Title:
TWO-PHASE BLOOD PUMP
United States Patent 3768496


Abstract:
A method and apparatus for pumping blood wherein pump elements are provided and operated in a manner to avoid injury to blood constituents. Such apparatus operates with respect to a two-phase combination of blood and an inert liquid which is immiscible with blood, wherein successive slugs of blood are encapsulated in the insert liquid, the encapsulated slugs of blood being separated from each other by predetermined amounts of the inert liquid. The major portion of the apparatus passes only inert liquid, whlie the two-phase combination of inert liquid and blood passes through valve means in the apparatus in a manner to avoid mechanical damage to the blood.



Inventors:
Hills, Brian A. (Bembridge, Isle of Wight, EN)
Fried, George (Stamford, CT)
Langner, Helmuth A. (New York, NY)
Application Number:
05/248055
Publication Date:
10/30/1973
Filing Date:
04/27/1972
Assignee:
BRIAN A HILLS,GB
Primary Class:
Other Classes:
137/154, 417/53, 422/44
International Classes:
A61M1/10; (IPC1-7): A61M1/00
Field of Search:
137/1,154,172,604 23
View Patent Images:
US Patent References:



Other References:

Chemical and Engineering News; June 16, 1969; page 45..
Primary Examiner:
Nilson, Robert G.
Claims:
We claim

1. Apparatus for pumping blood comprising first and second pumping means, two position valve means, injector means, and separator means, means for passing a flow of blood to said injector means, means for introducing an inert, heavy, blood immiscible liquid into said injector means for forming therein a succession of spaced slugs of encapsulated blood, conduit means preferentially wetable by said inert liquid carrying a pressure medium consisting of said inert liquid connecting said first pumping means and said valve means, said first pumping means and said valve means in one position thereof coacting to withdraw slugs of encapsulated blood from said injector means and said first pumping means and said valve means in the other position thereof coacting to pass said slugs of encapsulated blood to said separator means where the constituents of said slugs are gravimetrically separated, and conduit means connecting said separator means and said second pumping means for passing separated inert liquid from said separator means to said introducing means.

2. Apparatus as in claim 1 wherein said valve means comprises a stator member having two ports and a rotor member having a single port for registry with the ports in said stator member upon movement of said rotor member, means for adjustably operating said first and second pumping means, and adjustable means for operating said rotor member.

3. Apparatus as in claim 2, wherein said pumping means operating means and said rotor member operating means are adjusted to locate successive encapsulated blood slugs on either side of the interface of said rotor and stator members whereby relative movement of said rotor and stator members will induce shearing stresses only in the liquid between successive encapsulated slugs of blood

4. Apparatus as in claim 1 wherein said conduit means has an inner surface of polytetrafluoroethylene.

5. Apparatus as in claim 1 wherein said inert liquid is a fluorocarbon having a density greater then that of blood and preferentially wets the inner surface of said conduit means.

6. Apparatus as in claim 1 wherein said first pumping means includes a single inlet-outlet means.

7. Apparatus as in claim 1 wherein said second pumping means comprises a cylinder and a piston movable in said cylinder and a lost-motion linkage for operating said piston.

8. A method of pumping blood comprising the steps of injecting an inert, heavy, blood immiscible liquid into a flow of blood to form a stream of successive slugs of blood encapsulated in and separated by said liquid, pumping said stream with a pressure transmitting medium of inert, blood immiscible liquid through a two position valve in one position thereof, pumping said pumped stream through said valve in the other position thereof to a separator where the constituents of said stream are gravimetrically separated, pumping the separated inert liquid into said injecting step and withdrawing the separated blood.

9. A method as in claim 8 wherein said valve comprises a pair of relatively movable facing members, and pumping said stream of slugs of encapsulated blood through said valve members to dispose only encapsulating liquid at the interface of said valve members as said valve members move relative to each other.

10. A method of encapsulating blood comprising passing a stream of blood through a conduit having an inner surface of a fluorocarbon, injecting determined quantities of an inert, blood immiscible fluorocarbon liquid into said conduit, said liquid preferentially wetting the inner surface of said conduit whereby to encapsulate and separate slugs of blood with said liquid.

Description:
BACKGROUND OF THE INVENTION

Blood is a particularly difficult fluid to pump without injury to blood constituents. Blood consists of a suspension of erythrocytes (red cells) in a continuous liquid phase (plasma) in which various gases, crystalloids and electrolytes are dissolved; together with protein, largely in colloidal solution. The red cells constitute about 40 percent of the blood volume and normally consist of bi-concave discs about 8 microns in diameter. The red cells contain haemoglobin (chemical carrier for oxygen) some carbon dioxide, various other macromolecular substances, some crystalloids and electrolytes such as found in plasma, but in appreciably different proportions.

Most notable in this connection is the preponderance of potassium ions on the inside of the cells as compared to the sodium ions on the outside thereof. Thus, the very thin membrane separating the cell constituents from the plasma is believed to be actively involved in maintaining such ionic gradients. These are associated with other characteristics of the erythrocytes, such as its negative internal charge, without which blood does not remain in a viable condition.

Much of the protein in plasma is present in colloidal solution and therefore does not permeate the fine "pores" of the capillaries as easily as the crystalloids and electrolytes when the tissue is perfused with blood. Thus, plasma protein is preferentially retained within the vessels, setting up a concentration difference which tehn exerts an osmotic pressure tending to return water to the blood. The delicate balance between this colloidal osmotic pressure and the hydrostatic pressure of the blood then determines the water retention of the tissue. An increase in the permeability of the capillary wall to protein reduces the tendency to return water to the vascular system and so permits its retention in extravascular sites, thus producing oedema.

Some of the plasma protein is present as platelets whose deposition at wounds provides one of the initial stages of healing. However, they are also deposited upon the endothelium lining of the injured vessels and upon artificial surfaces such as plastic tubing. Red cells, a few white cells and sometimes fibrin can then attach themselves to this agglomerate to form a semisolid mass. This will tend to obstruct the flow of blood whose force may then cause part of it to break away from the wall. This thrombus is then swept away in the circulation where it may lodge in an artery of comparable diameter and stop blood flow to the corresponding region of tissue. If this occlusion occurs in brain or heart muscle, an extremely dangerous situation develops and which may prove fatal.

To avoid the risk of thrombosis, heparin can be used to inhibit the first stage of coagulation. However, this is also one of the first stages of healing so that the use of heparin in any effective quantity poses a serious problem for the surgeon.

In practice, the blood pump is commonly used, is most likely to cause damage to blood constituents. This damage can take many forms including: (1) bursting the erythrocyte membrane and spilling the contents thereof into the plasma, which allows cell fragments to occlude capillaries, particularly those of smaller diameter, leading to pulmonary conditions; (2) eryhthrocyte distortion may occur without wall fracture. This can give rise to cells of varying and unusual configurations, which, if not conducive to flow through a cappilary, can also lead to pulmonary conditions; (3) mechanical damage of the erythrocyte wall can interfere with its properties as a membrane and so disturb the delicate balance of electrolytes between the plasma and cell contents. This in turn can lead to a number of adverse conditions including the control of vasomotor reactions; (4) mechanical denaturation of the plasma proteins leads to water retention and consequent increased venous pressure; (5) different flow resistance distribution between organs with possible adverse effects; and (6) most of the clotting factors are depressed by protein denaturation which can lead to postperfusion bleeding.

Accordingly, an object of this invention is to provide apparatus for pumping blood in which blood does not come in contact with relatively movable surfaces or elements such as found in valves or pistons, thereby avoiding haemolysis.

Another object of this invention is to provide a pump of the character described, in which blood and an inert liquid are combined in a manner to provide a succession of slugs of blood individually encapsulated in inert liquid and separated from each other by predetermined amounts of inert liquid; the pump being operated in a manner such that shearing stresses arising from movement of valve parts are applied only to the inert liquid between the encapsulated slugs of blood, thereby leaving the slugs of blood free of applied shearing stresses.

A further object of this invention is to provide in apparatus of the character described conduits formed of a material which is preferentially wetted by the inert encapsulating liquid thereby assuring complete encapsulation of each slug of blood and insulating the slugs of blood from contact with the inner surface portions of such conduits and thus avoiding adverse interfacial reaction between such conduits and the slugs of blood.

Still another object of this invention is to provide a pump of the character described wherein all passages and spaces are filled with inert liquid and encapsulated slugs of blood at all times, thereby avoiding dead space and regions of stagnant blood, to thereby reduce thrombi formation.

Still a further object of this invention is to provide a pump of the character described which is adapted to deliver a determined volume of blood independent of load.

Yet another object of this invention is to provide a pump of the character described which may have a variable output in accordance with any desired pumping pattern.

Yet a further object of this invention is to provide a pump of the character described which may be pulsatile in operation , and allow for variations in pulse rate and pressure-time relationships.

Still another object of this invention is to provide a pump of the character described which may be readily operated with easy priming and which results in little or no suction on the inlet side thereof to thereby prevent collapse of the venous system of the subject connected to the pump.

Yet another object of this invention is to provide a method of pumping blood in a system which is operative to encapsulate slugs of blood in a selected inert liquid which also separates successive slugs of blood, the operation of valve means in the system being timed so as to subject only inert liquid to moving parts of the valve and applying resulting shear stresses only to the inert liquid, leaving the slugs of blood free of mechanical damage; the slugs of blood being insulated from surface portions of conduit portions of the system by the inert liquid to avoid interfacial damage to the slugs of blood.

Yet a further object of this invention is to provide a pump of the character described, which is of a relatively simple construction, economical to manufacture and lends itself to easy operation in use.

Other objects of this invention will in part be obvious and in part hereinafter pointed out.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic showing of a blood pump and its mode of operation, and which embodies the invention;

FIG. 2 is a side elevational view showing the pump system;

FIG. 3 is an end elevational view looking at the right hand end of FIG. 2, with parts cut away;

FIG. 4 is an end elevational view looking at the left hand end of FIG. 2, with parts in section and parts broken away;

FIG. 5 is a side elevational view showing elements of the pumping mechanism;

FIG. 5A is an end elevational view thereof;

FIG. 6 is an enlarged sectional view showing details of the injector means; and

FIG. 7 is an elevational view with parts in section, showing the mounting details for the pumps.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The pumping system of the instant invention is adapted to move blood between a pair of given points, in a manner to avoid mechanical or chemical damage to the selected constituents of the blood, to thereby avoid any adverse reactions which otherwise might accrue from the use of damaged blood by the recipient thereof.

Essentially, such a pumping system and its operation is predicated on the introduction of an inert liquid which is immiscible with blood and preferentially wets the selected material from which the conduits of the system are formed, into the system to encapsulate successive slugs of blood. Such inert liquid further provides a pressure transmitting medium per se which extends throughout a major portion of the pump system. The encapsulated slugs of blood move through a valve forming part of the pump system in a manner wherein the shear action of valve parts moving relative to each other is directed only to inert liquid portions which separate successive encapsulated slugs of blood, thus leaving such slugs of blood free of mechanical shear and consequent injury. Further, the slugs of blood are insulated against direct contact with the inner surface of conduits in the pump system by the encapsulating inert liquid, thereby avoiding adverse interfacial contact as between the slugs of blood and the inner surface of such conduits.

Thus, as shown in FIG. 1, the pump system of the instant invention comprises pumping means generally indicated at 10, valve means generally indicated at 11, injector means generally indicated at 12, and separator means generally indicated at 13.

Pumping means 10 comprises a pair of similar pumps 15, 16. Pump 15 comprises a cylinder 17, piston 18 and inlet-outlet 19. Pump 16 comprises a cylinder 20, a piston 21, inlet 22 including a one-way check valve, and an outlet 23 including a one-way check valve. The pumps 15, 16 are driven from a variable stroke mechanism generally indicated at 25 which is actuated by a cam 26 mounted on a cam shaft 27 rotated by a motor and gear box 28. The pumps 15, 16 are coupled to the driving means by means of suitable linkages, hereinafter described in detail.

The valve means 11 comprises a stator element 30 and a rotor element 31 spring pressed against stator element 30; the rotor element 31 having a single port 32 adapted to alternately register with ports 33, 34 on stator element 30 upon suitable oscillation of rotor element 31.

Injector means 12 takes the form of a generally Y shaped tubular member 35 having an upstanding arm 36, an upwardly inclined arm 37 and a depending arm 38, FIG. 6. A tubing 39 extends from a blood source A with a portion 39A thereof passing through communicating arms 36, 37 and a portion 39B thereof connected to port 33 of valve stator element 30. Arm 38 is connected by a tubing 40 to the outlet 23 of pump 16, with a check valve, not shown, inserted therein at a point adjacent arm 38. A slot 40A is formed in tubing portion 39A to provide communication between arm 38 and the tubing portion 39A.

Separator 13, which may be formed of glass, comprises a vertically disposed chamber 41 having a horizontal inlet 42 at a medial point therein and connected to port 34 of stator 30 by a tubing 43. Separator 13 also includes a depending outlet 44 which is connected to inlet 22 of pump 16 by a tubing 45; and an upstanding outlet 46.

The port 32 of valve rotor element 31 is connected to inlet-outlet 19 of pump 15 by a transfer tubing 47 whose terminal portion 48 is adapted to register with terminal portions of tubings 39B, 43, as rotor 31 is oscillated to register its portion 32 with ports 33, 34 of stator 30, by means of a cam 50 on cam shaft 27.

All tubings in the system are formed of TEFLON which is polytetrafluoroethylene and is readily wetted by an inert, blood immiscible liquid used in the system as a fluid pressure medium and as a means for encapsulating individual slugs of blood derived from source A. Such inert liquid may be a fluorocarbon known as FC-80, made by 3M Company and which is essentially perfluorobutyltetrahydrofuran and isomers thereof, with a density of 1.7 gm/cc as compared to a density for blood of 1.03 gm/cc. It is understood that other inert, heavy fluorocarbons may be used which are immiscible with blood and show a preferential wetting for TEFLON or the like.

The inert fluorocarbin liquid F is introduced into the system from a reservoir R which is connected to line 45 by a line 52 with an interposed valve 53. The liquid F occupies the pump cylinders 17, 20 as well as lines 40, 45, 51 and transmits pressure generated by pumps 15, 16 to the blood B brought into injector 12 by tubing 39.

OPERATION OF THE SYSTEM

Mode; 1

The pumping system operates as follows. With rotor 31 of valve means 11 positioned to register its port 32 with port 34 of stator 30, piston 21 of pump 16 is effective by way of line 40 to inject a determined quantity of liquid F into arm 38 of injector 12 by way of the check valves at pump outlet 23 and arm 38; the liquid passing by way of slot 40A into tubing portion 39A.

Since port 33 is closed at this time, the injected liquid by its preferential wetting of the inner surface of the tubing portions in injector 12, encapsulates a given quantity of blood and thereby rearwardly displaces the blood stream in line 39, and thus forming encapsulated slugs of blood B'. Such slug B' is received in transfer tubing portion 48 and with port 32 of rotor 31 in registry with port 34 of stator 30, the slug passes to separator 13 by way of tubing 43 and inlet 42, through the action of piston 18 of pump 15 which operates simultaneously with pump 16.

At the end of the stroke of pistons 18, 21, the pistons have a dwell period sufficient for the rotor 31 of valve 11 to move to its other position in which port 32 thereof registers with port 33 of stator 30. Such stoppage of the pistons 18, 21 allows the transfer line portion 48 of line 47 to be shifted between positions in which the same registers with lines 39B and 43. The check valves at inlet 22, outlet 23 and arm 38 insure flow of liquid in a single direction. The check valve at arm 38 also provides an additional safeguard against back flow and residual fluid flow tendencies at the juncture of arm 38 and tubing portion 39A.

While rotor 31 of valve 11 is positioned to register port 32 thereof with port 33 of stator 30, piston 21 of pump 16 is effective by way of the check valve at inlet 22 to pull inert liquid F out of the bottom of separator 13 by way of outlet 44 and line 45 and piston 18 of pump 15 pulls a two-phase portion comprising one encapsulated slug of blood B' and oneinjected portion of liquid F' through port 33 into transfer line portion 48 of line 47 in a manner to locate the liquid portion F' at the interface of rotor 31 and stator 30. Thus, upon relative movement of rotor 31 with respect to stator 32, only liquid F' is subjected to shearing stresses while slug B' is unaffected by the valve action.

When the stroke of pumps 15, 16 is completed, all liquid movement is halted and at this time, rotor 31 is operated by cam 50 and switches back to register port 32 thereof with port 34 of stator 30. At this time, piston 18 of pump 15 advances to move the two-phase combination of blood and inert liquid out of transfer line portion 48 through port 34.

The alternate slugs of encapsulated blood B' and liquid F' pass to separator chamber 41 where the constituents thereof are gravimetrically separated. The blood B under pressure generated by piston 18 of pump 15 returns to the source A or otherwise by way of outlet 46, air trap 60 and line 61, while the heavier inert liquid F is tapped from the lower portion of chamber 41 to be recycled to the injector means 12 by way of outlet 44, line 45, pump 16 and line 40.

During the separation process, any contaminating particle matter heavier than the inert liquid F will fall out into the liquid F. Particles having a density between that of water and the liquid F will collect at the interface of the blood and inert liquid F and will not be recirculated.

Significantly, pistons 18 and 21 of pumps 15, 16 are never in contact with blood; their action being transmitted to the blood by columns of inert liquid F. Further, the shearing action of valve elements 30, 31 takes place only in respect to liquid F' which straddles the interface of said elements 30, 31.

Pistons 18, 21 move simultaneously at all times and execute simple harmonic motion with stops at the end of each stroke to allow valve 11 to operate between its two positions, while the fluid columns are at rest. Thus, in Mode 1 of operation both pistons are either on a pressure stroke or on a suction stroke. The rotor 31 and transfer line portion 48 which contains the slugs of encapsulated blood B', movein partial harmonic motion. The check valve at outlet 23, handling liquid F only, is operated instantly by any flow produced by the piston 21 in the predetermined direction to prevent back flow.

Synchronization of the action of pumps 15, 16 and valve 11, is achieved by proper selection and phasing of a set of intermittent harmonic motion cams 26, 50 mounted on cam shaft 27.

The volume of liquid displaced by either of pumps 15, 16 may be independently varied by suitable operation of the variable stroke mechanism 25 or by using various size cylinder and piston assemblies, which may be interchangeable.

Since the amount of liquid F returned to the separator 13 by pump 16, valve 11 and injector 12 is uniform and equal to that pulled from separator 13, no buildup pf liquid F can occur at any point in the system.

Means may be provided to produce any desired pressure-time profile to be applied to the delivered blood B in line 61. To this end, a pump 62 operates as a pulse generator by way of line 64 connected to separator 13 on liquid F in said separator. Pump 62 is driven by a cam 63 which is operated by a gearbox-motor 65 so that the pulse can be controlled independent of the pump output. Alternatively, cam 63 may be mounted on cam shaft 27 for synchronization with pumps 15, 16.

It will be apparent that the volume of pumped blood may be increased by (1) increasing the frequency of the pumping cycle but this is limited by the flow turbulence which will cause blood damage; (2) increasing th volume of encapsulated blood per stroke and this is limited by slug diameter and length at which full encapsulation by liquid F occurs throughout the system; and (3) by decreasing the volume of injected liquid F which is limited by the volume at which liquid F no longer effectively straddles the interface of the stator and rotor elements of valve 11.

It has been found that encapsulation of the slugs of blood B' by liquid F will be maintained without separation of the constituents thereof, if the inner diameter of the tubings carrying the encapsulated slugs B' is less than one-fourth inch and preferably is from one thirty-second to three-sixteenths inch. Also, the slugs B' may have a length ranging from one-half to 12 inches, while the separation of successive slugs B' may be of the order of from one-fourth to one-half inch.

Mode 2:

Whereas in Mode 1, injection of liquid F is effected upon a stationary column of incoming blood B, thereby rearwardly displacing the column of blood by an amount equal to the injected liquid F; Mode 2 operation is such that liquid F is not injected until the greater part of the moving incoming column of blood B has already been pulled past the arm 38 of injector 35.

Thus, the liquid F is injected at the end of the suction stroke generated by pump 15, through transfer tubing 47 and tubing 39A by way of ports 31, 33 of valve 11. The flow rate of the liquid F being injected matches or slightly exceeds that of the blood B passing into injector 35, at that moment; thereby bringing the blood in tubing 39 up to slot 40A to a complete halt. This results in the formation of a slug of liquid F at the end of the still moving column of blood, thereby forming an encapsulated slug of blood.

This procedure is effected by the use of a lost motion linkage in pump 16, as hereinafter described. Such linkage may be adjusted to operate with either zero lost motion, as in Mode 1, or adjusted amounts of lost motion of optimum operation under Mode 2.

As shown in FIGS. 4 and 7 the pumps 15, 16 are arranged for angular movement to selected position whereby to adjust the throw of the pistons 18, 21 thereof. To this end, the pumps 15, 16 are mounted on a base member 70 by way of a cylindrical member 71 fixed thereto.

Member 71 is formed with laterally related, arcuate slots 72 located in the upper and side wall portions thereof. Dovetail members 75, 76 are disposed for angularly slidable motion in slots 72 of member 71. The upper member 75 provides means for suitably mounting the base portion of pump cylinders 17, 20 thereon. Screws, not shown interconnect each pair of members 75, 76 for clamping each pair of members 75, 76 in selected angular positions in slots 72, as indicated in FIG. 4.

The piston rods 18A, 21A of pumps 15, 16 respectively, pass through suitable openings in the base of the mounted cylinders 17, 20; the members 75, 76; and slots 72. The lower ends of said piston rods 18A, 21A are connected to a cross linkage element 21E which in turn is connected to a forked cam follower 26A. The upper end of cam follower 26A passes through an arcuate slot 73 formed in the base portion of cylindrical member 71 while a mid portion thereof is pivoted to member 71 by a cross pin 26B spanning slot 73.

The piston rod 18A is directly connected to linkage element 21E by way of bearing 18B, see FIG. 5. Piston rod 21A is adapted to provide varying degrees of lost motion, or alternatively may have a fixed motion similar to that of piston rod 18A. To this end, piston rod 21A terminates in an elongated loop portion 21B, defining an elongated slot 21C. The other end of linkage element 21E extends through slot 21C and a screw 21D mounted in the lower end of loop portion 21B to adjustably determine the effective length of the slot 21C and thereby determine the degree of lost motion relation between piston rod 21A and cam follower 26A, as well as no lost motion.

The piston rods 18A, 21A are operated by cam follower 26A which is oscillated by the cam 26 which is received in the forked lower portion of the cam follower 26A.

As indicated in FIG. 2, the rotor 31 of valve 11, is spring pressed against stator 30 by a spring assembly 31A to provide a tight interface relation between rotor 31 and stator 30. Rotor 31 is oscillated between its two positions by means of cam 50 on shaft 27, see FIG. 3. A cam follower 80 pivoted at one end thereof as at 81, to a base portion of the system; is formed with an opening 82 to receive the rotating cam 50. An arm 83 on cam follower 80 is pivotally connected as at 84 to a spring mounted linkage 85 which is pivotally connected to a projection 31B of rotor 31, as at 31C.

It is understood that conduits 39B and 43 have their terminal ends extending through ports 33, 34 respectively of stator 30 and terminating at the inner face of said stator 30. Similarly, the conduit portion 48 extends through port 32 of rotor 31 and terminates at the inner face thereof. Thus, the terminal end of conduit 48 registers with the terminal ends of conduits 39B and 43, as the rotor 31 is oscillated.

It may be desirable tooxygenate the blood flowing in the system. Accordingly, an oxygen source O is connected via a valved line to conduit 45 whereby the inert fluid F acts as a carrier for the oxygen and introduces the same to the injector 12. Bleeders may be provided at various points in the system, as required; such bleeders being indicated at X.