CA2141327A1

CA2141327A1 - Centrifugal blood pump

Info

Publication number: CA2141327A1
Application number: CA002141327A
Authority: CA
Inventors: Earl W. Clausen; Lloyd C. Hubbard
Original assignee: Individual
Current assignee: Cobe Cardiovascular Inc
Priority date: 1992-07-30
Filing date: 1993-07-28
Publication date: 1994-02-17
Also published as: DE69331271T2; WO1994003731A1; DE69331271D1; EP0653022A1; EP0653022B1; US5360317A; JP2003176800A; JP3399528B2; JPH08501366A; EP0653022A4

Abstract

A centrifugal pump (10) for pumping biological fluids such as blood includes a housing (12) which defines a pumping chamber (36).
The pumping chamber (36) encloses an impeller (14) mounted on a spindle (16). The impeller (14) carries coupling mechanisms which couple with an external source of rotation to rotate the impeller (14). The spindle (16) allows the impeller (14) to rotate freely, but both ends of the spindle (16) are constrained in the axial and lateral directions. The housing (12) includes an inlet (24) and an outlet (26).

Description

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w094/0373t 21~13~ 7 Pcr/US93/07110 I^ !:

CENTR~FUGAL BLOOD PUMP
BACKGROUN~ QETHE ~Q~
The present invention rela~es to pumps and more particularly to centrifugal blood pumps without the requirement of a rotating seal to pro~ect the S pump beanngs from the pumped blood.
Delicate surgical procedures require that the site of surgery remain motionless during the surgical process. This rnade early heart surgery difficult to impossible as interruption of the heart's pumping ac~on for the required length of time would be invanably fatal.
During the 1960s, prolonged and non-fatal stoppage of the heart became possible by use of newly developed "heart-lung" machines. These machines consisted of a mechanical blood pump combined with a blood oxygenator. They were capable of ta~ng over the function of the natural he~
and lungs for periods of up to several hours, enabling the development of 15 techniques leading to today's extensive practice of open-heart surgery.
The first practical mechanical b~ood pumps used were peristaltic or "soller" pumps. The pumping ac~on of a roller pump derives from the compression of a section of the flexible plastic tubing which ca~ies the blood through the heart-lung machine. A moving roller presses the tubing against a 20 semicircular platen, moving the blood forward in the tubing. The speed of themo~ing roller and the diameter of the tubing control the rate of blood flow.
Although the roller pump was and is simple and reliable, it has two characteristics which can endanger the patient undergoing surgery. First, if flow is inadvertently obstructed, the pressure produced by a roller pump may 25 exceed the bursting strength of the tubing circuit. Second, if air is accidentally introduced into the tubing circuit, it will be pumped to the patient along with the blood. Either of these conditions may result in serious or fatal consequences tOthe patient.
In 1976, centrifugal blood pumps began to replace the roller W O 94103731 PC~r/US93/07110 21~i~27 j :

-2-pump as the ~heart" of the heart-lung machine. The pumping action of a centrifugal pump derives from the rotation of an impeller within a pumping chamber. Pump pressure is controlled by the rotational speed of the impeller.
At operational speeds, excessive pressure cannot be produced. Additionally, the centrifugal forces in the pump form a natural air trap and, with massive introduction of air, deprime and discontinue pumping altogether. These two safety features, and the lower blood damage caused by these pumps, is now widely recogniæd, and has led to their extensive use for open heart surgery.
In the early 1980s it was demonstrated that a mechanîcal blood 10 pump could be used as a heart-assist pump for patients who could not be separated from the heart-lung machine following surgery. The readily available centrifugal blood pumps were quickly applied to this situation as well as to themore routine use during heart surgery.
The fragility of the blood presents several problems for the design 15 of mechanical blood pumps. Excessive shear forces cause rupture of the red blood cells (hemolysis). High flow velocity rates are needed over local areas of friction (such as seals) to prevent points of high temperature which cause blood damage and the accumulation of clot deposits.
Application of rotational impeller motion by conventional shaft 20 drives has not been practical due to the need for a sterile baITier between the pumped blood and the pump drive mechanism. For this reason, centrifugal blood pumps commonly utilize a magnetic coupling between the pump impeller (or impeller shaft) and the drive motor.
Previous centrifugal blood pumps have relied on conventional ball 25 bea;rings to support the impeller shaft. A rotating seal was used to protect the bea;rings ~rom contamination by the pumped blood. Some centrifugal blood pumps utilized magnets carried by the impeller, which was supported by bearings mounted on a stationary shaft. A shaft seal was also required to protect the bearings from ~ontamination by the pumped blood.

WO 94/03731 P~lUS93tO7110 2~`~I3~7 Due to the corrosive nature of blood, shaft seals usually fail after a relatively short time, exposing the bearings to cont~mination. If the failure is not detected, bearings may overheat, causing damage to the blood. Blood damage can lead to hemolysis, clot formation and s~oke. The short useful life of current cen~ifugal blood pumps mandates their frequent re~lacement and is the single most important problem yet to be solved with these devices.
SUMMARY QF l~ INVENTI~
The present invention is a sealless centrifugal pump for pumping biological fluids such as blood. The pump has a housing which defines a pumping chamber. An impeller which rotates about an ax~s is disposed within the pumping chamber. l~e pumping chamber has an inlet provided at the impeller axis of rota~on and an outlet provided along ~e periphery of the impeller. An ex~ernal source of ro~on is disposed outside the pumping chamber which causes the impeller to rotate. The hous~ng has constraining mechanisms (preferably journal bearings) which constrain both the inlet side andthe base side of the impeller from movement m both axial and lateral direc~ons.
Because there are no moving parts which extend through a wall of the housing, and particuhrly because there is no torque-providing shaft whichextends through a housing wall, the present invention has no seal around a moving part and no opporhlnity for seal failure. Because the source of rotation does not contact the blood, sterility can be ensured. Because the impeller is constrained both on its inlet and base side from movement in both the axial and lateral directions, there is no opportunity for dislocation or misalignment of the Impeller.
BRIEF DFSCRIP'llON QF THE I)RAWl~GS
FIG. 1 is an exploded perspective view of ~e present invention.
FIG. 2 is a top plan view of the present invention.
FIGS. 3A and 3B are top and bottom plan views of the impeller of the present invention.

w094/03731 PCr/US93/07110 21~3~
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FIG. 4 is a cross-se~tional side view of the present invention as ,,, seen from section line 4~ of FIG. 2. .
FIG. S is an cross-sectional side view of an alternate embodiment of the inlet bearing surface of the present invention.
FIG. 6 is a cross-sectional top view of the alternate embodiment -~
of the inlet beanng surface as seen from section line ~6 of FIG. 5. - `' DETAILED DE~I~LQF l~, P~EFERREl;) EMBODIMENTS
A Fi~s Embodiment ~ GS. 1~ ,,~--A preferred embodiment of a centrifugal blood pump 10 of the present invention is shown in FIGS. 1-4. Blood pump 10 includes housing 12 ' which encloses impella 14 and support shaft or spindle 16. Impeller 14 and i ' spindle 16 rotate about axis of rotation 18. Housing 12 has separate parts for ~ '-ease of assembly, including upper enclosure 12A and base 12B, which are ' ' connected and sealed together, such as by ultr,asonic welding. ' I5 Upper enclosure 12A includes inlet wall 20, circumfe~ential wall ~ ,' 22, inlet 24, and outlet 26. Base 12~ includestottom waIl 28, cylindrical side ~' wall 30, mounting flange 32, and pedestal 34. Pumping chamber 36 (FIG. 4) ,,' is defined as the volume enclosed by inlet wall 20, circumferential wall 22 and i ~
bottom wall 28. '' Inlet 24 is a J-shaped tubular member which has one end 38 attached to inlet wall 20 and an opposite free end 40. Ridge 42 on an outer surface of inlet 24 facilitates attachment of inlet tubing (not shown) from a reservoir/oxygenator or from the patient to free end 40 of inlet 24.
Outlet 26 is a tubular member which extends fro~n circumferential wall 22 to free end 44. Ridge 46, adjacent free end 44, facilitates attachment to outlet 26. of outlet tubing (not shown) which leads to the patient.
As shown in FIG. 3A, impeller 14 rotates about a~is of rotation `' 18 with a direction of rotation indicated by arrow R. Impeller 14 has full impeller blades 48 and short impeller blades 50 which are attached to platform wos4/n373l Pcr/us93/o7llo ¦ ~
~ ~ ~ 3 ~ 7 -s-section 52 of impeller 14. Platforsn section 52 is disk-sh~ped and includes top surface 54, bottom sur,face 56, outer cylindrical surface 58 and central circulation hole 60. Full blades 48 extend from hub 62 across central circulation hole 60 to platform section 52, while short blades 50 extend only S along top surface 54 of platform section 52.
As shown in FIG. 3B, bottom surface 56 of platform section 52 contains a plurality of r,adial grooves 63. The purpose of grooves 63 is to counteract a tendency of impeller 14 to shift in the a~cial direction toward inlet 24 as impeller 14 rotates.
FIG. 4 shows impeller 14 attached to spindle 16, so that impeller 14 and spindle 16 rotate together about axis of rotation 18. Inlet end 16A of spindle 16 extends into and rotates within journal bearing 64A. Base end 16B
of spindle 16 extends into and rotates within journal bearing 64B.
The constraining mechanism of the present invention is provided by journal bearings 64A and 64B, which capture and support spindle 16 while permitting spindle 16 to rotate. Journal bearings 64A,64B are disposed coaxially with and circumferentially around axis of rotation 18. Journal be~ring64A is press fit into recess 66 in the interior side wall of inlet 24. Journal beanng 64B is press fit into recess 68 in pedestal 34.
The inner diameters of the recesses of journal bearings 64A and 64B are slightly greater than the outer diameters of the respective ends 16A,16Bof spindle 16~ so that a small lateral clearance is defined. The distance between the inner end surfaces of journal bearings 64A,64B is slightly greater than the length of spindle 16~ defining a small axial clearance. ' ~5 Platforrn section 52 of impeller 14 contains magnets 70, whichcouple wi,th magnets 72 carried by rotor 74, to rotate impeller 14 and spindle 16 about axis of rotation 18. Electric motor drive shaft 76 is cor~nected to rotor 74 and provides torque to rotate magnets 72 and rotor 74 about axis of rotation 18. Magnets 70 and 72 couple together so that impeller 14 rotates at the same W O 94J03731 PC~r/US93/07110 ~ ~

2l4~3Z l I

speed as rotor 74. The speed of drive shaft 76, therefore, deterrnines the speed , of impeller 14. `
Impeller 14 is attached to spindle I6 such that bottom surface 56 of platform section 52 is a small distance above bottom wall 28. Impeller 14 fits within pumping chamber 36 to leave clea~ance between the top and sides of ~
impeller 14 and upper enclosure member 12A. G,'' Housing 12 is shown in ~:IG. 4 adjacent thin mounting surface 78. !:
Housing 12 includes mounting flange 32, which may facilitate attachment of the housing 12 to the mounting surface 78. Housing 12 may be attached to the mounting surface 78 by an attachment mechanism (not shown) so as to provide correct positioning of the blood pump 10 with respect to the external source of rotation (i.e., rotor 74 and magnets 72~.
eration of the Firs~ ~m~diment -Blood from the patient enters pumping chamber 36 through inlet 24. As it enters pumping chamber 36, inlet flow is in the axial direction at axis ~-of rotation 18. This orientation and location of inlet flow allows the blood to make a gentle directional t~ansition without placing excess forces on the blood.The blood contacts rotating impeller blades 48 and 50, and is propelled to and through outlet 26 and back to the patient.
Blood pump 10 of the present invention is magneticaIly driven by a source of rotation which is external to pumping chamber 36. Therefore, blood pump 10 of the present invention does not have a torque-providing shaft or otherpart extending through a wall of housing 12. This eliminates the need for a sealand the possibility of seal wear and leakage.
The possibility of dislocation or misalignment of impeller 14 is prevented by spindle 16 being constrained in the axial and the lateral directions by journal bearings 64A and 64B. Bottom surface 56 of impeller 14 does not contact bottom wall 28, preventing any friction between these surfaces. The clearance between the top and sides of impeller 14 and enclosure 12A likewise W O 94/03731 P~r/~S93/07110 1 ~
- 21~1327 ~ ~

prevents any friction bet veen these surfa~es.
l~e structure of tbe constraining mechanism reduces the amount of fri~on between the rotating spindle 16 and the housing 12. The small lateral clearance between the ends 16A,16B of spindle 16 and jourI~al bearings 564A,64B allows for slight lateral movement of spindle 16 and ensures minimal pressure between parts. This allows minimal f~ic~on and minimal heat buildup between ends 16A,16B of spindle 16 and journal beanngs 64A,64B. l~e small axial cl~nce between ends 16A,16B of the spindle 16 and the inner end surfaces of journal bearings 64A,64B ensures minimal pressure between parts, 10again reducing friction and heat buildup.
Bearings 64~ ~4B of the present invention are lo~ated in areas of high blood flow velocity. Base journal bearing 64B is located by pedestal 34 in the center of cen~al circula~on hole ~0. Inlet joumal bea~ing 64A is located in inlet 24, and is exposed to the inlet flow of blood int~ pumping chamber 36 15The location of bearings 64A,64B ensures rapid dissipation of any frictional heat that is created.
Mounting flange 32 allows blood pump 10 to be quicldy and easily removed, and a new pump can be quickly and easily attached. Quiclc and easy removal and attachment of the pump is useful for the frequent replacement 20necessary to ensure sterility. Quick replacement also aids in the event of a pump malfunction. Because the source of rotation does not have to be replaced with replacement of the rest of the pump, the cost of replacement is lowered.

An impor~ant feature of blood pump 10 is the èliminahon of the 25requir~ment for a shaft seal. It was described previously that early failure of the shaft seal is the primary reason for the reladvely short operational life ofcurrently available centnfugal blood pumps.
Elimination of the shaft seal requires that bearings be designed which can operate effectively in blood. By using spindle 16 with a minimum ~ 94/03731 Pcr/US93/071 10 t~

3~ ~

diameter consistent with the required shaft strength, surface velocity is minimized. Minimization of surface velocity also minirnizes friction, frictionalheat and shear forces, all of which can cause blood damage and clot formation.
While a small diameter for spindle 16 is beneficial in reducing S blood damage, it also reduces the areas of spindle 16 which senre as axial thrust bearings, namely at both ends 16A and 16B of spindle 16. Since pump 10 is driven by magnetic coupling, there is an axial load in the direction of the magnetic coupling (i.e., toward rotor 74) when pump 10 is at rest or operating at low speeds. The use of a magnetic coupling requires a close proximity of impeller magnet 70 and drive magnet 72. Therefore, the preferred design is to have impeller blades 48 and 50 only on the side of impeller 14 which faces the pump inlet 24. This causes an asymmetrical axial flow across the two faces of impeller 14 and results in an increasing axial foree toward pump inlet 24 as flow increases (the "lifting forcen). The required area of the asial thrust bearing and hence, the minimum diameter of spindle 16 is determined by this maximum axial load.
As shown in FIG. 3B, the lifting force is preferably counteracted by placing radial grooves 63 in the base side of impeller 14 to increase the axial flow across this surface. The use of grooves 63, rather than blades, does not require increased space between the driven and drive magnets 70 and 72 (which would require more or stronger magnets to maintain the same coupling strength). By proper selection of the number and depth of grooves 63, pump 10 can be designed such that the lifting force "floats" impeller 14 such that, within the operating rpm of pump lO, the axial load on both bearings 64A and 64B and both spindle ends 16A and 16B is minimal. This reduces frictional heat, blood damage and bearing wear.
In a preferred embodiment, a groove 63 extends radially between adjacent magnets 70 of opposite polarity. This is illustrated in FIG. 3B by the polarity symbols "N" and "S".

wo94/03731 PCr/US93/07110 ~ ~ 4 ~ ~3.2 7 A Se~ond Em~imçnt ~ 5-6 An alt~rnative embodiment of the present invention is shown in FI&S. S and 6. This embodiment has journal bearing 64A dispos~d in the cente~ of st~aight inlet tube 26'. Jours~al bearing 64A is supported in cup 90 by S struts 92, whieh extend from cup 90 to the inner wall of inlet 26'. This allows inlet 26' to remain straight ~rather than J-shaped as in FIG. l) while still providing inlet flow in the a7cial direction at a~is of rotation 18.
Although the present invention has been described with reference to preferred embodiments, worlcers skilled in the art will recognize that changes 10 may be made in form and detail without depar~ng from the spirit and scope of the invention. For instance, a stationary pin going through a central hole in hub 62 of impeller 14 may be substituted for spindle 16, such that the top side and the bottom side of impeller 14 are constrained from movement in the a7cial and lateral directions by the stationary pin, while impeller 14 remains ~ree to rotate 15 around the pin. Also, in some embodiments grooves 63 are not required and therefore are omitted.

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Claims

WHAT IS CLAIMED IS:

1. A centrifugal pump for pumping biological fluids such as blood, adapted to be coupled with an external source of rotation, comprising:
a housing defining a pumping chamber with an inlet and an outlet;
a spindle enclosed within the pumping chamber for rotation about a spindle axis of rotation, the spindle comprising an inlet end toward the inlet of the pumping chamber and a base end opposite the inlet end;
an impeller enclosed within the pumping chamber and being supported on the spindle in a spaced relationship to the external source of rotation, the impeller comprising coupling means for coupling with the external source of rotation for rotating the impeller about the spindle axis of rotation;
an inlet journal bearing for rotatably supporting and receiving the inlet end of the spindle; and a base journal bearing for rotatably supporting and receiving the base end of the spindle.

2. The centrifugal pump of claim 1 wherein the coupling means comprises:
magnetic means carried by the impeller for magnetically coupling with the external source of rotation for rotating the impeller about the spindle axis of rotation.

3. The centrifugal pump of claim 1 wherein the base journal bearing and the inlet journal bearing do not rotate with respect to the housing.

4. The centrifugal pump of claim 1 wherein:
the inlet is disposed externally of the pumping chamber and includes a tube circumferential wall; and the inlet journal bearing is supported from the tube circumferential wall of the inlet.

5. The centrifugal pump of claim 4 wherein:
the inlet curves so that the tube circumferential wall crosses the spindle axis of rotation.

6. The centrifugal pump of claim 1 and further comprising means for counteracting a tendency of the impeller to move axially toward the inlet when the impeller is rotating.

7. The centrifugal pump of claim 1 wherein the impeller carries blades on a first side facing the inlet and has a plurality of grooves on a second, opposite side.

8. A centrifugal pump for pumping biological fluids such as blood, comprising:
a housing defining a pumping chamber with an inlet and an outlet;
a spindle enclosed within the pumping chamber and positioned along a spindle axis, the spindle comprising an inlet end toward the inlet of the pumping chamber and a base end opposite the inlet end;
means of rotation disposed externally of the pumping chamber;
an impeller enclosed within the pumping chamber and being supported on the spindle in a spaced relationship to the means of rotation, the impeller comprising coupling means for coupling with the means of rotation for rotating the impeller about the spindle axis;
an inlet journal bearing supported from the housing for rotatably supporting and receiving the inlet end of the spindle; and a base journal bearing supported from the housing for rotatably supporting and receiving the base end of the spindle.

9. The centrifugal pump of claim 8 wherein the impeller carries blades on a first side facing the inlet and has a plurality of grooves on a second, opposite side.

10. A centrifugal pump for pumping biological fluids such as blood, adapted to be coupled with an external source of rotation, comprising:
a housing defining a pumping chamber with an inlet and an outlet;
a spindle enclosed within the pumping chamber for rotation about a spindle axis, the spindle comprising an inlet end and a base end opposite the inlet end;
an impeller enclosed within the pumping chamber and being supported on the spindle in a spaced relationship to the external source of rotation, the impeller comprising coupling means for coupling with the external source of rotation for rotating the impeller about the spindle axis of rotation; and an inlet journal bearing embedded in an inlet wall of the pumping chamber for rotatably supporting and receiving the inlet end of the spindle.

11. The centrifugal pump of claim 10 further comprising a base journal bearing for rotatably supporting and receiving the base end of the spindle.

12. A centrifugal pump for pumping biological fluids such as blood, comprising:
a housing defining a pumping chamber with an inlet and an outlet;
a spindle enclosed within the pumping chamber and positioned along a spindle axis, the spindle comprising an inlet end inserted in a first journal bearing and a base end inserted in a second journal bearing opposite the inlet end;
wherein the first journal bearing is embedded in an inlet wall of the pumping chamber;
means of rotation disposed externally of the pumping chamber;
an impeller enclosed within the pumping chamber and being supported on the spindle in a spaced relationship to the means of rotation, the impeller comprising coupling means for coupling with the means of rotation for rotating the impeller about the spindle axis.