.
Attorney, Agent or Firm: Stevens, Davis, Miller &
Mosher
Claims
We claim:
1. An extracorporeal blood circuit comprising, in combination:
a. a blood oxygenator;
b. a first peristaltic pump including a variable tube means of a
type having a capacity variable between maximum and minimum values
in proportion to the pump inlet pressure, the maximum capacity
being reached at an inlet pressure of atmospheric pressure .+-. 20
mm of mercury;
c. an inlet of said first pump connectable to a patient's blood
circuit;
d. an outlet of said pump connected in series with said
oxygenator;
e. a second peristaltic pump including a variable tube means of a
type having a capacity variable between maximum and minimum values
in proportion to the pump inlet pressure, the minimum capacity
being reached at an inlet pressure of atmospheric pressure .+-. 20
mm of mercury;
f. an inlet of said second pump connected in series with said blood
oxygenator; and
g. an outlet of said second pump connectable to said patient's
blood circuit.
2. A blood circuit as claimed in claim 1, and further comprising
means for driving said first and second pumps synchronously.
3. A blood circuit as claimed in claim 1, wherein the capacity of
said first pump reaches a maximum value for a liquid pressure at
its inlet which is less than atmospheric pressure.
4. A blood circuit as claimed in claim 1, wherein the capacity of
said second pump reaches a minimum value for a liquid pressure at
its inlet which is greater than atmospheric pressure.
5. A blood circuit as claimed in claim 1, wherein the useful
maximum flow rate capacity of said second pump is greater than the
useful maximum flow rate capacity of said first pump.
6. A blood circuit as claimed in claim 1, wherein the useful
minimum flow rate capacity of said second pump is less than the
useful minimum flow rate capacity of said first pump.
7. A blood circuit as claimed in claim 1, wherein the two pumps
further comprising an adjustable speed single motor, a common shaft
driven by said motor and identical rotors of said peristaltic pumps
mounted on said common shaft.
8. A blood circuit as claimed in claim 1, wherein, in the
oxygenator, the blood is separated from the oxygenating gas stream
by at least one microporous membrane.
9. A blood circuit as claimed in claim 8, in which the microporous
membrane is water-repellent.
10. A blood circuit as claimed in claim 1, wherein the internal
wall in contact with the blood of at least one component of the
circuit carries a smooth organosilicon coating.
11. A blood circuit as claimed in claim 1, and further comprising
at least one cannula connected to the inlet of the first pump for
removing the venous blood and a non-occlusive enlargement near its
end.
12. A blood circuit as claimed in claim 1, and further comprising a
flared-out prosthesis, connected to the outlet of the second pump,
and wherein said prosthesis can be stitched to a patient's
artery.
13. A blood circuit as claimed in claim 1, and further comprising
means for reheating the blood and means for sensing the temperature
of the blood located at the level of and downstream from the said
means for reheating the blood.
14. A blood circuit as claimed in claim 1, and further comprising
an auxiliary pump and at least one other source of blood or
medicinal liquid connected to the inlet of said first pump by said
auxiliary pump.
15. A blood circuit as claimed in claim 1, and further comprising a
manometer upstream from said first pump.
16. A blood circuit as claimed in claim 15, wherein said manometer
is of the type which measures the pressure across the wall of a
flexible tube.
17. A blood circuit as claimed in claim 1, and further comprising a
plurality of blood oxygenators connected in parallel and a further
one of said first and second pumps connected in series on either
side of each blood oxygenator.
18. An extracorporeal blood circuit comprising, in combination:
a. a blood oxygenator;
b. a first tubular variable membrane and valve pump of a type
having a capacity variable between maximum and minimum values in
proportion to the inlet pressure of the pump, the maximum capacity
being reached at an inlet pressure of atmospheric pressure .+-. 20
mm of mercury;
c. an inlet of said first pump connectable to a patient's blood
circuit;
d. an outlet of said pump connected in series with said
oxygenator;
e. a second tubular variable membrane and valve pump of a type
having a capacity variable between maximum and minimum values in
proportion to the inlet pressure, the minimum capacity being
reached at an inlet pressure of atmospheric pressure .+-. 20 mm of
mercury;
f. an inlet of said second pump connected in series with said blood
oxygenator; and
g. an outlet of said second pump connectable to a patient's blood
circuit.
19. An extracorporeal blood circuit comprising; in combination:
a. a blood oxygenator;
b. a first peristaltic pump of a type having a capacity which is
variable in proportion to the pump inlet pressure and having a tube
of circular cross-section at rest;
c. an inlet of said first pump connectable to a patient's blood
circuit;
d. an outlet of said pump connected in series with said
oxygenator;
e. a second peristaltic pump of a type having a capacity which is
variable in proportion to the pump inlet pressure and having a tube
of substantially ellipitical cross-section at rest, the internal
perimeter of the tube of the second pump being greater than that of
the tube of the first pump, so that the maximum capacity of the
first pump and the minimum capacity of the second pump is reached
at a pump inlet pressure of atmospheric pressure .+-. 20 mm of
mercury;
f. an inlet of said second pump connected in series with said blood
oxygenator; and
g. an outlet of said second pump connectable to said patient's
blood circuit.
20. An extracorporeal blood circuit comprising, in combination:
a. a blood oxygenator;
b. a first tubular membrane and valve pump of a type having a
capacity which is variable in proportion to the pump inlet pressure
and having a tubular membrane of circular cross-section at
rest;
c. an inlet of said first pump connectable to a patient's blood
circuit;
d. an outlet of said pump connected in series with said
oxygenator;
e. a second tubular membrane and valve pump of a type having a
capacity which is variable in proportion to the pump inlet pressure
and the tubular membrane having a substantially elliptical
cross-section at rest, the internal perimeter of the tube of the
membrane of the second pump being greater than that of the tubular
membrane of the first pump, so that the maximum capacity of the
first pump and the minimum capacity of the second pump is reached
at a pump inlet pressure of atmospheric pressure .+-. 20 mm of
mercury;
f. an inlet of said second pump connected in series with said blood
oxygenator; and
g. an outlet of said second pump connectable to said patient's
blood circuit.
Description
The present invention relates to an extracorporeal blood circuit
connecting a membrane-containing blood oxygenating device to the
vascular system of a patient, for assisting or replacing the
pulmonary, cardiac or cardiopulmonary system.
Extracorporeal blood circuits are known which utilise two
circulating pumps located in series on either side of a
membrane-containing blood oxygenator. However, either a pipeline
for partially recycling arterial blood through the oxygenator or
complex control systems are required in order to maintain a
definite pressure in the oxygenator, necessary for keeping the
blood in the form of thin films of constant thickness.
According to the present invention there is provided an
extracorporeal blood circuit comprising, a blood oxygenator; a
first peristaltic pump or tubular membrane and valve pump, having
an inlet connectable to a patient's blood circuit and an outlet
connected in series with the oxygenator and a second peristaltic
pump or tubular membrane and valve pump, having an inlet connected
in series with the blood oxygenator and an outlet connectable to
said patient's blood circuit, the useful internal volume of the
body of the first and second pumps, varying substantially
proportionally to the pressure of the blood at the inlet, between
minimum and maximum values, the maximum useful volume for the first
pump and the minimum useful volume of the second pump being reached
at a pressure of the blood at the inlet of the respective pump
within the range of atmospheric pressure .+-. 20 mm of mercury.
In order that the present invention will be better understood the
following description is given, merely by way of example, reference
being made to the accompanying drawings, in which:
FIG. 1 is a schematic view of one embodiment of an extracorporeal
blood circuit according to the invention;
FIG. 2 shows the characteristic flow rate-pressure curve of a
peristaltic pump which can be used in the circuit according to the
invention; and
FIG. 3 shows the combination of the characteristic flow
rate/pressure curves of two pumps located on either side of the
blood oxygenator.
In the present text, the expression blood oxygenator, which has
become accepted through use, denotes an exchanger of respiratory
gas, that is to say not only an oxygen exchanger, but also an
exchanger of carbon dioxide, water vapour and nitrogen and
optionally of gases or vapours with medicinal and/or anaesthetic
effects, and also possibly a heat exchanger.
Referring to FIG. 1, it is seen that the extracorporeal blood
circuit connects a blood oxygenator 1 of a type which is in itself
known, comprising at least one membrane 2, to the venous-arterial
system of a patient.
More precisely, a cannula 3 is introduced, for example, into the
inferior vena cava. A cannula which contains a non-occlusive
enlargement near its end is preferably used. This enlargement can
consist of three radial resilient branches 5 which press against
the venous walls and keep them spaced apart locally, which clears
the orifice of the cannula. Such a cannula prevents obstruction of
the vein and the restrictions in flow rate which result therefrom.
The branches can advantageously become smaller in order to pass
through a collateral of smaller size 4 (for example, the femoral
vein) sectioned for this purpose.
The cannula 3 is connected to the inlet of the blood oxygenator 1
via a flexible tube 7, for example made of silicone elastomer, on
which a first pump 6, of the peristaltic type or of the type with a
tubular membrane and valves (also called "a ventricular pump"), is
placed.
A flexible tube 11, also made of silicone elastomer, connects the
outlet of the blood oxygenator 1 to a cannula introduced into an
artery 9, or preferably to a flared-out prosthesis 8 sutured to the
artery, generally a femoral artery. A second pump 10, also of the
peristaltic type or of the type with a tubular membrane and valves,
is located on this tube 11.
Advantageously, the artery is slit longitudinally and the
prosthesis 8 is sutured obliquely onto the lips of the slit, so
that it slopes in the direction of preferential flow. The two sides
of the prosthesis move apart under the effect of the arterial
pressure. After the prosthesis has been removed, the artery is made
whole again in accordance with the usual practical procedure.
An auxiliary peristaltic pump 13, connected to the intake tube 7 of
the pump 6, makes it possible to drain the peripheral end of the
vein 4 and to introduce additional amounts of blood into the
extracorporeal circuit from a blood source such as the bottle 16 in
order to compensate for possible blood losses and optionally to
introduce medicinal liquids such as heparin.
Since the extracorporeal blood circuit represented by way of
example is of the venous-arterial type, it is necessary to control
three different pressures, namely the blood pressure at the inlet
of the pump 6, the pressure in the oxygenator and the arterial
pressure of the patient, in order to keep them at the desired
values.
A manometer 17 is placed on the tube 7, immediately upstream of the
inlet of the pump 6. Advantageously, this manometer measures the
blood pressure through the walls of the flexible tube 7, which
reduces the risks of blood coagulation. As the manometer, it is
possible to use, for example, that described in French Pat. No.
71/43,881. As will be seen from the text which follows, a knowledge
of the blood pressure at the inlet of the pump 6 makes it possible
to know its flow rate.
A manometer 14 makes it possible to check the blood pressure in the
oxygenator. Moreover, a device 21 for taking the arterial pressure
of the patient makes it possible to keep the latter at the desired
level, by acting, when necessary, either on the volume of blood by
means of the bottle 16 and the pump 13, or on the vascular
resistance of the patient.
The blood must be injected into the patient at a temperature of
approximately 37.degree.C. For this purpose, means for reheating
and checking the temperature of the blood are provided, for
example, on the tube 11. The reheating means advantageously consist
of a heating element comprising an electrical resistance 18
surrounding the tube 11 or preferably embedded in its wall. This
heating element is, for example, of the type described in French
Pat. No. 71/46,408.
Temperature probes of types which are in themselves known 19 and
20, which are placed respectively downstream from, and at the level
of, the heating element 18, are generally used. The probe 19 makes
it possible to check (and if necessary to control) the reheating of
the blood. The probe 20 makes it possible to avoid overheating the
blood locally, which could arise if the blood flow rate were
decreased or stopped momentarily.
Advantageously, the internal walls, which are in contact with the
blood, of the various components forming the circuit (especially
pump bodies, cannulas and connecting tubes) carry a smooth
organosilicon coating applied in accordance with the process
described in German patent application (DOS) No. 2,206,608.
In operation, the venous blood flows from the inferior vena cava,
where it is at a pressure close to atmospheric pressure, via a
cannula 3 and the tube 7 to the first peristaltic pump 6. The
latter carries the blood along into the membrane-containing
oxygenator 1 at a sufficient pressure to overcome the pressure
drops of the apparatus. The compartments of the oxygenator reserved
for the blood are kept full and the blood film of substantially
constant thickness, the blood pressure being kept within a
predetermined range indicated by the manometer 14. The oxygenated
blood is recovered at the outlet of the oxygenator by a second
peristaltic pump 10 which brings it to a pressure enabling it to be
injected into the arterial system of the patient through the
prosthesis 8, after suitable reheating in the tube 11.
The average blood flow rate, common to both pumps, is provided by
the veins of the patient. It must be possible for this flow rate to
vary in such a way as to prevent any increase in the venous
pressure which could cause disturbances for the patient (and
especially acute oedema of the lung); in order to prevent this, it
is then convenient to increase the flow rate of the pumps 6 and 10,
and in the opposite case, to decrease it if the venous pressure
became too low, which could lead to the collapse of the veins or
venous cavities.
For this purpose, pumps are used, the body of which provides an
internal volume which varies according to the blood pressure at the
inlet, which is not generally the case with pumps of the
peristaltic type or of the type with a tubular membrane and valves.
According to the invention, pumps are used which provide, within
the range of blood pressure at the inlet effectively used, a useful
internal volume which is substantially proportional to the blood
pressure at the inlet of the pump. Pumps such as those described in
British Pat. No. 1,287,836 are preferably employed as peristaltic
pumps.
The two peristaltic pumps 6 and 10, connected in series, are
generally driven synchronously, at one and the same rate or at
different rates, in order to provide the same average flow rate.
Preferably, they revolve at rates which are always equal to one
another, and to achieve this, they are advantageously mounted on
the same drive shaft. These rates can be adjustable, but it is
often of value to keep the rate constant.
The peristaltic pumps can also be driven at the same rates, each by
a separate motor but one which possesses the same rate/voltage
characteristics, each motor being supplied by a (fixed or
adjustable) common voltage source.
It is also possible to use pumps with a tubular membrane and
valves, containing an inlet valve which is either automatic or
preferably controlled. The controlled discharge valve can be of the
same type as the inlet valve. These pumps can be connected either
to separate pulse generators, synchronised on one and the same
frequency, or preferably to a common pulse generator.
The peristaltic pumps represented in FIG. 1 advantageously consist
of a flexible peristaltic tube made of silicone elastomer stretched
between two fixed points and revolving wheels. The peristaltic
tube, between the wheels, generally has an elliptical cross-section
which is flattened to a greater or lesser extent depending on the
pressure at the inlet of the pump. For a constant speed, the flow
rate is a function of the pressure at the inlet of the pump, which
can be seen clearly on the characteristic flow rate/intake pressure
curve of such a pump, represented in FIG. 2.
It is seen that, for a functioning pressure p.sub.A between two
limiting values p.sub.m and p.sub.M, at the inlet of the pump, the
pump provides a flow rate Q.sub.A between two limiting values
Q.sub.m and Q.sub.M ; the flow rate Q.sub.A being, within this
range, substantially proportional to the pressure p.sub.A at the
inlet.
In the remainder of the description, the useful minimum pressure
and the useful maximum pressure at the inlet of the pump will be
denoted respectively by p.sub.m and p.sub.M. Likewise, Q.sub.m and
Q.sub.M will be respectively the corresponding useful minimum and
useful maximum flow rates.
The useful minimum flow rate Q.sub.m is obtained when the pressure
at the inlet is sufficiently low for the tube to collapse and for
its opposite walls to press against one another; the cross-section
of the tube assumes a dumb-bell shape. Beyond, the cross-section of
the tube becomes more flattened out, but under the effect of much
lower intake pressures at the entrance of the pump, which
corresponds to a rapid change in the slope of the curve.
The useful maximum flow rate Q.sub.M is obtained when the pressure
at the inlet of the pump is sufficiently high for the tube to
assume a circular cross-section. Beyond, the tube can only expand,
which requires considerably higher pressures and also corresponds
to a rapid change in the slope of the curve.
In the extracorporeal blood circuit represented in FIG. 1, the flow
rate of the pump 6 varies for a given level according to the venous
pressure. Since the venous pressure at the level of the cannula 3
is close to atmospheric pressure, and since the pressure of the
blood at the inlet of the pump 6 differs therefrom by the pressure
drops in the intermediate tube 5, partially compensated for by the
difference in level between the cannula 3 and the pump 6, it is
generally less than atmospheric pressure. Thus a pump 6 is chosen,
the characteristic flow rate/pressure curve of which extends over a
region of pressures which are preferably less than atmospheric
pressure. The characteristic curve of the pump 6 is shown in FIG.
3. The useful region of the curve is between the points B.sub.m and
B.sub.M, and the corresponding extreme useful pressures p.sub.m6
and p.sub.M6 are, for example, in this case, both less than
atmospheric pressure (point 0, of abscissa zero). The pressure
p.sub.M6, like the maximum flow rate, is proportional to the speed
at which the pump 6 rotates.
It is advantageous for the useful maximum pressure p.sub.M6 to be
slightly less than atmospheric pressure, and generally less than 20
mm of mercury and preferably less than 10 mm of mercury below
atmospheric pressure. This condition is achieved with a pump, the
thin-walled peristaltic tube of which has, at rest, a circular
cross-section (between the wheels, if what is involved is a
rotating pump with wheels, as represented in FIG. 1); this useful
cross-section is the maximum and permits a useful maximum flow rate
Q.sub.M6. For a blood pressure p.sub.6 at the inlet of the pump 6,
between p.sub.m6 and p.sub.M6 and less than atmospheric pressure,
the peristaltic tube has a elliptical cross-section, with a surface
area less than that of the circular cross-section of the same
perimeter, corresponding to a flow rate Q.sub.6. When the pressure
p.sub.6 becomes equal to the useful minimum pressure p.sub.m6, the
peristaltic tube becomes more flattened and its cross-section
becomes practically zero; the flow rate falls to the useful minimum
flow rate Q.sub.m6.
Since the pump 10 is mounted in series with the pump 6, it provides
strictly the same average flow rate. The flow rate of the pump 10
is thus laid down by that of the pump 6, which itself depends on
the venous pressure.
The pumps 6 and 10 are generally located substantially at the same
level as the oxygenator. The combination consisting of the pumps 6
and 10 and the oxygenator is generally placed below the patient, at
an adjustable level, in order partially to compensate for pressure
drops upstream from the pump 6 and thus to adjust the blood flow
rate to the desired average value.
It is necessary to keep the pressure of the blood in the oxygenator
within a predetermined range of pressures in order to enable the
blood film to retain substantially constant thicknesses in contact
with the membranes and a controlled pressure gradient across the
thickness of the membrane.
Thus for a blood oxygenator consisting of an alternate stack of
membranes and spacers, it can be decided to keep the relative
pressure of the blood in this oxygenator, measured by means of the
manometer 14 within a predetermined range, for example, between 0
and 200 mm of mercury.
In fact, if the pressure of oxygen in this oxygenator is kept below
atmospheric pressure, the pressure difference between the blood and
the oxygen always remains positive, and this makes it possible to
use microporous membranes with a high gas flow rate which also
enable bubbles to be removed satisfactorily from the blood, even in
the case of foam or small bubbles; it forms a safety
bubble-remover. The membranes described in French Pat. No.
1,568,130 are very particularly suitable for this purpose.
Moreover, by maintaining this positive pressure difference, it is
possible to prevent the membranes from sticking to one another by
accident, since it is difficult to reverse this sticking.
If, on the other hand, the pressure of the blood were too much
greater than that of the oxygen, the blood could rupture the
membrane or overcome the hydrophobic nature of the microporous
membranes and pass through them, for example under a pressure of
800 mm of mercury.
The pressure of the blood in the oxygenator can be kept within a
chosen range by means of a pump 10, the characteristic flow
rate/pressure curve of which extends in a region of pressures which
are essentially greater than atmospheric pressure. The
characteristic curve of a pump 10 is shown in FIG. 3. The useful
region of the curve is between the points C.sub.m and C.sub.M, and
the corresponding useful extreme pressures p.sub.m10 and p.sub.M10
are, for example, in this case, both greater than atmospheric
pressure.
It is advantageous for the useful minimum pressure p.sub.m10 to be
equal to or slightly greater than atmospheric pressure, and
generally less than 20 mm of mercury, and preferably less than 10
mm, above atmospheric pressure. This condition is achieved with a
pump, the peristaltic tube of which, at rest, has a flattened
cross-section; this cross-section is practically the minimum and
allows a minimum useful flow rate Q.sub.m10. The tube of the pump
10 is quite thin-walled to enable the useful maximum flow rate
Q.sub.M10 to be reached for a useful maximum pressure p.sub.M10,
generally less than 200 mm of mercury above atmospheric pressure
and preferably of the order of 50 mm of mercury. Thus, for any flow
rate imposed by the pump 6, the tube of the pump 10 will have a
more or less flattened cross-section, corresponding to pressures,
at the outlet of the oxygenator, of between 0 and, for example, 50
mm of mercury above atmospheric pressure. The maximum pressure at
the inlet of the oxygenator depends on the pressure drops in the
latter, which are generally less than 100 mm of mercury for blood
flow rates of the order of 600 millilitres/minute in an oxygenator
with a surface area of 0.5 m.sup.2.
In order to be certain that the average blood pressure in the
oxygenator remains within the desired range, at any instant, it is
necessary for two conditions to be realised simultaneously.
The first condition is that the useful maximum flow rate capacity
of the pump 10 placed at the outlet of the oxygenator is greater
than that of the pump 6 placed at the inlet of the oxygenator.
Since, according to the invention, the pumps 6 and 10 are generally
driven synchronously, this condition can be satisfied by selecting
from the following means:
The pump 10 can be driven at a speed which is greater, by a fixed
percentage, than that of the pump 6. If a peristaltic pump with a
rotor is used, it is possible to equip the pump 10 with a rotor of
diameter greater than that of the pump 6. Preferably, the two pumps
are equipped with identical rotors revolving at the same speed
being mounted on a common shaft and these rotors act on different
tubes, the internal perimeter of a cross-section of the tube of the
pump 10 being greater than that of a cross-section of the tube of
the pump 6. Of course, several of these arrangements can be
combined with one another.
The second condition is that the useful minimum flow rate capacity
of the pump 10 placed at the outlet of the oxygenator is less than
the useful minimum flow rate capacity of the pump 6 placed at the
inlet of the oxygenator. To achieve this, a tube for the pump 10
can be chosen with more flexible walls than those of the tube of
the pump 6. Thus the cross-section provided by the flattened tube
10 at a pressure close to atmospheric pressure forms a dumb-bell or
cross-section less than that of the tube of the pump 6 for the
useful minimum pressure upstream from the latter. A tube is chosen
for the pump 10 which is substantially flat at rest and which
requires a smaller force to achieve the limiting dumb-bell shape
than does the tube of the pump 6 which is circular at rest. It is
possible to use a tube with thinner walls for the pump 10 than for
the pump 6 and to combine thin walls and flat shape.
It is thus seen that it is possible, according to the invention,
simultaneously to satisfy the two conditions listed above.
In practice, when a stable state is reached and when the flow rate
of the extracorporeal circulation is satisfactory, it is
advantageous, in order to reduce blood traumas, to decrease the
speed of the pump 6 in order to bring its actual flow rate to
approximately four-fifths of the maximum flow rate. The readings of
the manometer 17 which indicates the actual flow rate, are used for
this purpose.
Peristaltic pumps are generally preferred during cardiac or
cardiopulmonary replacements. However, during assistances, there is
the danger of competition between the more or less pulsed flow rate
of such pumps and that originating from the heart beats of the
patient.
This is why, if it is desired to take advantage of the diastolic
pause in order to inject the blood originating from the
extracorporeal circuit and to avoid competition between the latter
and the natural heart, it is preferable to resort to pumps, the
ejection of which can be synchronised relative to the cardiac
cycle. These pumps are generally chosen from amongst membrane pumps
adapted for blood flow. They are known by the name of ventricular
pumps or pumps with a tubular membrane and valves. Pumps such as
those described in French Pat. No. 72/07,863 can advantageously be
used.
These pumps are equipped with controlled valves upstream and
downstream. The maximum volume of the arterial ventricle forming
the pump 10 is greater by 50 percent at most and preferably by 20
percent at most than the maximum volume of the venous ventricle
forming the pump 6. The generally rigid casings of these pumps are
advantageously connected, in opposite phases, to one and the same
pulse generator.
The start of systole can be induced either by an
electrocardiographic signal, or preferably by the passage of the
arterial pressure of the patient below a definite threshold. The
control of the intake and discharge pressures of either pump can be
effected by controlling the pressures of the drive gaseous fluid.
This is thus again a method of functioning comparable to that of
peristaltic pumps with a flow rate which is a function of the
upstream pressure.
As with the latter, it is even possible to achieve protection
against injections of air by placing them vertically, the blood
passing through them in a downwards direction and the air thus
being trapped at the level of the inlet valve which may not provide
a rigorous seal.
The use of two pumps with a tubular membrane and valves and a fluid
pulse generator such as that which is the subject of French Pat.
No. 72/06,812 is particularly advantageous for reviving patients in
ambulances or helicopters, because it does not require any
electrical energy and can function solely by means of the expansion
of the oxygen used for flushing the oxygenator. In this case, the
gas monitor can be dispensed with and replaced by a simple open
circuit flushing, after expansion for driving the pumps. With a 0.5
m.sup.3 bottle of oxygen, independent operation is satisfactory for
minimum weight and bulk.
A combination connected to the venous-arterial system of a patient
has been described, but the same combination can be used in
venous-venous or arterial-venous extracorporeal circulation. In the
latter case, the pump 6 can be operated so that it functions at its
maximum flow rate (it acts as a flow rate limiting device) and the
latter is adjusted by controlling the speed of rotation of the
pump.
The extracorporeal circuit can comprise several auxiliary
combinations, arranged in parallel, each consisting of a blood
oxygenator located between two pumps 6 and 10. Such auxiliary
combinations are connected by taps 22 and 23 to the main circuit
represented in FIG. 1. They can be brought into operation or
short-circuited in order rapidly to meet variable requirements of
the patient.
Since the extracorporeal blood circuit according to the invention
uses pumps which cause a very small degree of haemolysis and since
it avoids any direct recycling of the blood, it can be used
advantageously for a long period. Since the pumps are
self-regulating, it provides great simplicity, reliability and
safety, particularly with respect to injection of air, since the
pumps act as bubble traps.
If the blood oxygenating device is equipped with microporous
membranes and if a gas stream passes through it under a pressure
less than atmospheric pressure, it can reabsorb the bubbles
introduced accidentally into the blood before the inlet of the
oxygenator, and does so the better, the finer are these bubbles. In
this function, the oxygenator behaves better than the bubble traps
usually employed (operating by gravity or by Archimedes thrust),
the latter acting the better, the larger are the bubbles; thus,
under these preferential conditions, there is no need to place such
a bubble trap in the circuit.
The characteristics and the advantages of the circuit according to
the invention will become more apparent from the following
examples:
EXAMPLE 1
The circuit is the same as that represented in FIG. 1, with the
exception of the means for driving the pumps 6 and 10. The pumps
are in effect driven at speeds which can be adjusted between 0 and
40 revolutions/minute by direct current motors supplied by a common
voltage source. The pumps 6 and 10 are of the type described in
British Pat. No. 1,287,836 the peristaltic tubes being made of
silicone elastomer. The tube of the pump 6 has an internal diameter
of 10 mm and an external diameter of 12.6 mm; the periphery of the
three-wheel rotor describes a circle of diameter 140 mm. The tube
of the pump 10 has an internal diameter of 11.25 mm and an external
diameter of 14.1 mm; the periphery of the rotor describes a circle
of diameter 140 mm. The pump 10 is placed at a height of 50 cm
above the blood oxygenator. The latter consists of two identical
combinations each comprising 16 microporous membranes and seven
spacers stacked and clamped between two end plates; it is of the
type described in French Pat. No. 1,597,874. Its surface area of
exchange is 1 m.sup.2. At constant load, it opposes the blood with
a pressure drop of 50 mm of mercury.
This circuit was used for cardiopulmonary assistance for a period
of 12 hours. At the end of the treatment, it was found that the
degree of haemolysis of the blood was less than 0.5 percent. The
blood pressure inside the blood oxygenator was kept within the
range 50-150 mm of mercury. For an average blood flow rate of 800
millilitres/minute, 40 millilitres/minute of oxygen and 60
millilitres/minute of carbon dioxide were transferred.
EXAMPLE 2
The circuit and the pumps 6 and 10 are similar to those of Example
1 and are the same as in FIG. 1. The rotors of the pumps 6 and 10
are mounted on a common shaft driven by a single motor 12 at a
speed which can be adjusted between 0 and 40 revolutions/minute.
Each rotor comprises three wheels at 120.degree., and the two
rotors are 60.degree. apart from one another.
The tube of the pump 6 has a circular cross-section at rest. The
internal diameter of the tube is 15.8 mm and the external diameter
is 20 mm. The tube of the pump 10 is elliptical at rest. The
internal long axis and short axis of the ellipse are respectively
24 and 4 mm. When deformed under pressure, this tube assumes a
circular cross-section of internal diameter 16.8 mm and of external
diameter 20 mm. The useful diameter of the rotors of the pumps 6
and 10 is 190 mm. The oxygenator has a membrane surface area of 3
m.sup.2.
This combination is used for subtotal cardiopulmonary replacement
on an adult patient for a period of 52 hours. The blood flow rate
is adjusted to an average value of 2 litres/minute and average
transfers of 130 millilitres/minute of oxygen and 150
millilitres/minute of carbon dioxide are observed. The pressure and
haemolysis conditions are the same as in Example 1. A second
identical combination is ready for use if the transfers prove to be
momentarily insufficient.
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