US2988001A - Apparatus for use in the extractorporeal circulation of blood - Google Patents

Description

J1me 1961 A. c. D'ARCEY ETAL 2,988,001

APPARATUS FOR USE IN THE EXTRACORPOREAL CIRCULATION OF BLOOD Filed April 30, 1956 4 Sheets-Sheet 1 Pulmonary Artery June 13, 1961 A. c. 'DARCEY ETAL 2,988,001

APPARATUS FOR USE IN THE EXTRACORPOREAL CIRCULATION OF BLOOD Filed April 30, 1956 4 Sheets-Sheet 2 [nven 101:;

W Alfred C DZI/"cey r Eliot M Wadsworth W By t/zezr Attorney l-lll z June 13, 1961 A. c. 'DARCEY ETAL 2,983,001

APPARATUS FOR USE IN THE EXTRACORPOREAL CIRCULATION OF BLOOD Filed April 30, 1956 4 Sheets-Sheet 3 Fig. 3

Inventars Alfred C Di l/"c619 Eliot M Wadsu/arzh B3 #261)" Azzorney June 13, 1961 A. c. DARCE'Y ETAL 2,988,001

APPARATUS FOR USE IN THE EXTRACORPOREAL CIRCULATION OF BLOOD Filed April 30, 1956 4 Sheets-Sheet 4 in van tom" Alfred C Dl lrcey Eliot M Wadsworth By their Attorney United States Patent 2,988,001 APPARATUS .FOR USE IN THE EXTRACOR- POREAL CIRCULATION OF BLOOD Alfred C. DArcey, Danvers, and Eliot M. Wadsworth,

Beverly Farms, Mass., assignors to United Shoe .Machinery Corporation, Flemington, N..l., a corporation of New Jersey Filed Apr. 30, 1956, Ser. No.'581,730 8 Claims. (Cl. 103-4) This invention rel-ates to apparatus for .use in the extracorporeal circulation of blood andis herein illustrated as erribodied in a novel and improved pump of the compressible tube-rotary impeller type.

As will be appreciated by those skilled in the art, it has been hitherto proposed to provide pumping means located exteriorly of the body for taking over, respectively, the pumping actions of the right and left sides of the heart, thus making it possible entirely to bypass the heart during surgical repair thereof which is very greatly facilitated by the dry field obtained as a result of relieving the heart of its usual taskof circulating the blood of the patient. Obviously, a prime requisite of a pump of this type is complete dependability, while other important characteristics include simplicity of construction, and ease of operation andcontrol. Inaddition, it is most imperative that the arrangement be such that the introduction of air into the blood stream is effectively avoided and the danger of damage to the blood corpuscles,trauma or hemolysis, substantially eliminated. It is, therefore, a principal object of this invention to provide a novel-and improved pump for use in the extracorporeal circulation of blood in which all of these essential characteristics are obtained.

As herein illustrated the improved pump includes two units each having an inlet and an outlet associated with a pair of reservoirs, preferably formed of .glass vor other transparent material, and having an open upper end, a closed lower end, and a separate inlet connection. The inlet and outlet of each pumping unit is connected to a reservoir by means of suitable conduit means, and located in each of the conduit means extending from a pumping unit outlet is a normally closed valve means. Leading from each of the mentioned conduit means, in a location between the pump outlet and the mentioned normally closed valve is a connection for a conduit means adapted to deliver blood to the patient, while two other conduit means are similarly associated, respectively, with the inlet connections of the reservoirs for receiving blood from the patient. .As will presently appear, the four conduit means for delivering and receiving blood are so cannulated to arteries and veins of the patient that one .of the pumping units is connected to a reservoir for receiving venous blood from the venae cavae and this pumping unit forces the blood into the pulmonary artery and thence to the lungs, this pumping unit thus functioning to perform the pumping action of the right auricle and right ventricle of the patients heart, while the other pumping unit is connected to the other reservoir which receives arterial blood from the pulmonary vein, and this pumping unit forces the blood into the aorta and thence through the patients body, this pumping unit thus functioning to perform the pumping action of the left awhile and left ventricle. Referring again to the two reservoirs which, as suggested :above, are preferably formed of 'trans parent material, these provide receptacles open to atmospheric pressure for receiving blood from the patient before this blood enters the pumping units. Preferably, and

as herein illustrated, these two reservoirs are connected at their lower ends by a suitable conduit in'which there is a normally closed valve means adapted to be opened for by-passing blood from one reservoir'to the other.

Although there are several well-known types of blood circulating pumps which possibly could be used with the apparatus outlined above, the compressible tube-rotary impeller type which is herein illustrated affords certain very definite advantages, especially when constructed in the novel and improved manner about to be explained and in accordance with features of this invention. In a pump of this type, a compressible tube is supported in a circular shape so as to be progressively compressed by the rotary impeller which is usually mounted on an arm extending radially from the drive shaft. By arranging'this tube so that its circular shape is somewhat less than a'full circle, the action of the impeller on the tube is interrupted once during each revolution of the drive shaft, thus causing the pump to have a cyclic action which simulates, at least in a general manner, the pulsations of the *heart. As suggested above, the two pumping units of the novel apparatus of this invention take over, respectively, the pumping actions of the right and left heart. It therefore may be desirable, during use-of the apparatus to circulate the blood of a patient, to change the cyclic rate of the two pumping units and/or'to vary the pumping action of one or the other of the two pumping units. For this purpose, and in accordance with features of this invention, the two pumping units are associated with a common drive shaft, the speed of which may be varied to change the cyclic rate of the two pumping units, while the rotary impeller of each pumping unit is mounted on an associated drive'shaft arm for radial adjustment thereon for varying the action of the impeller on the compressible tube and hence the pumping action of the unit. More particularly, with reference to the radial adjustment of the rotary impeller, novel adjusting mechanism "is provided which includes a control member readily accessible to, and adapted to .be seized by an operator, and which is arranged by movement axially of the drive shaft in one direction or the other to effect radial adjustment .of the rotary impeller in the desired direction in response to rotation of the drive shaft.

The above and other objects and features of the invention will become apparent from the following detailed description of the embodiment thereof which is illustrated in the accompanying drawings, and will bepointed out in the claims.

In the drawings,

FIG. 1 is a diagrammatic view of the novel apparatus of this invention;

FIG. 2 is a plan view of .an improved pump used in the novel apparatus shown in FIG. 1, this view also showing mechanism for driving the pump;

FIG. 3 is a view in end elevation, at an enlarged scale and with parts shown in vertical section substantially on line 'IIIIII of FIG. 5 and looking in the direction of the arrows, of the left-hand portion of the improvedpump shown in FIG. 2;

FIG. 4 is a view in side elevation of a part of the pump shown in FIG. 5 with certain parts omitted or broken away and others shown in vertical section; and

FIG. 5 is a view in side elevation of the portion of the pump shown in FIG. 3.

Referring to these drawings, the apparatus which is illustrated in part schematically in FIG. 1 comprises two reservoirs 10 and .12 formed of glass or other transparent material, and of the shape shown. Each of these reservoirs has an open upper end and a closed lower end and the two reservoirs are physically connected by means of two cross struts 14, 15, the latter of which is preferably formed of a tubular member, while the former is asolid rod. The upper end of each reservoir is disposed at an angle to the body portion thereof so that when the reservoirs are supported with their open upper ends extending substantially vertically, their body portions slope downvwhile the reservoir 12 has an inlet connection 22 and three other connections 24, 25 and 26.

Located adjacent to these two reservoirs is a pump comprising two pumping units. shown schematically in '7 FIG. 1, and indicated generally by reference characters P-1 and P-2. Each of these pumping units includes a compressible tube T-1 (T-2) and a cooperating rotary impeller R-l (R-2) mounted on a radially extending arm A-1 (A-Z). As is illustrated in FIG. 2 of the drawrngs, the arms A-1 and A-2 are mounted on the opposite ends of a common drive shaft S which is arranged to be rotated, through suitable speed reducing gearing G, bv means of the output shaft of a variable speed drive D driven by a motor M and having a control handle H. As will presently be explained, there is associated with each of the arms A-1 and A-2 an adjusting mechanism adapted to be controlled by means of a hand knob K-1 (K-2) for causing radial movement of the rotary impeller to varv the action of the rotary impeller on the compressible tube. The inlet and outlet of the pumping unit P-l are connected to the two connections 18 and 20 of the reservoir by conduit means comprising tubes 30, 32, and connecting glass tubes 31, 33. while the inlet and outlet of the pumping unit P-2 are connected to the connections 24 and 26 of the reservoir 12 by conduit means comprisinn tubes 34, 36 and connecting glass tubes 35 and 37. Associated with the tube 32, which is connected to and leads from the outlet of the tube T1 of the pumping unit P-l, is a valve means comprising a clamp device 4!? and a branch connection 42 which is located between the mentioned valve means and the outlet of the tube T-1. In a like manner, there is associated with the tube 35. which is connected to and leads from the outlet of the tube T-2. a valve means comprising a clamp device 44 and a branch connection 46 which is located between the last-mentioned valve means and the outlet from the tube T-2. Extending between the connections 19 and 25 is a tube 48 which provides a bv-pass conduit means in which there is a normally closed valve means comprisin a clamp device 50. Suitable conduit means 52, 54. 56

'and 58 are associated respectively with the inlet connections 16 and 22 and the branch connections 42 and The two pumping units P-1, P-2 of the pump are of identical construction, one being a mirror image of the other, so that a detailed description of one of these units, for examplethe one which is illustrated on the left in complete understanding of the construction and mode of operation of the double unit pump arrangement of this invention. Referring to FIG. 3 of the drawings, this pumping unit comprises a housing 60 shaped to provide a circular recess 62 having adjacent to its open end an annular flange 64. This housing is secured to a portion arms A-1 and A-2 of FIG. 1) which is grooved as indicated at 72 to receive a sliding block 74, held in the groove by means of a cover 76. Formed integrally with this block is a trunnion 78 on which a roll (corresponding to the rolls R1 and R-2 of FIG. 1) which serves as a rotary impeller, is journaled. The trunnion 78 projects through a clearance slot 82 formed in the arm 70- as shown in FIG. 3.

Secured to the arm 70 is a member 86 having a bore FIGS. 1 and 2 of the drawings, will be suflicient for a 88 therein for rotatably receiving the hub 90 of a bevel gear 92. This gear has a clearance hole 94 through which there passes a hollow lead screw 96 which is threaded into the arm 70 and to which the aforementioned bevel gear is drivingly connected by means of a set screw 98 and keyway 100 formed in the screw 96. The lead screw 96 is internally threaded to receive a second lead screw 102, of the same hand as the screw 96, which is threaded through a bore 104 in the block 74 and secured thereto by a locknut 106. The lead of the screw 96 is different from that of the screw 102 for a purpose which will presently appear.

For rotating the bevel gear to effect radial adjqustment of the roll 80, the following arrangement is provided. Secured to the arm 70, coaxially of the shaft S, is a stud on which there is rotatably and slidably supported an adjusting knob 112 (corresponding to the knobs K-1 and K4. of FIGS. 1 and 2) having an enlarged hub portion 114 which is provided with a circumferential groove 116 (FIG. 3). Formed in the arm 70 is a V-groove guideway 120, see FIG. 4, which is inclined downwardly and outwardly, as indicated in FIG. 3, in

which' there is slidably mounted a block 122 from which there projects a stud portion 124. Journaled on this stud portion is a bevel gear 126, held in place by means of a headed screw 128. Surrounding the hub of the gear 126 is the body portion of a yoke member 130 having a pair of arms 132, 132 which are received within the annular groove 116 of the hub portion of the adjusting knob 112. Also rotatably and slidably mounted on the stud 110 is a bevel gear 136 the hub of which is grooved as indicated at 140, 140 and projects into a recess 142 formed in the hub portion 114 of the adjusting knob 112. This gear is normally held yieldingly in the position shown in FIG. 3, by a spring 146, with its hub engaging a stop ring 148 on the stud 110. A relatively lighter spring 150, seated against an adjusting nut 152 on the stud 110, yieldingly holds the knob 112 and its hub por tion 114 in the position shown in FIG. 3 with the bottom of the recess 142 in engagement with the end of the hub of the gear 136. The hub portion 114 is drivingly connected to the gear 136 by means of pins 154, 154 which are received within the groove 140, 140.

Extending outwardly from the recess 62 are two grooves 160, 162, FIG. 5, which are disposed at substantially right angles to each other and extend generally tangential ,to the outer wall of the recess 62, indiciated in FIG. 3

by the reference character 164. A portion of the annular flange 64 is cut away, as indicated at 166, 168 in FIG. 5 of the drawings to provide a recess for a keeper plate 170,

preferably formed of a plastic or other transparent material, which is held in place by screws 172, 172, 172.

When this keeper plate is removed, a single loop of a compressible tube 180, formed of rubber or suitable jplastic materiaL'may be placed in the recess in engagement with the outer wall 164 thereof and with its opposite ends extending outwardly through the grooves 160, 162

.which are of a width substantially equal to the normal outside diameter of the tube. The grooves 162 are of the same depth as the recess 62 and inasmuch as the axial distance of the bottom of this recess to the inside of the flange 64, which is just sufiicient to accommodate the tube when it is fully flattened by the roll 80. is somewhat less than twice the diameter of the tube, the ends of the tube, as they project outwardly beyond the housing 60, are deflected slightly away from each other out .of the central plane of this housing.

during each revolution ofthe shaft S, while the roll 80 travels from a position"-a on one=end of the loop of the tube to a -pos'ition b on the other-end of the loop. The output of the pump can be varied'in two different ways, e.g., 'by increasing or'decreasing the amount the tube'180 is compressed by the roll 80 and/or by increasing or decreasing the speed of rotation of the shaft S. As will be apparent, the latter also has the effect of varying the cyclic rate of the pump, i.e., the rate at which the pumping action is interrupted as above explained.

When the parts are in the positions in which they are shown in FIG. 3 of the drawings, the gear 136 is out of mesh with the gears 92 and 126, while the gear 126 is partially meshed with the gear 92. Now,:if-the operator wishes to cause the roll to move radially outwardly along the arm 70, thereby to increase the pumping action, he grasps the knob 112 and pulls it outwardly, i.e., to the right FIG. 3, on the stud 110. As a result of this movement of the knob 112 and its hub portion 114, the gear 126 is moved downwardly completely in mesh with the gear 92 and outwardly into mesh with the gear 136, which latter gear is being held against axial movement by ring 148 and against rotation by the operator through the action of the pins 154, 154 on the grooves 140, 140. Therefore, as the arm 70 revolves in the direction of the arrow in FIG. 5 of the drawings, the gear 126 will be driven in a clockwise direction as viewed in FIG. 3, thus driving the gear 92 and screw 96 in a direction to cause the screw 96 to move upwardly wtihin the arm 70, as viewed in FIG. 3. At the same time, the screw 96 tends to draw the screw 102 downwardly, in a manner which will be apparent. Inasmuch as the lead of the screw 96 is greater than the lead of the screw 102, the net result will be a movement of the block 74 and roll 80 upwardly at a very slow rate. For example, with a lead on the screw 96 of ,4, and a lead on the screw 102 of 49. the block 74 will be moved upwardly, i.e., radially outwardly along the arm 70, approximately .0035" for each revolution of the gear 97. As soon as the operator releases the knob 112 it is returned to the position shown in FIG. 3 by the spring 150 and radial movement of the roll 80 will cease. In order to effect radial movement of the roll in the opposite direction, thereby to reduce the pumping action, the operator grasps the knob 112 and pushes it inwardly, i.e., to the left as viewed in FIG. 3. This causes the gear 136 to be engaged with the gear 92. Inasmuch as the gear 136 is held against rotation by the operator, in the manner explained above, as the arm 70 revolves in the direction of the arrow in FIG. 5, the gear '92 will be driven in a direction to effect radial movement of the roll 80 radially inwardly along the arm 70 toward the axis of the shaft S at the rate indicated above, i.e., approximately .0035" for each revolution of the gear 92. During this rotation :of gear 92, the gear 126 turns idly. As will be apparent, the adjusting mechanism. which .has been described above provides a very sensitive adjustment of the roll 80 and as a result affords an extremely accurate control over the pumping action of the unit. In order to adjust screws 96 and 102, relatively to each other, the nut 106 is removed and the screw 102 is threaded out of the screw 96 and the block 74. Now, the screw 96 may be adjusted by manual rotation, after which, with the block 74 held in the desired location and the screw 96 held against rotation, the screw 102 may be rethreaded into the screw "96 and block 74 and the nut 106 replaced. As will be apparent, when the roll 80 is being adjusted outwardly, to increase the pumping action, the screw 96 travels upwardly toward the block 74. Thus, by suitable adjustment of the screws 96' and 102, the outward limit of movement of the roll can be so determined that complete closure of the tube 180 isprevented and the possible damage to the corpuscles which might occur in this way avoided.

6 The mode of operation of the apparatus will now be outlined'withparticular re'ferenceto FIGS. 1 and 2 of the "drawings. The apparatus is set up in the operating room adjacent to the patient with the two reservoirs 10, 12 mounted on a suitable stand, or other type of support, at a level somewhat below the patient and with the pump unit, see FIG. 2, located close by on the floor. In order to save valuable floor space, the pump unit may be supported on a suitable frame and in the vertical position shown in FIG. 2. Without attempting to explain the details of the surgical procedure involved, which forms no part of .the present invention, the conduit means 52, 54, 56 and 58 are cannulated with appropriate blood vessels of the patient, as diagrammatically illustrated in .FIG. 1, so that the patients heart is entirely bypassed. Initially, each of the .two reservoirs is partially filled with a saline solution, or with blood, and with the values 40, 44 opened the pump is started. Now, as blood fiows from the pulmonary vein into the reservoir 10 through the conduit 52 and from venae cavae into the reservoir 12 through the conduit 54, these valves are gradually closed to cause the pump units to circulate the oxygenated blood which flows into the reservoir 10 through the body of the patient and the venous blood which flows into the reservoir 12 to the lungs of the patient.

The speed of rotation of the common drive shaft S of the pump is set, by means of the control handle H on the variable speed drive D, Fig. 2, so that the cyclic action of the two pumping units is comparable to the normal pulse of the patient, which this cyclic action of the .pump simulates, while the pumping action of each pumping unit P-1 and P-2 is initially adjusted to approximate that required to take care of the blood which flows into the two reservoirs and to equalize the flow through the reservoir 10 with thefiow through reservoir 12. This state of equality of how, or the lack thereof, is readily apparent to the operator by his observation of the level of the blood within these two reservoirs, which, as already indicated, are made of transparent material for this purpose. As will be apparent, the flow of blood through the reservoir '10 may be very quickly and accurately regulated by the operator through a suitable manipulation of the control knob K-l, while the flow through the reservoir 12 can similarly be regulated by means of the knob K-2. In this manner the action of the pump can .be controlled in accordance with the requirements of the patient during the operation. In the .event thatsuch action should become necessary for any reason, the quantity of the blood in the two reservoirs may be very quickly balanced by temporarily opening the by-pass valve 50.1ocated in the conduit 48. The hollow strut 15 provides an automatic by-pass for preventing overflow of one or the other ofthe reservoirs 10 or 12 should the level of the blood therein rise to an unduly high level.

The cyclic rate of the pump, i.e., the simulated pulse, may be readily increased or decreased by varying the speed of rotation of the common drive shaft S in the manner explained above and this change will be the same for each of the two units which, as explained above, correspond to the right and left sides of the heart. After such a change in the cyclic rate of the pump it may be necessary for the operator to make a slight readjustment in the pumpingaction of the two units in order to maintain the desired quantity and equality of flow through the two reservoirs. This can, of course, be readily accomplished in the manner explained above.

As will be apparent, with the apparatus of this invention, a single operator is enabled to control the operation of the pump and to regulate the flow through the two reservoirs in any desired manner appropriate to conditions met during the operation. Moreover, the novel and improved pump is very dependable in action and, because of the simplicity of its construction,there is little, if'any, likelihood of mechanical difliculties arising. The pump 7 tube 180 (T-l or T-2) is very easily replaceable in the event of damage during use and, should mechanical failure of one or both of the pumping units occur during an operation, these tubes could be quickly removed and placed in another standby pump with only a very brief interruption of the circulation of blood. As explained above, the limit of outward adjustment of the pressure roll 80 may be such that the compressible tube used in each pumping unit can never be entirely closed by the roll. Thus danger of damage to the blood by squeezing of the corpuscles may be effectively avoided. In addition, the action of the rotary impeller in moving the blood through the compressible tube is an easy one and such that other damage to the blood is avoided.

After use, the various pieces of tubing which have been employed for the several conduits referred to above, as well as the two pieces of tubing used in the pumping units themselves, may be entirely discarded or, if desired, these pieces of tubing may be cleaned and sterilized for future use. The same is also true with respect to the two reservoirs which may be made of glass or of a suitable transparent plastic of a type which can be either sterilized or such as would warrant being discarded after use.

The two reservoirs are connected together by the struts to form one unit. As indicated above, this unit is mounted on a suitable stand at a level slightly below that of the patient. As the blood flows into these two reservoirs through the conduit means provided, a syphon eifect is produced. This syphon effect may be increased or decreased by lowering or raising the two reservoirs, which is easily accomplished because of their simple construction, to facilitate or retard the rate of flow of blood from the patient into the reservoirs. As shown in FIG 1, the inlet 22 to the reservoir 12 which receives blood from the venae cavae is so located that the blood flows some distance down along the inner wall of the inclined body portion of the reservoir. This, it has been found, tends to avoid foaming of the blood and also provides a convenient visual indication of the rate of fiow of blood from the patient. On the other hand, the inlet 16 to the reservoir 12, which receives blood from the pulmonary vein, is located well below the level of blood in that reservoir to avoil entrainment of air. By providing the connections 18, 20 and 24, 26 adjacent to the lower portion of their respective reservoirs, the operator can, by maintaining the level of blood in these reservoirs well above these connections, avoid any danger of air entering the circulating blood stream. Should occasion require, blood from a donor may be added to either one or both of the reservoirs through their open upper ends and an automatic gravity feed device may be provided for this purpose.

Having thus described our invention, what we claim as new and desire to secure by Letters Patent of the United States is:

l. A pump for use in the extracorporeal circulation of blood comprising a pair of pumping units each having a circular shaped compressible tubular pumping member, a support for each of said pumping members, a pump shaft extending through said supports and centrally located relatively to said circular pumping members, a pair of arms secured to said shaft, an impeller member mounted for radial adjustment on each of said arms and adapted to cooperate with one of the pumping members, and a separate means carried by each of said arms for radially adjusting the impeller member mounted thereon to vary the action of said impeller member on its associated pumping member during the operation of the pumping unit, and power-operated means for rotating said pump shaft.

2. A pump for use in the extracorporeal circulation of blood comprising a pair of pumping units each having a circular shaped compressible tubular pumping member,

a support for each of said pumping members, a pump shaft extending through said supports and centrally located relatively to said circular pumping members, a

pair of arms secured to said shaft, an impeller member mounted for radial adjustment on'each of said arms and adapted to cooperate with one of the pumping members, a separate means carried by each of said arms and manually operable to effect radial adjustment of the impeller member thereon to vary the action of said impeller member on its associated pumping member during the operation of the pumping unit, and power-operated means for rotating said pump shaft.

3. A pump for use in the extracorporeal circulation of blood comprising a pair of pumping units each having a circular shaped compressible tubular pumping member, a support for each of said pumping members, a pump shaft extending through said supports and centrally located relatively to said circular pumping members, a pair of arms secured to said shaft, a rotary impeller member mounted for radial adjustment on each of said arms and adapted to cooperate with one of the pumping members, means carried by each of said arms and shiftable in directions extending axially of the pump shaft to effect radial adjustment of the impeller member thereon in response to rotation of the pump shaft to vary the action of said impeller member on its associated pumping member during operation of the pumping unit, and poweroperated means for rotating said pump shaft.

4. A pump having a circular shaped compressible tubular pumping member, a support for the pumping member, a pump shaft extending through said support and centrally located relatively to the circular pumping member, an arm secured to said pump shaft, a rotary impeller mounted on said arm for radial adjustment and adapted to cooperate with the pumping member, means carried by the arm and shiftable in directions extending axially of said pump shaft to effect radial adjustment of said rotary impeller thereon in response to rotation of said pump shaft to vary the action of the impeller on the pumping member during the operation of the pump, and power-operated means for rotating the pump shaft.

5. A pump for use in the extracorporeal circulation of blood comprising a pair of pumping units each having a circular shaped compressible tubular pumping member, a support for each of said pumping members, a pump shaft extending through said supports and centrally located relatively to said circular pumping members, a pair of arms secured to said shaft, a rotary impeller member mounted for radial adjustment on each of said arms and adapted to cooperate with one of the pumping members, an adjusting knob carried by each of said arms and shiftable axially of said pump shaft, means controlled by said knob and operable to effect radial adjustment of the impeller member thereon in response to rotation of the pump shaft to vary the action of said impeller member on its associated pumping member during the operation of the pumping unit, and power-operated means for rotating said pump shaft.

6. A pump having a circular shaped compressible tubular pumping member, a support for the pumping member, a pump shaft extending through the support-and centrally located relatively to said circular pumping memher, an arm secured to said pump shaft, a rotary impeller mounted on said arm for radial adjustment and adapted to cooperate with the pumping member, an adjusting knob carried by said arm and shiftable in directions extending axially of said pump shaft, means controlled by said knob and operable to effect radial adjustment of the impeller thereon in response to rotation of the pump shaft to vary the action of said impeller on the pumping member during the operation of the pump, and power-operated means for rotating the pump shaft.

7. A pump for use in the extracorporeal circulation of blood comprising a pair of pumping units each having a circular shaped compressible pumping member, a support for each of said pumping members, a pump shaft extending through said supports and centrally located relatively to said circular pumping members, a pair of arms secured to said shaft, a rotary impeller mounted on each of said arms for radial adjustment and adapted to cooperate with one of the pumping members, a differential screw associated with each arm for eifecting radial adjustment of the impeller mounted thereon, a reversible drive mechanism carried by each arm for operating the screw associated therewith, an adjusting knob carried by each of said arms and shiftable in directions extending axially of said pump shaft for controlling the drive mechanism carried thereby to cause rotation of its screw in response to rotation of the pump shaft to eifect radial adjustment of the impeller on said arm thereby to vary the action of the impeller on its associated pumping member, and power-operated means for rotating the pump shaft.

8. A pump having a circular shaped compressible tubular pumping member, a support for the pumping member, a pump shaft extending through the support and centrally located relatively to said circular pumping member, a rotary impeller mounted on said arm for radial adjustment and adapted to cooperate with said pumping member, a differential screw for effecting radial adjustment of the rotary impeller, a reversible drive mechanism for operating said screw, an adjusting knob carried by said arm and shiftable in directions extending axially of said pump shaft for controlling the drive mechanism to cause rotation of the screw in response to rotation of the pump shaft to efiect radial adjustment of said impeller on said arm thereby to vary the action of the impeller on the pumping member, and power-operated means for rotating the pump shaft.

References Cited in the file of this patent UNITED STATES PATENTS 459,053 Traux Sept. 8, 1891 459,055 Traux Sept. 8, 1891 487,136 Traux Nov. 29, 1892 1,099,473 Sundh June 9, 1914 1,284,212 Barber Nov. 12, 1918 1,703,361 Pohl Feb. 26, 1929 2,319,485 Alabrune May 18, 1943 2,334,148 Jones Nov. 9, 1943 2,612,839 Denny Oct. 7, 1952 2,651,264 Bmckmann Sept. 8, 1953 2,652,831 Chesler Sept. 22, 1953 2,705,493 Malmros et al. Apr. 5, 1955 2,787,456 Bowman Apr. 2, 1957 2,789,514 Hill Apr. 23, 1957 2,807,213 Rosen Sept. 24, 1957 FOREIGN PATENTS 21,859 Great Britain of 1892 339,735 'France June 17, 1904

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