Intravascular blood pump

Abstract

An intravascular blood pump has a rotatable shaft (25) carrying an impeller (34), the shaft extending through the opening (35), and a housing (20) having an opening (35), the impeller being positioned outside the housing. The shaft and the housing have surfaces (25A, 33A) forming circumferential slits that converge toward the impeller-side ends of the slits and have a minimum slit width that is preferably no more than 5 [mu] m, more preferably no more than 2 [mu] m.

Description

[0001] Divisional application

[0002] This application is a divisional application of the patent application with the application number 201980020590.5, the international filing date of March 21, 2019, the entry date into the Chinese national phase of September 17, 2020, and the invention title of "Intravascular Blood Pump". Technical Field

[0003] 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 also 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

[0004] A blood pump of the type mentioned above is known, for example, from EP 0 961 621 B1, which has a drive segment, a catheter 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 therethrough for supplying power to the drive segment, and a pump segment fastened to the distal end of the drive segment. The drive segment includes a motor housing having an electric motor disposed therein, wherein the motor shaft of the electric motor projects distally from the drive segment and into the pump segment. The pump segment in turn includes a tubular pump housing having an impeller rotating therein, the impeller being seated on the end of the motor shaft projecting from the motor housing. The motor shaft is mounted in the motor housing in two bearings, the two bearings being maximally separated from each other to ensure true and precisely centered guidance of the impeller within 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 shaft seal made of polytetrafluoroethylene that resists blood, polytetrafluoroethylene having a high hardness and a low coefficient of friction, thereby providing a bearing and at the same time preventing blood from entering the motor housing through such a distal bearing. In addition, a cleaning fluid is passed through the motor housing and the impeller-side shaft-seal bearing to resist the entry of blood into the motor housing. This is done at a cleaning fluid pressure higher than the pressure present in the blood.

[0005] Improvements to the blood pump mentioned above are disclosed in US2015 / 0051436 A1 and shown in the attached Figure 2 herein. 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-seal 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.

[0006] While the present invention will be described and preferably used in context with an intravascular blood pump having a motor housed in the housing of the type mentioned above, the present invention is equally advantageously applicable to other types of intravascular blood pumps, where the motor is outside the patient's body and the rotational energy for the impeller is transmitted through a catheter and by means of a flexible rotary drive cable attached to the housing at the distal end of the catheter. Further, in this type of intravascular blood pump, the cleaning fluid typically enters the patient's blood through an opening through which the drive shaft extends.

[0007] Heparin, which is typically mixed into the cleaning fluid, causes a general problem. That is, although the cleaning fluid flows through the gap formed between the shaft and the opening of the housing, whereby blood will tend to be pushed back into the housing through such a gap, blood entering the gap cannot be completely prevented. 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 blockage 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 an emergency, heparin can be counterproductive as it prevents blood clotting and thus healing or hemostasis. Further, the amount of heparin administered to the patient's blood along with the cleaning fluid is difficult to control for various reasons. Specifically, the amount of heparin is often more than what the doctor desires. Accordingly, doctors will often preferably supply heparin to the patient separately from the operation of the blood pump, if needed and in the required amount.

[0008] Accordingly, there is a need for an intravascular blood pump that can operate, if desired, with a cleaning fluid that contains no or at least less heparin. Summary of the Invention

[0009] 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 through which the shaft extends, the impeller being positioned outside the housing, the shaft and the housing having surfaces that form a circumferential gap within the opening. This is not different from the prior art discussed above, and the gap can particularly 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, such that the minimum width of the gap is 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.

[0010] The advantage of the gap converging towards the front end portion of the gap or the impeller side end portion or the distal end portion (these terms have the same meaning) is that the pressure drop generated in the cleaning fluid flowing along the length of the gap from the proximal end to the distal end can be kept low, compared with the pressure drop in a non-converging gap of the same length having the said minimum width over the entire length of the gap. More specifically, according to the present invention, it is desirable to have a relatively high velocity of the cleaning fluid at the impeller side end portion of the gap, which is the side of the gap in contact with the blood, to prevent blood from entering the gap. Thus, the smaller the gap, the better. However, a very small gap over the entire length of the gap requires the cleaning fluid to be delivered to the blood pump at extremely high pressure. By making the gap converge towards the distal end portion, even with a very small minimum gap width, a cleaning fluid pump providing a pressure of, for example, 1 to 1.5 bar can be used.

[0011] For example, a minimum gap of 5 μm in the region of the impeller side end portion of the gap can allow the cleaning fluid to leave the gap at such a high velocity that substantially no blood will enter the gap. Accordingly, it becomes possible to clean the gap using a cleaning fluid with relatively little or even no heparin.

[0012] A minimum gap width of 5 μm or less also provides a physical barrier to the entry of red blood cells into the gap to some extent, because of the relatively large blood cell diameter of approximately 8 μm. However, since the thickness of the blood cell is only approximately 2 μm, it is preferred that the minimum gap width is 2 μm or less. As stated, due to the smaller gap width, the cleaning fluid flows through the gap at a higher velocity, thereby pushing the blood back out of the gap with the highest possible kinetic energy.

[0013] In the case where the minimum gap width is actually limited to the impeller side end portion of the gap, i.e., limited to an infinitesimally short segment of the length of the gap, this may lead to increased wear in the various segments of the gap. Therefore, according to a preferred embodiment, the segment of the gap having the minimum gap width can extend over 50% or less, preferably 30% or less, but preferably not less than 20% of the length of the gap, to keep the wear low. The length of such a segment can range between 0.1 and 0.7 mm, more preferably between 0.2 and 0.4 mm.

[0014] The convergence of the gap can be achieved by tapering one or both of the surfaces forming the gap, namely the tapered outer surface of the gap formed by the inner surface of the opening passing through the wall of the housing and the tapered inner surface of the gap formed by the surface of the shaft. The tapering of the outer surface of the gap means a reduction in the diameter of the wall opening towards the impeller-side end of the gap, and the tapering of the inner surface of the gap means an increase in the diameter of the shaft towards the impeller-side end of the gap. Preferably, the taper is provided on the surface of the shaft, and the opening constituting the outer boundary of the gap can be cylindrical as it is easy to manufacture.

[0015] The preferred length of the gap ranges from 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 typically lies at the end of the gap opposite to the impeller-side end of the gap and reaches 15 μm or less, preferably 10 μm or less, more preferably 8 μm or less, and most preferably 6 μm or less. Most preferably, the converging gap has a maximum gap width of about 6 μm and a minimum gap width of 2 μm or less.

[0016] Furthermore, the gap can converge continuously, in particular linearly, over at least a part of its length until the gap reaches its minimum width.

[0017] In a particularly preferred embodiment, at least one of the two surfaces forming the circumferential gap is made of a material having a thermal conductivity λ≥100 W / mK.

[0018] By making the surface of a material with a relatively high thermal conductivity, the temperature in the gap can be kept low, preferably at 55 °C or lower, thereby preventing the denaturation of any fibrin in the plasma that may enter the gap despite all efforts.

[0019] A material with a thermal conductivity of 100 W / mK for one or more surfaces forming the gap may be sufficient to conduct heat away from the gap and thus keep the temperature inside the gap at 55 °C or lower. 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.

[0020] 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 flowing blood passing through the pump. According to thermodynamics, flowing blood carries away heat faster than non-flowing blood. The faster the blood flows, more heat can be carried away by conduction heat transfer. The blood flow velocity through the pump is generally higher than the blood flow velocity 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, since the distance for heat to flow axially through the shaft body and further through the impeller into the blood is relatively long, it is more preferred to conduct the heat (additionally or only) in the radial direction, i.e., through the radially outer surface forming the gap, away from the gap. Carrying away heat 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 the heat can be conducted in the radial direction, compared to the cross-sectional area of the shaft body through which the heat can be conducted in the axial direction. That is, the cross-sectional area A of the shaft body 轴向 is A 轴向 = πd 2 / 4 and the cross-sectional area A of the radially outer surface forming the gap 径向 is A 径向 = πdl. Thus, the positive effect of increasing the diameter of the gap (e.g., to d = 1 mm) is that the cross-sectional area A of the radially outer surface forming the gap 径向 is four times higher than that of the cross-sectional area A of the shaft body 轴向 . In addition, increasing the length (l) of the gap only has a positive effect on the cross-sectional area A of the radially outer surface forming the gap 径向 and has no effect on the cross-sectional area A of the shaft body 轴向 at all. In any case, the gap should preferably be long and have a large diameter. However, since a large diameter can counteract the amount of heat generated in the gap, the diameter of the gap should not be too large (preferably d ≤ 1 mm approximately). Most preferably, the thermal conductivity of both surfaces forming the gap is high, at least 100 W / mK, and in thermally conductive contact with the blood flow.

[0021] Such thermally conductive contact can be direct or indirect. Direct thermally conductive contact can be achieved if each thermally conductive surface forming the gap forms part of a structural element that is entirely made of the thermally conductive material and is in direct contact with the flowing blood passing through the pump when the intravascular blood pump is operating in the patient's blood vessel. This can be the case when the shaft and the impeller form an integral part made of one thermally conductive material and / or when the distal end of the housing forming the through-hole for the shaft to pass through is an integral part made of the thermally conductive material.

[0022] Alternatively, indirect thermally conductive contact can be achieved if one or more surfaces forming the gap are each part of a structural element which is entirely made of said thermally conductive material and has at least one additional surface thermally connected to a separate thermally conductive element which, when the intravascular blood pump is operating in a patient's blood vessel, is in direct contact with the flowing blood or is in indirect thermally conductive contact with the flowing blood via one or more additional thermally conductive elements, such that heat from one or more surfaces forming the gap can be dissipated into the flowing blood by heat conduction. Of course, the thermally conductive element itself should have a high thermal conductivity, preferably higher than the preferred thermal conductivity of one or more surfaces forming the gap, 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.

[0023] Since the surfaces forming the gap can preferably form a radial sliding bearing for the shaft, the surfaces should have a very low surface roughness, preferably a surface roughness of 0.1 μm or less. While 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 / 0051436A1, it is not possible with current technology to apply the DLC coating so precisely that a gap width of 2 μm or less can be achieved over the length of the gap. It is therefore preferred to manufacture one or more surfaces forming the gap from a material different from DLC and / or by a different method, most preferably from a ceramic material, in particular from a sintered ceramic element. That is, preferably, the thermally conductive 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.

[0024] A common problem with ceramics is that ceramic materials typically have very low thermal conductivities. For example, zirconia (ZrO2) as mentioned in US2015 / 0051436 A1 has a thermal conductivity of only 2.5 to 3 W / mK. Alumina (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 that of metals such as copper. One of the very few ceramics with a substantially higher thermal conductivity is silicon carbide (SiC). Commercially available silicon carbide has a thermal conductivity between 100 W / mK and 140 W / mK, but silicon carbide with an even higher thermal conductivity is also available. Pure silicon carbide has a thermal conductivity of 350 W / mK. Different from other ceramics, silicon carbide is very brittle and thus difficult to handle. It can easily break during manufacturing and assembly. However, due to its good heat capacity, silicon carbide is a preferred material for at least one of the surfaces forming the gap, preferably the radially outer surface of the gap, for the purposes of the present invention, and, because of its brittleness, is not a preferred material for the shaft. Accordingly, each surface or the entire structural element forming such a surface comprises silicon carbide or preferably consists of silicon carbide.

[0025] If silicon carbide forms one surface of a sliding bearing, then the mating opposite surface of the sliding bearing can substantially have any other type of material, particularly any other type of ceramic material. A preferred ceramic material for each of the other surfaces is alumina toughened zirconia (ATZ) because of its high durability, however it has a thermal conductivity of only 25 W / mK. Therefore, it is preferred to manufacture the shaft from ATZ and the sleeve in which the shaft is sleeved from SiC, such that heat can be easily conducted radially outwards from the gap into the flowing blood. Description of the Drawings

[0026] In the following, the present invention will be explained by way of examples with reference to the drawings. The drawings are not intended to be drawn to scale. In the drawings, each identical or approximately identical component illustrated in each of the drawings is denoted by a similar number. For the purpose of clarity, not every component may be labeled in every figure. In the drawings:

[0027] Figure 1 is a schematic view of an intravascular blood pump before being inserted into the left ventricle, with its inflow cannula positioned in the left ventricle,

[0028] Figure 2 is a schematic longitudinal section of an exemplary prior art blood pump,

[0029] Figure 3 is Figure 2 an enlarged view of a part of the blood pump, however, having a structure according to a preferred embodiment of the present invention, and

[0030] Figures 4A to 4I Partial enlarged view of the distal radial bearing of the pump, showing the varying form of the converging circumferential gap.

[0031] Figure 1 Illustrates the use of a blood pump in this specific embodiment for supporting the left ventricle. The blood pump includes 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 configuration. The pump segment 12 has an extension in the form of a flexible suction hose 13, and the suction hose 13 is often referred to as an "intubation tube". An impeller is provided in the pump segment 12 to cause blood flow from the blood flow inlet to the 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 such that it is mainly located in the ascending aorta 15b. The aortic valve 18 is in the closed state and abuts against the outer side of the pump segment 12 or its suction hose 13. The blood pump with the suction hose 13 in the front is advanced into the indicated position through the advancing catheter 14, optionally using a guide wire. When doing so, the suction hose 13 passes retrogradely through the aortic valve 18, so that blood is sucked through the suction hose 13 and pumped into the aorta 16.

[0032] The use of the blood pump is not limited to the Figure 1 application shown, and the application shown Figure 1 is only a typical example of the application. Therefore, the pump can also be inserted through other peripheral blood vessels, such as the subclavian artery. Optionally, a reverse application for the right ventricle can be envisaged.

[0033] Figure 2 Shows an exemplary embodiment of a blood pump according to the prior art US2015 / 0051436 A1, which is equally suitable for use in the context of the present invention, except for the improved use of the surrounded front end marked with "I" according to the present invention, and a preferred embodiment of such an improvement is shown Figure 3 In it. Accordingly, the motor segment 11 has an elongated housing 20, and the electric motor 21 can be accommodated in the elongated housing 20. 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 the outer cylindrical sleeve of the elongated housing 20. The stator 24 can surround the rotor 26 connected to the motor shaft 25 and consists of permanent magnets magnetized in the active direction. The motor shaft 25 can extend through the entire length of the motor housing 20 and project from the latter through an opening 35 at the distal end. There, it carries the impeller 34, from which the pump blades 36 project, and the impeller 34 can rotate within the tubular pump housing 32, and the tubular pump housing 32 can be firmly connected to the motor housing 20.

[0034] The proximal end of the motor housing 20 has a flexible conduit 14 sealed thereto. A cable 23 for supplying power to and controlling the electric motor 21 can extend through the conduit 14. Additionally, a cleaning fluid line 29 can extend through the conduit 14 and penetrate the proximal end wall 22 of the motor housing 20. Cleaning fluid can 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 to be higher than the existing blood pressure, thereby preventing blood from penetrating into the motor housing, between 300 and 1400 mmHg depending on the application.

[0035] As mentioned above, the same cleaning seal can be combined with a pump driven by a flexible drive shaft and a remote motor.

[0036] During rotation of the impeller 34, blood is drawn in through the distal opening 37 of the pump housing 32 and conveyed axially backward within the pump housing 32. Through the radial outlet opening 38 in the pump housing 32, the blood flows out of the pump section 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 section with the reverse conveying direction, causing blood to be drawn in along the motor housing 20 and exit through the distal opening 37 of the pump housing 32.

[0037] The motor shaft 25 is mounted in radial bearings 27, 31 at the proximal end of the motor housing 20 on one hand and in radial bearings 27, 31 at the distal end of the motor housing 20 on the other hand. The radial bearings, especially the radial bearing 31 in the opening 35 at the distal end of the motor housing, are configured as sliding bearings. Additionally, the motor shaft 25 is also axially mounted in the motor housing 20, and the axial bearing 40 is likewise configured as a sliding bearing. The axial sliding bearing 40 is used to bear the axial force acting on the motor shaft 25 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 provided at the proximal end of the motor housing 20 in a corresponding manner.

[0038] Figure 3 More detailed illustration is shown in Figure 2The part marked with "I" in [reference] is, however, structurally improved according to a preferred embodiment of the present invention. Radial sliding bearing 31 and axial sliding bearing 40 can be particularly seen. In one aspect, the bearing gap 39 of radial sliding bearing 31 is formed by the circumferential surface 25A of motor shaft 25, and, in another aspect, by the surface 33A of the through-hole in the bushing or sleeve 33 of end wall 30 of motor housing 20. The end wall 30 of motor housing 20 defines an outer gap diameter of about 1 mm, but the outer gap diameter can also be greater than this. In this embodiment, the bearing gap 39 of radial sliding 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 gap 39, converging 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 this embodiment, but can be larger. The length of the gap can range from 1 mm to 2 mm, preferably from 1.3 mm to 1.7 mm, such as 1.5 mm, corresponding to the length of radial sliding bearing 31. The surfaces forming the gap of radial sliding bearing 31 have a surface roughness of 0.1 μm or less.

[0039] Shaft 25 is preferably made of a ceramic material, most preferably made of alumina toughened zirconia (ATZ), to avoid shaft breakage. ATZ has a relatively high thermal conductivity, since aluminum has a thermal conductivity between 30 and 39 W / mK. The impeller 34 carried on the distal end of 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 radial sliding bearing 31 can be dissipated through shaft 25 and impeller 34 into the blood flowing along the outer surface of impeller 34.

[0040] However, in an embodiment where the impeller is made of a material with a low thermal conductivity such as PEEK, or even in an embodiment where the impeller is made of a material with a high thermal conductivity, as proposed above, in any case it is advantageous to use a material with a high thermal conductivity to make the sleeve 33 in the end wall 30 of the housing 20, preferably with 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 can be a ceramic sleeve, more specifically made of sintered ceramic material. As a particularly preferred ceramic material, the sleeve 33 can comprise or be entirely composed of SiC, because of its high thermal conductivity.

[0041] While the entire end wall 30 can be formed as a one-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 that are themselves thermally conductive. This can be particularly important in the case where the sleeve 33 is made of a brittle material such as SiC. Accordingly, the radially outer thermally conductive elements 33B are thermally 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, so as to ensure that heat from the sleeve 33 can be dissipated into the flowing blood through heat conduction and diffusion through the thermally conductive elements 33B.

[0042] As can be seen from Figure 3 further, compared to the prior art structure shown in Figure 2 the axial length of the end wall 30 of the housing 20 is relatively long. More specifically, the path for the 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 into the blood flow. For example, the blood flow can be guided outwardly along the end wall 30 of the housing 20 over a radial distance 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.

[0043] 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 opposite surface 42. This opposite surface 42 can be part of a ceramic disc 44 that can sit on the motor shaft 25 at the distal end of the rotor 26 and rotate with the rotor 26. Channels 43 can be provided in the bearing gap surface 41 of the end wall 30 to ensure that the cleaning fluid flows through the bearing gap between the surfaces 41 and 42 of the axial sliding bearing 40 towards the radial sliding bearing 31. In addition to this, the surfaces 41 and 42 of the axial sliding bearing 40 can be flat. The bearing gap of the axial sliding bearing 40 is very small, on the order of a few micrometers.

[0044] When the bearing gap surface 41 of the axial sliding bearing 40 is formed by the sleeve 33, as shown in Figure 3 and 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). Alternatively, the opposite bearing gap surface 42 can be DLC-coated or can equally be made of SiC.

[0045] The pressure of the cleaning fluid is regulated such 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) within the 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 for at least a few hours without any cleaning fluid in case of a cleaning failure.

[0046] Figures 4A to 4C A variant of the converging circumferential gap 39 of the radial sliding bearing 31 defined at the distal end of the blood pump housing 20 is shown. The arrows indicate the direction of flow of the cleaning fluid used to clean the radial sliding bearing 31.

[0047] A first embodiment of the converging gap 39 is shown in Figure 4A . Here, the gap converges continuously from the proximal end to the distal end, more specifically linearly, such that the minimum gap width is precisely located at the impeller side end 39A of the gap 39.

[0048] In Figure 4B the gap 39 in the embodiment shown likewise converges continuously and linearly from the proximal end to the distal end towards the impeller side end 39A of the gap 39, but the minimum gap width extends over a partial length of the gap 39 to form a cylindrical end section thereof. The cylindrical end section of the gap 39 as shown in Figure 4B is less prone to wear than the pointed end section as shown in Figure 4A . In both of the two embodiments the gap can alternatively converge non-linearly, in particular convexly or, in other words, decreasingly from the proximal end to the distal end.

[0049] Although in Figure 4A and Figure 4B the convergence of the gap 39 in the embodiments shown is due to a cone with an opening 35 having a narrower diameter at the distal end compared to the proximal end, but Figure 4C and Figure 4D relate to embodiments in which the convergence of the gap 39 is achieved by a cone 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 gap 39. In Figure 4C the outer diameter of the shaft 25 expands from an equal diameter shaft section at the proximal side of the gap 39 to the maximum outer diameter within the gap 39, the equal diameter shaft section extending through the end of the gap 39 opposite the impeller side end 39A of the gap 39. In Figure 4DIn the embodiment shown, the outer diameter of the shaft has a circumferential groove which also extends past 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 such that the minimum clearance is reached shortly before the impeller-side end 39A of the slot 39. However, instead of the linearly converging slot 39, the diameter of the shaft 25 can increase, for example, progressively towards the impeller-side end 39A of the slot 39.

[0050] Regarding the variations described for the embodiment shown in Figures 4A to 4D can be combined in any suitable way, i.e., the converging slot 39 can be formed by both the tapered diameter of the opening through which the shaft 25 extends and the tapered shaft 25.

[0051] Figures 4E to 4I Relates to an embodiment of the distal radial bearing 31 of a pump optimized for ease of manufacture with respect to the converging slot 39. In Figure 4E the bearing 31 is split into two bearing rings 31A and 31B, and the distal bearing ring 31A in contact with the blood has an opening with a smaller diameter than the opening of the proximal bearing ring 31B. In Figure 4F the converging slot is achieved by a circumferential groove 25B in the surface 25A of the shaft 25, the groove 25B having a cross-section of a simple curve. In Figure 4G the converging slot is likewise achieved 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 slot 39. In Figure 4H the bearing 31 is formed by a stepped hole having a smaller diameter at the distal end in contact with the blood compared to the proximal end of the slot 39, similar to the embodiment of Figure 4E . In Figure 4I again, the bearing 31 is split into two bearing rings 31A and 31B such that the distal bearing ring 31A in contact with the blood has a smaller diameter than the proximal bearing ring 31B. However, in this embodiment the proximal bearing ring 31B has a cylindrical inner surface, while the distal ring 31A has a conical inner diameter converging towards the impeller-side end 39A of the slot.

Claims

1. An intravascular blood pump includes a rotatable shaft (25) carrying an impeller (34), and further includes a housing (20) having an opening (35), wherein the shaft (25) extends through the opening (35), the impeller (34) is positioned outside the housing, and the shaft and the housing have surfaces (25A, 33A) forming a circumferential gap (39) within the opening (35), wherein the circumferential gap (39) has a length and a width, and the width has a minimum width located somewhere within 50% of the length of the circumferential gap (39) closest to the impeller-side end (39A) of the circumferential gap (39).

2. An intravascular blood pump includes a rotatable shaft (25) carrying an impeller (34), and further includes a housing (20) having an opening (35), wherein the shaft (25) extends through the opening (35), the impeller (34) is positioned outside the housing, and the shaft and the housing have surfaces (25A, 33A) forming a circumferential gap (39) within the opening (35), wherein the circumferential gap (39) has a length and a width, and the width has a minimum width, and wherein the circumferential gap (39) converges continuously over at least a portion of its length until the gap reaches the point where it has its minimum width.

3. An intravascular blood pump includes a rotatable shaft (25) carrying an impeller (34), and further includes a housing (20) having an opening (35), wherein the shaft (25) extends through the opening (35), the impeller (34) is positioned outside the housing, and the shaft and the housing have surfaces (25A, 33A) forming a circumferential gap (39) within the opening (35), wherein the circumferential gap (39) has a length and a width, and the width has a minimum width, and wherein the outer diameter of the shaft (25) expands towards the impeller-side end (39A) of the circumferential gap (39).

4. An intravascular blood pump includes a rotatable shaft (25) carrying an impeller (34), and further includes a housing (20) having an opening (35), wherein the shaft (25) extends through the opening (35), the impeller (34) is positioned outside the housing, and the shaft and the housing have surfaces (25A, 33A) forming a circumferential gap (39) within the opening (35), wherein the circumferential gap (39) has a length and a width, and the width has a minimum width, and wherein the minimum width of the circumferential gap (39) is 5 μm or less.

5. The intravascular blood pump according to any one of claims 2 to 4, wherein the minimum width is located somewhere within 50% of the length of the gap (39) closest to the impeller-side end (39A) of the gap (39).

6. The intravascular blood pump according to any one of claims 1 to 4, wherein the minimum width exists at the impeller-side end (39A) of the circumferential gap (39).

7. The intravascular blood pump according to any one of claims 1 to 4, wherein the minimum width extends through 30% or less of the length of the circumferential gap (39).

8. The intravascular blood pump according to claim 7, wherein the minimum width extends through no more than 20% of the length of the circumferential gap (39).

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

10. The intravascular blood pump according to claim 9, wherein the length of the circumferential gap (39) is in the range from 1.3 to 1.7 mm.

11. The intravascular blood pump according to any one of claims 1, 3, and 4, wherein the circumferential gap (39) converges continuously through at least a portion of its length until the circumferential gap (39) has the minimum width.

12. The intravascular blood pump according to claim 11, wherein the circumferential gap (39) converges linearly through at least a portion of its length.

13. The intravascular blood pump according to any one of claims 1 to 4, wherein the diameter of the opening (35) converges toward the impeller side end (39A) of the circumferential gap (39).

14. The intravascular blood pump according to any one of claims 1, 2, and 4, wherein the outer diameter of the shaft (25) expands toward the impeller side end (39A) of the circumferential gap (39).

15. The intravascular blood pump according to claim 3 or 14, wherein the outer diameter of the shaft (25) has a circumferential groove extending through the end of the gap (39) opposite the impeller side end (39A) of the circumferential gap (39).

16. The intravascular blood pump according to claim 3 or 14, wherein the outer diameter of the shaft (25) expands from an equal diameter shaft segment extending through the end of the gap (39) opposite the impeller side end (39A) of the gap (39) to a maximum outer diameter within the gap (39).

17. The intravascular blood pump according to any one of claims 1 to 3, wherein the minimum width of the circumferential gap (39) is 5 μm or less.

18. The intravascular blood pump according to claim 4 or 17, wherein the minimum width of the circumferential gap (39) is 2 μm or less.

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

20. The intravascular blood pump according to any one of claims 1 to 4, wherein the surfaces (25A, 33A) forming the circumferential gap (39) constitute a radial sliding bearing for the shaft (25).

21. An intravascular blood pump includes a rotatable shaft (25) carrying an impeller (34), and further includes a housing (20) having an opening (35), wherein the shaft (25) extends through the opening (35), 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), wherein the circumferential gap has a length and has a gap width of 2 μm or less passing through at least a portion of the length, and wherein at least one (33A) of the surfaces (25A, 33A) forming the circumferential gap is made of a material having a thermal conductivity of at least 100 10 W / mK.

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