Abstract
An intravascular blood pump comprises a catheter, a rotor, a housing in which the rotor is housed and a flexible drive shaft extending through the catheter and rotatably supported in a proximal bearing located proximally of the rotor. The proximal bearing comprises a bearing sleeve and an outer bearing ring. The bearing sleeve comprises a proximal portion located proximally of the outer bearing ring, the proximal portion of the bearing sleeve forming an axial bearing with a proximal surface of the outer bearing ring. The bearing sleeve further comprises a distal portion extending from the proximal portion of the bearing sleeve distally into the outer bearing ring, wherein the distal portion of the bearing sleeve forms a radial bearing with the outer bearing ring.
Claims
1. An intravascular blood pump, comprising: a catheter; a housing in which a rotor is housed, the housing being attached to a distal end of the catheter; a flexible drive shaft extending through the catheter and connected to the rotor, said drive shaft being rotatably supported in a proximal bearing located proximally of the rotor; wherein the proximal bearing comprises a bearing sleeve and an outer bearing ring, wherein the bearing sleeve comprises a proximal portion (30a) located proximally of the outer bearing ring, the proximal portion of the bearing sleeve forming an axial bearing of the proximal bearing together with a proximal surface of the outer bearing ring and wherein the bearing sleeve comprises a distal portion extending from the proximal portion of the bearing sleeve distally into the outer bearing ring, wherein the distal portion of the bearing sleeve forms a radial bearing of the proximal bearing together with the outer bearing ring.
2. The intravascular blood pump according to claim 1, wherein the bearing sleeve is fixedly connected to the flexible drive shaft.
3. The intravascular blood pump according to claim 1, wherein the outer bearing ring is located inside a distal end region of the catheter or inside a proximal end region of the housing.
4. The intravascular blood pump according to claims 1, wherein a restriction member limiting axial movement of the bearing sleeve relative to the outer bearing ring is located proximally of the bearing sleeve inside at least one of the catheter and the housing.
5. The intravascular blood pump according to claim 1, wherein the flexible drive shaft is at least partly filled with sealant.
6. The intravascular blood pump according to claim 1, wherein at least one of the bearing sleeve and the outer bearing ring comprises at least one of the following materials: ceramics and metals.
7. The intravascular blood pump according to claim1 1, wherein at least one of the bearing sleeve and the outer bearing ring comprises a coating.
8. The intravascular blood pump according to claim1 3, wherein one or both of the proximal end region of the housing or the distal end region of the catheter contains one or more radial through-holes.
9. The intravascular blood pump according to claim 1, wherein the flexible drive shaft contains a reinforcement element extending longitudinally within a central lumen of the drive shaft.
10. The intravascular blood pump according to claim 1, wherein a radial bearing gap between the outer bearing ring and the bearing sleeve is between 2 μm and 10 μm, preferably between 3 μm and 4 μm.
11. The intravascular blood pump according to claim 1, wherein the bearing sleeve comprises a portion extending distally of the outer bearing ring, wherein the rotor is mounted on the portion extending distally of the bearing sleeve.
12. The intravascular blood pump according to claim 1, wherein the rotor is located at a distance between 0.001 mm and 8 mm from the outer bearing ring.
13. The intravascular blood pump according to claim 1, comprising a purge fluid supply line arranged to supply purge fluid such that the purge fluid flows through a gap defined by the radial bearing.
14. The intravascular blood pump according to claim 1, wherein the flexible drive shaft has a section of reduced diameter and wherein at least the distal portion of the bearing sleeve is arranged at the section of reduced diameter.
15. The intravascular blood pump according to claim 1, wherein the rotor and the housing are radially expandable.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0066] Hereinafter the invention will be explained by way of example with reference to the accompanying drawings. The accompanying drawings are not drawn to scale. In the drawings, identical or corresponding components illustrated in various figures are represented by the same numeral. For purposes of clarity, not every component may be labeled in every drawing. In the drawings:
[0067] FIG. 1 is a schematic representation of an intravascular blood pump, which is positioned within the left ventricle of the heart;
[0068] FIG. 2 shows a schematic representation of an intravascular blood pump;
[0069] FIGS. 3A and 3B show schematic representations of an intravascular blood pump in an expanded and a compressed state;
[0070] FIGS. 4A, 4B and 4C show a schematic representation of an intravascular blood pump with a static support member extending into the distal end of the rotor according to a first embodiment;
[0071] FIG. 5 shows a schematic representation of an intravascular blood pump with a static support member extending into the distal end of the rotor according to a second embodiment;
[0072] FIGS. 6A to 6D show schematic representations of an intravascular blood pump with a rotor having a nose at its distal end according to a third embodiment;
[0073] FIG. 7 shows a schematic representation of an intravascular blood pump with a proximal and a distal bearing;
[0074] FIGS. 8A and 8B show a schematic representation of the path of purge fluid in an intravascular blood pump;
[0075] FIG. 9A shows a drive shaft comprising an outer layer and an inner layer;
[0076] FIG. 9B shows a drive shaft with a bearing sleeve, an outer bearing ring and protective rings;
[0077] FIG. 10A shows a hydraulically divided bearing sleeve;
[0078] FIG. 10B shows a bearing with a restriction member;
[0079] FIGS. 11A and 11B show bearings with restriction members and a rotor;
[0080] FIGS. 12A and 12B show two different embodiments of a proximal bearing with an outer bearing ring and a specifically formed bearing sleeve; and
[0081] FIGS. 13A to 13D show hydrodynamic axial bearings.
DETAILED DESCRIPTION OF THE DRAWINGS
[0082] FIG. 1 shows the use of an intravascular blood pump 1 for supporting, in this particular example, a left ventricle 2 of a human heart. The intravascular blood pump 1 comprises a catheter 5 and a pumping device, the pumping device comprising a pump section 4 mounted at a distal end region of the catheter 5. The intravascular blood pump 1 may be placed inside the heart using a percutaneous, transluminal technique. For example, the intravascular blood pump 1 may be introduced through a femoral artery. However, alternative vascular access is equally possible, such as access through the subclavian artery. After passing through the femoral artery, the catheter 5 may be pushed into the aorta such that the pump section 4 reaches through the aortic valve into the heart. The positioning of the pump section 4 in FIG. 1 serves purely as an example, whereas different placements are possible, such as positioning the pump section 4 inside the right ventricle of the heart.
[0083] The pump section 4 comprises a rotor 10 to cause blood to flow from a blood flow inlet 6 at a distal end of the pump section 4 to a blood flow outlet 7 located proximally of the blood flow inlet 6. The catheter 5 houses a drive shaft 12 driven by the electric motor 8, which is preferably placed outside the patient's body. The drive shaft 12 drives the rotor contained inside the pump section 4. At its distal end, the pump section 4 possesses a flexible atraumatic tip 9 having the form of a pigtail or a J-form, which facilitates placement of the intravascular blood pump 1 by aiding navigation inside the patient's vascular system. Furthermore, the softness of the flexible atraumatic tip 9 allows the pump section 4 to support itself atraumatically against the wall of the left ventricle 2.
[0084] FIG. 2 shows the intravascular blood pump 1 in further detail. The rotor 10 is located inside a housing 11. In this embodiment, both the rotor 10 and the housing 11 are compressible. In this case, the intravascular blood pump 1 is transported through the patient's vascular system while both the rotor 10 and the housing 11 are in their compressed state. Once the pump section 4 is at its target location, the housing 11 and rotor 10 are expanded. The flexible atraumatic tip 9 is situated at the distal end of the housing 11. The drive shaft 12 is realized as a drive shaft cable. The drive shaft 12 with the rotor 10 arranged at a distal end thereof can be seen protruding from the distal end of the catheter 5. When the rotor 10 inside the housing 11 is rotated by means of the drive shaft 12, blood is drawn into the blood flow inlet 6 at the distal end of the housing 11 and through the housing 11 into a downstream tubing 20, which is attached to the housing 11 and extends proximally. The blood is then ejected from the downstream tubing 20 into the aorta through the more proximally located blood flow outlet 7 provided in the downstream tubing 20, the blood flow outlet comprising a plurality of outlet openings. The downstream tubing 20 is made of a flexible material such that it can be compressed by the aortic valve as the patient's heart is pumping. The downstream tubing 20 is typically expanded mainly due to the active blood flow generated by the rotor 10 during rotation. By placing the blood flow inlet 6 inside the left ventricle 2 and the blood flow outlet 7 inside the aorta, the intravascular blood pump I may support the patient's systemic blood circulation. If the intravascular blood pump 1 is configured and placed differently, it may be used, e.g., to support the patient's pulmonary blood circulation instead.
[0085] In this example, a liquid, in particular a purge fluid, is supplied from outside the patient's body through the catheter 5 to the pump section 4. Inside the pump section 4, the liquid may be used to purge one or more bearings in order to reduce friction and cool the pump section 4, as will be explained further in relation to FIGS. 4 and 5. Preferably, the liquid is used to purge at least the distal bearing. In such case, the pressure of the purge fluid is chosen to be higher than the blood pressure of the patient in order to prevent blood from entering the bearing.
[0086] Preferably, the pressure of the purge fluid is in a range of 300 mmHg (0.4 bar) to 1500 mmHg (2 bar), more preferably in a range of 600 mmHg (0.8 bar) to 1100 mmHg (approx. 1.5 bar).
[0087] The housing 11 is preferably produced from a shape-memory material, such as Nitinol, and provides a cage around the rotor 10. As can be seen in FIG. 5, a central part of the housing 11 carries a sleeve, which defines a channel through which blood is pumped by means of the rotor 10. Proximally and distally of this channel, the housing 11 allows blood to be sucked into the housing 11 and pushed out of the housing 11 into the downstream tubing 20 (as shown in FIG. 2).
[0088] FIGS. 3A and 3B show the pump section 4, its rotor 10 as well as its housing 11 in an expanded and in a compressed state, respectively. A cannula 16 is arranged at the distal end of the catheter 5. Initially, before deployment of the intravascular blood pump 1, the pump section 4 is provided in its compressed state inside the cannula 16. The cannula 16 can be a cannula 16 pertaining to the catheter 5 or a peel-away-sheath to aid the insertion of the catheter 5 into the body of a patient. When a physician has determined that the catheter 5 is placed correctly inside a patient's vascular system, he or she will push the housing 11 out of the cannula 16. With the cannula 16 removed, the housing 11 will expand due to its shape-memory properties. At the same time, the rotor 10 expands due to its elasticity. As the housing 11 expands radially away from the drive shaft 12, it contracts in the longitudinal direction.
[0089] The rotor 10 is supported in a distal section of the rotor 10 by a distal bearing 14 comprising a static support member 18 with a pin 19, the static support member 18 being attached to the housing 11 at one end thereof and extending into the distal end of the rotor 10 with its pin 19 on the other end thereof so that upon the expansion of the housing 11 the pin 19 can move axially inside the distal end of the rotor 10. Preferably, the pin 19 is sufficiently long for it to remain inside the rotor 10 when the housing 11 is in its compressed state. When the intravascular blood pump 1 is in its expanded state and needs to be removed from the heart, the physician pulls the housing 11 back into the cannula 16, which will cause the housing 11 to compress radially and extend longitudinally so that the distal end of the housing 11 moves away from the rotor 10 along with the static support member 18 and its pin 19, which extends into the distal end of the rotor 10. The smaller diameter of the housing 11 thus achieved facilitates the removal of the intravascular blood pump 1 from the patient.
[0090] In prior art distal bearings 14, the drive shaft 12 sometimes extends distally of the rotor 10 and into the distal bearing. This, however, may cause tendinous chords of the heart to be entangled with the drive shaft 12 possibly leading to clotting and device failure. Therefore, the use of the static support member 18 as part of the distal bearing 14, which does not involve rotating parts distal to the rotor 10 and distal to the rotor blades, is advantageous.
[0091] FIGS. 4A and 4B show the pump section 4 according to a first embodiment in further detail including the housing 11 and the rotor 10, which is driven by the drive shaft 12. The drive shaft 12 is rotatably supported both in a proximal bearing 13 at the distal end of the catheter 5 proximally of the rotor 10 (or in a proximal part of the housing) and in a distal bearing 14 located at the distal end of the rotor 10. In FIG. 4A, the drive shaft 12 is hollow at its distal end or, more specifically, the rotor shaft is hollow so as to form a fluid line 15 through which a purge fluid may be pumped towards the distal bearing 14. Where the drive shaft is hollow and extends up to the distal end of the rotor 10, the rotor 10 may be formed directly on the distal end of the drive shaft 12 so that the rotor shaft is formed by the drive shaft, whereby in the regions of the proximal and distal bearings the drive shaft 12 may be stiffened, e.g., by injection-molded plastic material, and provided with appropriate outer and inner bearing surface finishes, respectively. Alternatively, the entire end region including the bearing sections of the drive shaft 12 may be stiffened in order to obtain a stiffer structure of the pump section. For example, the drive shaft 12 is thinned at its distal end and a stiff hollow tube is slipped over the thinned end and extends distally to form the rotor shaft and bearing sections. The purge fluid may be transported through the fluid line 15 in the rotor shaft to the distal bearing 14. In the embodiment shown in FIG. 4A, the purge fluid can be urged through the central fluid line 15 to exit the drive shaft 12 at its distal end and further through a bearing gap of the distal bearing 14 into the blood stream. The purging of the distal bearing 14 by the purge fluid leads to less friction and thus to less wear on the distal bearing and, furthermore, prevents blood from entering into and clogging the bearing gap.
[0092] For the intravascular blood pump 1 to be efficient, a large rotor diameter is desirable. However, as the gap between the rotor 10 and the housing 11 gets smaller, the risk of blood cells or the rotor 10 being damaged increases. If only a proximal bearing 13 is used, the system may oscillate and the gap between the tip ends of the blades of the rotor 10 and the inner surface of the housing 11 may undergo large variations. When the flexible atraumatic tip 9 touches the heart wall, the movement of the heart can cause bending of the housing, which could lead the housing to touch the rotor. Touching of housing and rotor during use could cause a significant increase of damage to blood cells and may also cause wear with particles from the housing and/or rotor getting into the blood stream. By using both a proximal bearing 13 and a distal bearing 14, as illustrated in FIGS. 4A and 4B, the position of the rotor 10 is more stable and the variation of the size of said gap is lower than with just one bearing. For a given housing 11, this may allow the rotor 10 diameter to be larger, which allows for a higher flow rate of the intravascular blood pump 1 without the housing touching the rotor.
[0093] At its distal end, the rotor 10 comprises a recess 17. The static support member 18 fixed relative to the distal end of the housing 11 protrudes with its pin 19 into the recess 17. The bottom 19 of the recess 17 in FIG. 4A is formed as a step and defines a stop inside the rotor 10 against which the pin 19 of the static support member 18 can rest. In FIG. 4A, the fluid line 15 penetrates the bottom of the recess 17 to allow purge fluid to exit the distal bearing 14 between the pin 19 and the recess 17.
[0094] The embodiment of the intravascular blood pump 1 in FIG. 4B is similar to the embodiment in FIG. 4A. Importantly, however, the distal bearing in FIG. 4B is not purged and is designed to operate in blood instead. Thus, the drive shaft 12 does not need to be hollow. Accordingly, there is no fluid line 15 in FIG. 4B. The bottom of the recess 17 does not contain an opening for purge fluid to flow through the bearing gap between the pin 19 and the recess 17. In such an embodiment, less purge fluid may be required. If the proximal bearing is not purged, the intravascular blood pump may require no purge fluid at all.
[0095] FIG. 4C shows a similar embodiment to FIGS. 4A and 4B. Here, the pin 19 is particularly long and extends proximally through the rotor shaft and into the drive shaft 12. In the embodiment of FIG. 4C, the proximal end of the pin 19 is located inside the part of the drive shaft 12, which is located inside the proximal bearing 13.
[0096] In alternative embodiments, the proximal end of the pin 19 may be located, e.g., proximally of the proximal bearing 13 or between rotor 10 and proximal bearing 13. By having the pin 19 extend into the proximal bearing 13, a greater stiffness of the intravascular blood pump 1 may be achieved. Furthermore, the pin 19 shown in FIG. 4C may help to reduce vibrations of the intravascular blood pump 1 during its operation and may decrease undesired bending.
[0097] The proximal bearing 13 in FIG. 4C is located inside the housing 11, distally of the proximal bearing's 13 location in FIGS. 4A and 4B. The distance between the proximal bearing 13 and the rotor 10 is particularly small in the embodiment shown, e.g., smaller than the outer diameter of the proximal bearing 13. The short distance may further increase the stiffness of the intravascular blood pump 1.
[0098] The pin 19 in FIG. 4C is combined with a hollow drive shaft 12 such that, in some embodiments, purge fluid may flow through the drive shaft 12 and past the pin 19 to exit at the distal end of the rotor 10. Alternatively, no purge fluid may be used in some embodiments. In this case, the long pin 19 of FIG. 4C may be combined with a drive shaft that is only hollow along some part of its length.
[0099] FIG. 5 shows the pump section 4 according to a second embodiment again with a compressible housing 11 and a rotor 10 driven by a hollow drive shaft 12, which is rotatably supported in a proximal bearing 13 arranged proximally of the rotor 10 at the distal end of the catheter 5. In this embodiment, the pin 19 of the static support member 18 forming part of the distal bearing 14 has a pointed end. If the dimensions of the housing 11 and the pin 19 are such that the pin 19 leaves the rotor 10 when the housing 11 is compressed, the pointed end of the pin 19 facilitates reintroduction of the pin 19 into the opening at the distal end of the rotor 10 when the housing 11 is expanded again. Preferably, the pin 19 is sufficiently long for the pin 19 to remain inside the rotor 10 when the housing 11 is in the compressed state. This may avoid the circumstance, in which the pin 19 fails to re-enter the rotor 10 when the housing 11 is being expanded. In some cases, it is not necessary for proper function that a required bearing gap is present over the full length of the pin 19. Rather, it is sufficient for the bearing gap between the outside of the pin 19 and its opposite bearing surface to be between 1 μm and 10 μm, more preferably between 2 μm and 8 μm wide in at least one location.
[0100] In this embodiment, rather than providing a bottom or a step in the opening at the distal end of the rotor 10, the static support member 18 may be provided with a shoulder against which the rotor 10 abuts in an expanded state of the housing 11, thereby limiting further expansion of the housing 11, if desired. In some embodiments, the distal bearing 14 may exclusively be a radial bearing.
[0101] Again, a purge fluid may be supplied through the fluid line 15 of the drive shaft 12 towards a distal bearing 14, pass by the pin 19, which forms a distal radial bearing for the rotor 10, and leave the rotor 10 at its distal end. This prevents blood from entering the rotor 10, reduces friction and cools the distal bearing 14. Alternatively, the distal bearing 14 may not be purged.
[0102] Accordingly, there may not be a fluid line 15.
[0103] Furthermore, in the embodiment shown in FIG. 5, the pin 19 is sitting inside the central duct 15 of the rotor 10 when the housing 11 is expanded. In this case, for example, the drive shaft 12 may terminate at the distal end surface of the rotor 10. Alternatively, the distal end of the drive shaft 12 may be located inside the rotor 10, e.g., at the level of the bottom of the recess as seen in the embodiment of FIG. 4 so as to form the stop for the pin 19.
[0104] FIGS. 6A, 6B, 6C and 6D show a third embodiment of the pump section 4 with the compressible housing 11 and the static support member 18, which is attached to the housing 11. The rotor 10 comprises a nose 21 at its distal end. In FIGS. 6A, 6B and 6C, the fluid line 15 inside the distal end of the drive shaft 12 leads to an opening in the nose 21 through which purge fluid may enter the bearing gap of the distal bearing 14 between the nose 21 and a corresponding recess 22 at the proximal end of the static support member 18. In FIG. 6D, however, the distal bearing 14 is unpurged. Thus, the embodiment in FIG. 6D does not possess a fluid line 15 and an opening in the nose 21. The unpurged distal bearing 14 may reduce the amount of purge fluid needed to operate the intravascular blood pump 1. In combination with an unpurged proximal bearing 13, the intravascular blood pump 1 may need no purge fluid at all.
[0105] When the housing 11 is compressed, the nose 21 dislodges from the recess 22 and thus the intravascular blood pump 1 becomes more flexible. When the housing 11 is expanded at the target site, the nose 21 automatically moves into the recess 22, wherein the conical or spherical or otherwise converging shape of the nose 21 helps to guide the nose 21 into the recess 22 and centers the rotor 10 with respect to the static support member 18. FIG. 6B shows an enlarged section of the distal bearing 14 with the nose 21 at the rotor 10 and the corresponding recess 22. A vertical dashed and dotted line in FIG. 6B shows the cross-sectional plane of FIG. 6C. The cross-section exhibited in FIG. 6c displays the distal bearing 14 in concentric circles. From periphery to center, the concentric circles show the recess 22, the distal bearing gap between recess 22 and nose 21, the nose 21 and the opening of the fluid line 15 into the distal bearing gap.
[0106] FIG. 7 shows schematically the intravascular blood pump 1 with its catheter 5 and its pump section 4. In this embodiment, the intravascular blood pump 1 comprises a proximal bearing 13 inside the distal end of the catheter 5. Inside the proximal bearing 13, an inner bearing sleeve 24 is glued onto the drive shaft 12 to provide a smooth bearing surface. To fit the bearing sleeve 24, the drive shaft 12 had some of its outer windings removed to reduce its diameter. Purge fluid may now flow through the catheter 5 and exit the proximal bearing 13 through its bearing gap. Some of the purge fluid also flows through the drive shaft 12 into the rotor 10.
[0107] The sleeve 24 of the proximal bearing may have an inner diameter preferably ranging from 0.3 mm to 1.5 mm, more preferably from 0.5 mm to 1.2 mm and most preferably from 0.7 mm to 0.9 mm.
[0108] The outer diameter of the bearing sleeve 24 of the proximal bearing is preferably between 0.5 mm and 2 mm, more preferably between 0.8 mm and 1.8 mm and most preferably between 0.9 mm and 1.2 mm. The bearing gap of the proximal bearing is preferably between 1 μm and 10 μm, more preferably between 2 μm and 8 μm.
[0109] From the drive shaft 12 inside the rotor, the purge fluid flows through the fluid line 15 into the recess 17 of the rotor 10. Arranged inside the recess 17 is the sleeve of the distal bearing 25 of the rotor 10. The inner surface of the sleeve of the distal bearing 25 and the outer surface of the pin 19 form the bearing surfaces of the distal bearing 14. The purge fluid leaves the rotor 10 via the bearing gap between the sleeve of the distal bearing 25 and the pin 19.
[0110] The sleeve of the distal bearing 25 has an inner diameter of preferably between 0.3 mm and 1.5 mm, more preferably between 0.5 mm and 1.2 mm and most preferably between 0.7 mm and 0.9 mm. The outer diameter of the sleeve of the distal bearing 25 is preferably between 0.5 mm and 1.7 mm, more preferably between 0.7 mm and 1.4 mm and most preferably between 0.9 mm and 1.1 mm. The bearing gap between the pin 19 and the sleeve of the distal bearing 25 is preferably between 1 μm and 10 μm, more preferably between 2 μm and 8 μm.
[0111] FIG. 8A shows schematically the purge fluid path inside the intravascular blood pump. Inside the housing of the motor 8, the purge fluid is supplied into the catheter 5 and into the drive shaft 12. Herein, the proximal bearing 13 is drawn schematically, its constituent parts, in particular the outer bearing ring 32 and the bearing sleeve 30, are not shown. At the proximal bearing 13, purge fluid leaves the catheter 5 through the bearing gap to reduce friction and cool the proximal bearing 13. A portion of the purge fluid does not leave the catheter 5 through the bearing gap but flows through the drive shaft 12 into the rotor 10. In some embodiments, the drive shaft 12 may comprise a cover such that the purge fluid may flow from the catheter 5 to the rotor 10 without leaking from the drive shaft 12 between the distal end of the catheter 5 and the proximal end of the rotor 10. Inside the rotor 10, the purge fluid continues to flow through the fluid line 15 and then into the recess 17 at the distal end of the rotor 10. In alternative embodiments, the drive shaft 12 may continue up to or into the recess 17 such that the purge fluid flows into the recess 17 directly from the drive shaft 12. From there, the purge fluid flows through the bearing gap of the distal bearing 14 between the pin 19 and the adjacent surface of the rotor 10.
[0112] FIG. 8B shows an embodiment of the blood pump similar to FIG. 8A. In FIG. 8B, the proximal bearing 13 is closer to the rotor 10 than in FIG. 8A and is separated from the rotor 10 by only a small gap. Through said gap, purge fluid may escape as shown by arrows.
[0113] FIG. 9A shows an example of the drive shaft 12 comprising one outer layer 28 and one inner layer 29. In this embodiment, the outer layer 28 and the inner layer 29 consist of helically wound wires, wherein the helix of the inner layer 29 is right-handed and the helix of the outer layer 28 is left-handed. As shown in FIG. 9A, a piece of the outer layer 28 is removed from the inner layer 29 and is shown separately. Removal of the piece of the outer layer 28 may be carried out by pulling the outer layer 28 while turning it slightly. A bearing sleeve 30 may be pushed onto the exposed inner layer 29 until it abuts the outer layer 28, and the piece of outer layer 28 may then be mounted back onto the inner layer 29 adjacent the bearing sleeve 30.
[0114] FIG. 9B shows the flexible bearing shaft 12 with the outer layer 28 and the inner layer 29, wherein the outer layer 28 is absent at a central location and the bearing sleeve 30 is situated on the inner layer 29 at the said central location. Furthermore, to both sides of the bearing sleeve 30 and overlapping therewith are two protective rings 31 which are slipped over the ends of the outer layers 28 facing the bearing sleeve 30. A shorter part of the protective rings 31 overlaps the bearing sleeve 30 while a larger part covers the outer layer 28. This way, the risk of breakage of the drive shaft due to a change of stiffness at the transition between the small and large shaft diameters is reduced.
[0115] During assembly, the outer layer 28 may be cut and removed from one end of the drive shaft 12. At this point, the drive shaft 12 resembles the representation in FIG. 9A. Thereafter, a first protective ring 31 is placed over the end of the remaining outer layer 28. The bearing sleeve 30 is then placed on top of the inner layer 29, where the outer layer 28 is removed, and overlaps with the protective ring 31. The outer bearing ring 32 is placed on top of the bearing sleeve 30. Then, the previously removed outer layer 28 is again mounted on top of the inner layer 29 with a second protective ring 31 overlapping the end of the outer layer 28 and the bearing sleeve 30. The bearing sleeve 30 and the protective rings 31 may be affixed to the drive shaft 12 using a low-viscosity adhesive. After the adhesive has set, the bearing sleeve 30 may be tested for tightness, i.e., it may be tested whether a purge fluid can pass through the bearing sleeve 30.
[0116] The bearing sleeve 30 is rotatably supported in the outer bearing ring 32 which, in turn, is fixed in the catheter or in a proximal end of the housing in which the rotor is housed. The bearing sleeve 30 and the outer bearing ring 32 form a radial bearing while the protective rings 31 form an axial stop and in some embodiments also an axial bearing with the outer bearing ring 32. The bearing sleeve 30 together with the protection rings 31 may be built from a single piece of material. As mentioned, the bearing sleeve 30 and the protective rings 31 are fixedly connected to the drive shaft 12, preferably glued. Glue is also used to fill the windings of inner layer 29 and outer layer 28 to prevent purge fluid from leaking through the drive shaft 12.
[0117] In this example, an internal diameter of the bearing sleeve 30 is approximately the same as an outer diameter of the inner layer 29. An outer diameter of the bearing sleeve 30 is approximately the same as an outer diameter of the outer layer 28.
[0118] FIG. 10A shows a hydraulically divided bearing sleeve 30 which contains a wall between two blind holes. The inner layer 29 is axially disconnected. Each of the blind holes of the bearing sleeve 30 receives a respective axial end of the axially disconnected inner layer 29. The bearing sleeve 30 does not let any purge fluid pass in an axial direction. Due to this, the inner layer 29 does not need to be filled with glue to prevent any flow of purge fluid through the inner layer 29. Glue may still be used to attach the inner layer 29 to the bearing sleeve 30, but alternative attachment techniques, such as soldering, crimping and welding, are also possible. The outer bearing ring 32 sits on the bearing sleeve 30 and is prevented from being pushed off of the bearing sleeve 31 by the two protective rings 31. Again, the bearing sleeve 30 together with one of the protective rings 31 may be built from a single piece of material.
[0119] FIG. 10B shows another embodiment with the outer bearing ring 32 forming a radial bearing with the bearing sleeve 30. Furthermore, a proximal protective ring 31a and a distal protective ring 31b are fixed axially relative to the bearing sleeve 30 in the manner as described before. If the drive shaft 12 moves distally (to the left in FIG. 10B), the proximal protective ring 31a will abut against the proximal surface of the outer bearing ring 32 and any further distal movement is prevented. If the drive shaft 12 moves in a proximal direction, the proximal protective ring 31a will abut against a distal surface of the restriction member 33, stopping any further movement in a proximal direction. If a maximal distance a.sub.max between the proximal surface of the distal protective ring 31b and the distal surface of the outer bearing ring 32 is greater than the maximal distance c.sub.max between a distal surface of the restriction member 33 and a proximal surface of the proximal protective ring 31a, then the distal protective ring 31b will never touch the outer bearing ring 32. This condition is equivalent to the inequation a>b+c, wherein b+c is constant.
[0120] If the rotor 10 is mounted on the distal protective bearing 31b as shown in FIG. 11A, then the distances a, b and c chosen according to the above inequation will prevent the rotor from touching the outer bearing ring 32. Similarly, and as shown in FIG. 11B, if the rotor 10 is mounted on a distal extension of the bearing sleeve 30, the above condition will prevent the rotor 10 on the bearing sleeve 30 from touching the outer bearing ring 32. A touching of the rotor 10 and the outer bearing ring 32 might otherwise cause damage to the rotor 10 or to the proximal bearing 13.
[0121] FIG. 12A shows the intravascular blood pump 1 with the housing 11 and the rotor 10 mounted on the drive shaft 12. The proximal bearing 13 comprises the bearing sleeve 30 rotatably supported in the outer bearing ring 32. The drive shaft 12 is glued into bearing sleeve 30. The drive shaft 12 surrounds a reinforcement element 35 implemented as a coaxial rod for stabilizing the distal end of the drive shaft. The rod extends from proximally of the proximal bearing 13 to the distal end of the rotor 10. Alternatively, the drive shaft 12 may be hollow to permit purge fluid to reach the distal bearing. The restriction member 33 is located proximally of the bearing sleeve 30 and prevents the bearing sleeve 30 from dislodging from the outer bearing ring 32. Both the restriction member 33 and the outer bearing ring 32 are press-fitted and/or glued into the distal end of the housing 11. In addition, the restriction member 33 is press-fitted and/or glued into the catheter 5. Thereby, the restriction member 33 connects the housing 11 and the catheter 5. The radial through-holes 34 in the housing 11 serve to introduce glue to fixedly connect the restriction member 33 and the outer bearing ring 32 to the housing 11. The glue may distribute circumferentially along grooves 36 provided in both the restriction member 33 and the outer bearing ring 32. Furthermore, the radial through-holes 34 may be used for position control of the outer bearing ring 32 and the restriction member 33. Both connections are glued in order to keep the connections tight and to prevent leakage of purge fluid.
[0122] As can be seen from FIG. 12A, the bearing sleeve 30 comprises a proximal portion 30a located proximally of the outer bearing ring 32 and a distal portion 30 b extending from the proximal portion 30a distally into the outer bearing 32. The proximal portion 30a forms an axial bearing with a proximal surface of the outer bearing 32, whereas the distal portion 30 b forms a radial bearing with the outer bearing ring 32. The axial bearing and the radial bearing together constitute the proximal bearing 13.
[0123] Purge fluid being pressed through the proximal bearing 13 from proximally to distally would first pass the proximal portion 30a of the bearing sleeve 30 along a radial outer surface thereof, then flow radially inwards through the bearing gap between the distal surface of the proximal portion 30a and the proximal surface of the outer bearing ring 32, and finally flow further in a distal direction through the bearing gap formed radially between the distal portion 30 b of the bearing sleeve 30 and the radial inner surface of the outer bearing ring 32. The bearing gaps can be designed with little tolerances so that the purge fluid flows through the bearing gaps in a closely controllable manner by applying a suitable pressure on the purge fluid from proximally. A radial notch or radial notches (not shown) may be provided in the proximal surface of the static outer bearing ring 32 to guarantee that purge fluid can flow to the radial bearing gap between the outer bearing ring 32 and the distal portion 30 b of the hearing sleeve 30 when, during operation, the rotor 10 pulls the bearing sleeve 32 in a distal direction.
[0124] FIG. 12B shows an alternative embodiment to the embodiment of FIG. 12A. Here, the drive shaft 12 has a section of reduced diameter, and the distal portion 30 b of the bearing sleeve 30 is arranged at the section of reduced diameter. This way, although not specifically shown in FIG. 12B, the outer diameter of the outer bearing ring 32 can be reduced accordingly, so that, in turn, the outer diameter of the catheter 5 can likewise be reduced. This way, a more flexible and better maneuverable catheter may be achieved.
[0125] The structure of the bearing sleeve 30 as shown in FIG. 12B is comparable to the bearing structures as described above in relation to FIGS. 13 to 15. More specifically, the proximal portion 30a of the bearing sleeve 30 corresponds to the proximal protective ring 31a (see FIG. 10B). Accordingly, the distal bearing ring 31b overlapping both the drive shaft 12 and the distal end of the distal portion 30 b of the bearing sleeve 30 is also provided in the embodiment shown in FIG. 12B. It limits the axial movement of the shaft 12 within the outer bearing ring 32 in the same manner as described in relation to FIGS. 13 to 15.
[0126] FIG. 13A shows a graphical representation of a stationary surface of a hydrodynamic axial bearing. Specifically. FIG. 13A shows the proximal surface of the outer bearing ring 32 with a centrally located drive shaft 12. The curved radial lines in FIG. 13A represent raised portions of the bearing surface, which is shown in more detail in FIG. 13B. The arrows in FIG. 13A and FIG. 13B illustrate the direction of movement of the opposing surface. This then corresponds to the movement direction of the lubricating film within the axial bearing gap. The surface has ramps which form converging gaps together with the opposing stationary surface, which is even. This causes a hydrodynamic pressure to build up in the lubricating film. Thereby, the surfaces forming the axial bearing gap remain at a distance.
[0127] FIG. 13C shows the bearing sleeve 30 and the outer bearing ring 32 inside the housing 11. The bearing sleeve 30 has an even distal surface. Here, the opposing proximal surface of the outer bearing ring 32 is slanted to form a convergent gap. During use, this creates the lubricating film required for a hydrodynamic bearing.
[0128] FIG. 13D shows spiral grooves in another embodiment of the proximal bearing surface of the outer bearing ring 32. The spiral grooves are preferably configured in the moving surface of the proximal bearing 13, i.e., in the proximal portion 30a of the bearing sleeve 30. In this case, several grooves are positioned in the shape of a spiral in the distal surface of the proximal portion 30a of the bearing sleeve 30. When the bearing sleeve 30 rotates in the direction pointed to by the arrow in FIG. 13D, the lubricating film is transported radially inward along the grooves and forms a pressure between the bearing surfaces, keeping them apart.
