Intravascular blood pump

Abstract

The intravascular blood pump has a rotatable shaft (25) carrying an impeller (34) and a housing (20) having an opening (35), through which the shaft extends, the impeller being positioned outside the housing. The shaft and the housing have surfaces (25A, 33A) forming a circumferential gap, which converges toward the impeller-side end of the gap and has a minimum gap width of preferably not more than 5 μm, more preferably not more than 2 μm.

Description

Technical Field

[0001] The present invention relates to an intravascular blood pump, in particular a percutaneously insertable blood pump, for supporting blood circulation in a human or, optionally, an animal body. For example, the blood pump can be designed to be percutaneously inserted into the femoral artery and guided through the body's vascular system to, for example, support or replace the pumping action in the heart. Background Art

[0002] A blood pump of the type mentioned above is known, for example, from EP 0 961 621 B1, which has a drive segment, a conduit attached to the proximal end of the drive segment (which is the end of the drive segment closer to the doctor or the "rear end" of the drive segment) and having a line extending through it for supplying power to the drive segment, and a pump segment fastened at the distal end of the drive segment. The drive segment comprises a motor housing with an electric motor arranged therein, wherein the motor shaft of the electric motor protrudes from the drive segment at the distal end and enters the pump segment. The pump segment in turn comprises a tubular pump housing having an impeller rotating therein, the impeller sitting on the end of the motor shaft protruding from the motor housing. The motor shaft is mounted in the motor housing in two bearings, which are separated from each other to the maximum extent to ensure a true and precisely centered guidance of the impeller in the pump housing. While radial ball bearings are used for the bearings at the proximal end of the motor housing, the impeller side bearing (which is the bearing closest to the blood) is constructed as a blood-resistant shaft seal made of polytetrafluoroethylene, which has a high hardness and a low friction coefficient, thereby providing a bearing and simultaneously preventing blood from entering the motor housing through such a distal bearing. In addition, the ingress of blood into the motor housing is resisted by the cleaning fluid being passed through the motor housing and the impeller side shaft seal bearing. This is done at a cleaning fluid pressure that is higher than the pressure present in the blood.

[0003] Improvements to the blood pumps mentioned above are disclosed in US 2015 / 0051436 A1 and in the accompanying Figure 2 Here, the impeller side bearing at the distal end of the motor housing includes an axial sliding bearing and a radial sliding bearing or a combined axial radial sliding bearing, wherein the radial sliding bearing replaces the shaft sealing bearing mentioned above. Accordingly, the cleaning fluid passes through the gap of the impeller side radial sliding bearing to prevent blood from entering the housing.

[0004] Although the present invention will be described and preferably used in the context of an intravascular blood pump of the type mentioned above having a motor housed in the housing, the present invention is equally advantageously applicable to other types of intravascular blood pumps in which the motor is outside the patient's body and the rotational energy for the impeller is transmitted through a catheter and the housing attached to the distal end of the catheter by means of a flexible rotary drive cable. In addition, in intravascular blood pumps of this type, a cleaning fluid usually enters the patient's blood through an opening through which the drive shaft extends.

[0005] Heparin, which is typically mixed into the cleaning fluid, causes a common problem. That is, although the cleaning fluid flows through the gap formed between the opening of the shaft and the housing, the blood that tends to enter the housing through such a gap is pushed back, but the blood cannot be completely prevented from entering the gap. In particular, some blood can always enter at least the distal segment of such a gap. Heparin helps prevent blood from clotting in the gap or blood from adhering to the surface, and thus prevents the blocking of the shaft rotation. However, doctors often do not want heparin to be administered to the patient's blood through the cleaning fluid. For example, during emergency treatment, heparin may be counterproductive because it prevents the clotting of blood and therefore healing or hemostasis. In addition, the amount of heparin administered to the patient's blood together with the cleaning fluid is difficult to control for various reasons. Specifically, the amount of heparin is often more than the amount desired by the doctor. Accordingly, the doctor will often preferably supply heparin to the patient separately from the operation of the blood pump, if necessary and in the required amount.

[0006] Accordingly, there is a need for an intravascular blood pump that can, if desired, be operated using a purge fluid that contains no or at least less heparin. Summary of the invention

[0007] Thus, according to a first aspect of the invention, an intravascular blood pump may comprise a rotatable shaft carrying an impeller and a housing having an opening, wherein the shaft extends through the opening, the impeller being positioned outside the housing, the shaft and the housing having surfaces with a circumferential gap formed in the opening. This is not different from the prior art discussed above, and the gap may in particular constitute a radial sliding bearing for the shaft. However, in the blood pump disclosed herein, the gap converges towards the front end or the impeller-side end, so that the minimum width of the gap is located somewhere within 50% of the length of the gap closest to the impeller-side end of the gap. More preferably, the minimum width is present at least at the impeller-side end of the gap.

[0008] The advantage of the slit converging towards the front end or the impeller-side end or the distal end (these terms have the same meaning) of the slit is that the pressure drop generated in the cleaning fluid flowing along the length of the slit from the proximal end to the distal end can be kept low, compared to the pressure drop in a non-converging slit of the same length having the minimum width over the entire length of the slit. More specifically, it is desirable according to the present invention to have a relatively high velocity of the cleaning fluid at the impeller-side end of the slit, which is the side of the slit that is in contact with the blood, to prevent blood from entering the slit. Therefore, the smaller the slit, the better. However, a very small slit along the entire length of the slit requires that the cleaning fluid be delivered to the blood pump at an extremely high pressure. By converging the slit towards the distal end, a cleaning fluid pump providing a pressure of, for example, 1 to 1.5 bar can be used even with a very small minimum slit width.

[0009] For example, a minimum gap of 5 μm in the region of the impeller-side end of the gap can allow the cleaning fluid to leave the gap at such a high speed that virtually no blood will enter the gap. It is thereby possible to clean the gap using a cleaning fluid with relatively little or even no heparin.

[0010] A minimum slit width of 5 μm or less also provides a physical barrier to entry of red blood cells into the slit to some extent because of the relatively large blood cell diameter of approximately 8 μm. However, because the thickness of a blood cell is only approximately 2 μm, it is preferred that the minimum slit width be 2 μm or less. As stated, due to the smaller slit width, the cleaning fluid flows through the slit at a higher velocity, thereby pushing the blood back out of the slit with the highest possible kinetic energy.

[0011] In case the minimum gap width is practically limited to the impeller-side end of the gap, i.e. to an infinitesimally short segment of the length of the gap, this can lead to increased wear in individual segments of the gap. Therefore, according to a preferred embodiment, the segment of the gap with the minimum gap width can extend over 50% or less of the length of the gap, preferably 30% or less, but preferably not less than 20% of the length of the gap, in order to keep the wear low. The length of such a segment can be in the range between 0.1 and 0.7 mm, more preferably between 0.2 and 0.4 mm.

[0012] The convergence of the slot can be achieved by a taper of one or both of the slot-forming surfaces, i.e. a tapered outer surface of the slot formed by the inner surface of the opening through the wall of the housing and a tapered inner surface of the slot formed by the surface of the shaft. The taper of the outer surface of the slot means a reduction in the diameter of the wall opening towards the impeller-side end of the slot, and the taper of the inner surface of the slot means an increase in the diameter of the shaft towards the impeller-side end of the slot. It is preferred to provide the taper in the surface of the shaft, while the opening forming the outer boundary of the slot can be cylindrical, because of ease of manufacture.

[0013] The preferred length of the slot is in the range from 1 to 2 mm, preferably 1.3 to 1.7 mm, while the minimum slot width may be 5 μm or less, preferably 4 μm or less, more preferably 3 μm or less, and most preferably 2 μm or less. The maximum slot width is typically located at the end of the slot opposite the impeller-side end of the slot and amounts to 15 μm or less, preferably 10 μm or less, more preferably 8 μm or less, and most preferably 6 μm or less. Most preferred are converging slots with a maximum slot width of about 6 μm and a minimum slot width of 2 μm or less.

[0014] Furthermore, the gap may converge continuously, in particular linearly, over at least a portion of its length until the gap has its smallest width.

[0015] In a particularly preferred embodiment, at least one of the two surfaces forming the circumferential gap is produced from a material having a thermal conductivity λ≧100 W / mK.

[0016] By manufacturing the surface from a material having a relatively high thermal conductivity, the temperature in the gap can be kept low, preferably at 55°C or lower, thereby preventing denaturation of any fibrin in the plasma that may enter the gap despite all efforts.

[0017] A material forming one or more surfaces of the gap having a thermal conductivity of 100 W / mK may be sufficient to conduct heat away from the gap and thus maintain the temperature within the gap at 55° C. or less. However, the thermal conductivity is preferably at least 130 W / mK, more preferably at least 150 W / mK and most preferably at least 200 W / mK.

[0018] In order to transfer heat away from the gap into the blood, it is preferred that the surface forming the gap is in thermally conductive contact with the blood flowing through the pump. According to thermodynamics, flowing blood carries away heat faster than non-flowing blood. The faster the blood flows, the more heat can be carried away by conductive heat transfer. The blood flow rate through the pump is generally higher than the blood flow rate outside the pump. Accordingly, for example, the heat generated in the gap and heating the surface forming the gap can be further conducted from the surface of the shaft through the shaft body into the impeller at the end of the shaft, and from there into the blood flowing along the impeller. However, because the distance for heat to flow through the shaft body in the axial direction and further through the impeller into the blood is relatively long, it is more preferred to conduct the heat away from the gap (in addition or only) in the radial direction, i.e. through the radial outer surface forming the gap. Carrying heat away in the radial direction is preferred not only because of the relatively short radial distance for heat to flow from the gap to the flowing blood, but also because it is easier to increase the heat conduction area through which heat can be conducted in the radial direction, compared to the heat conduction cross-sectional area of ​​the shaft body through which heat can be conducted in the axial direction. That is, the cross-sectional area A of the shaft body 轴向 Yes A 轴向 =πd 2 / 4 and the cross-sectional area A of the radial outer surface forming the gap 径向 Yes A 径向 =πdl. Therefore, increasing the diameter of the gap (for example to d=1 mm) has a positive effect on the cross-sectional area A of the radially outer surface forming the gap. 径向 Four times higher than the cross-sectional area A of the shaft body 轴向 In addition, increasing the length of the gap (l) only increases the cross-sectional area A of the radial outer surface forming the gap. 径向 Has a positive influence on the cross-sectional area A of the shaft body 轴向 No effect at all. In any case, the slit should preferably be long and have a large diameter. However, because a large diameter can counteract the amount of heat generated in the slit, the diameter of the slit should not be too large (preferably d is about ≤ 1 mm). Most preferably, the thermal conductivity of both the surfaces forming the slit is high, at least 100 W / mK, and is in thermally conductive contact with the blood flow.

[0019] Such a heat-conducting contact may be direct or indirect. Direct heat-conducting contact can be achieved if the respective heat-conducting surface forming the gap constitutes part of a structural element which is entirely made of said heat-conducting material and which is in direct contact with the blood flowing through the pump when the intravascular blood pump is in operation in a patient's vessel. This may be the case when the shaft and the impeller form an integral part formed of one heat-conducting material and / or when the distal end of the housing forming the through hole for the passage of the shaft is an integral part made of a heat-conducting material.

[0020] Alternatively, indirect heat-conductive contact can be achieved if one or more of the gap-forming surfaces respectively constitute part of a structural element which is entirely made of said heat-conductive material and has at least one further surface which is heat-conductively connected to a separate heat-conductive element which is in direct contact with the flowing blood or indirectly in heat-conductive contact with the flowing blood via one or more further heat-conductive elements when the intravascular blood pump is operating in a patient's blood vessel, so that heat from the one or more gap-forming surfaces can be dissipated into the flowing blood by heat conduction. Of course, the heat-conductive element itself should have a high thermal conductivity, preferably higher than the preferred thermal conductivity of the one or more gap-forming surfaces, i.e. higher than 100 W / mK, preferably higher than 130 W / mK, more preferably higher than 150 W / mK and most preferably higher than 200 W / mK.

[0021] Since the surface forming the gap can preferably constitute a radial sliding bearing for the shaft, the surface should have a very small surface roughness, preferably a surface roughness of 0.1 μm or less. Although such a surface roughness can be obtained using a diamond-like carbon coating (DLC), as proposed as a coating for a shaft in US 2015 / 0051436 A1, it is impossible to apply the DLC coating so accurately that a gap width of 2 μm or less can be achieved over the length of the gap using current technology. It is therefore preferred that one or more gap-forming surfaces are made of a material different from DLC and / or by a different method, most preferably of a ceramic material, in particular of a sintered ceramic element. That is, preferably, the heat-conducting surface is not a coating on a structural element, but the surface of one or more structural elements, i.e. the surface of one or more elements of the assembled pump.

[0022] A common problem with ceramics is that ceramic materials typically have very low thermal conductivity. For example, zirconium oxide (ZrO2) mentioned in US2015 / 0051436 A1 has a thermal conductivity of only 2.5 to 3 W / mK. Aluminum oxide (Al2O3) is a well-known ceramic with a relatively high thermal conductivity of 35 to 40 W / mK, but it is still substantially lower than the thermal conductivity of metals such as copper. One of the very few ceramics with substantially higher thermal conductivity is silicon carbide (SiC). Silicon carbide of typical processes has a thermal conductivity between 100 W / mK and 140 W / mK, but silicon carbide with higher thermal conductivity is also available. Pure silicon carbide has a thermal conductivity of 350 W / mK. Unlike other ceramics, silicon carbide is very brittle and therefore difficult to handle. It can be easily broken during manufacturing and assembly. However, due to its good heat capacity, silicon carbide is for the purposes of the present invention the preferred material for at least one of the surfaces forming the slot, preferably the radially outer surface of the slot, and, because of its brittleness, is not the preferred material for the shaft. Therefore, the respective surface or the entire structural element forming such a surface comprises or preferably consists of silicon carbide.

[0023] If silicon carbide forms one surface of the plain bearing, the mating opposite surface of the plain bearing can have virtually any other type of material, in particular any other type of ceramic material. The preferred ceramic material for the respective other surface is alumina toughened zirconia (ATZ) because of its high durability, which however has a thermal conductivity of only 25 W / mK. It is therefore preferred to make the shaft from ATZ and the sleeve in which the shaft is sleeved from SiC so that heat can be easily conducted radially outwards from the gap into the flowing blood. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In the following, the present invention will be explained by way of example with reference to the accompanying drawings. The accompanying drawings are not intended to be drawn to scale. In the accompanying drawings, each identical or approximately identical component illustrated in each of the drawings is represented by a similar number. For the purpose of clarity, not every component may be labeled in every figure. In the accompanying drawings:

[0025] Figure 1 is a schematic diagram of an intravascular blood pump before insertion into the left ventricle, with its inflow cannula positioned in the left ventricle,

[0026] Figure 2 is a schematic longitudinal cross-section of an exemplary prior art blood pump,

[0027] Figure 3 yes Figure 2 An enlarged view of a portion of a blood pump, however, having a structure according to a preferred embodiment of the present invention, and

[0028] Figures 4A to 4I is an enlarged partial view of the distal radial bearing of the pump showing the variation in the converging circumferential gaps.

[0029] Figure 1 It is indicated that a blood pump is used to support the left ventricle in this specific embodiment. The blood pump comprises a catheter 14 and a pumping device 10 attached to the catheter 14. The pumping device 10 has a motor segment 11 and a pump segment 12, which are coaxially arranged one behind the other and result in a rod-shaped construction. The pump segment 12 has an extension in the form of a flexible suction hose 13, which is often referred to as a "cannula". An impeller is arranged in the pump segment 12 to cause blood flow from a blood flow inlet to a blood flow outlet, and the rotation of the impeller is caused by an electric motor arranged in the motor segment 11. The blood pump is placed so that it is mainly located in the ascending aorta 15b. The aortic valve 18 becomes against the outside of the pump segment 12 or its suction hose 13 in the closed state. The blood pump with the suction hose 13 in front is advanced into the indicated position through the front exploration catheter 14, optionally using a guide wire. During this process, the suction hose 13 is passed retrogradely past the aortic valve 18 , so that blood is sucked in through the suction hose 13 and pumped into the aorta 16 .

[0030] The use of blood pumps is not limited to Figure 1 The application represented in Figure 1 The applications shown in are only typical examples of applications. Thus, the pump can also be inserted through other peripheral blood vessels, such as the subclavian artery. Alternatively, reverse applications for the right ventricle can be envisaged.

[0031] Figure 2 An exemplary embodiment of a blood pump according to the prior art US 2015 / 0051436 A1 is shown, which is also suitable for use in the context of the present invention, except that the front end portion marked with an "I" is improved according to the present invention. A preferred embodiment of such an improvement is shown in Figure 3 . According to this, the motor segment 11 has an elongated housing 20 in which an electric motor 21 can be accommodated. The stator 24 of the electric motor 21 can generally have a number of circumferentially distributed windings and a magnetic return path 28 in the longitudinal direction. The magnetic return path 28 can form an outer cylindrical sleeve of the elongated housing 20. The stator 24 can surround a rotor 26 connected to a motor shaft 25 and consist of permanent magnets magnetized in the active direction. The motor shaft 25 can extend over the entire length of the motor housing 20 and protrude from the latter through an opening 35 at the distal end. There, it carries an impeller 34, from which pump blades 36 protrude, and the impeller 34 can rotate in a tubular pump housing 32, which can be firmly connected to the motor housing 20.

[0032] The proximal end of the motor housing 20 has a flexible conduit 14 sealingly attached thereto. A cable 23 for supplying power to and controlling the electric motor 21 may extend through the conduit 14. Additionally, a cleaning fluid line 29 may extend through the conduit 14 and penetrate the proximal end wall 22 of the motor housing 20. Cleaning fluid may be supplied into the interior of the motor housing 20 through the cleaning fluid line 29 and exit through the end wall 30 at the distal end of the motor housing 20. The cleaning pressure is selected so that it is higher than the existing blood pressure to thereby prevent blood from penetrating into the motor housing, between 300 and 1400 mmHg depending on the application.

[0033] As mentioned above, the same cleaned seal may be combined with a pump driven by a flexible drive shaft and remote motor.

[0034] During the rotation of the impeller 34, blood is sucked in through the distal opening 37 of the pump housing 32 and conveyed in the axial direction backwards within the pump housing 32. Through the radial outlet openings 38 in the pump housing 32, the blood flows out of the pump segment 12 and further along the motor housing 20. This ensures that the heat generated in the motor is carried away. It is also possible to operate the pump segment with reverse conveying direction, so that the blood is sucked in along the motor housing 20 and leaves from the distal opening 37 of the pump housing 32.

[0035] The motor shaft 25 is mounted in radial bearings 27, 31 at the proximal end of the motor housing 20 on the one hand, and in radial bearings 27, 31 at the distal end of the motor housing 20 on the other hand. The radial bearings, in particular the radial bearing 31 at the distal end of the motor housing in the opening 35, are constructed as sliding bearings. In addition, the motor shaft 25 is also axially mounted in the motor housing 20, and the axial bearing 40 is also constructed as a sliding bearing. The axial sliding bearing 40 is used to absorb the axial forces of the motor shaft 25 acting in the distal direction when the impeller 34 conveys blood from the distal end to the proximal end. If the blood pump is used to convey blood also or only in the reverse direction, then the corresponding axial sliding bearing 40 can (also or only) be arranged in a corresponding manner at the proximal end of the motor housing 20.

[0036] Figure 3 In more detail, Figure 2The parts marked with "I" in the figure are however structurally improved according to a preferred embodiment of the present invention. In particular, the radial plain bearing 31 and the axial plain bearing 40 can be seen. On the one hand, the bearing gap 39 of the radial plain bearing 31 is formed by the circumferential surface 25A of the motor shaft 25, and, on the other hand, by the surface 33A of the through hole in the bushing or sleeve 33 of the end wall 30 of the motor housing 20, which defines an outer gap diameter of about 1 mm, but the outer gap diameter can also be larger than this. In the present embodiment, the bearing gap 39 of the radial plain bearing 31 has a gap with a minimum gap width of 2 μm or less in the region of the front end or impeller-side end 39A of the gap 39, which converges from the proximal end to the distal end. Preferably, the minimum gap width is between 1 μm and 2 μm. The maximum gap width is about 6 μm in the present embodiment, but can be larger. The length of the gap may range from 1 mm to 2 mm, preferably from 1.3 mm to 1.7 mm, for example 1.5 mm, corresponding to the length of the radial sliding bearing 31. The surface forming the gap of the radial sliding bearing 31 has a surface roughness of 0.1 μm or less.

[0037] The shaft 25 is preferably made of a ceramic material, most preferably of alumina toughened zirconia (ATZ), to avoid shaft fracture. ATZ has a relatively high thermal conductivity, since aluminum has a thermal conductivity of between 30 and 39 W / mK. The impeller 34 carried on the distal end of the shaft 25 is preferably made of a material with an even higher thermal conductivity. In this way, the heat generated in the very narrow gap 39 of the radial sliding bearing 31 can be dissipated through the shaft 25 and the impeller 34 into the blood flowing along the outer surface of the impeller 34.

[0038] However, in an embodiment in which the impeller is made of a material with low thermal conductivity, such as PEEK, or even in an embodiment in which the impeller is made of a material with high thermal conductivity, as proposed above, it is in any case advantageous to use a material with high thermal conductivity to make the sleeve 33 in the end wall 30 of the housing 20, preferably a thermal conductivity of at least 100 W / mK, more preferably at least 130 W / mK, even more preferably at least 150 W / mK and most preferably at least 200 W / mK. In particular, the sleeve 33 may be a ceramic sleeve, more particularly made of a sintered ceramic material. As a particularly preferred ceramic material, the sleeve 33 may contain or consist entirely of SiC, because of its high thermal conductivity.

[0039] Although the entire end wall 30 may be formed as a single piece made of a highly thermally conductive material, it may be preferred to assemble the end wall 30 from the sleeve 33 and one or more radially outer elements 33B which are themselves thermally conductive. This may be particularly important in case the sleeve 33 is made of a brittle material such as SiC. Accordingly, the radially outer thermally conductive elements 33B are thermally conductively connected to the sleeve 33 and themselves have a thermal conductivity which is preferably higher than the thermal conductivity of the sleeve 33 and in any case is at least 100 W / mK, thereby ensuring that the heat from the sleeve 33 can be dissipated into the flowing blood through the thermally conductive elements 33B by thermal conduction and diffusion.

[0040] If you can Figure 3 Further, we can see that Figure 2 , the axial length of the end wall 30 of the housing 20 is relatively long compared to the prior art structure shown in FIG. More specifically, the path for blood to flow along the outer surface of the end wall 30 of the housing 20 is longer in the axial direction than in the radial direction. This provides a large surface area for heat to be transferred from the end wall 30 of the housing 20 into the blood flow. For example, the blood flow can be directed outwardly along the end wall 30 of the housing 20 through a radial distance of between 0.5 and 1 mm, preferably about 0.75 mm, while flowing 1.5 mm to 4 mm, preferably about 3 mm, in the axial direction.

[0041] Regarding the bearing gap of the axial sliding bearing 40, it is formed by the axial inner surface 41 of the end wall 30 and the surface 42 opposite thereto. The opposite surface 42 may be a part of a ceramic disc 44, which may be seated on the motor shaft 25 at the distal end of the rotor 26 and rotate with the rotor 26. A channel 43 may be provided in the bearing gap surface 41 of the end wall 30 to ensure that the cleaning fluid flows between the bearing gap surfaces 41 and 42 of the axial sliding bearing 40 toward the radial sliding bearing 31. In addition to this, the surfaces 41 and 42 of the axial sliding bearing 40 may be flat. The bearing gap of the axial sliding bearing 40 is very small, being several microns.

[0042] When the bearing gap surface 41 of the axial sliding bearing 40 is formed by the sleeve 33, as in Figure 3 , and when the sleeve 33 is made of SiC, the ceramic disc 44 forming the opposite surface 42 of the axial sliding bearing 40 is preferably made of alumina toughened zirconia (ATZ). Optionally, the opposite bearing gap surface 42 can be DLC coated or can also be made of SiC.

[0043] The pressure of the cleaning fluid is adjusted so that the pressure drop along the radial sliding bearing 31 is preferably about 500 mmHg or more to maintain a high axial cleaning flow velocity (≥0.6 m / s) in a narrow 1 to 2 μm gap. The blood pump 10 can be operated using a cleaning fluid without heparin. The blood pump can even operate without any cleaning fluid for at least several hours if the cleaning fails.

[0044] FIG. 4A to FIG. 4C A variation of the converging circumferential gap 39 of the radial plain bearing 31 defined at the distal end of the blood pump housing 20 is shown. The arrows indicate the flow direction of the cleaning fluid with which the radial plain bearing 31 is cleaned.

[0045] A first embodiment of the converging gap 39 is Figure 4A Here, the gap converges continuously from the proximal end to the distal end, more specifically linearly, so that the minimum gap width is located precisely at the impeller-side end 39A of the gap 39 .

[0046] exist Figure 4B The slots 39 in the embodiment shown in FIG. 1 likewise converge continuously and linearly from the proximal end to the impeller-side end 39A of the slots 39 , but the minimum slot width extends over part of the length of the slots 39 to form a cylindrical end section thereof. Figure 4B The cylindrical end section of the slot 39 shown in FIG. Figure 4A The pointed end segment shown in the embodiment of is less prone to wear. In both embodiments, the gap can optionally converge nonlinearly, in particular convexly or, in other words, converge decreasingly from the proximal end to the distal end.

[0047] Although in Figure 4A and Figure 4B The convergence of the gaps 39 in the embodiment shown in FIG. 1 is due to the tapering of the opening 35 having a narrower diameter distally than at the proximal end, but Figure 4C and Figure 4D Embodiments are concerned in which the convergence of the slot 39 is achieved by a conical shape of the shaft 25. More specifically, in both cases the outer diameter of the shaft 25 extends towards the impeller-side end 39A of the slot 39. Figure 4C In the embodiment, the outer diameter of the shaft 25 expands from a constant diameter shaft section on the proximal side of the slot 39, which extends through the end of the slot 39 opposite to the impeller-side end 39A of the slot 39, to a maximum outer diameter within the slot 39. Figure 4DIn the embodiment shown in FIG. 1 , the outer diameter of the shaft has a circumferential groove, which likewise extends through the end of the slot 39 opposite the impeller-side end 39A of the slot 39. In the embodiment shown, the diameter of the groove increases linearly from the proximal end to the distal end, so that the minimum gap is reached shortly before the impeller-side end 39A of the slot 39. However, instead of a linearly converging slot 39, the diameter of the shaft 25 may increase, for example gradually, towards the impeller-side end 39A of the slot 39.

[0048] About FIG. 4A to FIG. 4D The variations described with respect to the embodiment shown in may be combined in any suitable manner, ie the converging slit 39 may be formed by both the tapered diameter of the opening through which the shaft 25 extends and the tapered shaft 25 .

[0049] FIG. 4E to FIG. 4I The invention relates to an embodiment of a distal radial bearing 31 of a pump which is optimized for ease of manufacture with respect to a converging gap 39. Figure 4E The middle bearing 31 is divided into two bearing rings 31A and 31B, and the distal bearing ring 31A in contact with blood has an opening with a smaller diameter than the opening of the proximal bearing ring 31B. Figure 4F The converging gaps are realized by a circumferential groove 25B in the surface 25A of the shaft 25, the groove 25B having a simple curved cross section. Figure 4G The converging gap 39 is likewise realized by a circumferential groove 25B in the surface 25A of the shaft 25, but here the groove 25B gives the shaft 25 a conical axial cross section in the region of the gap 39. Figure 4H The middle bearing 31 is formed by a stepped hole having a smaller diameter at the distal end in contact with the blood than at the proximal end of the slit 39, Figure 4E The implementation method is similar. Fig. 4I In the embodiment, the bearing 31 is again divided into two bearing rings 31A and 31B, so that the distal bearing ring 31A in contact with the blood has a smaller diameter than the proximal bearing ring 31B. However, in the present embodiment, the proximal bearing ring 31B has a cylindrical inner surface, while the distal ring 31A has a conical inner diameter that converges toward the impeller-side end 39A of the slit.

Claims

1. An intravascular blood pump comprising a housing (20) and a rotatable shaft (25) carrying an impeller (34), wherein the shaft (25) extends from the housing (20) through an opening (35) of the housing (20), the impeller (34) being positioned outside the housing (20), the shaft (25) and the housing (20) having surfaces (25A, 33A) forming a circumferential gap (39) in the opening (35) so that a cleaning fluid can flow along the length of the gap from a proximal end to a distal end and exit the gap, wherein the gap (39) converges toward an impeller-side end (39A) of the gap (39), the gap (39) having a length and having a width, the width having a minimum width located somewhere within 50% of the length of the gap (39) closest to the impeller-side end (39A) of the gap (39).

2. The intravascular blood pump according to claim 1, wherein the minimum width exists at the impeller-side end (39A) of the gap (39).

3. An intravascular blood pump according to claim 1, wherein the minimum width extends over 30% or less of the length of the slit (39).

4. Intravascular blood pump according to claim 3, wherein said minimum width extends over no more than 20% of said length of said slit (39).

5. Intravascular blood pump according to any one of claims 1 to 4, wherein the length of the gap (39) is in the range from 1 to 2 mm.

6. Intravascular blood pump according to claim 5, wherein the length of the gap (39) is in the range from 1.3 to 1.7 mm.

7. Intravascular blood pump according to any one of claims 1 to 4, wherein the slit (39) converges continuously through at least a portion of its length until the point where the slit (39) has the minimum width.

8. Intravascular blood pump according to claim 7, wherein the slit (39) converges linearly over at least a portion of its length.

9. The intravascular blood pump according to any one of claims 1 to 4, wherein the diameter of the opening (35) converges towards the impeller-side end (39A) of the slit (39).

10. The intravascular blood pump according to any one of claims 1 to 4, wherein the outer diameter of the shaft (25) expands toward the impeller-side end (39A) of the gap (39).

11. An intravascular blood pump according to claim 10, wherein the outer diameter of the shaft (25) has a circumferential groove extending through the end of the slot (39) opposite to the impeller-side end (39A) of the slot (39).

12. An intravascular blood pump according to claim 10, wherein the outer diameter of the shaft (25) expands from a constant diameter shaft segment extending through the end of the gap (39) opposite to the impeller-side end (39A) of the gap (39) to a maximum outer diameter within the gap (39).

13. Intravascular blood pump according to any one of claims 1 to 4, wherein the minimum width of the gap (39) is 5 μm or less.

14. Intravascular blood pump according to claim 13, wherein the minimum width of the gap (39) is 2 μm or less.

15. The intravascular blood pump according to any one of claims 1 to 4, wherein the maximum width of the gap (39) is 15 μm or less.

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