Reference is made to our co-pending applications, serial numbers

07/867,258 and 07/866,620, filed on even date herewith entitled PUMPING

APPARATUS WITH WAVE SHAPED IMPELLER and PUMPING APPARATUS WITH DIRECTED FLOW IMPELLER, respectively, which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

FIELD OF THE INVENTION

The present invention relates generally to centrifugal pumps used in pumping delicate fluids. More particularly, it relates to centrifugal pumps used for extracorporeal pumping of blood.

DESCRIPTION OF THE PRIOR ART

Blood is a complex and delicate fluid. It is essentially made up of plasma, a pale yellow liquid containing microscopic materials including the red corpuscles (erythrocytes), white corpuscles (leukocytes), and platelets (thrombocytes). These and the other constituents of blood, as well as the nature of suspension of these materials in blood, are fairly readily affected by the manner in which blood is physically handled or treated. Blood subjected to mechanical shear, to impact, to depressurization, or the like, may be seriously damaged. The balance between the blood constituents may be affected. Commencement of deterioration may result from physical mishandling of blood. Blood which has been damaged may be unfit for use. It is, therefore, important that any pumping apparatus used for blood accomplishes the pumping in a gentle, non-harmful manner.

Centrifugal pumps have been utilized in the prior art for the pumping of blood and other delicate biological and non-biological fluids. One of the problems which has been encountered in utilizing this type of pump is that because of the relatively delicate nature and structure of blood, physical

deterioration of the blood and at least some of its components invariably results.

This is especially true in those pumps which employ an open vane impeller structure in which the impeller vanes are positioned perpendicular to the flow of blood. These pumps are efficient in that they are capable of pumping a relatively large volume of blood at relatively low speeds of rotation. Such pumps can, however, subject the blood to sudden pressure changes, low pressure turbulence regions, impacts, and rapid changes in direction of flow, all of which can cause blood hemolysis. The pumping action obtained by these pumps can be described as radially increasing pressure gradient pumping, or in some cases, more specifically as constrained force vortex radially increasing pressure gradient pumping. In centrifugal pumps, the fluid acted on by the vanes of the impeller is positively driven or thrown outwardly (radially) by the vane rotation. The fluid, as it moves from the vanes to the ring shaped volute space beyond the tips of the vanes, is reduced in velocity, and as the velocity decreases, the pressure increases according to Bernoulli's theorem. Handling of many delicate fluids, such as blood, in this fashion would destroy them for use.

The problems associated with these conventional vane type pumps have been largely overcome in vaneless pumps which utilize rotors with smooth surface impellers. Examples of such pumps are shown in U.S. Pat. No. 3,864,855 to Kletschka, et al., U.S. Pat. No. 3,647,324 to Rafferty, et al., and U.S. Pat. No.

3,970,408 to Rafferty, et al. A commercial version of this type of pump, the BP- 80, is marketed by BioMedicus, Inc., of Minneapolis, Minnesota. This type of pump has no conventional vanes but instead provides a smooth surface rotator which moves blood from a central inlet to the periphery of a pump housing. Such pumps are capable of handling blood gently. The absence of vanes minimizes low pressure turbulence regions, cavitation and over pressurization of the blood. This results in very low hemolysis and no appreciable damage to the formed elements of the blood. These pumps, however, are operated at a relatively high speed of rotation. In general, the friction and heat generated by pump operation are

decreased the slower the pump is operated. Friction and heat can cause increased blood coagulation.

Another pump variation is shown in U.S. Pat. No. 4,570,048 to Belenger, et al. This pump utilizes a rotator comprising a central cone having a base and an apex connected by helical blades to a flared skirt with a central opening which surrounds the central cone. The helical blades commence approximately 1/3 to

1/2 of the way between the central opening of the flared skirt and the base and radiate outwardly in a helical configuration in the direction opposite to that of the blood flowing out of a tangential peripheral outlet. This configuration produces at least one annular gap or channeled blood path between the central cone and the outflaring skirt and constitutes the impelling means by which blood is moved from the inlet to the outlet of the pump. Although this pump configuration combines some of the structure found in both conventional vaned pumps and vaneless pumps it is undesirable for several critical reasons. First, the substantial distance between the central opening of the flared skirt and the leading edges of the helical blades adversely affects the blood handling characteristics of the pump. The velocity of the leading edges of the blades with respect to the blood increases as the distance of the edges of the blades from the central opening increases. Consequently, in this pump the relatively high velocity of the leading edges of the blades creates increased stress and turbulence which can damage the formed elements of the blood and increase hemolysis. Second, since the leading edges of the blades are spaced a relatively substantial distance from the central opening, the length of the channeled blood paths are substantially shorter than they would be if the leading edges extended to the central opening. This results in a reduced pressure differential from the inlet of the pump to the outlet since pressure differential decreases as the length of the channeled blood path decreases. In blood pumps it is generally desirable to have a large pressure differential between the blood inlet and outlet in order to increase the pumping capacity and increase the pump's ability to trap air. If the pressure differential is large any air bubbles which have inadvertently entered the pump are more likely to remain

near the inlet and less likely to pass through the pump. Therefore, the position of the leading edges of the blades of this pump not only reduces the pumps ability to handle blood gently but also decreases the pumps ability to trap air.

Therefore, a centrifugal blood pump capable of operating efficiently at reduced speeds of rotation like conventional vaned pumps while retaining the gentle blood handling characteristics of vaneless pumps would be desirable.

SUMMARY OF THE INVENTION

The present invention accomplishes the objectives of reducing the speed of pump operation and increasing pump efficiency while maintaining the beneficial blood handling capabilities associated with vaneless pumps. These objectives are accomplished by providing an improved pumping apparatus and method of pumping blood and other delicate fluids. The improved pump includes a housing for defining a chamber having a generally circular base. A rotor is disposed for rotation about an axis within the chamber and includes an impeller having a peripheral edge. The impeller includes an upper section having a central opening and a lower section. The upper and lower sections have oppositely disposed surfaces. Separation means are included between the upper and lower sections of the impeller for defining a plurality of fluid passages between the oppositely disposed surfaces. The separation means includes a leading edge and a trailing edge. The leading edge is disposed such that it commences generally at the central opening and the trailing edge is disposed generally at the peripheral edge of the impeller such that the separation means commences at a point at or near the central opening and terminates at a point at or near the peripheral edge. Thus, the fluid passages extend radially from a position at or near the central opening outwardly to a position at or near the peripheral edge of the impeller.

Inlet means are positioned within the housing for introducing fluid through the central opening into the fluid passages. The pump includes outlet means positioned peripherally within the housing and generally tangential to the circular base. Means are provided for rotating the rotor at a speed such that fluid

introduced in to the fluid passages is caused to rotate spirally outward between the inlet and the outlet. As the fluid flows outwardly toward the outlet it is collected in an annular unobstructed chamber about the impeller and then discharged through the outlet. Various alternative designs of the impeller are included. In one alternative, the fluid passages radiate straight out linearly in a direction from the axis of rotation to the peripheral edge. In another alternative the fluid passages radiate spirally in the direction of the flow of blood through the outlet. In still another alternative design the fluid passages radiate spirally in the opposite direction of the flow of fluid through the outlet.

The improved pump design provides significant advantages over conventional blood pumps. It has the pumping efficiency of conventional vaned blood pumps while reducing low pressure turbulence regions and related adverse blood handling characteristics associated with these pumps. The improved pump of this invention is able to handle blood gently in the manner of vaneless blood pumps but is able to operate more efficiently at a slower speed of rotation, thus reducing the risks of hemolysis associated with friction and heat generated by higher speeds of rotation. The improved pump achieves these benefits without the problems associated with prior blood pumps which have utilized a channeled blood flow construction. As discussed above, these prior pumps do not have desirable air entrapment capacity or gentle blood handling characteristics. Contrary to the design of these prior art pumps, the construction of the improved pump of this invention eliminates those problems by providing channeled blood flow passages extending generally from the central opening of the upper section of the impeller to the peripheral edge. This minimizes blood turbulence at the central opening while providing sufficient air entrapment capacity necessary to safe blood handling.

Although in the preferred embodiment the improved pump of the present invention is described as it would be used as a blood pump, it could also be

utilized to pump other delicate biological or non-biological fluids which are capable of damage from turbulence, pressure changes or sheer stresses.

Various advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and objects obtained by its use, reference should be had to the drawings which form a further part hereof, and in which like reference numerals designate like parts throughout the figures thereof, and to the accompanying descriptive matter, in which there are illustrated and described certain preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a pump according to the present invention. FIG. 2 is a sectional view of the pump of FIG. 1 taken along line 2-2. FIG. 3 is a perspective view of the lower section and separating surfaces of the impeller of FIGS. 1 and 2.

FIGS. 4 and 5 are perspective views of alternative impellers configurations.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The pump of the present invention is illustrated in FIGS. 1 and 2. FIG. 1 is a top view of a pump 10. Although pump 10 will be described with respect to the pumping of blood it is equally effective for pumping other delicate fluids.

FIG. 2 is a cross-sectional view of pump 10 taken along line 2-2 of FIG. 1 through the axis of rotation of the pump rotor 12. Rotor 12 rotates in the direction of arrow 13. In addition to rotor 12, pump 10 includes pumping chamber 14 which may, as in this embodiment, be constructed of a transparent material, and base 16 which is essentially circular. Rotor 12 includes a shaft (not shown), and an impeller 18 having a lower section 20 and an upper section 22 which, in this embodiment, is made of a transparent material to allow the blood to be viewed as it passes through the pump. Upper section 22 is provided with a central opening

24. Upper section 22 and lower section 20 have oppositely disposed surfaces 26 and 28, respectively, which are separated by a plurality of separating surfaces 30.

In this embodiment, separating surfaces 30 are integrally formed as a portion of lower section 22 although it should be realized that they could be formed as separate pieces or as an integral portion of upper section 22. Alternatively, impeller 18 could be formed of integral construction in any conventional manner.

Separating surfaces 30 divide the space between oppositely disposed surfaces 26 and 28 a plurality of fixed chambers or blood flow passages 32 which extend radially from central opening 24 to the peripheral edge 34 of impeller 18. Blood enters pump 10 through an axial inlet 36 and is discharged through a tangential outlet 38. Although inlet 36 and outlet 38 maybe located elsewhere, the locations shown in this embodiment are preferred for optimum pump efficiency and blood handling characteristics.

The pump rotor 12 may be driven in any conventional manner such as by the magnetic coupling of rotating drive magnets located in a controller console and driven magnets embedded in rotor 12. Such a drive system is well known and utilized commercially, for example in the BioMedicus, Inc., BP-80 blood pump and is not shown in the figure.

During pump operation, blood enters the pump through inlet 36. Drive means coupled to rotor 12 causes impeller 18 to rotate. Blood enters central opening 24 and is caused to move downwardly and outwardly through blood flow passages 32 by the centrifugal action of the pump and the forces exerted upon the blood by oppositely disposed surfaces 26 and 28 and separating surfaces 30. The blood is collected in an unobstructed annular chamber 40 located between impeller 18 and housing 14. Some of the blood is then discharged through outlet

38.

A portion of the blood collected in annular chamber 40 is not discharged through outlet 38 but flows back towards inlet 36 in the space 42 between the upper section 22 of impeller 18 and housing 14. This backflow of blood is significant since air bubbles which have been inadvertently introduced into the

blood or which have formed in the blood are carried along with the back flowing blood towards inlet 36. These air bubbles collect in an air entrapment pocket 44 located near inlet 36. The precise location at which air is entrapped is dependant upon the position of the pump during use and upon the pressure differential between the inlet and outlet of the pump. Preferably, the pressure differential is large with the pressure at the outlet being greater than at the inlet. This enhances the air entrapment capabilities of the pump since any bubbles which are pumped with the blood through blood flow passages 32 are forced along with the back flowing blood in space 42 to the area of low pressure near the inlet. Blood flow passages 32 are constructed to maximize the inlet to outlet pressure differential and thus increase the air entrapment capabilities of the pump. This is done by extending the leading edge 45 and trailing edge 47 of separating surfaces 30 generally the entire distance from central opening 24 to peripheral edge 34. This maximizes the length of the fixed chambers or blood flow passages 32. Since the pressure differential between inlet and outlet increases as the length of the blood flow passages 32 increases, this construction maximizes the pressure differential thus enhancing the air entrapment capabilities of the pump. By varying the length of the blood flow passages 32 the pressure differential can be changed in order to tune the pump to any desired blood flow dynamics. This may be done by shortening the length of separating surfaces 30 such that trailing edge 47 is moved closer to the leading edge 45 and central opening 24. This tuning procedure may be used for all of the impeller variations shown herein and is not illustrated in the drawings. It is important to note that the pump should not be tuned by altering the position of leading edges 45. Leading edges 45 are positioned generally at central opening 24 in order to reduce the velocity of the edges with respect to the blood entering the pump from inlet 36. If separating surfaces 30 are shortened by moving leading edges 45 away from central opening 24 the velocity of the leading edges 45 with respect to the entering blood will be increased. This increased velocity creates turbulence that

will result in increased hemolysis and damage to the formed elements of the blood.

FIG. 3 is a perspective view of lower section 20 of impeller 18. Separating surfaces 30 radiate straight out in a linear fashion in a direction from the axis of rotation to peripheral edge 34 to form blood flow passages 32 between lower section 20 and upper section 22 (not shown in this figure).

FIGS. 4 and 5 show alternative designs for lower section 20 of impeller 18.

In FIG. 4 separating surfaces 30 radiate spirally in a direction opposite to that of the flow of blood through tangential outlet 38. In FIG. 5 separating surfaces 30 of lower section 20 radiate spirally in the direction of the flow of blood through tangential outlet 28. In this variation the blood flowing through blood flow passages 32 is urged by partitioning surfaces 30 to flow in the direction of the blood being discharged through tangential outlet 38 thus further improving pump efficiency. The pump of the present invention is able to pump blood in a gentle yet efficient manner. Separating surfaces 30, which extend generally from the central opening 24 of upper section 22 to peripheral edge 34 impart an impelling force on the blood with an efficiency exceeding conventional vaned pumps. This is done, however, with the added advantage of the elimination of the low pressure turbulence areas which existed in the area behind the vanes in conventional vaned pumps. These low pressure turbulence areas are eliminated by enclosing the blood flow paths between the upper section 22 and lower section 20 forming blood flow paths 32. Since this design does not allow blood to flow over the top of separating surface 30, no low pressure turbulence region is created. Thus, the blood is handled with less damage to the formed elements and with lower hemolysis. Additionally, by extending the leading edge 45 of separating surfaces 30 substantially all the way to central opening 24, the velocity of leading edges 45 with respect to the entering blood is minimized thus further enhancing the gentle blood handling characteristics of the pump. This construction also increases the

ability of the pump to trap air since the pressure differential from the blood inlet to the blood outlet is maximized.

Although not shown in the figures, the shape, number and arrangement of separating surfaces 30 may be varied. Thus, the cross-sectional configuration of blood flow passages 32 could be formed in a variety of shapes including rectangular, circular or oval.

Having thus described the Preferred Embodiments of the present invention, those of skill in the art will readily be able to adapt the teachings found herein to yet other embodiments within the scope of the claims hereto attached.