Intravascular blood pump

Abstract

To provide an intravascular blood pump.SOLUTION: An intravascular blood pump has: a rotatable shaft (25) carrying an impeller (34); and a housing (20) with an opening (35) through which the shaft extends with the impeller positioned outside the housing. The shaft and the housing have surfaces (25A, 33A) forming a circumferential gap which has a gap width of 2 μm or less over at least a part of a length of the gap, and at least one of the surfaces forming the gap is made of a material having thermal conductivity of at least 100 W / mK, in particular a ceramic material such as SiC.SELECTED DRAWING: Figure 4A

Description

[Technical Field]

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

[0002] A blood pump of the above-mentioned type is known, for example, from EP 0961621 B1, which comprises a drive section, a catheter attached to the proximal end of the drive section (the end of the drive section closer to the physician or the "rear end" of the drive section) and through which wires for supplying power to the drive section extend, and a pump section fixed to the distal end of the drive section. The drive section comprises a motor housing in which an electric motor is arranged, the motor shaft of the electric motor projecting distally from the drive section into the pump section. The pump section, in turn, comprises a tubular pump housing containing a rotating impeller mounted on the end of the motor shaft projecting outward from the motor housing. The motor shaft is supported in two bearings maximally spaced apart in the motor housing to guide the impeller precisely centered within the pump housing. While the proximal end of the motor housing is a radial ball bearing, the impeller-side bearing, which is closest to the blood, is configured as a blood shaft seal made of polytetrafluoroethylene, a material with a high hardness and low friction coefficient, to provide a bearing and prevent blood from entering the motor housing through the distal bearing. Blood ingress into the motor housing is further mitigated by passing a purge fluid through the motor housing and the impeller-side shaft seal bearing. This is achieved by using a purge fluid pressure that is higher than the pressure present in the blood.

[0003] An improved version of the blood pump described above is disclosed in U.S. Patent Publication No. 2015 / 0051436A1 and shown in Figure 2 attached hereto. Here, the impeller-side bearing at the distal end of the motor housing comprises an axial plain bearing and a radial plain bearing, or a combined axial-radial plain bearing, with the radial plain bearing replacing the shaft sealing bearing described above. Thus, the purge fluid passes through the gap of the impeller-side radial plain 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 described above in which the motor is contained within the housing, the present invention is equally advantageously applicable to other types of intravascular blood pumps in which the motor is external to the patient's body and rotational energy for the impeller is transmitted through a catheter and the housing attached to the distal end of the catheter by a flexible rotary drive cable, and in these types of intravascular blood pumps, a purge fluid is typically passed through the patient's blood through an opening through which the drive shaft extends.

[0005] A common problem arises with heparin, which is typically mixed into the purge fluid. While the purge fluid flows through the gap formed between the shaft and the housing opening, pushing back any blood that might otherwise seep into the housing through the gap, it cannot completely prevent blood from seeping into the gap. In particular, there is always the possibility that some blood will seep into at least the distal section of the gap. Heparin helps prevent blood from clotting within the gap or adhering to surfaces, thereby preventing interference with shaft rotation. However, physicians often do not want to administer heparin to a patient's blood via the purge fluid. For example, in first aid, heparin can be counterproductive because it inhibits blood clotting and therefore healing or hemostasis. Furthermore, the amount of heparin administered to a patient's blood with the purge fluid is difficult to control for various reasons. In particular, the amount of heparin is often greater than physicians desire. Therefore, physicians often prefer to administer any necessary heparin to the patient separately from the operation of the blood pump. Summary of the Invention [Problem to be solved by the invention]

[0006] Therefore, there is a need for an intravascular blood pump that can, when desired, flow a purge fluid that is free of heparin, or at least contains less heparin. [Means for solving the problem]

[0007] Thus, according to a first aspect of the present invention, an intravascular blood pump can include a rotatable shaft carrying an impeller and a housing having an opening, the shaft extending through the opening so that the impeller is positioned outside the housing, and the shaft and housing having surfaces forming a circumferential gap within the opening. This is not different from the prior art discussed above, and the gap can particularly constitute a radial plain bearing for the shaft. However, in the blood pump disclosed herein, the width of the gap is 2 μm or less over at least a portion of the length of the gap; for example, only the front end or the impeller side of the gap can have a gap width of 2 μm or less, or in one embodiment, the width of the gap is 2 μm or less along its entire length, and further, at least one of the two surfaces forming the circumferential gap is made of a material with a thermal conductivity λ≧100 W / mK.

[0008] The following explains why the above-described technique contributes to an intravascular blood pump that can operate with a purge fluid that does not contain heparin, and even temporarily without a purge fluid. Specifically, due to the small gap width of less than 2 μm, red blood cells, which are approximately 8 μm in diameter and 2 μm in thickness, have difficulty entering the gap and are believed to clog the gap. Furthermore, due to the small gap width, the purge fluid passes through the gap at high speed, thereby pushing the blood back out of the gap with high kinetic energy. However, although red blood cells appear to be successfully prevented from entering the gap, experiments have shown that biological material accumulates within the gap and obstructs the shaft. This biological material is believed to originate from plasma that penetrated the gap despite the strong purge fluid flow. More specifically, the biological material deposited within the gap is believed to consist primarily of denatured portions of plasma, particularly fibrin, which adhere to the surfaces that form the gap and clog it. This is presumably caused by the high temperature generated in the gap due to the small gap width, combined with the shear-induced heat in the gap. Further experiments showed that by making the surface from a material with a relatively high thermal conductivity, the temperature in the gap can be kept low, preferably below 55°C, thereby preventing the denaturation of fibrin in the plasma.

[0009] Most surprisingly, it has been found that intravascular blood pumps having the above-mentioned characteristics function unhindered for longer periods of time, even when no purge fluid passes through the gap. This is believed to be due to the plasma penetrating the gap and forming a slippery biofilm on one or more surfaces inside the gap. This constitutes a substantial safety factor for intravascular blood pumps and is therefore of utmost benefit to these pumps.

[0010] A thermal conductivity of 100 W / mK for the surface or surface materials forming the gap may be sufficient to conduct heat away from the gap and thereby maintain a temperature within the gap below 55°C, although 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.

[0011] To transfer heat from the gap to the blood, the gap-forming surface is preferably in heat-conducting contact with the blood flowing through the pump. According to thermodynamics, flowing blood transfers heat faster than still blood. The faster the blood flow, the more heat can be transferred away by conductive heat transfer. The blood flow velocity through the pump is generally greater than the blood flow velocity outside the pump. Thus, for example, heat generated within the gap and the temperature rise of the gap-forming surface can be further conducted from the surface of the shaft through the shaft body to the impeller at the end of the shaft, and from there to the blood flowing along the impeller. However, because the distance that heat must travel axially through the shaft body and then through the impeller to the blood is relatively long, it is preferable to (additionally or exclusively) remove heat radially from the gap by conduction, i.e., via the radially outer surface that forms the gap. Radial heat removal is preferred not only because the radial distance over which heat must travel from the gap to the bloodstream is relatively short, but also because it is easier to increase the heat transfer area available for radial heat transfer compared to the cross-sectional area of ​​the shaft body available for axial heat transfer. axial is A axial =πd 2 / 4, and the cross-sectional area A of the radially outer surface forming the gap radial is A radial = πdl. Therefore, the beneficial effect of increasing the diameter of the gap (for example, to d = 1 mm) is the increase in the cross-sectional area A of the shaft body. axial The cross-sectional area A of the radially outer surface forming the gap is radial Furthermore, the beneficial effect of increasing the gap length (l) is that the cross-sectional area A of the radially outer surface that defines the gap radialonly for the cross-sectional area A of the shaft body axial ) has no effect on the blood flow. In any case, the gap should preferably be long and have a large diameter, although the diameter of the gap should not be too large (preferably approximately d≦1 mm), as a larger diameter may limit the amount of heat generated within the gap. Most preferably, both surfaces forming the gap have a high thermal conductivity, at least 100 W / mK, and are in thermally conductive contact with the blood flow.

[0012] Such thermally conductive contact may be direct or indirect. Direct thermally conductive contact can be achieved when each thermally conductive surface forming the gap is part of a structural element made entirely of the thermally conductive material that is in direct contact with the blood flowing through the intravascular blood pump when the pump is operating within a patient's blood vessel. This can be the case when the shaft and impeller form a unitary part made of a single thermally conductive material and / or when the distal end of the housing, which forms the through opening for the shaft, is a unitary part made of a thermally conductive material.

[0013] Alternatively, indirect thermally conductive contact can be achieved if one or more surfaces forming the gap are each part of a structural element made entirely of the thermally conductive material, at least one further surface of which is thermally conductively connected to a separate thermally conductive element that is in direct contact with the flowing blood or in indirect thermally conductive contact via one or more further thermally conductive elements when the intravascular blood pump is operating within a patient's blood vessels, thereby enabling heat from the gap-forming surface(s) to be dissipated into the flowing blood by thermal conduction. Naturally, the thermally conductive elements should themselves have a high thermal conductivity, preferably higher than the preferred thermal conductivity of the gap-forming surface(s), i.e., greater than 100 W / mK, preferably greater than 130 W / mK, more preferably greater than 150 W / mK, and most preferably greater than 200 W / mK.

[0014] Because the gap-forming surfaces may preferably constitute radial plain bearings for shafts, these surfaces should have a very low surface roughness, preferably 0.1 μm or less. While such surface roughness can be achieved using diamond-like carbon (DLC) coatings, such as those proposed for shaft coatings in U.S. Patent Publication No. 2015 / 0051436 A1, current technology does not allow for the application of DLC coatings with sufficient precision to achieve gap widths of 2 μm or less across the length of the gap. Therefore, it is preferable to form one or more gap-forming surfaces from a material other than DLC, most preferably from a ceramic material, particularly from a sintered ceramic element, and / or by a different method. That is, the heat-conducting surface is preferably not a coating on a structural element, but rather the surface of one or more structural elements, i.e., the surface of one or more elements constituting the pump.

[0015] A common problem with ceramics is that the thermal conductivity of ceramic materials is typically very low. For example, zirconium oxide (ZrO2), as described in U.S. Patent Publication No. 2015 / 0051436A1, has a thermal conductivity of only 2.5 to 3 W / mK. Aluminum oxide (Al2O3), a well-known ceramic, has a relatively high thermal conductivity of 35 to 40 W / mK, which is still significantly lower than that of metals such as copper. One of the few ceramics with a comparatively high thermal conductivity is silicon carbide (SiC). Typical practical silicon carbide has a thermal conductivity between 100 W / mK and 140 W / mK, although silicon carbide with higher thermal conductivities is also available. The thermal conductivity of pure silicon carbide is 350 W / mK. Unlike other ceramics, silicon carbide is very brittle and therefore difficult to handle. It can easily break during manufacturing and assembly. Nevertheless, due to its good heat capacity, silicon carbide is, for purposes of this application, the preferred material for at least one of the surfaces forming the gap, preferably the radially outer surface of the gap, and due to its brittleness, is not preferred for the shaft, and therefore each surface or the entire structural element forming such a surface comprises, or preferably consists of, silicon carbide.

[0016] When silicon carbide forms one surface of the plain bearing, the cooperating opposing surface of the plain bearing may be essentially any other type of material, particularly any other type of ceramic material. A preferred ceramic material for the other corresponding surface is alumina-toughened zirconia (ATZ) because of its durability, but its thermal conductivity is only 25 W / mK. Therefore, it is preferred to make the shaft from ATZ and the sleeve in which the shaft is journaled from SiC, so that heat can be easily conducted radially outward to the flowing blood, away from the gap.

[0017] Because the pressure drop of purge fluid flowing from proximal to distal through the gap is large due to the small gap width, the gap width preferably converges from wide to narrow toward the impeller end of the gap, the side of the gap that contacts the blood, so that only the distal end of the gap or a relatively short distal section has a gap width of 2 μm or less. That is, the advantage of a gap that converges toward the front end, impeller end, or distal end of the gap (these terms have the same meaning) is that it can maintain a lower pressure drop for purge fluid flowing from proximal to distal along the length of the gap, compared to the pressure drop for a non-converging gap of the same length that has the minimum width described above along its entire length. In this way, even with a very small minimum gap width, a purge fluid pump that provides a pressure of, for example, 1 to 1.5 bar can be used.

[0018] More specifically, the gap may converge toward the front or impeller end of the gap such that the minimum width of the gap is located within 30% of the length of the gap nearest the impeller end of the gap, and more preferably, the minimum width is at least at the impeller end of the gap.

[0019] If the minimum gap width were practically limited to the impeller end of the gap, i.e., to an infinitesimal portion of the gap length, this could lead to increased wear on the corresponding portion of the gap. Therefore, according to a preferred embodiment, the portion of the gap having the minimum gap width can extend over no more than 50% of the gap length, preferably no more than 30%, but preferably over 20% or more of the gap length to keep wear low. The length of such a portion can range between 0.1 and 0.7 mm, more preferably between 0.2 and 0.4 mm.

[0020] The convergence of the gap can be achieved by tapering one or both surfaces that define the gap, i.e., the tapered outer gap surface formed by the inner surface of the opening through the housing wall, and the tapered inner gap surface formed by the surface of the shaft. A tapered outer gap surface refers to a decrease in the diameter of the wall opening toward the impeller end of the gap, while a tapered inner gap surface refers to an increase in the diameter of the shaft toward the impeller end of the gap. While a tapered shaft surface is preferred, the opening that defines the outer boundary of the gap may be cylindrical for ease of manufacture.

[0021] The preferred length of the gap is in the range of 1 to 2 mm, preferably 1.3 to 1.7 mm, while the minimum gap width can 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 gap width is typically located at the end of the gap opposite the impeller end of the gap and is 15 μm or less, preferably 10 μm or less, more preferably 8 μm or less, and most preferably 6 μm or less. Most preferred is when the converging gap has a maximum gap width of about 6 μm and a minimum gap width of 2 μm or less.

[0022] Furthermore, the gap may converge continuously, in particular linearly, over at least a portion of its length to a point where the width of the gap is at a minimum.

[0023] The present invention will now be described, by way of example only, with reference to the accompanying drawings, which are not intended to be drawn to scale. In these drawings, identical or nearly identical components shown in various figures are represented by like numerals. For clarity, not every component will be labeled in every drawing. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 is a schematic diagram of an intravascular blood pump inserted before the left ventricle with the inflow cannula positioned within the left ventricle. [Figure 2] 1 is a schematic longitudinal cross-sectional view of an exemplary prior art blood pump. [Figure 3] 3 is an enlarged view of a portion of the blood pump of FIG. 2, but with a configuration according to a preferred embodiment of the present invention. [Figure 4A] FIG. 10 is a close-up view of a portion of the distal radial bearing of the pump showing the converging circumferential clearance variation. [Figure 4B] FIG. 10 is a close-up view of a portion of the distal radial bearing of the pump showing the converging circumferential clearance variation. [Figure 4C] FIG. 10 is a close-up view of a portion of the distal radial bearing of the pump showing the converging circumferential clearance variation. [Figure 4D] FIG. 10 is a close-up view of a portion of the distal radial bearing of the pump showing the converging circumferential clearance variation. [Figure 4E] FIG. 10 is a close-up view of a portion of the distal radial bearing of the pump showing the converging circumferential clearance variation. [Figure 4F] FIG. 10 is a close-up view of a portion of the distal radial bearing of the pump showing the converging circumferential clearance variation. [Figure 4G] FIG. 10 is a close-up view of a portion of the distal radial bearing of the pump showing the converging circumferential clearance variation. [Figure 4H] FIG. 10 is a close-up view of a portion of the distal radial bearing of the pump showing the converging circumferential clearance variation. [Figure 4I] FIG. 10 is a close-up view of a portion of the distal radial bearing of the pump showing the converging circumferential clearance variation. DETAILED DESCRIPTION OF THE INVENTION

[0025] FIG. 1 illustrates the use of a blood pump, which in this particular embodiment is for left ventricular assist. The blood pump includes a catheter 14 and a pumping device 10 attached to the catheter 14. The pumping device 10 includes a motor section 11 and a pump section 12, which are coaxially arranged one behind the other, resulting in a rod-shaped configuration. The pump section 12 has an extension in the form of a flexible intake hose 13, often referred to as a "cannula." An impeller is provided within the pump section 12 to drive blood from a blood inlet to a blood outlet. Rotation of the impeller is induced by an electric motor disposed within the motor section 11. The blood pump is positioned to reside primarily within the ascending aorta 15b. In its closed state, the aortic valve 18 abuts against the outer surface of the pump section 12 or its intake hose 13. The blood pump, with the intake hose 13 at its front, is advanced to the depicted position by advancing the catheter 14, optionally using a guidewire. In doing so, the suction hose 13 passes retrograde through the aortic valve 18 so that blood is drawn through the suction hose 13 and pumped into the aorta 16 .

[0026] The use of the blood pump is not limited to the application depicted in Figure 1, which only includes a typical application. For example, the pump can be inserted through other peripheral blood vessels, such as the subclavian artery. Alternatively, a retrograde application for the right ventricle can be envisioned.

[0027] FIG. 2 shows an exemplary embodiment of a blood pump according to prior art U.S. Patent Publication No. 2015 / 0051436 A1, which is also suitable for use in the context of the present invention, but with a modified front end marked with an "I" in accordance with the present invention, a preferred embodiment of such modification being shown in FIG. 3 . Thus, motor section 11 includes an elongated housing 20, which can house an electric motor 21. The stator 24 of electric motor 21 can typically have multiple circumferentially distributed windings and a longitudinal magnetic return path 28. The magnetic return path 28 can form a cylindrical outer sleeve of elongated housing 20. The stator 24 can surround a rotor 26, which consists of a permanent magnet magnetized in the operating direction and is connected to a motor shaft 25. The motor shaft 25 extends the entire length of motor housing 20 and protrudes distally therefrom through an opening 35. The motor shaft 25 then carries an impeller 34 with projecting pump blades 36 which can rotate within a tubular pump housing 32 which can be rigidly connected to the motor housing 20 .

[0028] A flexible catheter 14 is sealingly attached to the proximal end of the motor housing 20. An electrical cable 23 may extend through the catheter 14 for powering and controlling the electric motor 21. Additionally, a purge fluid conduit 29 may extend through the catheter 14 and penetrate the proximal end wall 22 of the motor housing 20. Purge fluid may be supplied to the interior of the motor housing 20 through the purge fluid conduit 29 and exit through an end wall 30 at the distal end of the motor housing 20. The purge pressure is selected to be between 300 and 1400 mmHg depending on the application, so as to be higher than existing blood pressure and thereby prevent blood from entering the motor housing.

[0029] As mentioned above, the same seal that is purged can be combined with a pump driven by a flexible drive shaft and a remote motor.

[0030] As the impeller 34 rotates, blood is drawn through a distal opening 37 in the pump housing 32 and conveyed axially in the reverse direction within the pump housing 32. The blood exits the pump section 12 through a radial outlet opening 38 in the pump housing 32 and continues along the motor housing 20, thereby carrying away heat generated in the motor. It is also possible to operate the pump section in the reverse conveying direction, so that blood is drawn along the motor housing 20 and exits the distal opening 37 in the pump housing 32.

[0031] The motor shaft 25 is supported in radial bearings 27, 31, one at the proximal end of the motor housing 20 and the other at the distal end of the motor housing 20. The radial bearings, particularly the radial bearing 31 in an opening 35 at the distal end of the motor housing, are configured as plain bearings. The motor shaft 25 is also supported axially within the motor housing 20, with its axial bearing 40 also configured as a plain bearing. The axial plain bearing 40 serves to absorb the axial force of the motor shaft 25 acting in the distal direction when the impeller 34 transports blood from distal to proximal. If the blood pump is used to transport blood in the reverse direction as well, or only in the reverse direction, a corresponding axial plain bearing 40 can be provided in a corresponding manner (additionally or exclusively) at the proximal end of the motor housing 20.

[0032] FIG. 3 shows in more detail the portion marked "I" in FIG. 2, with further structural modifications according to a preferred embodiment of the present invention. In particular, the radial plain bearing 31 and the axial plain bearing 40 are visible. The bearing gap of the radial plain bearing 31 is formed by the peripheral surface 25A of the motor shaft 25 on the one hand and by the surface 33A of the through-hole of the bushing or sleeve 33 in the end wall 30 of the motor housing 20 on the other hand, which defines a gap outer diameter of approximately 1 mm, although this gap outer diameter may be larger. In this embodiment, the bearing gap of the radial plain bearing 31 has a gap width of 2 μm or less, not only at the front or impeller-side end of the gap, but also along the entire length of the radial plain bearing. Preferably, the gap width is between 1 μm and 2 μm. The length of the gap may be between 1 mm and 2 mm, preferably between 1.3 mm and 1.7 mm, e.g., 1.5 mm, corresponding to the length of the radial plain bearing 31. The surface roughness of the surfaces forming the gaps of the radial sliding bearing 31 is 0.1 μm or less.

[0033] The shaft 25 is preferably made of a ceramic material, most preferably alumina-toughened zirconia (ATZ) to avoid shaft fracture. ATZ has a relatively high thermal conductivity due to aluminum, which 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, heat generated within the very narrow clearance of the radial plain bearing 31 can be dissipated through the shaft 25 and impeller 34 to the blood flowing along the outer surface of the impeller 34.

[0034] However, in embodiments in which the impeller is made of a material with low thermal conductivity, such as PEEK, or even in embodiments in which the impeller is made of a material with high thermal conductivity, such as those presented above, it is advantageous in any case to make the sleeve 33 in the end wall 30 of the housing 20 from a material with high thermal conductivity, preferably 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 from a sintered ceramic material. As a particularly preferred ceramic material, the sleeve 33 may comprise or consist entirely of SiC due to its high thermal conductivity.

[0035] While the entire end wall 30 may be formed as a unitary piece made of a highly thermally conductive material, it may be preferable to assemble the end wall 30 from the sleeve 33 and one or more radially outer elements 33B, which themselves are thermally conductive. This may be important, particularly if the sleeve 33 is made of a brittle material such as SiC. The radially outer thermally conductive elements 33B are therefore thermally conductively connected to the sleeve 33 and themselves have a thermal conductivity that is preferably higher than that of the sleeve 33, and in any case at least 100 W / mK, to ensure that heat from the sleeve 33 is dissipated by thermal conduction and diffusion through the thermally conductive elements 33B into the bloodstream.

[0036] As can be further seen in Figure 3 compared to the prior art design shown in Figure 2, the axial length of the end wall 30 of the housing 20 is relatively long. 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 transfer from the end wall 30 of the housing 20 to the blood flow. For example, blood flow may be directed outward along the end wall 30 of the housing 20 for a radial distance of between 0.5 and 1 mm, preferably about 0.75 mm, while flowing axially for 1.5 to 4 mm, preferably about 3 mm.

[0037] Regarding the bearing gap of the axial plain bearing 40, it is formed by the axial inner surface 41 of the end wall 30 and the opposing surface 42. This opposing surface 42 may be part of a ceramic disc 44 that can be mounted on the motor shaft 25 distal to the rotor 26 and rotated therewith. To ensure that the purge fluid flows between the bearing-gap surfaces 41 and 42 of the axial plain bearing 40 towards the radial plain bearing 31, a channel 43 may be provided in the bearing-gap surface 41 of the end wall 30. Otherwise, the surfaces 41 and 42 of the axial plain bearing 40 may be flat. The bearing gap of the axial plain bearing 40 is very small, on the order of a few micrometers.

[0038] 3, when the bearing-gap surface 41 of the axial plain bearing 40 is formed by the sleeve 33, which is made of SiC, the ceramic disc 44 forming the opposing surface 42 of the axial plain bearing 40 is preferably made of alumina toughened zirconia (ATZ). Alternatively, the opposing bearing-gap surface 42 may be coated with DLC or may also be made of SiC.

[0039] The pressure of the purge fluid is adjusted so that the pressure drop along the radial plain bearing 31 is preferably about 500 mmHg or greater to maintain a high axial purge flow velocity (≧0.6 m / s) within a narrow gap of 1 to 2 μm. The blood pump 10 can be operated using a heparin-free purge fluid. The blood pump can even operate without any purge fluid for at least several hours in the event of a poor purge.

[0040] 4A to 4C show variations in the circumferential gap (here explicitly designated by reference numeral 39) that defines the radial plain bearing 31 at the distal end of the blood pump housing 20. More specifically, the circumferential gap 39 converges from proximal to distal in these variations. The arrows indicate the flow direction of the purge fluid that purges the radial plain bearing 31.

[0041] A first embodiment of a converging gap 39 is shown in Figure 4A, where the gap converges continuously, more specifically linearly, from proximal to distal, with the minimum gap width located just at the impeller end 39A of the gap 39.

[0042] Gap 39 in the embodiment shown in Figure 4B also converges continuously and linearly from proximal to distal toward impeller end 39A of gap 39, but the minimum gap width extends over a portion of the length of gap 39 to form its cylindrical end section. The cylindrical end section of gap 39 as shown in Figure 4B is less susceptible to wear than the sharpened section shown in the embodiment of Figure 4A. In either embodiment, the gap may alternatively converge nonlinearly, particularly concavely, or in other words, gradually decreasing from proximal to distal.

[0043] In the embodiment shown in Figures 4A and 4B, the convergence of gap 39 results from a taper of opening 35, which is narrower in diameter distally compared to proximally, whereas Figures 4C and 4D relate to an embodiment in which the convergence of gap 39 is achieved by a taper of shaft 25. More specifically, the outer diameter of shaft 25 extends toward impeller end 39A of gap 39 in both cases. In Figure 4C, the outer diameter of shaft 25 flares from a constant diameter shaft section proximal to gap 39, which extends beyond the end of gap 39 opposite impeller end 39A, to a maximum outer diameter within gap 39. In the embodiment shown in Figure 4D, the outer diameter of the shaft has a circumferential groove, which also extends beyond the end of gap 39 opposite impeller end 39A of gap 39. In the embodiment shown, the groove diameter increases linearly from proximal to distal, reaching a minimum gap just before the impeller end 39A of the gap 39. However, instead of a linearly converging gap 39, the diameter of the shaft 25 could increase gradually, for example, toward the impeller end 39A of the gap 39.

[0044] The variations described in connection with the embodiment shown in Figures 4A to 4D can be combined in any suitable manner, i.e., the converging gap 39 can be formed by both the tapered diameter of the opening through which the shaft 25 extends and by the tapered shaft 25.

[0045] Figures 4E to 4I relate to an embodiment of the pump's distal radial bearing 31 optimized for easy manufacturing of the converging gap 39. In Figure 4E, the bearing 31 is divided into two bearing rings 31A and 31B, with the distal bearing ring 31A, which is in contact with the blood, having an opening with a smaller diameter than the opening of the proximal bearing ring 31B. In Figure 4F, the converging gap is realized by a circumferential groove 25B in the surface 25A of the shaft 25, which has a simple curved cross-section. In Figure 4G, the converging gap is also realized by a circumferential groove 25B in the surface 25A of the shaft 25, but in this case, the groove 25B is such that the shaft 25 has a cone-like axial cross-section in the region of the gap 39. In Figure 4H, similar to the embodiment of Figure 4E, the bearing 31 is formed by a stepped bore with a smaller diameter at its distal end, which is in contact with the blood, compared to its proximal end. 4I, bearing 31 is similarly divided into two bearing rings 31A and 31B, with the distal bearing ring 31A, which is in contact with the blood, being smaller in diameter than the proximal bearing ring 31B, except that in this embodiment, the proximal bearing ring 31B has a cylindrical inner surface, while the distal ring 31A has a cone-like inner diameter that converges toward the impeller end 39A of the gap.

Claims

1. 1. An intravascular blood pump comprising: a rotatable shaft (25) carrying an impeller (34); and a housing (20) having an opening (35), wherein the shaft (25) extends through the opening (35) so that the impeller (34) is positioned outside the housing; the shaft and the housing have surfaces (25A, 33A) forming a circumferential gap within the opening (35), the gap having a length and a width of 5 μm or less over at least a portion of the length, and at least one (33A) of the surfaces (25A, 33A) forming the gap being made of a material having a thermal conductivity of at least 100 W / mK.

2. 2. The intravascular blood pump of claim 1, wherein the thermal conductivity is at least 130 W / mK.

3. 2. The intravascular blood pump of claim 1, wherein the thermal conductivity is at least 150 W / mK.

4. 2. The intravascular blood pump of claim 1, wherein the thermal conductivity is at least 200 W / mK.

5. 5. An intravascular blood pump according to any one of claims 1 to 4, characterized in that the surfaces forming the gap constitute a radial plain bearing for the shaft.

6. 6. An intravascular blood pump according to claim 1, wherein at least one of the surfaces forming the gap is part of a structural element that is made entirely of the material and that is in direct contact with the flowing blood when the intravascular blood pump is in use in a patient's blood vessel.

7. 6. An intravascular blood pump according to claim 1, wherein at least one of the surfaces forming the gap is part of a structural element made entirely of the material and having at least one further surface connected in a thermally conductive manner to a thermally conductive element, the thermally conductive element being either in direct contact with the flowing blood or in indirect thermally conductive contact with the flowing blood via one or more further thermally conductive elements when the intravascular blood pump is operating in a patient's blood vessel, such that heat from the at least one of the surfaces forming the gap can be dissipated into the flowing blood by thermal conduction, and wherein the thermal conductivity of the one or more thermally conductive elements is at least 100 W / mK.

8. 8. An intravascular blood pump according to any one of claims 1 to 7, characterized in that each of the surfaces (25A, 33A) forming the gap has a surface roughness of 0.1 μm or less.

9. 9. Intravascular blood pump according to any one of claims 1 to 8, characterized in that said at least one surface (33A) is made of a ceramic material.

10. 10. An intravascular blood pump according to any one of claims 1 to 9, characterized in that the at least one surface (33A) is part of a ceramic sleeve (33) in which the shaft (25) can be journalled.

11. 11. An intravascular blood pump according to any one of claims 1 to 10, characterized in that the shaft (25), including the surface (25A) of the shaft that forms the gap, is made of a ceramic material.

12. 12. An intravascular blood pump according to claim 11, characterized in that the surface (25A) of the shaft forming the gap is made of alumina toughened zirconia (ATZ).

13. 12. An intravascular blood pump according to any one of claims 1 to 11, wherein the at least one surface (33A) comprises silicon carbide (SiC).

14. 14. The intravascular blood pump of claim 13, wherein one (33A) of the at least one surface (25A, 33A) comprises silicon carbide (SiC) and the other (25A) of the at least one surface (25A, 33A) comprises alumina toughened zirconia (ATZ).

15. 15. An intravascular blood pump according to any one of claims 1 to 14, further comprising a purge fluid supply conduit (29) connected to the housing and configured to direct purge fluid into the housing and out of the housing through the opening (35).

16. 16. An intravascular blood pump according to claim 1, wherein the gap (39) converges towards an impeller-side end (39A) of the gap (39), and the width of 5 μm or less is located anywhere within 50% of the length of the gap (39) closest to the impeller-side end (39A) of the gap (39).

17. 17. An intravascular blood pump according to claim 16, characterized in that the width of 5 μm or less is present at the impeller-side end (39A) of the gap (39).

18. 18. An intravascular blood pump according to claim 16 or 17, wherein the width of 5 μm or less extends over 30% or less of the length of the gap (39).

19. 19. An intravascular blood pump according to any one of claims 16 to 18, characterized in that the diameter of the opening (35) converges towards the impeller-side end (39A) of the gap (39).

20. 20. An intravascular blood pump according to any one of claims 16 to 19, characterized in that the outer diameter of the shaft (25) expands towards the impeller-side end (39A) of the gap (39).

21. 21. An intravascular blood pump according to claim 20, characterized in that the outer diameter of the shaft (25) has a circumferential groove extending beyond the end of the gap (39) opposite the impeller end (39A) of the gap (39).

22. 21. An intravascular blood pump according to claim 20, wherein the outer diameter of the shaft (25) flares to a maximum outer diameter within the gap (39) from a constant diameter shaft section extending beyond the end of the gap (39) opposite the impeller end (39A) of the gap (39).

23. 23. An intravascular blood pump according to any one of claims 16 to 22, characterized in that the maximum width of the gap (39) is less than or equal to 15 μm.

24. 24. An intravascular blood pump according to claim 23, characterized in that the maximum width of the gap (39) is less than or equal to 6 μm.

25. 25. An intravascular blood pump according to any one of claims 1 to 24, characterized in that the length of the gap (39) is in the range of 1 to 2 mm.

26. 26. An intravascular blood pump according to claim 25, characterized in that the length of the gap (39) is in the range of 1.3 to 1.7 mm.

27. 27. An intravascular blood pump according to any one of claims 1 to 26, characterized in that the width of the gap is between 1 μm and 2 μm.

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