US2689565A

US2689565A - Blood pump

Info

Publication number: US2689565A
Application number: US324687A
Authority: US
Inventors: Gobel Charles
Original assignee: Individual
Current assignee: Individual
Priority date: 1952-12-08
Filing date: 1952-12-08
Publication date: 1954-09-21
Anticipated expiration: 1971-09-21

Description

Sept. 2l, 1954 c. GOBEL 2,689,565

BLOOD PUMP Filed Dec. 8, 1952 4 Sheets-Sheet 2 66" Fly' 5.

l I l l g3 La# \5, 103 for 10.3 ro/BJ 59 8o 74 27' l G` 58 5 100 8? 33 v n .2.2 '75 53' /0 q 5'? E L9 o E 8 I 172 T 22 2 L 97 26 l 33 G Q a 'o' o 55 58 00 78 80 5&2 lNvENToR Sept. 21, 1954 C, GQBEL 2,589,555

BLoon PUMP v Filed Dec. 8, 1952 4 Sheets-Sheet- 1 for 83 as `llllllllllli IIIIHIIIIIIIIIII .III- Il.

INVENTOR Sept. 21, 1954 C. GOBEL 2,689,565

BLOOD PUMP Filed DBG. 8, 1952 4 Sheets-Sheet 4 lNvENToR CHARLES GOBEL Patented Sept. 21, 1954 UNITED 5S OFFICE {BLOOD PUMP Charles GobeL Philadelphia, (Pa. Application December 8, 19521, Serial Nog-$24,687

(Cl. 12S-214) 14 Claims. il

The present invention urelates -te pumps, par.- ticularly of the `character fused Vin `the pumping of blood in medical treatment.

A purpose `of the invention is Ato permit the circulation of blood `'frcnngthe body lof a living patient without fdamage lto the blood.

Afurtherpurpose fis tosubstitute a mechanical pump for the animal .or human heart .during cardiac surgery.

A further purpose `is to aid the vfunctioning .of lthe human heart vin medical treatment by making available an additional source of pumping pressure to circulate zblood.

A further purpose is to avoid regurgitation in the pumping of liquidsand especially of blood during medical treatment.

A further purpose `is to facilitate cleaning and especially vsterilizing of pumps, particularly blood pumps.

A further :purpose is. to Asimplify the mechanism required vfor pumping blood in medical treatment.

A further purpose is -,to .connect positive displacement piston pumps tofthetops Lof respective reservoirs and to connectelastomer inlet and outlet tubes to rthe bottoms of the respective reservoirs and to pinch `fthe tubes to gmake them function as valves Yunder conditions which are nontraumatic` to the blood.

A `further purposeis lto .open and close the inlet tube of one reservoir and. fthe `outlet tube of another reservoir by the same depressor.

A Vfurther purpose is :to :delay the .opening of the outlet .tubeof a particular reservoir when the inlet tube of zthe otherfreseryoir is open ing, desirably by Van auxiliary .depressor so that .the outlet tube will ,not open until the .discharge structure of thefpump .'hasbuilt up .a pressure at least .-.equal :to that the discharge tube beyond the valve.

A `further..purpose is to mount those.,parts :of theipump r.which .require sterilization, particularly the `reservoirs and :the .-valves, .on .1a read-ily removable plate `suitably..carrying anyils .against which `the `depressors act.

`A further purposeis to 115618,11 extremely fthin curved :edge ontheidenressor toavod the likelihood of orushinared @muscles rofithefblood.

.A .further purpose 'isfto `zvarfy ati-1e :point of beginning and ending offyalve closure by ediuetment o f the dwellofpams.

A further purpose is to avoid-.damage tothe fragile pumpsfvbyipixzoting 1the-sa-meon rocking pivots.

UA1-further .purpose is to ymmomplsh a -seal to 12 ztlae tops of fthe reservoirsiwithout athe --necessity of providing bulges or ground glass .edges von the reservoirs.

Further purposes appear in the specification and in fthe plaims. Y

In the drawings `I ,have Achosen to illustrate onefon-ly fof the :numerous embodiments vin which my `invention lmay appear, selecting the form `.Slliriwr-1 from thestandpoints .of convenience in i1- lustration, satisfactory operation and .-clea-r demonstration :of ,the lprinciples involved.

Figure 1 Ais asimplied diagram of the pump of 'the `ir ryention `showing :only one cycle.

vFigure Zis a diagram yof the ltwo cycle `pump but .omitting the` eonnections Lto fthe fdialyzer and to the patient.

Figline :3 :is .a iside :elevation of thezpreferred embodiment Offthe pump .oizthe invention.

,Figure y4 :is .a `top plan view ofthe pump `of Eigure V3.

Figure 5 is a front elevation of the pump of the invention.

.Figure 6 lis `arfcli'illfe.1113911157,rear elevation .of the 'Dump .of fthe invention showing the .i drive but Qmitting. the structure :at the fron-t.

LFl'gilre y"7 is @fragmentary section .on "the line l-.l of "Figure-,3. l

Figure is ia fragmntary section, `on the line 8-8 of Figure 4.

Figure :9 is an .enlarged fragmentary .section 0.11 :the clin@ .8f- 9 vof .Figure A.

Figure is ran enlarged fragmentary section .on Vthe :line :Li-.m of `Figure i3.

.Figui-Cdl isgan enlarged fragmentary .elevation .of ftheca-m and follower.

'Describing :in illustration Vbut not in limitation :and .referring to the drawings:

YThe .pump of fthe invention has other applications and can 4be `used forpumping other liquids, but -it is especiallyvsuited 'for pumping blood to a mechanical kidneypor `as `alieart pump. As the difference from thestandpoint of the pumpis merely one .of site., .it `.will 'be sufeient to illusm trete thedeyceapplied to the .mechanicalkidney "The .methaliieal .kidney .is 2prilnarily .used treatment of injuries .anddiseases which have .caused temporary .maltunctjoning of zthe kidneya'where .it is desired to minimize theieiieets 0f premia @edil-1111s prolong the. :life y0f the `patient funtiksueh time ,las `his 'kidneys :may :regain prOpSl 4function. Such temporary,fmaltunctioning' may #be due to ingestionfof poisons, shock, transfusion of mismatched :blood andsevere trauma, such as is seen in battle casualties. The condition is referred to as acute renal failure, anuria or lower nephron nephrosis.

The dialyzer has a semi-permeable membrane which permits the transfer of soluble blood components other than protein materials to the opposite side of the membrane, and the transfer of electrolytes such as sodium chloride either way, depending on the relative concentrations on the two sides of the dialyzer. The dialyzer thus is an effective way of removing poison from the blood, and of readjusting the salt content of the blood. The dialyzer also can act as a lter to remove excess water from the blood and thus relieve edema.

A number of blood pumps have been developed which draw off blood from the body and pass it through the dialyzer and return it to the body.

acute They have, however, in the past been subject to several diiiiculties of which the following are examples:

l. Blood is an extremely fragile material, as any impacting or crushing during pumping has a traumatic or destructive effect upon red corpuscles, with disastrous consequences to the patient.

2. Standard hospital practice requires that the blood pump be sterilized after each use, and some of the prior art blood pumps have been so complicated that the cleaning and sterilizing requires a day, thus restricting the availability of the equipment.

3. Many of the prior art devices have required the use of very extensive rubber components which have not been capable of withstanding the repeated autoclaving. Complexity and high expense has been a common difficulty in Such prior art devices.

The device of the present invention has the advantage that it is not traumatic, is very simple and inexpensive to produce, is easy to clean and sterilize, and can quickly be made available for the next use.

The device of the invention was rst used successfully in connection with the mechanical kidney to save the life of a patient who had already begun apparently fatal convulsions at the University of Pennsylvania Hospital on July 30, 1952. Careful tests for evidence of traumatic effect were made and the device has proved to be free from damage to the blood.

Figure l illustrates a typical set-up in connection with the mechanical kidney, only one phase of the pump being shown. An artery tube is connected into an artery of the patient 2| and this leads through inlet tube 22 and inlet check valve 23 to T connection 24 at the bottom of one of the

pump reservoirs

25 or 26. The top of each pump reservoir is connected by tube 21 to one of the positive displacement piston pumps 28 or 30 having cylinders 3| and pistons 32. The pumps are suitably glass hypodermic syringes, as well known in the art. An outlet tube 33 extends through cheek valve 34 to dialyzer 35. A pressure gage 35 is connected to the outlet.

The dialyzer has an inlet tube for fresh dialyzing solution 31 and a discharge connection 38 for dialyzate to waste 4U. Dialyzed blood passes from the dialyzer through tube 4I tov air trap 42 which maintains an air space 43 to allow any entrapped or entrained air to float out and prevent its entry into the body, and the trap has a valve controlled tube 44 at the top to determine the desired blood level in the trap. From the bottom of the trap blood passes by tube 45 to venous catheter 46, which returns the blood to the body of the patient 2l.

It will be evident for an understanding of the device, that during pumping the blood ranges in each reservoir between a lower level 41 which is achieved at the end of the discharge stroke and an upper level 48 which is achieved at the end of the suction stroke, and that the space in the tubes 21, in the

pumps

28 and 30 and in the reservoirs above the blood level 48 is filled with air, the pumping being accomplished by the change in liquid level due to the air pumped by the syringes. In the actual device shown, the pump is of two cycle construction, but' it will be evident that the pumping can be carried out less desirably on a single cycle basis and also more desirably on a multicycle basis.

The piston pumps as seen in Figure 2 operate alternately at any suitable speed desired, approximately 6 R. P. M. having been found to be a desirable speed in blood pumping. When one pump is on the suction strokethe other is on the compression stroke ancl vice versa.

The inlet tubes 22 branching at T 22 and the outlet tubes 33 joining at T 33 are of elastomer such as soft rubber or synthetic rubber, and the valves are produced by depressors 50 and 5| which act alternately. The inlet tube of one reservoir is carried beside the outlet tube of the other reservoir and the same depressor closes the inlet tube of one reservoir and the outlet tube of the other reservoir at approximately the same time and opens the two tubes together. However, as later explained, it is very desirable that the outlet tube should not open until slightly after the inlet tube has opened.

lThe structure of Figures 3 to ll inclusive embodies the device of Figures l and 2 in a convenient form. Base 52 mounts legs 53 which support a bodily removable plate 54 by Allenhead screws 55 extending into the legs. The plate mounts a standard 56 which at the top carries a cross arm 51 and at opposite ends the cross arm carries fittings 58 which engage and support the

respective reservoirs

25 and 26. Pipes 55 extend up through the plate to the cross arm 51 and at the bottom are connected to tubes 21 from the

respective pump

28 or 30. At the top the cross arm has a separate passage @I on each side connecting to the appropriate tube 55 to communicate with a male threaded hollow tubular portion 52 of the fltting 58. The male threaded portion at its lower end has a comparatively thin tubular portion 53.

A hollow female threaded cap 54 engages the male threaded portion 52 and has an inwardly extending fiange 55 at the lower end which has an interior bore in line with the bore of the tubular portion 53.

The upper end of the reservoir has a straight glass tube E6 which is surrounded and firmly engaged by a resilient rubber or other elastomer collar 61 which fits immediately inside the tubular portion B3 of the fitting part 62 and also inside the flange 65 of the fitting cap 64. An annular radially extending flange 55 on the collar intermediate its ends extends between and is gripped by the end of the tubular portion 63 of the male fitting and the upper portion of the flange 65 of the female fitting. By pinching the nange 68 by tightening the

metallic parts

62 and 64, pressure on the collar is applied to seal the top of the reservoir. The reservoir is thus eifectively connected and sealed to the fitting 58 and supported by the cross arm 51.

A main drive shaft 10 journalled at 1I on the base carries a bevelled pinion 12 which engages bevel gear 13 on cross shaft 14 journalled in drive rhausng -II5 :mounted 4cn the back E of :the .face plate IiZ.` Cross shaft im also :carries Lspeed reduction fgear I5 which intergea-rs with gear 111 ion `crank shaft `I3 `carrying ;cranks 80 :at the opposite xvends, `iwhichcranks.are A180" out rof phase. lThe 'cranks mivotally connect vat `8| with extensions x82 on pump pistcms .32 to manipulate the pistons `back rand :forth Theindividualpump barrels or cyl- :inders are pivotecllat B3 on pivot lugs 184 extending `up from 4.the base plate |52. Because of the `rfragile liglass) `character of the rpumps .in `the preferred form, the danger of `slight fmisalign- `ment which Wouldzcause crackingof the .parts is considerable, anda `rocking pivot Vis provided at 283. '.This is accomplished by providing an eniflargedopening 8.5 (Figure Vl7) acrossthe lug 84, "and reducing the fsection vof the pivot Lpin at 86 `from bothsides so that 'there is wide clearance forrocking in the opening 05.

The .crank shaft I8 carries, 180 vout of phase thereon, adjustable cams "81. Each-of the cams v:consistsof 'a camhub which is keyed or other- Awise fastened to thelshaft, a 'cam segment 90 vengaging one face` of the hub 88 fand `surrounding :the shaft and a cam segment 9| engaging one 4rface of the cam segment 9maand-surrounding the lshaft. An arcuate slit I 92 Ais provided in each of "the cam segments 90 and 9 I, and acam screw "93 `passes through both slots and is threaded into ring 38 to lock the cam segments in a predetermined position. Thus the beginning andend of "the cam dwell can be changedon either cam to :determine the exact setting desired. The seg- "ments oi course extend radially beyond the ring.

The dwell portion of the composite cam on each sideengages a follower roller `94 pivoted on afollower pin 95 which is guided in a holder 96 -`secured on the side of the housing "I5, Pointed ends 91 of the followers 95 engage in longitudinal slots 98 on the upper sides at the ends of valve fdepressor levers |00 pivoted intermediate their ends at |0I on journals Ill-2 on the base. The -opposite ends ofthe depressor levers carry `de "pressors 50 or 5| which'extend upwardly through `slots |03 inthe removable plate 54. Leaf springs |04 `under the rearward ends of the levers VIIlIl cause them to retract and keep the 'followers against the cams. The springs are `anchored at |05 to the base. Y

The form of the upper ends l|06 ofthe depres- "sors is important. While they should not be absolutely'sharp knifeedges, they should definitely be very narrow curves, so thatfthey will not crush blood in closing the `valve and cause trauma. Each depressorV passes 4immediately under 'the inlet tube of onereservoir and the `outlettube Aof "the other reservoir. The depressors operate qagainst anvils -Iill which are mounted by bolts |08 and spacer washers H0 on the removable plate'so that the appropriate vinlet ,tube 22 and the outlet tube 33 of the opposite phase pass between the depressor i0 or '5I and the anvil above. In order to prevent the outlet'from op'eningas quickly as the inlet, an auxiliary depressor 'plunger III (Figure 9) is mounted .in a cylinder H2 above the outlet tube 33 in line with thedepressor `in `the preferred embodiment. The auxiliary `depressor II I is spring urged vtoward .the tube 33 by spiral ,compression springr I I3 and .the limit of movement of the auxiliary depressor .downwardly is controlled `by screw I4 and adjustment nuts H5 and .H6 which .engage on the :top of `the cylinder aII2. AIn the form .shown in figures `the outlet .tubeissmaller than the inlet 6 tube, Vso that more Aiadvanceof the Lauxiliary depressor is needed to prevent the outlet tube from fopening when the -inlet -tube opens, but this Ycan Vbe :readily :adjusted with respect to the size of the tubes by adjusting the nuts I I5 and =I I 5 and screws `I I .4.

-In operation it will be -evident that when one `piston pump begins its suction stroke, the elastomer tubes which are -its valves are vadjusted so that `,the inlet -tube is open and the outlet tube is closed due to the `fact that the depressor engaging 4the inlet tube is ,down `and the depressor 4engagingrthe outlet tube is up. The opposite condition applies to the other pump and reservoir and Atheir valves. It :is very desirable that .the outlet valves close early 4and open `late. .If we considerreservoir 25 at the Vposition in whichits syringe is :retracted at the end of' `its .suction stroke, `there `is no superatmospheric pressure in theaircompartment of thatpreservoir. Whenznow the compression stoke starts, if the corresponding outlet `valve were to open immediately, as soon as the 'inlet -valve closes there would be regurgitation :back through the outlet tubing since `the outlet tubing is under a hydrostatic pressure -oi `as much Vas .100 to 200 millimeters of mercury above atmospheric. It is therefore desirable that the Aoutlet valve open later, the time lag being determined by adjustment of nuts H5 and H6 and screw `I t4 so that the pressure in the pump yand reservoir can build up to at least the equal of the pressure in the outlet tubing beyond the' -outlet valve before the outlet valve opens.

The same feature to advantage will take place 'if a substantial pressure exists in the inlet, but since the inlet pressure is normally much lower, of the order of 0 to 40 millimeters of mercury below atmospheric, this is less important in the case of the inlet.

When the depressormoves down, theinlettube opens irst but the `outlet tube remains closed for a small interval, and then opens when the pressures on either side ofthe depressor are equalized. On the closing cycle, when the depressor is moving up, the cam has been so shaped as to allow rapid upsweep 0I" the depressor so that the inlet `and outlet tubes `are closed almost simulV taneously. The cam, however, provides for lowering of the Adepressor more slowly so that the "-inlettubes do not open at the same time.

rlherea-son for desiring to avoid regurgitation "in bloodpumping is not only the desire to get 'greater :emciency in pumping and more rapid flow, but to avoid the possibility oi. detaching mforeign material inthe tubing and reservoirs such Yas minute iibrous clots, which might injure the patient.

it will'be evident that the two depressors work oppositely, Aeach opening and closing the inlet and outletoi a diierent reservoir.

The-extremely narrow curvededgeon each depressor-prevents the possibility of trapping and squeezing bood and cau'singtraumaticl deterioration.

-Ii -the adjustment is not that desired, it isvvery to stop the pump and readjust the cam positions, changing either the beginning or the end -of the dwell.

It has been found in service thatthe device can 'be used without danger of breakage of the syringe pumps, due tothe rocking action at their pivots.

Thepump oi'the invention has proved to be an improvement over more complicated Vdevices `since tit `appears less formidable to the 'patient' at the bedside and therefore is less likely to frighten him.

After the use on a particular patient has been completed, it is very simple to clean and sterilize the equipment. For this purpose the fittings 58 at the tops of the reservoirs are loosened, and then the screws holding the removable plate are released. The plate can readily be removed forward, after which the tubes 27 are detached from pipe 60. All the equipment which requires sterilizing is then supported on the removable plate and can be retained in this position during Washing and during sterilizing including autoclaving.

The fitting using the rubber collar at the top of the reservoirs is very sanitary as the collars can be pulled oif for separate sterilizing if desired after the fittings are loosened and the upper ends of the reservoirs being straight tubes do not have any interior recesses which are difcult to clean.

In view of my invention and disclosure variations and modications to meet individual whim or particular need Will doubtless become evident to others skilled in the art, to obtain all or part of the benefits of my invention Without copying the structure shown, and I therefore claim all such insofar as they fall Within the reasonable spirit and scope of my invention.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. In a blood pump, a reservoir, a positive displacement air pump connected to the top of the reservoir, an inlet valve connected to the bottom of the reservoir, an outlet valve connected to the bottom of the reservoir, a connection adapted to Withdraw blood from the body of a living animal to the inlet valve, a connection adapted to return blood to the body of the animal from the outlet valve, means for opening the inlet valve and closing the outlet valve during the suction stroke and means for opening the outlet valve and closing the inlet valve during the discharge stroke, the means for opening the outlet valve becoming operative after the discharge stroke has commenced and built up a pressure sufficient to overcome the pressure in the outlet connection.

2. In a blood pump, a pair of pumping reservoirs, a pair of piston air pumps each connected to the top of a different reservoir, a pair of inlet valves each connected to the bottom of a different reservoir, a pair of outlet valves each connected to the bottom of a diierent reservoir, a connection adapted to receive blood from a living animal to both inlet valves, a discharge connection adapted to return blood to the animal connected to both of the outlet valves, means for opening each of the inlet valves and closing each of the outlet valves during the suction stroke of the corresponding pump, means for closing each of the inlet valves during the compression stroke .of the corresponding pump, and means operative at a point after the beginning of the compression stroke of each pump for opening the corresponding outlet valve at a time at which the pressure above the reservoir has built up to a value at least equal to the pressure in the discharge connection.

3. In a blood pump, a pair of pumping reservoirs, a pair of piston air pumps each connected to the top of a different reservoir, a pair of inlet valves each connected to the bottom of a different reservoir, a pair of outlet Valves each connected to the bottom of a different reservoir,

Ya connection adapted to receive blood froma living animal to both inlet valves, a discharge confnection adapted to return blood to the animal connected to both of the outlet valves, common means for opening and closing the inlet valve of one reservoir and the outlet valve of the other reservoir and means for delaying the opening of the outlet valve of one reservoir behind the closing of the inlet valve of that reservoir to permit building up of air pressure on the compression stroke above the pressure of the blood in the discharging reservoir to prevent regurgitation from the discharge line.

4. In a blood pump, a pair of pumping reser voirs, a pair of piston air pumps each connected to the top of a different reservoir, a pair of inlet valves each connected to the bottom of a different reservoir, a pair of outlet valves each connected to the bottom of a dierent reservoir, a connection adapted to receive blood from a living animal to both inlet valves, a discharge connection adapted to return blood to the animal connected to both of the outlet valves, common means for opening and closing the inlet valve of one reservoir and the outlet valve of the other reservoir and means for accelerating the closing of the outlet valve of one reservoir ahead of the opening of the inlet valve of that reservoir to permit holding the pressure in the discharge connection on the suction stroke to prevent regurgitation from the discharge line.

5. In a blood pump, a pair of pumping reservoirs, a pair of piston air pumps each connected to the top of a different reservoir, a pair of inlet valves each connected to the bottom of a difierent reservoir, a pair of outlet valves each connected to the bottom of a different reservoir, a connection adapted to receive blood from a living animal to both inlet valves, a discharge connection adapted to return blood to the animal connected to both of the outlet valves, common means for opening and closing the inlet valve of one reservoir and the outlet valve of the other reservoir and means for delaying the opening of the outlet Valve on one reservoir behind the closing of the inlet valve of that reservoir to permit building up of air pressure on the compression stroke above the pressure of the blood in the discharging reservoir to prevent regurgitation from the discharge line and means for accelerating the closing of the outlet valve of one reservoir ahead of the opening of the inlet valve of that reservoir to permit holding the pressure in the discharge connection on the suction stroke to prevent regurgitation from the discharge line.

6. In a pump, a pair of reservoirs, a pair of positive displacement pumps connected to the tops of the respective reservoirs, a resilient inlet tube connected to the bottom of each reservoir, a resilient outlet tubelconnected to the bottom of each reservoir, the inlet tube of one reservoir being positioned beside the outlet tube of the other reservoir, a pair of depressors each operating on the inlet tube of one reservoir and the outlet tube of the other reservoir and means for bringing the depressors into closing relationship of the respective tubes alternately.

7. In a pump, a pair of reservoirs, a pair of positive displacement pumps connected to the tops of the respective reservoirs, a resilient inlet tube connected to the bottom of each reservoir, a resilient outlet tube connected to the bottom of each reservoir, the inlet tube of one reservoir being positioned beside the outlet tube of the other reservoir, a pair of depressors each operating on the inlet tube of one reservoir and the outlet tube 9 of the other reservoir, means for bringing the depressors into closing relationship of the respective tubes alternately, and means for holding the outlet tube of a particular depressor closed during the initial stage of the opening motion of the depressor after the inlet tube has closed and then opening the outlet tube.

`8. In a pump, a pair of reservoirs, a pair of positive displacement piston pumps connected to the tops of the reservoirs, a resilient inlet tube connected to the bottom of each reservoir, a resilient outlet tube connected to the bottom of each reservoir, the inlet tube of one reservoir being carried beside the outlet tube of another reservoir, means for manipulating the pistons alternately, depressors synchronized with the pistons and moving to close the inlet tube of one reservoir and the outlet tube of another reservoir and then to open the same, anvils engaging the opposite sides of the tubes from the depressors, auxiliary depressors mounted on the anvils engaging the outlet tubes and spring means urging the auxiliary depressors toward the outlet tubes so that the outlet tube remains closed after the inlet tube closes when the main depressor is retracted.

9. In a pump, a pair of reservoirs, a pair of positive displacement piston pumps connected to the tops of the reservoirs, a resilient inlet tube connected to the bottom of each reservoir, a resilient outlet tube connected to the bottom of each reservoir, the inlet tube of one reservoir being carried beside the outlet tube of another reservoir, means for manipulating the pistons alternately, depressors synchronized with the pistons and moving to close the inlet tube of one reservoir and the outlet tube of another reservoir and then to open the same, anvils engaging the oppositelsides of the tubes from the depressors, auxiliary depressors mounted on the anvils engaging the outlet tubes, spring means urging the auxiliary depressors toward the outlet tubes so that the outlet tube remains closed after the inlet tube closes when the main depressor is retracted, and adjustments for the maximum strokes of the auxiliary depressors.

10. In a pump, a pair of reservoirs, a pair of positive displacement piston pumps connected to the reservoirsr means for driving the pumpsin unison and opposite in phase, an elastomer inlet tube connected to the bottom of each reservoir, an elastomer outlet tube connected to the bottom of each reservoir, the inlet tube `of one reservoir and the outlet tube of the other reservoir extending in side by side relation, depressor cams having dwell positions driven by the means for driving the pumps respectively out of phase and having adjustments of the beginning and end of the cam dwell position, and depressors operatively connected to the depressor cams, one of which engages and closes and opens the inlet tube of one reservoir and the outlet tube of the other reservoir While the other engages and opens and closes the inlet tube of one reservoir and the outlet tube of the other reservoir.

11. In a pump, a pair of reservoirs, a pair of positive displacement piston pumps connected to the reservoirs, means for driving the pumps in unison and "opposite in phase, an elastomer inlet tube connected to the bottom of each reserbottom of each reservoir, the inlet tube of one reservoir .and the outlet tube of the other reservoir extending in side by side relation, depressor cams having dwell positions driven by the means for driving the pumps respectively out of phase and having adjustments of the beginning and end of the cam dwell position, depressors operatively connected to the depressor cams, one of which engages and closes and opens the inlet tube of one reservoir and the outlet tube of the other reservoir while the other engages and opens and closes the inlet tube of one reservoir and the outlet tube of the other reservoir, anvils engaging the opposite sides of the tubes with respect to the depressors and auxiliary depressors on the anvils engaging the opposite sides of the outlet tubes to maintain the same closed after the inlet tube is closed on the compression stroke.

12. In a blood pump, a pair of reservoirs, positive displacement piston pumps connected to the respective reservoirs at the tops, an inlet tube connected to the bottom of each reservoir, an outlet tube connected to the bottom of each reservoir, the inlet and outlet tubes of the opposite reservoirs being carried side by side, and depressors having very thin rounded edges extending across the pairs of inlet and outlet tubes .and resiliently closing the same, the valves being non-traumatic due to thenarrow compression face on each depressor.

13. In a blood pump, a pair of positive displacement pston pumps, means for driving the pumps in alternate phases, a base supporting the means for driving the pumps, a readily removable plate mounted detachably on the base, a pair of reservoirs mounted on the plate, a connection from the top of each reservoir to a different purnlp, elastomer inlet tubes' extending over the plate and connected to the bottom of each reservoir, elastomer outlet tubes extending over the plate and connected to the bottom of each reservoir, the inlet tube of one reservoir being carried beside the outlet tube of the other reservoir, an .anvil over the inlet tube of each reservoir and the outlet tube of the other reservoir in contact therewith and depressor means beneath the plate operatively connected to the driving means and acting on the tubes to make them function as valves against the anvil, the reservoirs and tubes being removable as a unit for sterilization. ,Y

14g. In a pump, a pair of positive displacement piston pumps of fragile material, a rocking pivot supporting one end of each pump, crank means manipulating the pistons of the pumps out of phase, a pair of reservoirs, one connected at the top to each pump, an elastomer'inlet tube connected to the bottom of each reservoir, an elastomer outlet tube connected to the bottom of each reservoir, and depressor means for closing the tubes and opening the same to permit them tounction as valves. Y

References Cited in the ille of this patent UNITED STATES PATENTS Number Name Date 2,099,722 Byers Nov. 23, 1937 2,474,665 Guarino June 28, 1949 2,625,932 Salisbury Jan. 20, 1953