Patent Description:
Blood pumps of different types are known such, as axial blood pumps, centrifugal blood pumps and mixed-type or diagonal blood pumps, where the blood flow is caused by both axial and radial forces. Intravascular blood pumps are usually inserted percutaneously, such as through the femoral artery into the left ventricle so as to bridge the aortic valve or through the femoral vein into the right ventricle.

A rotary blood pump has an axis of rotation. In this patent application, the terms "radial" and "axial" refer to the axis of rotation and mean "in radial direction in relation to the axis of rotation" and "along the axis of rotation", respectively. The term "inner" means radially toward the axis of rotation, and the term "outer" means radially away from the axis of rotation.

An intravascular blood pump typically comprises a pumping device as a main component. The pumping device has a pump section including a primary impeller for pumping the blood from a blood flow inlet to a blood flow outlet and a drive section including a motor for driving the primary impeller. The pump section may include a flexibly bendable cannula between the blood flow inlet and outlet.

The pumping device comprises a pump section end which is arranged at a pump side of the pumping device. The pumping device further comprises a drive section end which is arranged at a drive side of the pumping device. The blood pump may further comprise a catheter connected to the pumping device in order to supply the pumping device e.g. with energy, and/or a purge fluid. The catheter may be connected to the pump section end but is mostly connected to the drive section end of the pumping device. It is also conceivable to rotate the impeller in a forward and in a reverse direction. Then, the blood flow inlet and the blood flow outlet of the pump section may interchange.

Usually, the impeller is supported within the pumping device by means of at least one impeller bearing. <CIT> discloses a pumping device with an impeller bearing supporting an upstream end of the impeller. Different rotor bearing types are known, such as sliding bearings, in particular hydrodynamic sliding bearings, pivot bearings, hydrostatic bearings, ball bearings etc., and combinations thereof. In particular, contact-type bearings may be realized as "blood-immersed bearings", where the bearing surfaces have blood contact. Problems during operation may be friction and heat. In case of a blood-immersed bearing, a further problem may be blood clotting due to heat or not enough rinse.

An example for blood-purged radial sliding rotor bearings is disclosed in <CIT> which describes an intravascular blood pump comprising a generally cylindrical primary impeller and a generally cylindrical secondary impeller which rotate together. The secondary impeller is arranged at the radial center of the primary impeller. Vanes of the secondary impeller extend toward an axis of rotation of both impellers. The tips of the vanes of the secondary impeller form an outer bearing surface of a sliding bearing. A cylindrical outer surface of a pin which is arranged at the center of the secondary impeller forms the inner bearing surface of the sliding bearing. In another embodiment, blood from the center of an arriving blood stream can enter the blood pump through a central axial passage in the impeller. In all embodiments the primary and the secondary impeller are mounted on a non-rotating central pin. This increases the hydraulic resistance of the secondary blood flow.

It is an object of the present invention to provide a blood pump with reduced hydraulic resistance for the pumped blood.

This is achieved according to the present invention by a blood pump having the features of independent claim <NUM>. Preferred embodiments and further developments of the invention are specified in the claims dependent thereon.

According to a first aspect of the invention, an intravascular blood pump comprises a pumping device with a pump casing having a primary blood flow inlet and a primary blood flow outlet which are hydraulically connected by a primary blood flow passage, wherein a primary impeller has an upstream end and a downstream end and is configured to convey a primary blood flow from the primary blood flow inlet to the primary blood flow outlet along the primary blood flow passage. The pumping device further comprises a drive unit configured to rotate the primary impeller about an axis of rotation. An impeller bearing supports the upstream end of the primary impeller, wherein a central opening axially extends through the impeller bearing. The pumping device further comprises at least one secondary blood flow passage in the primary impeller, the at least one secondary blood flow passage having a secondary blood flow inlet in axial alignment with the central opening of the impeller bearing. Each secondary blood flow passage has a secondary blood flow outlet and is configured to convey a secondary blood flow from the secondary blood flow inlet to the secondary blood flow outlet. The secondary blood flow outlet connects the at least one secondary blood flow passage to the primary blood flow passage at a location axially between the upstream and downstream ends of the primary impeller.

In other words, the secondary blood flow passage or passages extend diagonally through the primary impeller, starting centrally at the distal tip of the impeller and terminating in a lateral surface of the impeller so that the secondary blood flow is taken from the center of the arriving blood stream, where the blood stream is fastest and has the most kinetic energy, and meets and supports the primary blood flow in the primary blood flow passage.

Due to their diagonal extension, the secondary blood flow passages also generate pressure in the secondary blood flow by centrifugal forces. Thus, blood can be pumped through the intravascular blood pump with greater ease.

Thus, the secondary blood flow outlet is not arranged at the downstream end of the primary impeller. In such a case, the secondary blood flow would mix with the primary blood flow downstream beyond the primary impeller. This would require a comparably long secondary blood flow passage with increased hydraulic resistance.

A further advantage of the construction is that no stationary parts are present along the secondary blood flow passage. This reduces the hydraulic resistance of the blood pump.

The velocity of the blood can be utilized as it is not decelerated by a stationary pin bearing as according to the state of the art.

The one or more secondary blood flow passages can be considered to constitute a secondary impeller within the primary impeller. The primary and secondary impeller rotate together. The secondary impeller may be realized completely or partly as an inlay part in the tip end of the primary impeller.

It is preferred that at least a part of the secondary impeller is arranged inside the central opening. Then, arriving blood can immediately be conveyed by the secondary impeller. The impeller bearing can be arranged at an outer circumference of the secondary impeller.

The central opening may define the outer impeller bearing surface of the impeller bearing. Inside the central opening, a part of the primary or the secondary impeller may be arranged and form a corresponding inner impeller bearing surface. Preferably, at least one secondary blood flow passage extends into the central opening. For example, the inner impeller bearing surface may be formed by the outer circumference of one or more secondary impeller vanes defined by the secondary blood flow passages.

It is, however, also possible that the inner impeller bearing surface is arranged at the outer circumference of a part of the primary impeller which is not the secondary impeller. This part can be arranged inside the central opening.

Preferably, the primary blood flow inlet is separated from the secondary blood flow inlet by an inflow separator. The inflow separator preferably has the form of a ring. Thus, blood that arrives at the blood pump is divided and flows into the primary or into the secondary blood flow inlet. Preferably, the inflow separator is stationary. Then, the inflow separator can form the outer impeller bearing surface of the impeller bearing. Alternatively, an outer surface of the inflow separator may form an inner impeller bearing surface of the impeller bearing. The impeller bearing radially supports the primary impeller. It is possible that the primary impeller is mounted on the impeller bearing by the secondary impeller or a part thereof.

The inflow separator may comprise an additional impeller bearing ring as a separate component. The impeller bearing ring may form the outer or inner impeller bearing surface of the impeller bearing, but it is preferably arranged on the inside of the inflow separator to form an inner impeller bearing surface. The impeller bearing ring may be made of a material that is different from the material of the inflow separator. Particularly, the impeller bearing ring may be made of a ceramic material, especially of silicon carbide.

The inflow separator may be supported by at least one strut that connects the inflow separator with the pump casing. Preferably, a minimum of three struts is provided. The struts may extend across the primary blood flow inlet. It is preferred that the struts are configured with a low hydraulic resistance.

The inflow separator preferably comprises at least one cut-out at a downstream end of the inflow separator. Preferably, the cut-out has a circumferential width that is comparable to a circumferential width of a secondary blood flow passage. This way, the rotational position of the primary impeller may be defined by at least one secondary blood flow passage extending into and matching the circumferential position of the cut-out. Then, blood clots that begin to build up on the inner (or outer) impeller bearing surface can be removed by an edge of the cut-out when the inner (or outer) impeller bearing surface rotates over it. In case that the corresponding outer (or inner) impeller bearing surface is discontinuous, such as the tip ends of the vanes defined by the second blood flow passages of the secondary impeller, the outer (or inner) impeller bearing surface at the inflow separator can be cleaned by an edge of such vanes in a similar way. A further advantage of the cut-outs is that the cleaning edges of the cut-outs can be flushed by blood flowing through the cut-outs such that blood clots or debris do not accumulate. An inner or outer impeller bearing surface formed by the primary or secondary impeller preferably overlaps the cut-outs axially such that the whole impeller bearing surface of the primary or secondary impeller will be cleaned. Preferably, the outer impeller bearing surface of the inflow separator preferably overlaps axially with the end surfaces of the vanes of the secondary impeller, which form the inner impeller bearing surface, such that the whole outer impeller bearing surface will be cleaned. It is preferred that the tips of the vanes of the secondary impeller have a greater axial length than the circumferential length of the cut-outs. Preferably, at least one cut-out extends between two struts.

The cut-out is preferably not only arranged in the inflow separator, but extends through the aforementioned impeller bearing ring which may be present optionally. Then, the cut-out is completely open on both sides such that the cut-out can be washed effectively.

The impeller bearing may be a sliding bearing. Preferably, the impeller bearing is a blood-purged sliding bearing. This has the advantages that the blood from the blood stream can be used to purge the bearing and, thereby, also cool the bearing.

Preferably, a center of area in a mathematical sense, meaning the middle of a certain region, of the primary blood flow inlet is arranged in the secondary blood flow inlet. The primary blood flow inlet is arranged around the secondary blood flow inlet such that the middle of a blood stream that arrives at the blood pump enters the blood pump through the secondary blood flow inlet. The middle of a laminar blood stream has the highest velocity and is, thus, supplied to the secondary blood flow.

After the blood has passed the primary and secondary blood flow inlet, it enters the primary impeller and secondary impeller, respectively, at respective primary and secondary channel intakes into the primary and secondary blood flow passages. Preferably, at least one secondary channel intake is arranged at a position of the axis of rotation. Usually, the tip end of an impeller does not have a rational velocity so that blood may clot by adhesion and accumulation may arise on a stationary solid tip end. However, with the proposed arrangement, the middle part of the bloodstream flows into the intakes of the secondary blood flow passages. Thus, blood clotting cannot occur.

The secondary channel intakes are preferably arranged upstream of the primary channel intakes. An end of the secondary impeller may then be arranged inside the impeller bearing.

The primary impeller comprises at least one blade having a primary pitch at the upstream end of the primary impeller and a secondary blood flow passage having a secondary pitch, the secondary pitch being approximately or exactly the same as the primary pitch. The pitches may deviate from each other as much as necessary to prevent undesirable flow conditions, such as turbulences.

Preferably, at least two of the at least one secondary blood flow passages are arranged asymmetrically in regard to the axis of rotation. This renders it possible to arrange a secondary channel intake at the axis of rotation.

Preferably, two secondary blood flow passages are arranged opposite to each other in regard to the axis of rotation. This enables a compact design of the secondary impeller.

Preferably, as already mentioned, a secondary blood flow passage defines an edge moving over the outer impeller bearing surface upon rotation of the secondary impeller so as to clean the outer impeller bearing surface. The edge acts as a wiper for the outer impeller bearing surface, and blood clots or debris can be removed in this way.

As also briefly mentioned above, the primary impeller may comprise an inlay in which the at least one secondary blood flow passage is formed. Then, the secondary impeller may be made of another material as the primary impeller. For example, the secondary impeller may be made of a ceramic material. This is advantageous for the inner impeller bearing surface. The primary impeller and the secondary impeller may alternatively form one integral piece.

The aforegoing summary as well as the following detailed description of preferred embodiments will be better understood when read in conjunction with the appendant drawings. The scope of the disclosure is not limited, however, to the specific embodiments disclosed in the drawings. In the drawings:.

In <FIG>, a cross sectional view of a first embodiment of an intravascular blood pump is illustrated. Rotating parts are not shown cut. The intravascular blood pump <NUM> comprises a pumping device <NUM> and a supply line in the form of a catheter <NUM> attached thereto.

The pumping device <NUM> comprises a pump casing <NUM> of substantially cylindrical form, at least in an intermediate section thereof. The pump casing <NUM> comprises a blood flow inlet <NUM> and a blood flow outlet <NUM>. In <FIG>, the pump casing <NUM> seems to comprise two separate sections, but these sections are either integral or connected to form a single piece.

As can be better seen in the enlarged representation of the pump section shown in <FIG>, together with the front perspective views depicted in <FIG> and <FIG>, the blood flow inlet <NUM> comprises a primary blood flow inlet <NUM> and a secondary blood flow inlet <NUM>. The primary blood flow inlet <NUM> surrounds the secondary blood flow inlet <NUM>. The primary blood flow inlet <NUM> and the secondary blood flow inlet <NUM> are separated by an inflow separator <NUM>. Inside the inflow separator <NUM>, the inflow separator <NUM> comprises an impeller bearing ring <NUM>, which is separately shown in <FIG>. Further, the pumping device <NUM> comprises a primary impeller <NUM> which has integrated therein a secondary impeller <NUM>. The primary and secondary impellers <NUM>, <NUM> are rotatable together about an axis of rotation <NUM>. The secondary impeller <NUM> may, as shown in <FIG>, have the form of an inlay and may be arranged inside a secondary impeller cavity <NUM> of the primary impeller <NUM>. The secondary impeller cavity <NUM> is open toward a pump section end PSE of the pumping device <NUM>. Alternatively, the primary and secondary impellers <NUM>, <NUM> are integrally formed.

A primary blood flow 1BF flows from the primary blood flow inlet <NUM> to the primary impeller <NUM> outside of the inflow separator <NUM> to be conveyed further by the primary impeller <NUM> through a primary blood flow passage <NUM> to the primary blood flow outlet <NUM>. A secondary blood flow 2BF flows from the secondary blood flow inlet <NUM> through the inflow separator <NUM> to the secondary impeller <NUM> to be conveyed further by the secondary impeller <NUM> through a plurality of secondary blood flow passages <NUM> to the primary blood flow passage <NUM>.

Thus, a blood stream arriving at the pumping device <NUM> at the pump section end, preferably about almost the whole cross section of the pumping device <NUM>, can flow into the primary and secondary blood flow inlets <NUM>, <NUM> without significant deflection. Because of the central position of the secondary blood flow inlet <NUM>, also blood from the middle of the blood stream can enter the pumping device <NUM> without deflection. This is advantageous because usually a blood stream is a laminar flow in which the flow velocity is greatest in the center.

The primary impeller <NUM> comprises primary impeller vanes <NUM> which extend into the primary blood flow passage <NUM> and between which primary impeller channels <NUM> are arranged. The primary impeller channels <NUM> have a primary pitch at a primary channel intake <NUM> at each end of the primary impeller channels <NUM> toward the pump section end PSE. The secondary impeller <NUM> comprises at least one and particularly exactly two secondary blood flow passages <NUM> in channel form, which are therefore referred to hereinafter also as secondary impeller channels <NUM> (see also <FIG>). The secondary impeller channels <NUM> have a secondary pitch at a secondary channel intake <NUM> which is arranged at an upstream end of the secondary impeller channel <NUM>. The secondary pitch is preferably the same as the primary pitch or may vary to a certain degree as long as undesirable flow conditions, such as turbulences, are prevented. At an end of the secondary impeller <NUM> toward a drive section end DSE, a connecting breakthrough <NUM> between the secondary impeller cavity <NUM> and one of the primary blood flow passages <NUM> is arranged. An end of this breakthrough <NUM> in the direction of the blood flow defines the secondary blood flow outlet <NUM>. The secondary blood flow outlet <NUM> is arranged further radially outward in regard to the axis of rotation <NUM>. Therefore, blood is forced outward in a radial direction by centrifugal forces caused by the rotation of the secondary impeller <NUM>. In this way, the secondary blood flow 2BF is conveyed through the secondary blood flow inlet <NUM> and further through the secondary impeller channel <NUM> of the secondary impeller <NUM> and unites with the primary blood flow 1BF flowing through the primary impeller channel <NUM> of the primary impeller <NUM>. In this way, a pumped blood flow PBF is formed. The pumped blood flow PBF leaves the pumping device <NUM> at the blood flow outlet <NUM>.

The primary and secondary impellers <NUM>, <NUM> are jointly mounted in an impeller bearing <NUM>. They are connected via the secondary impeller cavity <NUM> or integrally formed as one single piece. The inflow separator <NUM> comprises an impeller bearing ring <NUM> arranged inside the inflow separator <NUM>. An outer impeller bearing surface <NUM> of the impeller bearing <NUM> is arranged at the inside of the impeller bearing ring <NUM>. The impeller bearing <NUM> further comprises an inner impeller bearing surface <NUM> which is arranged at an outer circumference of the secondary impeller <NUM>.

The primary impeller <NUM> is fixedly connected to a tapered section <NUM> leading to the blood flow outlet <NUM>. The tapered section <NUM> directs the pumped blood flow PBF in a direction radially outward in regard to the axis of rotation <NUM>. The blood then reaches the blood flow outlet <NUM>.

From the tapered section <NUM> in a direction toward the pump section end PSE, a drive section <NUM> is arranged inside the pump casing <NUM> of the pumping device <NUM>, which comprises a stator <NUM> and a rotor <NUM>. Between the stator <NUM> and the rotor <NUM>, an axial gap <NUM> is arranged. In order to cool the stator <NUM> and the rotor <NUM>, the axial gap <NUM> is blood-purged. For this, an ancillary blood flow ABF enters the drive section <NUM> through an ancillary blood flow inlet <NUM> arranged at the drive section end DSE. The blood is then conveyed by an ancillary impeller <NUM> through an ancillary pump gap <NUM> which is arranged between the ancillary impeller <NUM> and an inner wall of the pump casing <NUM>. From there, the blood continues to flow into the axial gap <NUM>. From the axial gap <NUM>, the ancillary blood flow ABF enters a radial gap <NUM>. At the radial outer end of the radial gap <NUM>, an ancillary blood flow outlet <NUM> is arranged. The ancillary blood flow ABF flows in the axially gap <NUM> in a direction opposite to the pumping direction of the primary and secondary impellers <NUM>, <NUM>. The ancillary blood flow ABF inside the drive section <NUM> also flows substantially in an opposite direction to a general blood flow GBF flowing around the blood pump <NUM>.

As can be better seen in reference to the enlarged representation shown in <FIG>, a rotor bearing ring <NUM> surrounds the ancillary impeller <NUM>. The ancillary impeller <NUM> comprises ancillary impeller vanes <NUM>. The ancillary impeller vanes <NUM> protrude in a direction of the axis of rotation <NUM> toward the drive section end DSE of the pumping device <NUM>. A radial rotor bearing <NUM> is arranged at the drive section end DSE and comprises an outer rotor bearing surface <NUM> and an inner rotor bearing surface <NUM>, between which an axially extending bearing gap is arranged. The outer rotor bearing surface <NUM> is arranged on the rotor bearing ring <NUM>. Blood conveyed by the ancillary impeller <NUM> flows through the bearing gap and further to the axial gap <NUM> between the rotor <NUM> and the stator <NUM>. From the axial gap <NUM>, the blood flows to a radial gap <NUM>. The radial gap <NUM> extends between the tapered section <NUM> of the primary impeller <NUM> and the stator <NUM>. An ancillary blood flow outlet <NUM> is arranged at the transition between the radial gap <NUM> and the surrounding of the pumping device <NUM>. The ancillary blood flow outlet <NUM> is arranged perpendicularly to the axis of rotation <NUM>. Here, the blood from the ancillary blood flow ABF unites with the pumped blood flow PBF from the pump section <NUM> and the surrounding general blood flow GBF. When the ancillary blood flow outlet <NUM> is, as shown, arranged close to the outer diameter of the pump casing <NUM> and close to the primary blood flow outlet <NUM>, the pumped blood flow PBF and the general blood flow GBF support the drawing of blood out of the radial gap <NUM> because of their flow velocity. This enhances the ancillary blood flow ABF through the axial gap <NUM>.

At a center of the ancillary impeller <NUM>, through which the axis of rotation <NUM> extends, and at a side of the ancillary impeller <NUM> opposite to the rotor <NUM>, a hump <NUM> is arranged. In a direction of the axis of rotation <NUM> toward the drive section end DSE and adjacent to the hump <NUM>, a bearing pin <NUM> is arranged. The bearing pin <NUM> is connected to the pump casing <NUM>. An axial bearing surface of the bearing pin <NUM> toward the ancillary impeller <NUM> has a convex shape. The axis of rotation <NUM> runs through an apex of the axial bearing surface of the bearing pin <NUM> and through an apex of the axial bearing surface of the hump <NUM>. In this way, the bearing pin <NUM> interacts with the hump <NUM> and forms a thrust bearing in order to transmit axial forces in regard to the axis of rotation between the hump <NUM> and the bearing pin <NUM>, wherein the aforementioned parts are rotatable relative to each other. Obviously, the contact surface is small, such that rotational friction is low.

The drive section end of the blood pump <NUM> comprises one or more, preferably three, ancillary inlet through-holes <NUM>. The ancillary inlet through-holes <NUM> extend from the ancillary blood flow inlet <NUM> to an ancillary impeller cavity <NUM> in which the ancillary impeller <NUM> is arranged. Thus, the blood flows from the ancillary blood flow inlet <NUM> to the ancillary impeller <NUM> via the ancillary inlet through-hole <NUM>.

At least one wire through-hole <NUM> is arranged at the drive section end DSE of the pumping device <NUM>. The wire through-holes <NUM> may extend from the catheter <NUM> to the stator <NUM>. Preferably, three wire through-holes <NUM> are arranged about the axis of rotation <NUM>. Between two ancillary inlet through-holes <NUM>, one wire through-hole <NUM> may be arranged. In a wire through-hole <NUM>, at least one supply line <NUM>, <NUM> and/or <NUM> may extend to be connected to the stator <NUM>. Preferably, as shown, the supply wires <NUM>, <NUM> and/or <NUM> extend through the inside of the catheter <NUM> to the outside of the patient's body. The supply wires <NUM>, <NUM> and/or <NUM> run from the catheter <NUM> to the stator <NUM> without contact to blood.

<FIG> shows a perspective front view on the pump section end PSE of the pump section <NUM>. As is shown, the secondary impeller <NUM> is arranged inside the impeller bearing ring <NUM>. The impeller bearing ring <NUM> is arranged inside the inflow separator <NUM>. Alternatively to this embodiment, the additional impeller bearing ring <NUM> can be omitted such that the outer impeller bearing surface <NUM> is formed by the inflow separator <NUM>. Here, the inflow separator <NUM> is mounted between the primary blood flow 1BF and the secondary blood flow 2BF by three struts <NUM>. It is shown that the secondary blood flow 2BF flows into the secondary impeller <NUM> through the secondary blood flow inlet <NUM> which is arranged at an inflow into the impeller bearing ring <NUM>. In the secondary impeller <NUM>, the blood flows along the secondary impeller channel <NUM> and through the through-opening <NUM> to the secondary blood flow outlet <NUM>. Here, the secondary blood flow 2BF unites with the primary blood flow 1BF to form the pumped blood flow PBF.

<FIG> shows the pump section end PSE of the pump section <NUM> in a perspective view, wherein the pump casing <NUM> is shown in transparency. It is visible that through-opening <NUM> and the secondary blood flow outlet <NUM> are arranged between two primary impeller vanes <NUM>. As shown, the struts <NUM> are connected by an outer strut connection ring <NUM>. The strut connection ring <NUM> is arranged inside an inner circumferential surface of the pump casing <NUM> at the pump section end PSE. The impeller bearing ring <NUM> is supported by the struts <NUM>. It is conceivable to manufacture the strut connection ring <NUM> and the struts <NUM> as one piece. Preferably, also the impeller bearing ring <NUM> is a part of this piece. Said piece may also be formed in one piece with the pump casing <NUM>.

<FIG> shows a perspective view of the pump section end PSE of the pump section <NUM> in which the pump casing <NUM> is shown in transparency. Different from the embodiment shown in <FIG>, the inflow separator <NUM> comprises at least one, preferably three, cut-outs <NUM> at a downstream end of the inflow separator <NUM>. The cut-out <NUM> is arranged between two struts <NUM>. The impeller bearing ring <NUM> is part of and fixedly connected to the inflow separator <NUM>, and the cut-out <NUM> also extends through the impeller bearing ring <NUM>. Due to the cut-out <NUM>, the secondary impeller channel <NUM> has an increased cross section when it aligns with the cut-out <NUM> during rotation of the secondary impeller. The secondary impeller <NUM> extends inside the impeller bearing ring <NUM> in a direction toward the pump section end PSE maximally up to an end of the cut-out <NUM>. This has the effect that, in operation, an edge of the cut-out <NUM> runs over the inner impeller bearing surface <NUM> and removes blood clots at the beginning of their formation or preferably prevents their formation, since the mating part of the rotating axial thrust bearing surface <NUM> is in direct blood contact at the cut-out <NUM>. This helps to avoid stagnant blood within the axial thrust bearing. Also the inner impeller bearing surface <NUM> has edges <NUM>, as can be seen in <FIG>, which have the effect to remove blood clots from the outer impeller bearing surface <NUM> (<FIG>).

<FIG> shows the secondary impeller <NUM> in detail in a perspective view. There, the secondary impeller <NUM> is configured as an inlay and has roughly the form of a cylinder. It may be made of different material as the primary impeller <NUM>, for instance of a ceramic material. The inlay comprises a cylindrical section <NUM> which is arranged inside the secondary impeller cavity <NUM> of the primary impeller <NUM>. A circumferential protrusion <NUM> forms an axial stop for the secondary impeller <NUM> in the secondary impeller cavity <NUM>. The inner impeller bearing surface <NUM> is arranged at an outer circumference of the secondary impeller <NUM>. Two secondary impeller channels <NUM> are arranged at the end of the secondary impeller <NUM> toward the pump section end PSE. The secondary impeller channels <NUM> have their largest cross section at the upstream end of the secondary impeller <NUM>. Thus, the channels <NUM> decrease in cross section away from the blood flow inlet <NUM>. In this way, blood is directed from a mainly axial direction to an axial-radial direction when it flows through the secondary impeller channel <NUM>.

The secondary impeller channels <NUM> are arranged asymmetrically in regard to the axis of rotation <NUM> of the secondary impeller <NUM>. At an end of the secondary impeller <NUM> directed toward the blood flow inlet <NUM>, the axis of rotation <NUM> extends through one of the secondary impeller channels <NUM>. In this way, the center of rotation, which is located at the axis of rotation <NUM>, does not coincide with a solid part of the secondary impeller <NUM>. This has the advantage that blood clotting at the center of rotation, where no differential velocity to neighboring blood flow is present, can be avoided.

At the transition between the secondary impeller channels <NUM> and the inner impeller bearing surface <NUM>, edges <NUM> are arranged. As mentioned above, such edges <NUM> serve to push away formations of blood clotting on the outer impeller bearing surface <NUM>. The inner impeller bearing surface <NUM> provides an inner surface of a radial bearing at the pump section end PSE. The secondary impeller <NUM> further comprises an axial impeller bearing surface <NUM>. It is arranged at the circumferential protrusion <NUM>. The axial impeller bearing surface <NUM> forms a part of the above-mentioned axial stop or axial thrust bearing. The axial stop may be configured as an axial bearing which is capable of transmitting forces from the secondary impeller <NUM> to the bearing ring <NUM> during rotation of the impeller. The axial bearing is necessary to counter the axial force which stems from the purging action of the impeller.

<FIG> shows an enlarged view of the impeller bearing ring <NUM>. The outer impeller bearing surface <NUM> is arranged at the inside of the impeller bearing ring <NUM>. The impeller bearing ring <NUM> comprises an axial bearing ring surface <NUM>. As shown, the axial bearing ring surface <NUM> may be arranged at an axial end of the impeller bearing ring <NUM>.

<FIG> shows a perspective view of an impeller bearing ring <NUM> according to a further embodiment which differs from the embodiment shown in <FIG> in that it comprises the cut-outs <NUM>, as previously mentioned, which are arranged at a downstream end of the impeller bearing ring <NUM>. The number of cut-outs <NUM> preferably matches the number of struts <NUM>.

<FIG> shows a perspective view of a cross section through the drive section end DSE of the drive section <NUM>. Rotating parts are not shown cut. As shown, the ancillary blood flow ABF enters the pump casing <NUM> at the ancillary blood flow inlet <NUM>. The ancillary impeller <NUM> accelerates the blood, which continues to flow into the axial gap <NUM>. As is shown by the arrow ABF inside the axial gap <NUM>, the blood does not flow directly in the direction of the axis of rotation <NUM>, but rather has a strong circumferential flow component so that it flows along the axial gap <NUM> along helices.

<FIG> shows a perspective view of an end of the rotor <NUM> at the drive section end DSE of the pumping device <NUM>. The ancillary vanes <NUM> of the ancillary impeller <NUM> are clearly recognizable, and they extend straight in a radial direction. The ancillary impeller vanes <NUM> provide, at their outer circumference, the inner rotor bearing surface <NUM> of the radial rotor bearing <NUM>. Further, the ancillary impeller vanes <NUM> each have a chamfer <NUM>. This chamfer <NUM> is advantageous in order to build a tapered drive section end DSE of the pumping device <NUM> as shown in <FIG>. Further, the ancillary impeller vanes <NUM> comprise radially extending end surfaces <NUM> at an axial end of the secondary impeller <NUM>. A hump <NUM> is formed at the center of the axial end of the secondary impeller <NUM>. The hump <NUM> interacts with the bearing pin <NUM>, as shown in <FIG>.

<FIG> further shows the rotor bearing ring <NUM> to be arranged around the inner rotor bearing surface <NUM> of the secondary impeller <NUM>. The outer rotor bearing surface <NUM> of the rotor bearing ring <NUM> forms the rotor bearing <NUM> together with the inner rotor bearing surface <NUM> of the ancillary impeller <NUM>. The ancillary impeller <NUM> has an axial Length L and a diameter D. Alternatively, as shown in <FIG>, the rotor bearing ring <NUM> may have cut-outs with a form, function and arrangement similar to the cut-outs <NUM> of above-described impeller bearing ring <NUM>.

Claim 1:
An intravascular blood pump, comprising a pumping device (<NUM>) with
- a pump casing (<NUM>) having a primary blood flow inlet (<NUM>) and a primary blood flow outlet (<NUM>) which are hydraulically connected by a primary blood flow passage (<NUM>),
- a primary impeller (<NUM>) having an upstream end and a downstream end and being configured to convey a primary blood flow (1BF) from the primary blood flow inlet (<NUM>) to the primary blood flow outlet (<NUM>) along the primary blood flow passage (<NUM>),
- a drive unit (<NUM>) configured to rotate the primary impeller (<NUM>) about an axis of rotation (<NUM>),
- an impeller bearing (<NUM>) supporting the upstream end of the primary impeller (<NUM>), and
- a central opening (<NUM>) axially extending through the impeller bearing (<NUM>), characterized in that the pumping device further comprises at least one secondary blood flow passage (<NUM>) in the primary impeller (<NUM>), the at least one secondary blood flow passage (<NUM>) having a secondary blood flow inlet (<NUM>) in axial alignment with the central opening (<NUM>) of the impeller bearing (<NUM>) and each of the at least one secondary blood flow passage (<NUM>) having a secondary blood flow outlet (<NUM>), wherein the at least one secondary blood flow passage (<NUM>) is configured to convey a secondary blood flow (2BF) from the secondary blood flow inlet (<NUM>) to the secondary blood flow outlet (<NUM>), and wherein the secondary blood flow outlet (<NUM>) connects the at least one secondary blood flow passage (<NUM>) to the primary blood flow passage (<NUM>) at a location axially between the upstream and downstream ends of the primary impeller (<NUM>).