WO2002027225A1

WO2002027225A1 - Turbo blood pump with inclined impeller vanes

Info

Publication number: WO2002027225A1
Application number: PCT/IB2001/002343
Authority: WO
Inventors: Kenji Araki
Original assignee: Jms Co., Ltd.
Priority date: 2000-09-29
Filing date: 2001-09-28
Publication date: 2002-04-04
Also published as: AU2002218444A1

Abstract

A blood pump used for extra corporeal circulation, and more particularly, a small turbo blood pump including a casing (3) having an interior region, an aperture formed in an upper portion defining a blood inlet (1), and an aperture formed in a lower portion defining a blood outlet (2). An impeller is rotatably mounted within said casing interior region and includes a rotary shaft (12) and at least one vane depending therefrom. The at least one vane has an upper radius adjacent the blood inlet (1) that is less than a lower radius adjacent the blood outlet (12). The base of the at least one vane forms an exterior angle of less than 90° with the axis of the rotary shaft (12). A driven magnet (15) is mounted to the at least one vane. The impeller is rotationally driven by a non-contacting driving magnet that is exterior to the casing (3).

Description

TURBO BLOOD PUMP WITH INCLINED IMPELLER VANES

This is a continuation-in-part patent application based on U.S. Patent Application Serial No. 08/942,680, filed October 2, 1997, which gains priority from Japanese Patent Application No. 8-281460, filed October 2, 1996. BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a turbo blood pump that is extra corporeal or implantable in a patient's body so as to conduct circulatory assistance or extra corporeal circulation of blood for a cardiopulmonary bypass operation, hemo purification, or other treatments, and, more particularly, to a turbo blood pump of mixed flow which creates a flow of blood spreading in all directions within a casing of the pump and has a smooth and efficient circulation of blood in spite of its small size and low revolution ratio.

2. Description of the Related Art

Conventionally, a roller blood pump for pumping out blood by compressing a tube was often used for extra corporeal circulation. However, this kind of roller pump needs a special pump segment tube to be fit thereto, and the lack of strength and durability of the tube causes problems. A further important problem is that the roller type blood pump is bulky and difficult to handle. Thus, it is difficult to use, for example, in the sterile area of an operating field. Therefore, in recent years, turbo blood pumps such as centrifugal pumps and axial flow pumps which can be used, for example, in the sterile area of an operating field, have been developed. See, for example, Japanese Granted Patent No. 1914715, Japanese Unexamined Patent Publication No. 4-2358, Japanese Unexamined Patent Publication No. 6-218043, Japanese Granted Utility Model No. 1792315, Japanese Unexamined Patent Publication No. 2-99800, Japanese Unexamined Patent Publication No. 7-75667, and Japanese Unexammed Patent Publication No. 7-178165.

In the centrifugal pump, liquid is fed into a casing inlet and flows substantially perpendicular to an impeller axis. In comparison, in an axial flow pump liquid is fed into a casing and flows in parallel relation to the axis. When developing these types of pumps, it is necessary to design a suitable rotation number in order to feed liquid efficiently or feed liquid so as to assure a stable state in which, for example, flow separation, collision, vortex, cavitation or the like is not caused. That is, a relatively low rotation number in a range of 1,000-4,000 rpm is desired to feed liquid efficiently by means of a normal left ventricular assistance centrifugal type pump (flow rate: SL/min, pressure head : 100 mm Hg.) Further, a relatively high rotation number in a range of 9,000 — 30,000 rpm is desired to feed liquid efficiently by means of an axial flow pump.

The discharge rate (flow rate) of the above turbo type pumps is determined mainly by the rotation speed and the size of the impeller. Thus, to assure a large discharge rate in a centrifugal type pump, the size of the pump including the impeller and casing needs to be enlarged. Generally, a centrifugal pump used for extra corporeal circulation has an impeller diameter as large as 40-80 mm and a large priming volume. However, as described below, enlargement of the pump is not desirable.

On the other hand, because the axial flow pump ensures a larger rotation number to achieve efficient fluid feeding than the centrifugal pump, it can provide a large discharge rate if the same impeller diameter is used. However, conventional axial flow pumps could not provide a sufficient driving power for cardiopulmonary bypass, because they are about 5-16 mm in impeller diameter. Furthermore, the axial flow pump has a higher impeller rotation number than the centrifugal pump, and, therefore, blood injury such as hemolysis is more likely to occur. Thus, usually, the axial flow pump is designed so that the rotation speed is low and the impeller vane is as large as possible, in order to reduce a possibility of hemolysis. However, in this case, hydraulic efficiency drops so that the advantage of the axial flow pump is not fully realized.

Further, because the conventional turbo blood pump of, for example, a centrifugal pump, is connected to a driving source, many types have shaft sealing. However, a blood pump having shaft sealing is difficult to operate for more than two weeks because a lack of durability of the shaft sealing. Also, because thrombus is likely to occur, shaft sealing is a problem with respect to anti-thrombogenicity. To solve the above problem, an impeller that does not require shaft seals was developed. Such an impeller is disclosed in US Pat. No. 4,507,048 issued to Belenger et al. According to this invention, the upper and lower ends of a rotary shaft of an impeller are supported in the casing. External to the casing is a magnetic driving mechanism such as an electric coil which generates a rotating magnetic field for driving the impeller. A disadvantage of this invention is that rotor stability is lost when the supporting means is deformed. Deformation is caused by variations in the distance between the upper and lower bearings and the contacting pressure of the upper and lower supporting structure. Such deformation may cause hemolysis and thrombus formation in the blood pump. SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide a blood pump which can be installed in, for example, the sterile area of an operating field, and will not disturb the operation procedure. Another object of the present invention is to provide a small-size, implantable blood pump which can be implanted in the body and will reduce anatomical limitations at the time of implantation, thereby simplifying operation. Yet another object of the present invention is to provide a blood pump which has a sufficient discharge rate and driving power; thereby achieving efficient feeding of liquid. A further object of the present invention is to provide a blood pump which reduces an influence upon blood due to dynamic action such as shear stress and heat generation; thereby reducing damage upon blood such as hemolysis. A still further object of the present invention is to provide a blood pump which limits the formation of thrombus and is highly durable.

According to a first aspect of the present invention, there is provided a turbo blood pump including an impeller having a rotary shaft and vanes formed so as to connect to the rotary shaft. The impeller is mounted to rotate within a casing and about the rotary shaft. The top of the casing includes a blood inlet while the bottom of the casing includes a blood outlet. The vanes taper out radially from the inlet to the outlet. The casing closely follows the impeller taper. Means is provided for rotating the impeller. The bottom edge of the impeller as viewed from the side forms an angle delta between 0° < 8 < 65° with the axis of the rotary shaft.

According to a second aspect of the present invention, there is provided a turbo blood pump according to the first aspect wherein, at least, a part of the impeller vane is a three-dimensional structure vane which is not in parallel relation to the rotary axis of the impeller (hereinafter referred to as vane structure I ). According to a third aspect of the present invention, there is provided a turbo blood pump according to the first aspect wherein the impeller vane is of a threedimensional structure formed of twisted curved faces (hereinafter referred to as vane structure 2).

According to a fourth aspect of the present invention, there is provided a turbo blood pump according to the first aspect wherein an angle formed by the impeller vane relative to a circumference at an upper end of .the vane at the exit is different from an angle formed thereby relative to a circumference at a bottom end of the vane at the exit (hereinafter referred to as vane structure 3).

Each vane of vane structures 1 through 3 described above may be positively inclined with respect to the rotary shaft. That is, the back of each vane may face upward toward the blood inlet of the pump and the front of each vane may face downward toward the blood outlet of the pump.

Alternatively, each vane of vane structures 1 through 3 described above may include a radially interior portion that is positively inclined with respect to the rotary shaft and a radially exterior portion that is negatively inclined with respect to the rotary shaft. That is, unlike a vane structure where the entire length of each vane is positively inclined, the back of the radially exterior portion of each vane faces downward toward the blood outlet of the pump and the face of the radially exterior portion of each vane faces upward toward the blood inlet of the pump. Providing such negatively inclined radially exterior portions reduces damaging collisions of the blood with the pump's inside walls as the pump is operated. It is preferable that each vane forms a negatively inclined angle theta of about 0° to about 45° with respect to a vertical axis defined by the rotary shaft and at a location proximate the blood outlet. It is even more preferable that each vane forms a negatively inclined angle theta of about 0° to about 40°.

According to a fifth aspect of the present invention, there is provided a turbo blood pump according to the above mentioned three aspects wherein an upper portion and lower portion of the impeller rotary shaft are structured in a pivot bearing structure and sliding bearing structure, the sliding bearing of the cylindrical face contacting type. A driven magnet is mounted on the impeller, so that the driven magnet is magnetically coupled with a driving magnet mounted outside the casing, the driving magnet is radially adjacent to the impeller rotary shaft, (hereinafter referred to as the shaft structure 1).

Further, by combining the above vane structures 1 through 3 and the shaft structure 1, a more preferable turbo blood pump can be realized. According to a sixth aspect of the present invention, there is provided a turbo blood pump as mentioned above, further comprising an impeller having a vane structure in which the vane structure 1 and the vane structure 3 are combined (hereinafter referred to as the vane structure 4).

According to a seventh aspect of the present invention, there is provided a turbo blood pump as mentioned above, further comprising an impeller having a vane structure in which the vane structure 2 and the vane structure 3 are combined (hereinafter referred to as the vane structure 5).

According to an eighth aspect of the present invention, there is provided a turbo blood pump as mentioned above in which the vane structure 1 and the shaft structure 1 are combined.

According to a ninth aspect of the present invention, there is provided a turbo blood pump as mentioned above in which the vane structure 2 and the shaft structure 1 are combined.

According to a tenth aspect of the present invention, there is provided a turbo blood pump as mentioned above in which the vane structure 3 and the shaft structure 1 are combined.

According to an eleventh aspect of the present invention, there is provided a turbo blood pump as mentioned above in which the vane structure 4 and the shaft structure 1 are combined.

According to a twelfth aspect of the present invention, there is provided a turbo blood pump in which the vane structure 5 and the shaft structure 1 are combined.

The above and other features of the subject invention will be made more readily apparent to those having ordinary skill in the art from the following detailed description of the invention taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

Although the turbo blood pump of the present invention can be embodied in various ways in terms of its components and allocation, preferred drawings and embodiments are described and illustrated below:

Fig. 1 is a side elevational view in cross-section of a turbo blood pump according to the present invention with magnetic coupling in the radial direction;

Fig. 2 is a perspective view of a rotary shaft and a vane of an impeller, the vane being positively inclined with respect to the rotary shaft; Fig. 3 is a side elevational view in cross-section of another turbo blood pump constructed in accordance with a preferred embodiment of the subject invention with magnetic coupling in the radial direction;

Fig. 4 is a side elevational view in cross-section of another turbo blood pump constructed in accordance with a preferred embodiment of the subject invention -with magnetic coupling in the axial direction;

Fig. 5 is a top plan view of the impeller of FIG. 2 as viewed along line 5-5 including four vanes and a vane-attaching disk 26, and illustrating the relationship between the vane top face angle (a) and the vane base angle ((3),

Fig. 6 is a perspective view of a rotary shaft and a vane of an impeller similar to the rotary shaft and vane shown in FIG. 2, however, the vane further includes a radially exterior portion that is negatively inclined with respect to the rotary shaft; and

Fig. 7 is a top plan view of the impeller of FIG. 6 as viewed along line 7-7. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Features and preferred embodiments of a turbo blood pump of the present invention will be described in detail with reference to the accompanying drawings.

1. Pump flow type

Turbo pumps may be generally classified as centrifugal flow pumps, mixed flow pumps, or axial flow pumps. The pump of the present invention may be described as a mixed flow pump, which makes a flow of blood that spreads in all directions of the conical housing of the pump. The turbo blood pump of the present invention will be described herein below in detail with respect to each of its components.

With respect to its small size and discharge rate, the mixed flow pump is most desirable. Referring to FIG. 1, there is illustrated a mixed flow pump of the present invention. In the mixed flow pump, blood in an impeller flows neither parallel or perpendicular to the pump axis, but in an oblique direction as illustrated by the arrows. The mixed flow pump utilizes a centrifugal force so as to give energy to fluid such as blood. Thus, the impeller of the mixed flow pump has a larger diameter at its vane exit (2 x B) than at its vane entrance (2 x A) - unlike the axial flow pumps. The bottom of the vane 22 has an exterior angle b of 0° < delta < 90°with respect to the axis of the impeller shaft. In viewpoints of efficiency of flow and damage upon fluid, the above angle delta is preferred to be 0° <delta< 65°, and 25° <delta< 65° is further preferable. The optimum specific speed of the mixed flow type blood pump is higher than centrifugal type pumps, thus a higher rotation number and thereby a higher efficiency can be obtained. Because the higher rotation number is achieved, the size of the impeller and casing can be reduced, so that reduction of the pump size and assurance of the large discharge rate are achieved without decreasing the efficiency.

2. Impeller Structure a. Three-dimensional structure of the vanes

Because, in the turbo blood pump according to the present invention, the upper portion and lower portion of the impeller vane have different diameters at both the entrance and exit ((2 x A) and (2 x B), respectively), as a result of considering optimization of blood flow in the pump, it has been found that the vane shape is desired to be of the above vane structures 1 through 5. The vane structures 4, 5 are further preferable. The above vane structures are favorable in either the mixed flow pump or the non-mixed flow pump, and particularly it has been recognized that they are further favorable in the mixed flow pump. In the case of the above mentioned vane structures, as shown in the plan view of FIG. 5, the upper end of the vane 7 reaches a more outside circumference (virtual circumference D) than the circumference (virtual circumference C) of bottom end 8 thereof.

With continuing reference to FIG. 5 there is illustrated the vane top face angle alpha and the vane base angle beta. The top face angle alpha is defined as the angle formed between a line tangent to the top face of said vane at point 7 on virtual circumference D and a line tangent the circle formed by the impeller vane at that point 7. The vane base angle beta is defined as the angle formed between a line tangent the base of said vane at a point 8 on virtual circumference C and a line tangent the circle formed by the impeller vane at that point 8. It is notable that the vanes of the impeller illustrated in FIGS. 2 and 5 are positively inclined with respect to the rotary shaft. That is, the back of each vane faces upward toward the blood inlet of the pump and the face of each vane faces downward toward the blood outlet of the pump.

Referring to FIGS. 6 and 7 there is illustrated an alternate embodiment impeller that is similar to the impeller illustrated in FIGS. 2 and S; however, the radially exterior portion of each vane is negatively inclined with respect to the rotary shaft. That is, the back of the radially exterior portion of each vane faces downward toward the blood outlet of the pump and the face of the radially exterior portion of each vane faces upward toward the blood inlet of the pump. Providing such negatively inclined radially exterior portions reduces damaging collisions of the blood with the pump's inside walls as the pump is operated. It is preferable that each vane forms a negatively inclined angle theta of about 0° to about 45° with respect to a vertical axis defined by the rotary shaft and at a location proximate the blood outlet as illustrated in FIG. 6. It is even more preferable that each vane forms a negatively inclined angle theta of about 0° to about 40°.

The turbo blood pump of the present invention has a three-dimensional structure in that the impeller vane is twisted with respect to the rotational axis as described above. Thus, blood flow disturbances such as flow separation, collision, vortex formation, cavitation or the like are reduced. That is, the blood flow is made more efficient. Further, if the blood flow is made efficient, shear stress of blood is reduced, so that the generation of heat due to energy loss in the pump is suppressed. As a result, hemolysis is suppressed, the durability of the impeller vane and rotary shaft subjected to high speed rotation is improved, formation of thrombus is suppressed and other positive effects are produced, b. b. Vane diameter

Referring to FIG. 1, the diameter of the vane (2 x B) of the turbo blood pump of the present invention is preferred to be in a range of 4-80 mm. A range of 15-40 mm is further preferred. Such a blood pump in which the impeller vane diameter is 15-30 mm is most suitable for use in a long-term implantation type artificial heart. Further, a blood pump having a diameter of 20-40 mm is suitable for extra corporeal circulation or paracorporeal circulatory assistance because it can generate a higher pressure head than the former. c. Vane material and thickness

The material forming the vanes is required to have the following characteristics; (1) harmless to the human body (excellent bio-compatibility), (2) excellent long-term durability, (3) ability of being precision processed, (4) excellent in hemocompatibility such as anti-thrombogenicity, and (5) appropriate hardness. For example, synthetic resin such as acrylic, polyacrilate, polymetacrilate, polycarbonate and fluoresin and stainless steel, titanium, titanium alloy, fine ceramics or the like are preferable materials.

If the thickness of the vane is too small, there is a problem in strength and durability. If the thickness thereof is too large, too much driving energy is loaded thereon. The preferred thickness of the vane is 1.5-2.0 mm when using polyacrilate and polymetacrilate, 1.0-1.5 mm when using polycarbonate (which has a higher strength than the former), and 0.5-1.5 mm when using stainless, titanium, titanium alloy or the like.

If the thickness of the vane is made to vary gradually from the proximal end of the vane to the distal end thereof, it is effective for maintaining a flow path in the pump or ensuring efficient flow. By gradually thinning the vane from the proximal end to the distal end, flow separation can be reduced so that turbulent flow near the exit is reduced. By gradually thickening the vane structure, the percentage of blood flow at the entrance can be increased. d. Number of vanes

Usually there are provided 2-8 vanes, however 3 vanes are preferred. A blood pump having an impeller comprising one vane cannot produce a stable driving force and a blood pump having nine or more vanes is difficult to produce. e. Full-open structure

In the turbo blood pump of the present invention, a full-open impeller is employed. A full-open impeller is one in which there are no attaching discs attached to, and connecting, either the upper or lower portions of the vanes. As a result, a structure without blood stagnation is provided so that a place likely to form thrombus is eliminated, thereby achieving excellent anti-thrombogenicity. f. Other impeller structure

An alternate embodiment impeller includes one or more vane-attaching disks. Such an embodiment may include one or more disks extending either partially or fully, or a combination thereof, along the upper and/or the lower portion of each vane. A fully enclosed impeller includes an impeller blood inlet and impeller blood outlet allowing the blood to pass across the vane faces and between the vane-attaching disks. 3. Impeller shaft and bearing structures, and impeller drive system a. Material forming the shaft

The impeller shaft is to be formed of material having the following characteristics; (1) excellent in hemo-compatibility such as anti-thrombogenicity, (2) suitable hardness, for example, stainless steel, titanium, ceramics or the like is preferable. A bearing for supporting such a shaft is desired to be formed of material having excellent anti-abrasion in addition to the above characteristics. For example, highly durable plastic such as ultra-high density polyethylene or ultra-high molecular weight polyolefm may be used (e.g., LubmerTM: manufactured by MITUI SEKIU AGAKU Co. Ltd.) b. Bearing structure and magnet coupling system

As shown in Fig. 3, a magnet casing 14 is mounted to the impeller vane 4 and a driven magnet 15 is mounted within the magnet casing 14. The driven magnet 15 is magnetically coupled with a driving magnet 16 mounted outside the magnet casing 14 and radially adjacent the driven magnet 15. As a result, a force of the magnetic coupling is not applied to shaft 12 and pivotal bearing 9 and sliding bearing 13 so that no unnecessary stress is applied between the shaft and the bearings. Thus, a relation between an upper shaft end 17 and the upper bearing 9 is desired to be of pin-point contacting or pivot bearing structure in which little abrasion or heat is produced. However, when the driving magnet and the driven magnet are magnetically coupled with each other in the direction of the radius, there sometimes occurs a deflection and the impeller becomes unstable in the radial direction of the shaft. Thus, a lower shaft end 18 is structured to be in cylindrical contacting relationship with the sliding bearing 13. As a result, the lower bearing provides a fail-safe function.

Further, as shown in Fig. 4, it is permissible to place the driven magnet 15 directly on the impeller vane and magnetically couple the driven magnet 15 with the driving magnet 16 located out of the casing 3, in the vertical direction relative to the impeller shaft. When the magnets 15, 16 are magnetically coupled with each other in the vertical direction, the lower shaft end 18 is never deflected in the radial direction of the shaft. Thus, like the relation between the upper shaft end 17 and the upper bearing 9, it is permissible to couple the lower shaft end 18 and the lower bearing 13 with each other in a pin-point contacting or pivot bearing structure. Magnet material.

It is desirable that the driven magnet 15 and driving magnet 16 are formed of material which reduces inertia mass of the impeller and raises pump speed response, so as to increase the stability of impeller rotation and durability of the shaft, and further reduce shearing stresses in the fluid in the pump; thereby reducing hemolysis and reducing the size of the pump. To satisfy the above requirements, it is preferable that the magnet be a rare earth magnet, for example, neodymium, samarium cobalt or the like. Other drive systems

Other drive systems may be employed to rotate the impeller. For example, the rotary shaft to which the vanes are attached may be directly connected to a rotor housed in a separate chamber as described and illustrated in U.S. Patent No. 5,399,145, the contents of which are incorporated herein. As a further example, the rotary shaft to which the vanes are attached may be connected to a motor through direct attachment, a clutch, a gear train, belt arrangement, etc. Those of ordinary skill in the art will appreciate the various standard systems that may be employed to drive the impeller of the turbo blood pump of the present invention. From the above, the term "driving means" encompases the drive systems described above and any other drive systems useful for rotating the impeller. hi the blood pump of the present invention, the space (called volute) formed between the impeller vanes and the interior region of the casing should be maintained as small as possible. Although the efficiency of the pump is increased as the space is reduced, too small a space tends to cause blood damage due to the shearing forces produced there between. The desirable clearance has been found to be between 0.1-1.0 mm. Blood flow is also optimized when the casing is formed such that its cross-sectional area is gradually expanded in the flow direction toward the blood exit. 4. Casing and other blood pump components

Also, because joints between the casing and the bearings can have microscopic gaps, thrombus formation and hemolysis can easily occur. For this reason, it is desirable that the bearings described above are formed integrally with the casing.

5. Impeller production method a. Synthetic resin produced impeller

If the material of the vane is synthetic resin such as acrylic, polyacrylic, polymetacrylilate, polycarbonate, fluoresin or the like, the impeller can be produced by any of the appropriate methods described below. For example, it is permissible to mold a predetermined shape vane by injection molding polycarbonate and then bond the magnet casing to this vane by adhesive. Or it is permissible to form the vanes and the magnet casing integrally. b. Metallic impeller

If the material of the vanes are metal such as stainless steel, titanium, titanium alloy or the like, the impeller can be produced by the same methods as described above for synthetic resin type impellers. For example, it is possible to produce the vane, shaft and magnet casing independently or integrally by lost-wax molding. In lost-wax molding, a male die is made of wax which is replaced by metal or the like. Further, the vane, shaft and magnet casing can be integrally produced. Or the impeller can be produced by cutting stainless steel, titanium, titanium alloy or the like integrally. While the former is suitable for mass production, the latter is suitable for small quantity production of multiple product types.

6. Preferred embodiment

A preferred embodiment of the turbo blood pump according to the present invention will be described hereinbelow.

FIG. 1 schematically shows a construction of the present invention. The casing 3 comprises an inlet 1 at its upper end and an outlet 2 at the bottom thereof, i a plurality of the vanes of the impeller, driven magnets 15 in the magnet casing 14 at the lower portion are magnetically coupled with the driving magnet 16 located out of the casing 3. Driving magnet 16 is rotated by a motor placed out of the pump. As a result, the impellers and associated driven magnets 15 are rotated so as to supply energy to the blood. The impeller is supported by the shaft 12 and the shaft 12 is supported by the upper bearing 9 and the lower bearing 13. The upper bearing 9 is supported by an upper bearing holder 10.

With continuing reference to FIG. 1, a top face of the vane connecting the upper end S of the vane at the entrance and the upper end 7 of the vane at the exit has an angle phi of 45° with respect to the axis of the shaft 12. Abottom face of the vane connecting the lower end 6 of the vane at the entrance and the lower end delta of the vane at the exit has an angle delta of 30° with respect to the axis of the shaft 12. Consequently, fluid flow within the impeller becomes an oblique flow which is neither perpendicular nor parallel to the shaft 12.

Referring now to FIGS. 2 and 5, the upper end 7 and the lower end 8 have different diameters at the distal end of the impeller vane. In addition, the impeller vane has been shaped so as to optimize the flow. More specifically, the vane top face angle alpha the angle of the upper end of the vane at the exit, relative to virtual circumference D - is designed so as to be smaller than the vane base angle beta - the angle of the lower end of the vane at the exit, relative to virtual circumference C. According to the instant embodiment, the top face angle alpha is 11 ° and the base angle beta is 13°. In the turbo blood pump of the present invention, the impeller vanes are of a three-dimensional structure formed of twisted curved faces, in order to ensure flow efficiency and reduce blood injury. That is, in the instant embodiment, the vane structure 5 described previously is employed. FIG. 2 shows a perspective view of an impeller vane having the three-dimensional structure formed of twisted curved faces.

Referring to FIG. 1, the driven magnet 15 mounted on the impeller vane 4 and the driving magnet 16 mounted outside the casing 3 are magnetically coupled with each other radially relative to the rotary shaft 12. This coupling force produces no axial forces so that the rotary shaft and the bearing are not loaded; thereby improving the durability of the rotary shaft and the bearing. The upper bearing 9 is made of high density polyethylene which is a highly durable synthetic resin.

According to the instant embodiment, a fine ceramic ball 11 is embedded in the upper end of the shaft and made to contact the bearing 9 in pin-point contacting relationship, thereby improving the durability. The entire impeller is formed of stainless steel. The lower bearing 13 is formed in a cylindrical shape and made of a high durability synthetic resin such as high density polyethylene. The impeller shaft 12 is formed in a cylindrical shape corresponding to the shape of the bearing 13. The impeller shaft 12 is supported in face contacting relationship with the lower bearing 1 . Because of the face contacting relationship, even if the upper bearing 9 becomes slightly abraded, the lower shaft end 18 will not slip out of the lower bearing 13. This ensures a fail-safe function; thereby contributing to the long-term stability of the rotary shaft.

According to the instant embodiment, both the driving magnet 16 and the driven magnet 15 are made of neodymium. If an electric magnet is installed instead of the driving magnet 16, the driven magnet 15 is rotated by that electric magnet, and an independent motor is not required. Thus, a smaller size, more durable pump is realized. EXAMPLES

All of the examples provided below are intended to be illustrative of several aspects of the invention. They are not intended to limit the scope or the underlying principles of the invention in any way.

EXAMPLE 1

A volute type mixed flow pump was used. The height thereof, including the casing, is 38 mm and the diameter thereof is 48 mm. The impeller is of the full-open type to improve antithrombogenicity, having its maximum diameter of 20 mm, and is driven by magnetic coupling having no axial seal. This blood pump shows a discharge rate of 5 1/min at a pressure head of 100 mm Hg under 5,800 rpm; thereby sufficient for replacing the entire cardiac function. The maximum efficient point of the pump is 6.91/min in flow rate, 136 mm Hg at the pressure head, and 7,000 rpm in rotation number, so that its maximum total hydraulic efficiency is 66% and specific velocity calculated from the maximum efficient point is 368. EXAMPLE 2

Hemolysis test: With hepalinized fresh bovine blood being used at a blood priming volume of 400 ml, a hemolysis test was conducted under a condition in which the . flow rate was 51/min, at a pressure head of 100 mm Hg for 0-5 hours. The same test was conducted by means of a commercially available Delphin pump. Table 1 shows the results, according to which the hemolytic index is 0.O15g/1001, which is less than half the hemolytic index of 0.033 g of the Delphin pump. Table. 1 (Result of Hemolysis test)

Blood Fresh bovine blood

Priming volume (ml) 400

Flow rate(ml/min) 5,000

Pressure head (rrimHg) 100

Pump A mixed flow pump Delphin pump

Time (min) Ht Free Hb Ht Free Hb

0 32.4 10 32.1

30 31.5 20 31.5 24

60 31.9 27 31.9 41

120 32.8 51 30.9 76

180 33.7 62 31.6 118

240 32.4 79 31.9 155

HI= (100-Ht)CV/100QT Q: Blood Flow rate (ml/min)

HI: Hemolysis index T: Time (min)

Ht: Hematocrit (%)

C: Increase of free hemoglobin (mg/dl)

V: Priming volume (ml)

Claims

What is claimed is:

1. A turbo blood pump comprising: a) a casing having an interior region, an aperture formed in an upper portion of said casing defining a blood inlet, and an aperture formed in a lower portion of said casing defining a blood outlet; b) an impeller rotatably mounted about a vertical axis within said interior region, said impeller including:

1) a rotary shaft, and

2) at least one vane depending from said rotary shaft, said at least one vane positively inclined with respect to said rotary shaft and having an upper radius adjacent said blood inlet and a lower radius adjacent said blood outlet, said upper radius being less than said lower radius; and c) a driving means for rotating said impeller about the vertical axis.

2. The turbo blood pump according to claim 1, wherein said at least one vane further includes a radially exterior portion that is negatively inclined with respect to said rotary shaft.

3. The turbo blood pump according to claim 2, wherein said radially exterior portion has a negative inclination of about 0° to about 45° at a location proximate said blood outlet.

4. The turbo blood pump according to claim 2, wherein said radially exterior portion has a negative inclination of about 0° to about 40° at a location proximate said blood outlet.

5. The turbo blood pump according to claim 1 , wherein the base of said at least on vane forms an exterior angle of less than 65° with the axis of said rotary shaft.

6. The turbo blood pump according to claim 1 , wherein a partial face of said at least one vane includes a three-dimensional structure which is not in parallel to the rotary axis of said impeller.

7. The turbo blood pump according to claim 1, wherein said at least one vane includes a three-dimensional structure formed of twisted curved faces.

8. The turbo blood pump according claim 1 , wherein the distal portion of said at least one vane includes a vane top face angle and a vane base angle and said top face angle is unequal to said vane base angle.

9. The turbo blood pump according to claim 1, wherein the distal portion of said at least one vane includes a vane top face angle and a vane base angle and said top face angle is smaller than said vane base angle.

10. The turbo blood pump according to claim 1, wherein the upper portion of said impeller rotary shaft is rotatably supported in a pivot bearing structure and the lower portion of said impeller rotary shaft is rotatably supported in a sliding bearing structure, said sliding bearing of a cylindrical face contacting type, and wherein said driving means for rotating said impeller includes a driven magnet mounted on said at least one vane and a driving magnet mounted radially adjacent said driven magnet and outside said casing, whereby said driven magnet is magnetically coupled with said driving magnet.

11. The turbo blood pump according to claim 1, wherein said impeller includes at least one vane-attaching disk connecting adjacent vanes depending from said rotary shaft.

12. The turbo blood pump according to claim 1, wherein said interior region of said casing increases in diameter from said blood inlet to said blood outlet.

13. A turbo blood pump comprising: a) a casing having an interior region, an aperture formed in an upper 3 portion of said casing defining a blood inlet, and an aperture formed in a lower portion of said casing defining a blood outlet; b) an impeller rotatably mounted about a vertical axis within said interior region, said impeller including:

1) a rotary shaft, and

2) at least one vane depending from said rotary shaft, said at least one vane positively inclined with respect to said rotary shaft and including a driven magnet attached thereto; c) a pivot bearing structure mounted in said casing and rotatably supporting the upper portion of said impeller rotary shaft; d) a sliding bearing structure mounted in said casing and rotatably supporting the lower portion of said impeller rotary shaft, said sliding bearing of a cylindrical face contacting type; and e) a driving magnet mounted radially adjacent said driven magnet and outside said casing, whereby said driven magnet is magnetically coupled with said driving magnet and rotates said impeller about the vertical axis.

14. The turbo blood pump according to claim 13, wherein said at least one vane further includes a radially exterior portion that is negatively inclined with respect to said rotary shaft.

15. The turbo blood pump according to claim 14, wherein said radially exterior portion has a negative inclination of about 0° to about 45° at a location proximate said blood outlet.

16. The turbo blood pump according to claim 13, wherein the base of said at least one vane forms an exterior angle of less than 90° with the axis of said rotary shaft.

17. The turbo blood pump according to claim 13, wherein the distal portion of said at least one vane includes a vane top face angle and a vane base angle and said top face angle is unequal to said vane base angle.

18. The turbo blood pump according to claim 13, wherein the distal portion of said at least one vane includes a vane top face angle and a vane base angle and said top face angle is smaller than said vane base angle.

19. The turbo blood pump according to claim 13, wherein said impeller includes at least one vane-attaching disk connecting adjacent vanes depending from said rotary shaft.

20. The turbo blood pump according to claim 13, wherein said interior region of said casing increases in diameter from the blood inlet to the blood outlet.