Pressure modulator for an artificial blood circuit

Abstract

A pressure modulator for an artificial blood circuit, including at least one readily deformable wall forming a blood chamber having inlet and outlet ducts and a pair of substantially rigid plates arranged one on either side of said blood chamber, pulsation chambers disposed on the sides of said rigid plates remote from the blood chamber and a fluid pulse generator connected to the pulsation chambers, the rigid plates forming part of a rigid plate exchanger such as a haemodialyser, an artificial lung or a heat exchanger, the pulses inducing slight flexing of the plates and thus pulsing of the liquid in the blood chamber.

Description

The subject of the present invention is a pressure modulator for an artificial blood circuit.

By artificial blood circuit there is meant a blood circuit outside the body, the two ends of which are connected to a patient, or a circuit of blood or natural or artificial serum feeding a chamber for the culture or preservation of living cells.

It has already been proposed to convey the blood by means of diaphragm pumps comprising on the one hand a blood chamber interposed in the blood circuit and possessing a deformable wall and, on the other hand, a pulsation chamber controlling the deformable wall and connected to a pulse generator (see for example U.S. Pat. No. 3,513,836).

It is also known to make the blood pass into a plate exchanger, especially an artificial kidney, by means of a blood pump, usually of the peristaltic type (see for example U.S. Pat. No. 3,631,986).

According to the present invention we provide a pressure modulator for an artificial blood circuit, such modulator comprising at least one readily deformable wall forming a blood chamber, having an inlet duct and an outlet duct, a pair of substantially rigid plates arranged one on either side of said blood chamber, and forming part of a rigid plate exchanger, at least one pulsation chamber disposed on the side of at least one of said plates remote from said blood chamber; and fluid pulse producing means connected to said pulsation chamber or chambers, to cause slight flexing of the plates and thereby pulsing of liquid in the blood chamber.

The modulator according to the invention allows pulsations of any nature to be imposed on this circuit, and in particular to reproduce in it, with great accuracy, the wave of natural pulsation.

In the text which follows, the description will be simplified by referring only to the haemodialyser.

The plates of the haemodialysers are usually constructed from substantially rigid materials such as polystyrene, and the pressure of the blood between the plates tends to separate them by a very small, but not negligible, amount. This separation is variable and is the greater the more the point considered is separated from the zone of action of the mechanical clamping frame, and so an unequal distribution of the blood flow in the dialyser is introduced.

The construction of the present invention applies pressure pulses on the exterior of the plate so that the plates transmit the variations in pressure produced by the pulse producing means to the blood.

It thus becomes possible to recreate pulsations in a dialyser and downstream from the latter, even if it is fed by a pump with a substantially constant pressure at the outlet.

In the absence of a pump, the slight variations of separation of the plates of the dialyser can be used profitably to assist the displacement of the blood. It is then sufficient to equip the dialyser with suction and delivery valves.

The pulsation chamber may be provided with a rigid external wall or may be a flexible pouch and can be inflated by liquid (for example, water), especially if the dialyser is used in an inclined position. It can be inflated by gas (for example, air or CO.sub.2) and this simplifies the connection to a gas pressure pulse generator.

The pulse generator can be of any known type. It can be a piston which compresses the gas in a hermetic chamber connected to the pulsation chamber or chambers, according to the modulations imposed by a cam. It can be an assembly of electromagnetic valves (compressed gas, purging) combined with contact pressure gages by a programmer or by a cardiac rhythm detector. These examples are obviously given without implying any limitation.

The modulation by means of the plates imposes only compression stresses on the readily deformable walls, which may be dialysis membranes, at the level of the shoulder zones of adjacent plates; the displacement of the plates are slight and reproducible; finally, these displacements are perpendicular to the direction of flow of the blood and thus do not interfere with this flow.

On the other hand, a modulation by means of the dialysis liquid would impose large and unevenly distributed bending stresses on the membranes, and would have difficulty in being compatible with a counter-current operation.

In order that the invention may be more readily 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 circuit according to the invention;

FIG. 2 is an enlarged cross-section through the exchanger of the circuit of FIG. 1 during the pressure applying stage;

FIG. 3 is a view similar to FIG. 2 during the non-pressure applying stage; and

FIG. 4 is a schematic cross-section through a modified form of the exchanger.

With regard to FIG. 1 there is illustrated a pump 1 arranged to feed blood to a rigid plate exchanger 2 in the form of a dialyser or diaphragm oxygenator and thence, via an arterial inlet 12 to an organ, for example, a kidney 3. A venous outlet 13 from the kidney is connected back to the inlet of the pump 1. A pressure gauge 4 is connected in parallel across the exchanger 2 and controls the flow rate of the pump 1 to provide a predetermined mean pressure in the arterial inlet 12. The pressure gauge also allows the form of the pressure wave of the perfusion liquid to be recorded.

On either side of the exchanger 2 are arranged pulsation chambers 2a and these are connected by means of a duct 14 to a source of fluid, in particular air, under controlled pressure, for example 200 mm mercury above atmospheric pressure and to a vacuum source or atmosphere 6. The connection of these sources to the pulsation chambers is effected by means of a three way electromagnetic valve 10 which can be controlled by contact pressure gages 7 and 8; the contact pressure gage 7 senses a predetermined maximum pressure at which the valve is changed from connecting source 5 to connecting source 6 to the pulsation chambers. Contact 8 is a minimum pressure contact which switches valve 10 from connection to source 6 to connection of source 5. Variable fluid resistances 9 and 11 are provided between sources 5 and 6 respectively and valve 10.

The above described apparatus was used to perfuse blood into a pig's kidney. Pump 1 was controlled to maintain an average pressure of 100 mm of mercury in the arterial inlet. When the pulsation chambers 2a are connected to atmosphere at 6 the pressure of the blood separates the support plates 2b (FIG. 2) of the exchanger, the volume of the blood in the blood chamber 2c increases as is shown in FIG. 2. When the pressure has reached a minimum value (in this case 65 mm of mercury) the contact 8 or an electrical signal given by pressure gauge 4 reverses the direction of the valve 10 and connects the chambers 2a to the pressure source 5. The pressure introduced in the pulsation chambers causes the support plates 2b to come closer as shown in FIG. 3 and a certain volume of blood is ejected into the arterial inlet 12, the pump 1 acting as a non-return valve. When the predetermined maximum pressure, in this particular case 140 mm of mercury, is reached, the contact 7 or the signal from gauge 4 reverses the system again.

The wave form produced can be varied by throttling to a greater or lesser extent the admission and the escape of the gases through the resistances 9 and 11 or by modifying the volume of the pulsation chambers. In particular, it is possible to produce a blood pressure curve which is very close to the physiological curve at a peripheral artery, and which comprises, like the physiological curve, a systolic peak followed by a diastolic decrease.

This arrangement has allowed a living isolated kidney to be kept for 15 hours in an organ preservation circuit also equipped with an artificial lung and a thermostat. Working in the same circuit, but without pulsations, it is not possible to preserve the kidney for more than 7 hours.

FIG. 4 illustrates a modified form of exchanger used for the haemodialysis of a patient and having the same system of pneumatic movement as in FIG. 1 and which can, for example, be connected to a patient by means of an arterio-venous short circuit or a fistula. In this construction the blood pump 1 is unnecessary since non-return valves 15 and 16, such as butterfly valves or ball valves are included in the inlet or outlet ducts 17 and 18 of the exchanger 2.

With a dialyser with a diaphragm surface area of 1 m.sup.2 and a volume of blood of about 200 cm.sup.3 (that is, an average thickness of blood of 400 .mu.), a pulse frequency of 60 beats per minute allowed a flow rate of 200 cm.sup.3 /minute, that is to say 3.3 cm.sup.3 per pulse, to be provided.

Claims

We claim:

1. A pressure modulator for an artificial blood circuit, said modulator comprising, in combination:

a. at least one resilient wall defining part of a blood chamber;

b. an inlet duct and an outlet duct for said blood chamber;

c. a pair of substantially rigid plates arranged one on either side of said blood chamber, and forming part of said rigid blood exchanger;

d. at least one pulsation chamber disposed on the side of at least one of said plates remote from said blood chamber; and

e. a fluid pulse generator connected to said at least one pulsation chamber, effective to cause slight flexing of said substantially rigid plates and thereby pulsing of liquid in said blood chamber, according to a time/pressure curve which is very close to the physiological curve at a peripheral artery.

2. A pressure modulator as claimed in claim 1, and further comprising a pump connected to said inlet duct.

3. A pressure modulator as claimed in claim 1, and further comprising one way valve means in said inlet and outlet ducts effective to allow inflow into said inlet duct and outflow out of said outlet duct.

4. A pressure modulator as claimed in claim 1 and including two resilient walls in the form of semi-permeable membranes.

5. A pressure modulator as claimed in claim 1, wherein said pulse generator comprises a first and second source of fluid pressure, said first source being at a substantially higher pressure than said second source; a three way valve selectively connectable between either of said two sources and to said pulsation chamber, and switch means operating said three way valve.

6. A method of use of a fluid exchanger as a blood exchanger, disposed in an extracorporeal blood circuit, and comprising, in combination:

a. a plurality of substantially rigid pairs of plates stacked in overlying relation to one another, each of said plates being substantially rectangular and symmetrical, and comprising a front face and a back face, with the front faces of a pair of plates being in facing relation;

b. a pair of semi-permeable membranes between the front faces of each pair of plates, whereby each membrane has a plate adjacent thereto;

c. means defining a first exchange zone between each membrane and its adjacent plate;

d. means defining a blood exchange zone between the two membranes of a pair;

e. means to feed a first liquid to and from the first exchange zone;

f. means to feed blood to and from the blood exchange zone;

g. at least one flexible wall chamber exerting a uniform controlled pressure on at least a portion of said plates, said flexible wall chamber defining a pulsation chamber;

h. a plurality of longitudinal, parallel grooves separated by a plurality of longitudinal parallel ribs defined on said front faces, the ribs of a pair of plates being in register with one another;

i. a depression on the back face of each plate of substantially constant cross-section;

j. diagonally opposite ducts to feed said first liquid to and from said first exchange zone, said ducts being defined between the back faces of the plates of adjacent pairs and communicating with said depression;

k. apertures defined in said plates and communicating said groove with said depression;

l. recesses on the front face of said plates communicating with said grooves; and

m. diagonally opposite passages, complementary to said ducts, to feed said blood to and from said blood exchange zone; said method comprising varying the pressure of the said at least one flexible wall chamber according to a time/blood pressure curve which is very close to the physiological curve at the level of a peripheral artery.