INTRAVASCULAR BLOOD PUMP

Abstract

An intravascular blood pump having a rotatable shaft carrying an impeller and a housing with an opening through which the shaft extends with the impeller positioned outside the housing. The shaft and the housing have surfaces forming a circumferential gap which converges towards the impeller-side end of the gap and which has a minimum gap width of preferably no more than 5 μm, more preferably no more than 2 μm.

Claims

1-15. (canceled)

16. An intravascular blood pump comprising: a shaft carrying an impeller, the shaft being rotatable; and a housing having an opening and an end wall having a sleeve, a circumferential gap defined by a circumferential surface of the shaft and a surface of the sleeve; wherein the shaft extends through the opening with the impeller positioned outside the housing; and wherein the circumferential gap has a length and a width, the width having a minimum width selected to provide a physical barrier against ingress of red blood cells into the gap.

17. The intravascular blood pump according to claim 16, wherein the sleeve is a ceramic sleeve comprising a sintered ceramic material or silicon carbide.

18. The intravascular blood pump according to claim 16, wherein at least one of the shaft, the sleeve or the end wall comprises a thermoconductive material.

19. The intravascular blood pump according to claim 18, wherein the end wall of the housing further comprises one or more radially outer thermoconductive elements.

20. The intravascular blood pump according to claim 19, wherein the radial outer thermoconductive element is thermoconductively connected to the sleeve.

21. The intravascular blood pump according to claim 19, wherein the one or more radially outer thermoconductive elements have a thermal conductivity that is higher than a thermal conductivity of the sleeve.

22. The intravascular blood pump according to claim 16, wherein the minimum width is located somewhere within 50% of the length of the gap closest to an impeller-side end of the gap.

23. The intravascular blood pump according to claim 22, wherein the minimum width extends over 30% or less of the length of the gap.

24. The intravascular blood pump according to claim 23, wherein the minimum width extends over not more than 20% of the length of the gap.

25. The intravascular blood pump according to claim 16, wherein the length of the gap is in a range of from 1 to 2 mm.

26. The intravascular blood pump according to claim 25, wherein the length of the gap is in the range of from 1.3 to 1.7 mm.

27. The intravascular blood pump according to claim 16, wherein the circumferential gap converges continuously over at least part of its length up to where the gap has the minimum width.

28. The intravascular blood pump according to claim 16, wherein the circumferential gap converges linearly over at least part of its length.

29. The intravascular blood pump according to claim 16, wherein a diameter of the circumferential gap converges towards an impeller-side end which is an end of the circumferential gap closest to the impeller.

30. The intravascular blood pump according to claim 16, wherein an outer diameter of the shaft expands towards an impeller-side end which is an end of the circumferential gap closest to the impeller.

31. The intravascular blood pump according to claim 30, wherein the outer diameter of the shaft has a circumferential groove stretching over an end of the gap opposite the impeller-side end of the circumferential gap.

32. The intravascular blood pump according to claim 30, wherein the outer diameter of the shaft expands from a constant diameter shaft section stretching over an end of the circumferential gap opposite the impeller-side end of the circumferential gap to a maximum outer diameter within the gap.

33. The intravascular blood pump according to claim 16, wherein the minimum width of the gap is 5 μm or less.

34. The intravascular blood pump according to claim 33, wherein the minimum width of the gap is 4 μm or less.

35. The intravascular blood pump according to claim 34, wherein the minimum width of the gap is 3 μm or less.

36. The intravascular blood pump according to claim 35, wherein the minimum width of the gap is 2 μm or less.

37. The intravascular blood pump according to claim 16, wherein a maximum width of the gap is 15 μm or less.

38. The intravascular blood pump according to claim 22, wherein the minimum width is present at the impeller-side end of the gap.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0025] Hereinafter, the 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 drawings, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labelled in every drawing. In the drawings:

[0026] FIG. 1 is a schematic representation of an intravascular blood pump inserted before the left ventricle, with its inflow cannula positioned in the left ventricle,

[0027] FIG. 2 is a schematic longitudinal cross-section of an exemplary prior art blood pump,

[0028] FIG. 3 is an enlarged representation of a part of the blood pump of FIG. 2, however, with a structure according to a preferred embodiment of the invention, and

[0029] FIGS. 4A to 4I are enlarged partial views of the pump's distal radial bearing showing variations of a converging circumferential gap.

DETAILED DESCRIPTION

[0030] FIG. 1 represents the employment of a blood pump for supporting, in this particular example, the left ventricle. The blood pump comprises a catheter 14 and a pumping device 10 attached to the catheter 14. The pumping device 10 has a motor section 11 and a pump section 12 which are disposed coaxially one behind the other and result in a rod-shaped construction form. The pump section 12 has an extension in the form of a flexible suction hose 13, often referred to as “cannula”. An impeller is provided in the pump section 12 to cause blood flow from a blood flow inlet to a blood flow outlet, and rotation of the impeller is caused by an electric motor disposed in the motor section 11. The blood pump is placed such that it lies primarily in the ascending aorta 15b. The aortic valve 18 comes to lie, in the closed state, against the outer side of the pump section 12 or its suction hose 13. The blood pump with the suction hose 13 in front is advanced into the represented position by advancing the catheter 14, optionally employing a guide wire. In so doing, the suction hose 13 passes the aortic valve 18 retrograde, so the blood is sucked in through the suction hose 13 and pumped into the aorta 16.

[0031] The use of the blood pump is not restricted to the application represented in FIG. 1, which merely involves a typical example of application. Thus, the pump can also be inserted through other peripheral vessels, such as the subclavian artery. Alternatively, reverse applications for the right ventricle may be envisioned.

[0032] FIG. 2 shows an exemplary embodiment of the blood pump according to the prior art US 2015/0051436 A1, which is likewise suitable for use in the context of the present invention, except that the encircled front end marked with “I” is modified according to the invention, a preferred embodiment of such modification being shown in FIG. 3. Accordingly, the motor section 11 has an elongated housing 20 in which an electric motor 21 may be housed. A stator 24 of the electric motor 21 may have, in the usual way, numerous circumferentially distributed windings as well as a magnetic return path 28 in the longitudinal direction. The magnetic return path 28 may form an outer cylindrical sleeve of the elongate housing 20. The stator 24 may surround a rotor 26 connected to the motor shaft 25 and consisting of permanent magnets magnetized in the active direction. The motor shaft 25 may extend over the entire length of the motor housing 20 and protrude distally out of the latter through an opening 35. There, it carries an impeller 34 with pump vanes 36 projecting therefrom, which may rotate within a tubular pump housing 32 which may be firmly connected to the motor housing 20.

[0033] The proximal end of the motor housing 20 has the flexible catheter 14 sealingly attached thereto. Through the catheter 14, there may extend electrical cables 23 for power supply to and control of the electric motor 21. In addition, a purge fluid line 29 may extend through the catheter 14 and penetrate a proximal end wall 22 of the motor housing 20. Purge fluid may be fed through the purge fluid line 29 into the interior of the motor housing 20 and exit through the end wall 30 at the distal end of the motor housing 20. The purging pressure is chosen such that it is higher than the blood pressure present, in order to thereby prevent blood from penetrating into the motor housing, being between 300 and 1400 mmHg depending on the case of application.

[0034] As mentioned before, the same purged seal can be combined with a pump which is driven by a flexible drive shaft and a remote motor.

[0035] Upon a rotation of the impeller 34, blood is sucked in through the distal opening 37 of the pump housing 32 and conveyed backward within the pump housing 32 in the axial direction. Through radial outlet openings 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 produced in the motor is carried off. It is also possible to operate the pump section with the reverse conveying direction, with blood being sucked in along the motor housing 20 and exiting from the distal opening 37 of the pump housing 32.

[0036] 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 at the distal end of the motor housing 20, on the other hand. The radial bearings, in particular the radial bearing 31 in the opening 35 at the distal end of the motor housing, are configured as sliding bearings. Furthermore, the motor shaft 25 is also mounted axially in the motor housing 20, the axial bearing 40 likewise being configured as a sliding bearing. The axial sliding bearing 40 serves for taking up axial forces of the motor shaft 25 which act in the distal direction when the impeller 34 conveys blood from distal to proximal. Should the blood pump be used for conveying blood also or only in the reverse direction, a corresponding axial sliding bearing 40 may (also or only) be provided at the proximal end of the motor housing 20 in a corresponding manner.

[0037] FIG. 3 shows the portion marked with “I” in FIG. 2 in greater detail, yet structurally modified according to a preferred embodiment of the invention. There can be seen in particular the radial sliding bearing 31 and the axial sliding bearing 40. The bearing gap 39 of the radial sliding bearing 31 is formed, on the one hand, by the circumferential surface 25A of the motor shaft 25 and, on the other hand, by the surface 33A of a through bore in a bushing or sleeve 33 of the motor housing's 20 end wall 30 defining an outer gap diameter of about 1 mm, but the outer gap diameter may also be larger than this. In this embodiment, the bearing gap 39 of the radial sliding bearing 31 has a gap converging from proximal to distal with a minimum gap width of 2 μm or less in the area of the front end or impeller-side end 39A of the gap 39. Preferably the minimum gap width is between 1 μm and 2 μm. The maximum gap width is about 6 μm in this embodiment, but may be larger. The length of the gap may range from 1 mm to 2 mm, preferably from 1.3 mm to 1.7 mm, e.g., 1.5 mm, corresponding to the length of the radial sliding bearing 31. The surfaces forming the gap of the radial sliding bearing 31 have a surface roughness of 0.1 μm or less.

[0038] The shaft 25 is preferably made of ceramic material, most preferably from alumina toughened zirconia (ATZ) to avoid shaft fractures. ATZ has a relatively high thermal conductivity due to the 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 having an even higher thermal conductivity. This way, heat generated in the very narrow gap 39 of the radial sliding bearing 31 can dissipate through the shaft 25 and the impeller 34 into the blood flowing along the outer surface of the impeller 34.

[0039] However, in an embodiment where the impeller is made of a material having low thermal conductivity, such as PEEK, or even in embodiments where the impeller is made of a material having high thermal conductivity, as suggested above, it is in any case advantageous to make the sleeve 33 in the housing's 20 end wall 30 of a material with high thermal conductivity, 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 specifically made of sintered ceramic material. As a particularly preferred ceramic material, the sleeve 33 may comprise or entirely consist of SiC, because of its high thermal conductivity.

[0040] While the entire end wall 30 may be formed as an integral piece made of a highly thermoconductive material, it may be preferable to assemble the end wall 30 from the sleeve 33 and one or more radially outer elements 33B which are itself thermoconductive. This may be important in particular where the sleeve 33 is made of brittle material, such as SiC. Accordingly, the radial outer thermoconductive element 33B is thermoconductively connected to the sleeve 33 and has itself a thermal conductivity which is preferably higher than the thermal conductivity of the sleeve 33 and in any case at least 100 W/mK so as to guarantee that the heat from the sleeve 33 can dissipate through the thermoconductive element 33B into the flowing blood by thermal conduction and diffusion.

[0041] As can further be seen from FIG. 3 as compared to the prior art structure shown in FIG. 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 housing's 20 end wall 30 is longer in the axial direction than in the radial direction. This provides a large surface area for heat to transfer from the housing's 20 end wall 30 into the blood flow. For instance, the blood flow may be guided outwardly along the end wall 30 of the housing 20 over a radial distance of between 0.5 and 1 mm, preferably about 0.75 mm, while flowing in an axial direction of 1.5 mm to 4 mm, preferably about 3 mm.

[0042] As regards the bearing gap of the axial sliding bearing 40, this is formed by the axially interior surface 41 of the end wall 30 and a surface 42 opposing it. This opposing surface 42 may be part of a ceramic disc 44 which may be seated on the motor shaft 25 distally 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 purge fluid flow through between the bearing-gap surfaces 41 and 42 of the axial sliding bearing 40 towards the radial sliding bearing 31. Other than 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 a few micrometer.

[0043] When the bearing-gap surface 41 of the axial sliding bearing 40 is formed by the sleeve 33, as shown in FIG. 3, and the sleeve 33 is made of SiC, the ceramic disc 44 forming the opposing surface 42 of the axial sliding bearing 40 is preferably made of alumina toughened zirconia (ATZ). Alternatively, the opposing bearing-gap surface 42 may be DLC-coated or may likewise be made of SiC.

[0044] The pressure of the purge fluid is adjusted such that the pressure drop along the radial sliding bearing 31 is preferably about 500 mmHg or more to maintain high axial purge flow velocity (≥0.6 m/s) within the narrow 1 to 2 μm gap. The blood pump 10 can be operated with purge fluid which is free from heparin. The blood pump can even be run without any purge fluid at least for hours if the purge fails.

[0045] FIGS. 4A to 4C show variations of the converging circumferential gap 39 defining the radial sliding bearing 31 at the distal end of the blood pump housing 20. The arrows indicate the flow direction of the purge fluid with which the radial sliding bearing 31 is purged.

[0046] A first embodiment of the converging gap 39 is shown in FIG. 4A. Here, the gap converges continuously, more specifically linearly, from proximal to distal with the minimum gap width being located exactly at the impeller-side end 39A of the gap 39.

[0047] The gap 39 in the embodiment shown in FIG. 4B likewise converges continuously and linearly from proximal to distal towards the impeller-side end 39A of the gap 39, but the minimum gap width extends over a partial length of the gap 39 so as to form a cylindrical end section thereof. The cylindrical end section of the gap 39 as shown in FIG. 4B is less prone to wear than the pointed end section as shown in the embodiment of FIG. 4A. In both embodiments the gap may alternatively converge non-linearly, in particular convexly or, in other words, degressively from proximal to distal.

[0048] While in the embodiments shown in FIGS. 4A and 4B the convergence of the gap 39 is due to a taper of the opening 35 having a narrower diameter distal as compared to proximal, FIG. 4C and FIG. 4D relate to embodiments where the convergence of the gap 39 is realized by a taper of the shaft 25. More specifically, an outer diameter of the shaft 25 extends towards the impeller-side end 39A of the gap 39 in both cases. In FIG. 4C, the outer diameter of the shaft 25 expands from a constant diameter shaft section at the proximal side of the gap 39, which constant diameter shaft section stretches over an end of the gap 39 opposite the impeller-side end 39A of the gap 39, to a maximum outer diameter within the gap 39. In the embodiment shown in FIG. 4D, the outer diameter of the shaft has a circumferential groove, the groove likewise stretching over an end of the gap 39 opposite the impeller-side end 39A of the gap 39. In the embodiment shown, the diameter of the groove increases linearly from proximal to distal so that the minimum gap which is reached shortly before the impeller-side end 39A of the gap 39. However, instead of a linearly converging gap 39, the diameter of the shaft 25 may increase e.g., progressively towards the impeller-side end 39A of the gap 39.

[0049] The variations described in relation to the embodiments shown in FIGS. 4A to 4D may be combined in any suitable manner, i.e., the converging gap 39 may be formed by both a tapering diameter of the opening through which the shaft 25 extends and a tapering shaft 25.

[0050] FIGS. 4E to 4I relate to embodiments of the pump's distal radial bearing 31 which are optimized regarding an easy manufacture of the converging gap 39. In FIG. 4E the bearing 31 is divided in two bearing rings 31A and 31B with the distal bearing ring 31A in contact with the blood having an opening with a smaller diameter than the opening of the proximal bearing ring 31B. In FIG. 4F the converging gap is realized by a circumferential groove 25B in the surface 25A of the shaft 25, the groove 25B having a simple curved cross section. In FIG. 4G the converging gap is likewise realized by a circumferential groove 25B in the surface 25A of the shaft 25, but here the groove 25B is such that the shaft 25 has a conical axial cross section in the region of the gap 39. In FIG. 4H the bearing 31 is formed by a stepped bore having a smaller diameter at the distal end being in contact with the blood as compared to the proximal end of the gap 39, similar to the embodiment of FIG. 4E. In FIG. 4I, again, the bearing 31 is divided in two bearing rings 31A and 31B with the distal bearing ring 31A in contact with the blood having a smaller diameter than the proximal bearing ring 31B. However, in this embodiment the proximal bearing ring 31B has a cylindrical inner surface, whereas the distal ring 31A has a conical inner diameter converging towards the impeller-side end 39A of the gap.