blood pump

Abstract

This invention relates to a blood pump. [Solution] The blood pump 1 comprises a pump casing 2 having a blood inlet 5 and a blood outlet 6 connected by a passage 7, and an impeller 3. The impeller 3 has blades 4 sized and shaped to transport blood along the passage 7 from the blood inlet 5 to the blood outlet 6, and is rotatably supported within the pump casing 2 by a first bearing 10 at the first axial end of the impeller 3, and a second bearing 20 spaced axially apart from the first bearing 10. The first bearing 10 comprises a projection 11 extending along a rotation axis 9 and connected to one of the impeller 3 and the pump casing 2, and a cavity 13 on the other of the impeller 3 and the pump casing 2, the projection 11 having an enlarged portion 12 that engages with the cavity 13 such that the first bearing 10 and the second bearing 20 are positioned to receive axial forces in the same axial direction.

Description

Technical Field

[0001] The present invention relates to a blood pump implanted in a patient to assist the patient's heart. In particular, the blood pump may be used as a "bridge to recovery" device that temporarily assists until the patient's heart fully recovers.

Background Art

[0002] Various types of blood pumps are known, such as axial flow blood pumps, centrifugal blood pumps, or hybrid blood pumps in which blood flow is generated by both axial and radial forces. The blood pump may be inserted into a patient's blood vessel, such as the aorta, using a catheter, or may be disposed within the thoracic cavity. The blood pump generally includes a pump casing having a blood flow inlet and a blood flow outlet connected by a passage. An impeller equipped with blades for transporting blood is rotatably supported within the pump casing to generate blood flow from the blood flow inlet to the blood flow outlet along the passage.

[0003] The impeller is supported within the pump casing by at least one bearing, but the bearing may be of a different type depending on the intended use of the blood pump, for example, whether the blood pump is intended for short-term use (a few hours or a few days) or long-term use (a few weeks or a few years). Various types of bearings are known, such as contact bearings and non-contact bearings. In non-contact bearings, for example, in magnetic bearings where the bearing surfaces "levitate" due to repulsive magnetic force, the bearing surfaces do not contact each other. Generally, contact bearings may include all types of bearings, such as sliding bearings, pivot bearings, hydrodynamic bearings, hydrostatic bearings, ball bearings, or any combination thereof, where the bearing surfaces may be in at least partial contact at any point during pump operation (i.e., always or intermittently). In particular, contact bearings may be "blood-immersed bearings" where the bearing surfaces have blood contact. Contact bearings, such as pivot bearings, can heat up during use and are prone to mechanical wear. Mechanical wear can be increased by the magnetic coupling between the pump's electric motor and the impeller used to drive the impeller. If the contact bearing and magnetic coupling are located at the same axial end of the impeller, the magnetic coupling can increase mechanical wear of the bearing by attracting the impeller, thereby increasing the contact pressure on the bearing surface. This can lead to high loads (e.g., 10 Newtons) on a small bearing surface (e.g., in the pivot bearing of a catheter pump, for example, in the range of 1 mm in diameter). [Overview of the project] [Problems that the invention aims to solve]

[0004] The main object of the present invention is to provide a blood pump having an impeller supported within a pump casing by bearings, which can reduce the mechanical wear of the bearings. In particular, another object of the present invention is to relieve the bearings within the blood pump from excessive loads. [Means for solving the problem]

[0005] The primary objective is achieved by a blood pump having the features of independent claim 1 in accordance with the present invention. Preferred embodiments and further developments of the present invention are specified in claims dependent on the independent claim.

[0006] Like known blood pumps, the blood pump according to the present invention comprises a pump casing having a blood inlet and a blood outlet connected by a passage. An impeller or rotor is disposed within the pump casing so as to be rotatable about an axis of rotation which may be the longitudinal axis of the impeller, and the impeller comprises blades sized and shaped to transport blood along the passage from the blood inlet to the blood outlet. The impeller is rotatably supported within the pump casing by a first bearing at the first axial end of the impeller and a second bearing axially spaced apart from the first bearing.

[0007] According to the present invention, the first bearing comprises a projection extending along the axis of rotation and connected to one of the impeller and the pump casing, and a cavity in the other of the impeller and the pump casing. The term “cavity” may include any kind of cavity, hollow space, recess, opening, or bore. The projection comprises an enlargement that engages with the cavity such that the first and second bearings are positioned to receive axial forces in the same axial direction. For example, the enlargement may be supported by the cavity or contained within the cavity. In other words, the first bearing releases the second bearing by holding at least a portion of the axial forces acting on the bearing surface of the second bearing. Since both bearings support the impeller in the same “bearing direction”, the load on each bearing can be reduced. They “share” the load. This is achieved by providing a simple mechanical means in the form of a projection with an enlargement, and a corresponding cavity, such that the impeller is “suspended” to a certain extent by the first bearing. Preferably, the protruding and enlarged portions are included in the impeller, and the cavity is static and part of the pump casing. The cavity may be disposed in the support structure of the pump casing. However, it will be understood that the arrangement may be reversed without affecting functionality.

[0008] Preferably, the size and shape of the cavity correspond to the enlarged portion. This improves the bearing characteristics by reducing or avoiding impeller displacement in the axial direction, radial direction, or both, when the size and shape of the cavity and the enlarged portion are matched to each other. In particular, the first bearing can be positioned to receive axial forces in two opposing axial directions. However, it is not essential that the size and shape of the cavity correspond to the enlarged portion, as long as the first bearing can receive axial forces in the same axial direction as the second bearing. For example, in the opposite axial direction, i.e., away from the second bearing, the cavity may be open, or at least provide sufficient space to allow the impeller to move in this direction.

[0009] Preferably, the enlarged portion is at least partially spherical. For example, the enlarged portion may be a spherical cap. Thus, the cavity may also be at least partially spherical. However, the enlarged portion may have any shape suitable for achieving the concept of the present invention. In particular, any shape that is rotationally symmetric and has a ledge that receives axial forces may be suitable for the first bearing. The enlarged portion may be, for example, cylindrical or conical. The enlarged portion may be snap-fitted into the cavity, which is a simple way to mount the first bearing. The material of the enlarged portion or the cavity or both may have enough elasticity to allow for a snap-fit ​​connection. In another embodiment, the cavity or enlarged portion may be formed by molding it onto an existing part made of, for example, a metal or ceramic material, allowing shrinkage of the molded plastic to create a dynamic joint.

[0010] In one embodiment, the second bearing may be a contact bearing, preferably a pivot bearing, having a bearing surface of the impeller facing the bearing surface of the pump casing. The pivot bearing allows for rotational and pivotal movement to a certain extent.

[0011] The blood pump may further comprise a shaft extending along and rotatable about the axis of rotation, on which an impeller is mounted. The shaft has a first end portion forming part of a first bearing and a second end portion forming part of a second bearing. In particular, the first end portion of the shaft may comprise an enlarged portion such as a spherical cap. The shaft may have an outer diameter substantially equal to the outer diameter of the enlarged portion, and the projection forms a neck portion positioned between the shaft and the enlarged portion. This allows for a compact arrangement and is advantageous for snap-fit ​​connections. The second end portion of the shaft may comprise the bearing surface of a second bearing, the bearing surface being concave, for example spherical, and forming part of a pivot bearing, for example. It will be understood that the shaft may be formed separately from the impeller or integrally with it. Furthermore, it will be understood that components of the shaft may be in direct contact with the blood for the purpose of improving heat transfer to the surrounding blood. The shaft is preferably made of a thermally conductive material (metal, silicon carbide, or similar material) so that the heat generated within the bearing portion can be effectively transferred to the surrounding blood in order to limit the temperature to 55°C or below.

[0012] In one embodiment, the cavity wall may comprise at least two compartments, e.g., two, three, or four compartments, separated by gaps. The gaps may be fluidly connected to passages so that blood can enter the cavity. This allows the first bearing to be flushed by blood flowing through the blood pump or by any other rinsing fluid.

[0013] In one embodiment, the enlarged portion of the first bearing may include at least one magnet, and the pump casing, preferably the cavity, may also include at least one magnet. The magnets may be arranged to generate a repulsive magnetic force in the axial direction away from the second bearing. This arrangement allows the magnetic force of the first bearing to pull the impeller away from the second bearing, thereby releasing the second bearing. Separately, the design of the first bearing as a magnetic bearing can avoid axial mechanical wear of the first bearing.

[0014] In one embodiment, at least one bearing surface of at least one of the first and second bearings may be supported by at least one spring, the at least one spring being positioned to receive an axial force in the axial direction from the second bearing toward the first bearing. Specifically, the second bearing can be released by providing at least one spring that receives and dampens a portion of the load acting on the bearing surface of the second bearing. The at least one spring may be disposed on the surface of the second bearing facing away from the first bearing. For example, the at least one spring may be disposed on a portion of the casing supporting the stationary bearing surface of the second bearing. The spring force may be selected to be less than the load on the second bearing. In this case, the load on the second bearing is limited to the amount of the spring force, and the remainder of the load is supported by the first bearing. Alternatively, or in addition to the above, the first bearing may be spring-supported by at least one spring, in particular a portion of the pump casing having a cavity, the spring generating an axial force away from the second bearing. It will be understood that the spring may be made of a metallic material, or may be formed from a polymer material in the form of an O-ring or similar shape that provides the same function as a metal coil spring, for example. In one embodiment, at least one of the bearing surfaces of the second bearing may be supported by a flexible structure that may have a known force when bent.

[0015] Further means for releasing the second bearing can be provided. For example, a repulsive magnet can be provided on or near the bearing surface of the second bearing, for example, around it. A magnetic drive device may be arranged radially to reduce or eliminate the axial force generated by the attractive magnetic force that transmits rotation to the impeller, and the magnetic drive may be arranged circumferentially around the impeller. Similarly, in an arrangement in which the magnetic drive is arranged axially with respect to the impeller, the magnetic flux may be deflected so that it acts radially on the impeller. Furthermore, as an alternative method, or in addition, a support bearing may be provided to hold a portion of the load of the second bearing. The support bearing may be a ball bearing having a plurality of balls that pass between the surface of the impeller and the surface of the housing, preferably in aligned grooves surrounding the second bearing.

[0016] According to this invention, it will be understood that two mechanical bearings are used to center the impeller. By spatially distributing both bearings along the axis of rotation, a rigid bearing / impeller arrangement is made possible. The latter enables a pulsating pump action in which the impeller moves from below critical velocity with each heartbeat. The rigid arrangement provided by the two mechanical bearings can reduce impeller vibration between critical velocities. A pump action that pulsates and synchronizes with the heart is considered highly advantageous in achieving cardiac recovery. In addition, it will be understood that mechanical bearings are used because of their small size, which is required by any small pump intended to be placed inside a patient's blood vessels.

[0017] The above summary, as well as the following detailed description of preferred embodiments, will be better understood in conjunction with the accompanying drawings. The drawings are referenced for illustrative purposes of this disclosure. However, the scope of this disclosure is not limited to the specific embodiments disclosed in the drawings. [Brief explanation of the drawing]

[0018] [Figure 1] This is a cross-sectional view of the blood pump according to the present invention. [Figure 2] Cross-sectional view showing a blood pump according to another embodiment. [Figure 3] Cross-sectional view showing a blood pump according to yet another embodiment. [Figure 4A] Diagram showing various embodiments of a first bearing. [Figure 4B] Diagram showing various embodiments of a first bearing. [Figure 4C] Diagram showing various embodiments of a first bearing. [Figure 4D] Diagram showing various embodiments of a first bearing. [Figure 5] Cross-sectional view of a blood pump according to one embodiment designed as a catheter pump. [Figure 6] Cross-sectional view showing a first shaft of a blood pump. [Figure 7] Cross-sectional view showing a second shaft of a blood pump. [Figure 8] Cross-sectional view showing a support structure of a first shaft. [Figure 9A] Cross-sectional view showing a support structure of a first shaft according to other embodiments. [Figure 9B] Cross-sectional view showing a support structure of a first shaft according to other embodiments. [Figure 9C] Cross-sectional view showing a support structure of a first shaft according to other embodiments. [Figure 10] Cross-sectional view showing a blood pump according to another embodiment. [Figure 11] Cross-sectional view showing a support structure of a first shaft connected to the embodiment of FIG. 10. [Figure 12] Cross-sectional view showing a blood pump according to another embodiment. [Figure 13] Cross-sectional view showing a blood pump according to another embodiment. [Figure 14] Cross-sectional view showing a blood pump according to another embodiment. [Figure 15] Cross-sectional view showing a blood pump according to another embodiment. [Modes for carrying out the invention]

[0019] Referring to Figure 1, a cross-sectional view of the blood pump 1 is shown. The blood pump 1 is designed for extracorporeal, extracardiac, or extraluminal applications and comprises a pump casing 2 having a blood inlet 5 and a blood outlet 6. During operation, the pump casing 2 is located outside the patient's body, and the blood inlet 5 and blood outlet 6 are connected to their respective connectors (particularly the inflow from the heart and the outflow into the aorta). Blood is transported along a passage 7 connecting the blood inlet 5 and the blood outlet 6. An impeller 3 having a shaft 14 is provided to transport blood along the passage 7 and is rotatably mounted within the pump casing 2 about a pivot axis 9 by a first bearing 10 and a second bearing 20. The pivot axis 9 is preferably the longitudinal axis of the impeller 3. Both bearings 10 and 20 are contact bearings as described in more detail later. The second bearing 20 is a pivot bearing having a spherical bearing surface that allows rotational and pivotal movement to a certain extent. A first bearing 10 is disposed within a support member 15 to stabilize the rotation of the impeller 3, and the support member 15 has at least one opening 16 for blood flow. Blades 4 are provided on the impeller 3 to transport blood as the impeller 3 rotates. The rotation of the impeller 3 is caused by an electric motor 8 magnetically coupled to an end portion 37 of the impeller 3. As will be understood by those skilled in the art, other suitable drive mechanisms are possible. The illustrated blood pump 1 is a mixed-type blood pump, and the primary flow direction is axial. Depending on the arrangement of the impeller 3, and in particular the blades 4, it will be understood that the blood pump 1 may also be a pure axial-flow blood pump.

[0020] The impeller 3 includes a portion 33 that extends radially outward. The portion 33 may be called a yoke, flange portion, or end portion. Two or more flush channels 30, preferably three, four, five, or six, although only one is shown in Figure 1, extend through the impeller 3, particularly through portion 33, to allow flushing or rinsing of the gap 31 between the impeller 3 and the stationary portion of the blood pump 1, particularly the pump casing 2 or the motor 8 which may be considered associated with the pump casing 2. At least one flush channel 30 may also extend, at least partially, beyond portion 33 into the main portion of the impeller 3. The flush channel 30 has a first opening 34 and a second opening 35. The first opening 34 forms a fluid connection between the passage 7 and the flush channel 30, and the second opening 35 is fluidly connected to the gap 31. In particular, the second opening 35 is fluidly connected to the central bore or central opening 32 of the portion 33 that receives the second bearing 20, thereby allowing the second bearing 20 to be flushed and cooled.

[0021] The second bearing 20 comprises a first bearing surface 23 (see Figure 6) disposed on the second end portion 24 of the first shaft 14, and a second bearing surface 22 (see Figure 7) located on the end portion of the second shaft 21, particularly in a recess in the center of the second shaft 21. Both bearing surfaces 22 and 23 are preferably spherical. Magnetic coupling between the electric motor 8 and the end portion 37 causes the impeller 3 to be attracted toward the motor 8, thereby increasing the pressure between the bearing surfaces 22 and 23 of the second bearing 20. To release the second bearing 20, the first bearing 10 is located on the opposite axial end portion 19 of the first shaft 14 and is positioned to receive axial loads in the same axial direction as the second bearing 20.

[0022] The first bearing 10 includes an enlarged portion 12 that engages with a cavity 13 of a support structure 15, which may be considered part of the pump casing 2. In particular, the enlarged portion 12 may be supported by, enclosed within, or captured within the cavity 13. The enlarged portion 12 may be snap-fitted into the cavity 13 or otherwise mounted. More specifically, the first bearing 10 includes an axially extending projection 11 at the first end portion of the shaft 14, which includes the enlarged portion 12. In the illustrated embodiment, the enlarged portion 12 is formed as a partially spherical cap. However, any rotationally symmetrical shape suitable for receiving axial loads in the same direction as the second bearing 20 may be selected for the enlarged portion 12. The projection 11 forms a neck having a smaller diameter than the enlarged portion 12. As shown in Figure 6, the enlarged portion 12 has the same diameter as the shaft 14. The diameters of the enlarged portion 12 and the shaft 14 may be different. In particular, the diameter of the enlarged portion 12 may be smaller or larger than the diameter of the shaft 14. The neck portion may also be omitted. The shaft 14 may also be formed integrally with the impeller 3.

[0023] In the embodiment of Figure 1, the size and shape of the cavity 13 substantially correspond to the enlarged portion 12. Thus, the first bearing 10 supports the impeller 3 in both axial directions, as well as being loaded in the same axial direction as the second bearing 20. In the embodiment of Figure 2, the cavity 13' is open to the side facing away from the second bearing 20. However, the support structure 15 is sized and shaped to correspond to the size and shape of the neck portion 11, so that the impeller 3 is supported in both axial and radial directions. It will be understood that the support structure 15 may be smaller to allow some axial movement away from the second bearing 20. In the embodiment of Figure 3, the impeller 3 may move axially away from the second bearing 20, which may occur by rotational movement of the impeller 3 in the blood flow. In this embodiment, the cavity 13'' is enlarged axially away from the second bearing 20.

[0024] Figures 4A–4D show various embodiments of the first bearing 10, particularly the enlarged portion 12 and the cavity 13. In Figure 4A, the enlarged portion is substantially spherical, similar to the enlarged portions shown in Figures 1–3. The portion that contacts the cavity 13 of the support structure 15 may have a different diameter from the rest of the enlarged portion 12 and may be convex. Alternatively, this portion may be concave. In the embodiment of Figure 4B, the enlarged portion 12 is conical or rhomboid. Figures 4C and 4D show similar embodiments in which the enlarged portion 12 has a conical or tapered portion. This facilitates the assembly of the bearing 10. In Figure 4C, the portion of the enlarged portion 12 that contacts the cavity 13 of the support structure 15 is spherical and convex, and in Figure 4D it is concave. It will be understood that any rotationally symmetrical shape may be used for the enlarged portion 12.

[0025] Referring now to Figure 5, one embodiment is shown that is similar to the embodiments described above in Figures 1-3, particularly the embodiment in Figure 2, but differs in that it is designed as a catheter pump 1'. The blood inlet 5' is at the end of a flexible catheter 50 positioned through a cardiac valve such as the aortic valve, and during use, the blood outlet 6' is located on the side of the pump casing 2' and is positioned within a cardiovascular vessel such as the aorta. The blood pump 1' is connected to a catheter 51, and an electrical wire 52 extends through the catheter 51 to drive the pump 1'. Both blood pumps 1 and 1' function in the same way. It will be understood that all the features described are applicable to both extracorporeal pumps and catheter pumps.

[0026] Referring next to Figure 8, a cross-section through the support structure 15 is shown, including an opening 16 that allows blood to flow through the support structure 15. The support structure 15 may contribute to one or more columns. In the embodiments of Figures 9A-9C, the wall of the cavity 13 comprises a segment or compartment 17 separated by a gap 18. The gap 18 allows blood to flow into the cavity 13 and flush it out, particularly to cool the first bearing 10. The compartment 17 may be called a stator blade that supports the rotating parts of the first bearing. Figures 8 and 9A show a support structure 15 having three columns and three openings 16. The support structure 15 may have fewer or more columns and openings, such as one (Figure 9B), two (Figure 9C), four, five, six or more.

[0027] An embodiment of the blood pump 1 substantially similar to the embodiments described above is shown in Figure 10. However, in this embodiment, the first bearing 10'' is designed as a magnetic bearing instead of a contact bearing. The enlarged portion 12' comprises at least one magnet 40 positioned to produce a repulsive magnetic force against magnets 41 located in the support structure 15. The enlarged portion 12' is disposed on a projection 11' that engages with the cavity 13''. The repulsive magnetic force helps to release the second bearing 20. Figure 11 shows a cross-sectional view through an embodiment of the blood pump in which the first bearing 10 is designed as a magnetic bearing. Similar to the embodiments described above, the support structure comprises three columns 15, and the wall of the cavity 13''' is divided into three segments 17' separated by gaps 18'. In the wall segments 17', magnets 41 are disposed that act on each of the magnets 40 (not shown in Figure 11) of the enlarged portion 12'.

[0028] Figures 12–15 show embodiments of the blood pump 1 in which either the first bearing 10 or the second bearing 20 is supported by at least one spring. It will be understood that the embodiment in Figure 12 and at least one of the embodiments in Figures 13–15 can be combined to form a single embodiment. As shown in Figure 12, a spring 42, such as a coil spring, is provided to support the shaft 21', and the shaft is substantially similar to the second shaft 21 described in association with Figure 7, except that it is axially movable and shorter to provide room for the spring 42. A sealing ring 45 is provided to prevent blood from entering the motor assembly. The spring 42 is relatively weak, and in particular, the spring force is less than the load that would act on the second bearing 20 without the spring 42 and without the first bearing 10. Thus, the load on the second bearing 20 is limited to the amount of the spring force of the spring 42. The rest of the load is supported by the first bearing 10.

[0029] Alternatively, or in addition, as shown in Figure 13, the first bearing 10, particularly its stationary portion, may be spring-supported. In this embodiment, the support structure 15 is separated from the pump casing 2 and supported by a spring 43, such as a coil spring, which is held in place by a ledge 44. The spring force of the spring 43 acts in a direction away from the second bearing 20 in order to release the second bearing 20. The same function can be achieved instead of the spring 43 by a flexible ring 46, such as a polymer O-ring, as shown in Figure 14. Alternatively, or in addition, the support structure 15 may be made of a flexible, elastic, or stretchable material that provides a spring function as shown in Figure 15. Similarly, a spring device may be disposed on the first shaft 14 to release the second bearing 20.

Claims

1. A pump casing (2) having a blood inlet (5) and a blood outlet (6) connected by a passage (7), An impeller (3) is disposed within the pump casing (2) so as to be rotatable about a rotation axis (9), and comprises blades (4) whose size and shape are determined to transport blood along the passage (7) from the blood inlet (5) to the blood outlet (6), The impeller (3) is coupled to an electric motor that causes the impeller (3) to rotate, The impeller (3) is rotatably supported within the pump casing (2) by a first bearing (10) located at the first axial end of the impeller (3), and a second bearing (20) spaced axially apart from the first bearing (10). The first bearing (10) comprises a projection (11) extending along the rotation shaft (9) and connected to one of the impeller (3) and the pump casing (2), and a cavity (13) on the other of the impeller (3) and the pump casing (2), wherein the projection (11) comprises an enlarged portion (12) that engages with the cavity (13) such that the first bearing (10) and the second bearing (20) are positioned to receive axial force in the same axial direction. The blood pump (1) is characterized in that the electric motor is magnetically coupled to the end portion of the impeller (3) to cause the impeller (3) to rotate, and the first bearing (10) and the second bearing (20) are arranged to receive the axial force caused by the magnetic coupling between the electric motor and the end portion of the impeller (3) attracting the impeller (3) toward the electric motor.

2. It is a blood pump, A pump casing (2) having a blood inlet (5) and a blood outlet (6) connected by a passage (7), An impeller (3) is disposed within the pump casing (2) so as to be rotatable about a rotation axis (9), and comprises blades (4) of a size and shape determined to transport blood along the passage (7) from the blood inlet (5) to the blood outlet (6), The impeller (3) is rotatably supported within the pump casing (2) by a first bearing (10) located at the first axial end of the impeller (3), and a second bearing (20) spaced axially apart from the first bearing (10). The first bearing (10) comprises a projection (11) extending along the rotation shaft (9) and connected to one of the impeller (3) and the pump casing (2), and a cavity (13) on the other of the impeller (3) and the pump casing (2), wherein the projection (11) comprises an enlarged portion (12) that engages with the cavity (13) such that the first bearing (10) and the second bearing (20) are positioned to receive axial force in the same axial direction. The blood pump further comprises a shaft (14) on which the impeller (3) is mounted, extending along the rotation axis (9) and rotatable about the rotation axis (9), the shaft (14) having a first end portion (19) that forms part of the first bearing (10) and a second end portion (24) that forms part of the second bearing (20), The first end portion (19) of the shaft (14) is provided with the enlarged portion (12), A blood pump characterized in that the shaft (14) has an outer diameter equal to the outer diameter of the enlarged portion (12), and the protruding portion (11) forms a neck portion positioned between the enlarged portion (12) and the rest of the shaft (14).

3. A pump casing (2) having a blood inlet (5) and a blood outlet (6) connected by a passage (7), An impeller (3) is disposed within the pump casing (2) so as to be rotatable about a rotation axis (9), and comprises blades (4) of a size and shape determined to transport blood along the passage (7) from the blood inlet (5) to the blood outlet (6), The impeller (3) is rotatably supported within the pump casing (2) by a first bearing (10) located at the first axial end of the impeller (3), and a second bearing (20) spaced axially apart from the first bearing (10). The first bearing (10) comprises a projection (11) extending along the rotation shaft (9) and connected to one of the impeller (3) and the pump casing (2), and a cavity (13) on the other of the impeller (3) and the pump casing (2), wherein the projection (11) comprises an enlarged portion (12) that engages with the cavity (13) such that the first bearing (10) and the second bearing (20) are positioned to receive axial force in the same axial direction. A blood pump characterized in that the enlarged portion (12) is provided with at least one magnet (40) and the pump casing (2) is provided with at least one magnet (41) such that a repulsive magnetic force is generated between the magnets (40, 41) pointing in the axial direction away from the second bearing (20).

4. A blood pump according to claim 1 or 3, further comprising a shaft (14) on which the impeller (3) is mounted, the shaft (14) extending along the rotating shaft (9) and rotatable about the rotating shaft (9), wherein the shaft (14) has a first end portion (19) that forms part of the first bearing (10) and a second end portion (24) that forms part of the second bearing (20).

5. A blood pump according to claim 4, characterized in that the first end portion (19) of the shaft (14) comprises the enlarged portion (12).

6. A blood pump according to claim 5, wherein the shaft (14) has an outer diameter equal to the outer diameter of the enlarged portion (12), and the protruding portion (11) forms a neck portion that is positioned between the enlarged portion (12) and the rest of the shaft (14).

7. A blood pump according to any one of claims 2, 4 to 6, characterized in that the second end portion (24) of the shaft (14) is provided with the bearing surface (23) of the second bearing (20), and the bearing surface (23) is concave.

8. A blood pump according to any one of claims 1, 2, 4 to 7, characterized in that the enlarged portion (12) is provided with at least one magnet (40) and the pump casing (2) is provided with at least one magnet (41) such that a repulsive magnetic force is generated between the magnets (40, 41) pointing in the axial direction away from the second bearing (20).

9. A blood pump according to any one of claims 1 to 8, characterized in that at least one bearing surface of at least one of the first and second bearings (10, 20) is supported by at least one spring, and the at least one spring is arranged to receive an axial force in the axial direction from the second bearing toward the first bearing.

10. A blood pump according to any one of claims 1 to 9, characterized in that the blood pump (1) is an axial flow blood pump, a centrifugal blood pump, or a mixed-type blood pump.

11. A blood pump according to any one of claims 1 to 10, characterized in that the enlarged portion (12) is enclosed within a cavity (13).

12. A blood pump according to any one of claims 1 to 11, characterized in that the size and shape of the cavity (13) correspond to the enlarged portion (12).

13. A blood pump according to any one of claims 1 to 12, characterized in that the enlarged portion (12) is at least partially spherical.

14. A blood pump according to any one of claims 1 to 13, characterized in that the enlarged portion (12) is snap-fitted into the cavity (13).

15. A blood pump according to any one of claims 1 to 14, characterized in that the second bearing (20) is a contact bearing having a bearing surface of the impeller (3) that faces the bearing surface (22) of the pump casing (2).

16. A blood pump according to any one of claims 1 to 15, characterized in that the second bearing (20) is a pivot bearing.

17. A blood pump according to any one of claims 1 to 16, wherein the wall of the cavity (13) comprises at least two compartments (17) separated by a gap (18), the gap (18) being fluidly connected to the passage (7), and allowing blood to enter the cavity (13).

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