Blood pump for supporting cardiac performance

Abstract

The invention relates to a blood pump for supporting cardiac performance, comprising a housing with a housing inlet (1) and a housing outlet (2), said housing forming a first pump housing (4) and a second pump housing (9), and comprising a rotor (14) which is mounted in the housing and can be rotated about an axis (3), wherein the rotor (14) comprises a first pump stage with a first impeller (5) arranged in the first pump housing (4) and a second pump stage with a second impeller (10) arranged in the second pump housing (9), the first and second stage are designed as respective radial or diagonal pumps, and blood to be pumped can flow through the pump stages one after the other from the housing inlet (1) to the housing outlet (2). The first pump housing (4) and the second pump housing (9) are connected via a channel (7) which runs radially outside of a housing central section (15) arranged between the first and second pump housing (4, 9).

Description

[0001] Blood pump to support cardiac performance

[0002] The invention relates to a blood pump for supporting cardiac output, comprising a housing with a housing inlet and a housing outlet, wherein the housing forms a first pump housing and a second pump housing, a rotor which is mounted in the housing and can be rotated about an axis, wherein the rotor comprises a first pump stage with a first impeller arranged in the first pump housing and a second pump stage with a second impeller arranged in the second pump housing, wherein the first and the second pump stage are each designed as a radial or diagonal pump and can be flowed through one after the other by the blood to be pumped from the housing inlet to the housing outlet.

[0003] Heart failure (HF) is the most common cause of death in Western countries. Modern mechanical circulatory support (MCS) devices promote survival and improve the quality of life of many HF patients. Rotodynamic blood pumps (RBPs) represent the vast majority of MCS devices implanted in the last decade, with a two-year survival rate exceeding 70%. Nevertheless, clinical outcomes remain limited by severe side effects, most of which are caused by suboptimal interactions between the pump system and blood. Only 20% of all RBP recipients remain free of life-threatening serious side effects, including bleeding or stroke, one year after implantation. Consequently, the quality of life of these patients remains severely limited, and the cost-effectiveness of this therapy has not yet been achieved.Modern implantable blood pumps are designed for adult patients suffering from HFrEF-type heart failure, i.e., heart failure with reduced left ventricular ejection fraction. Such patients require implantable blood pumps that provide a comparatively high mean flow (4-5 l / min). The use of such pumps in low-flow applications (1-2.5 l / min) carries the risk of increased blood trauma and a higher complication rate.

[0004] There is a need for a hemocompatible implantable blood pump suitable for patients in whom the pump is intended to provide a comparatively low blood flow. Such cases include:

[0005] (i) pediatric HF patients,

[0006] (ii) HFrEF patients with a less severe degree of heart failure, particularly NYHA stage 3-3b heart failure, to stop or reverse the progression of symptoms,

[0007] (iii) the large population of HF patients with preserved ejection fraction (HFpEF), a population for whom no other effective long-term treatment option is currently available.

[0008] The article by Thamsen et al.: "A two-stage rotary blood pump design with potentially lower blood trauma: a computational study" in Int J Artif Organs, 2016 Jun 15; 39(4): 178-83, describes a two-stage blood pump to reduce blood damage. The pressure build-up is divided between two pump stages through which blood can flow one after the other, which leads to a reduction in the circumferential speed of the impeller and thus reduced blood damage. Particularly with small flows and comparatively high pressure differences (low specific speed), a two-stage design can lead to more efficient and blood-sparing operation. However, the embodiment proposed in Thamsen et al. does not enable miniaturization to the extent required for implantation. Another concept for a two-stage blood pump is described in the document WO 2004 / 098677 A1.In applications where the first-stage outlet is connected in series with the second-stage inlet, the peripheral speeds can also be reduced. The concept is based on active control of the rotor position in the axial and / or radial directions using a "bearingless motor" and additional sensors for determining the rotor position. However, the integration of these sensors requires a larger installation space and thus leads to larger pump dimensions.

[0009] In summary, currently available blood pumps are either too large for implantation and / or have an increased risk of blood trauma and complication rates at lower blood flows when used to treat children or adults with less advanced heart disease. These observations can be explained by the fact that operating conditions with low pump flows at comparatively high pressures result in pump designs with low specific speeds – a key parameter indicating that these operating conditions are incompatible with high hydraulic efficiencies. Consequently, comparatively high power is required to generate pressure and flow. This reduced efficiency is reflected in increased peripheral speeds, which in turn can lead to increased blood damage.The present invention therefore aims to create a miniaturized implantable blood pump with the potential to mitigate hemocompatibility-related complications. In particular, the invention addresses the need for a low-flow blood pump for i) the pediatric population with heart failure and ii) adult patients with heart failure with either reduced (HFrEF) or preserved (HFpEF) ejection fraction.

[0010] To achieve this object, the invention essentially provides for a blood pump of the type mentioned at the outset in which the first pump housing and the second pump housing are connected via a channel which runs radially outside a central section of the housing arranged between the first and the second pump housing. Because the blood to be transported from the first pump stage to the second pump stage is not guided along the rotor, i.e. within the central section of the housing, but outside the central section, a short design of the blood pump in the axial direction is possible. In particular, the central section can be used as a rotor bearing due to the blood being guided via the external channel. In this regard, a preferred embodiment of the invention provides for the rotor to be rotatably mounted in the central section of the housing.Particularly preferably, the central section of the housing forms a hydrodynamic bearing with the rotor. The central section is designed with a preferably cylindrical inner surface which interacts with a cylindrical rotor surface to form the hydrodynamic bearing. The bearing gap is, for example, 50-200 μm. To ensure almost wear-free operation, the cylindrical surfaces can either be coated (Diamond Like Carbon, DLC) or made from suitable materials (polyetheretherketone (PEEK) or ceramics). To optimize the washout of the hydrodynamic bearing, structures (e.g. spiral grooves) can be formed on one of the two cylindrical surfaces.

[0011] Because the blood pump has two serially flow-through pump stages, the pressure build-up is distributed over the two stages and allows operation at up to 30% lower speeds compared to single-stage pumps.

[0012] In a fluidically favorable manner, the channel can be provided to surround the central section of the housing in a helical shape, with the direction of rotation of the helical shape being adapted to the direction of rotation of the rotor or impellers. The helical channel can extend along an angle of, for example, 150-210° around the pump axis. The helical channel can provide radial space for the drive and bearing of the rotor.

[0013] A flow-technically favorable and space-saving arrangement of the channel can be achieved according to a preferred embodiment of the invention if the first pump housing has an annular region (outlet housing / volute) surrounding the first impeller, from which the channel leads away tangentially.

[0014] A flow-optimized drainage of the blood pumped by the pump is preferably achieved by the second pump housing having an annular region surrounding the second impeller (outlet housing / volute), from which the housing outlet leads tangentially. Furthermore, the second pump housing can have an inlet housing section spaced axially from the second impeller, into which the channel opens tangentially.

[0015] With regard to the electrical drive of the blood pump, a preferred embodiment provides that the rotor interacts with a stator which surrounds the central section of the housing and has motor windings to form an electric motor. The rotor can be provided with permanent magnets, the motor being designed as a brushless DC motor. The pump is thus driven by an electromagnetic motor which is integrated around the hydrodynamic bearing area. The motor windings of the stator are preferably formed by a single set of coils arranged one after the other in the circumferential direction, the winding axes of which are aligned radially to the axis of rotation and arranged in a plane which is perpendicular to the axis of rotation.At the same time, the interaction of the stator with the rotor enables axial suspension of the rotor based on magnetic reluctance forces, which favors a miniaturized implementation of the blood pump. Since the axial support of the rotor is achieved solely by the reluctance forces acting between the stator with a single set of coils and the permanent magnets of the rotor, additional axial support of the rotor is not necessary. The reluctance forces act mainly between the magnetic return of the stator and the permanent magnets of the rotor. Using Halbach arrays as permanent magnets increases the axial reluctance forces. In addition, the reluctance force can be favored by a minimal distance between the permanent magnets of the rotor and the motor stator.Very thin wall thicknesses (<0.5mm) in the middle section of the housing and the rotor are therefore advantageous for an optimal axial reluctance force.

[0016] Since no active control of the rotor position in the radial and axial positions is necessary, no sensors or additional coils are required. This allows for a compact pump design.

[0017] Due to the lack of active control of the axial rotor position, an axial force during operation leads to a corresponding axial displacement of the rotor position. To enable such a displacement, an axial gap is present between the housing and the first and second impeller respectively. However, the axial gaps increase the return flows in the pump and the axial size of the blood pump. To reduce this effect, a preferred embodiment of the invention provides that the rotor, in the rest position of the pump, is not arranged in an axial center position between the corresponding housing surfaces, but is shifted in the direction of the second pumping stage.From a structural point of view, this preferred embodiment is characterized in that a first axial gap is provided between the first impeller and the first pump housing on the side facing away from the central section of the housing, and a second axial gap is provided between the second impeller and the second pump housing on the side facing away from the central section of the housing, and in that the rotor in its rest position is held in an axial position by the reluctance force acting between the motor windings and the permanent magnets of the rotor, so that the first gap is larger than the second gap. Only during operation is the rotor displaced into the axial center position due to the axial force acting on it, the second gap being enlarged and the first gap being reduced.

[0018] In particular, the reluctance force is designed such that the rotor assumes a center position due to a mean pressure difference (between the inlet and outlet of the entire pump) of 25-75 mmHg, in which the first gap and the second gap are equal. The size of the first and second gaps is measured at the same radial distance from the rotation axis.

[0019] Preferably, the housing inlet opens into the first pump housing on the side facing away from the central section of the housing, and the inlet housing section opens into the second pump housing on the side facing away from the central section of the housing, so that the axial forces acting on the rotor during operation act in opposite directions. However, in the second pumping stage, the fluid pressure is higher than in the first pumping stage, so that an overall resultant axial force is exerted in the direction of the first pumping stage.

[0020] Preferably, the blood pump according to the invention is designed to provide an average pressure difference of 35-150 mmHg.

[0021] In the center position of the rotor, the size of the first and second gaps is each 0.3-1 mm, in particular approximately 0.5 mm. The invention is explained in more detail below with reference to an exemplary embodiment shown schematically in the drawing. In this drawing: Fig. 1 shows an axial section through a blood pump according to the invention, Fig. 2 shows an axial section along the line III-II of Fig. 1, and Fig. 3 shows a modified embodiment of the blood pump.

[0022] The blood pump comprises a housing which has an inlet pipe 1 which converges slightly in the direction of flow 3 and an outlet 2. The blood sucked in through the inlet pipe 1 first passes through a first pumping stage and then a second pumping stage. The first pumping stage comprises a first pump housing 4 in which a first impeller 5 is arranged to rotate. The impeller 5 drives the blood radially / diagonally outwards into an annular region 6 surrounding the first impeller 5, from which a channel 7 leads away tangentially. The blood reaches an inlet housing section 8 via the channel 7, from which it flows to the second pumping stage in which a second impeller 10 arranged in a second pump housing 9 rotates. The second impeller 10 drives the blood radially / diagonally outwards into an annular region 11 of the second pump housing 9 surrounding the second impeller 10, from which the housing outlet 2 or the outlet pipe 12 leads away tangentially.

[0023] The first and second pump stages are thus arranged one behind the other along the pump axis 13, with the first impeller 5 and the second impeller 10 being arranged on the same rotor 14, which is mounted to rotate in a central section 15 of the housing arranged between the first pump housing 4 and the second pump housing 9, forming a hydrodynamic bearing. Motor windings 16 are arranged around the central section 15 of the housing and interact with the rotor 14 to form an electric motor. At the same time, this enables the rotor 14 to be axially positioned on the basis of magnetic reluctance forces, with a first axial gap 17 being provided between the first impeller 5 and the housing and a second axial gap 18 being provided between the second impeller 10 and the housing.

[0024] Furthermore, it can be seen that the channel 7 connecting the first pump housing 4 and the second pump housing 9 runs radially outside the central section 15 of the housing.

[0025] The axially sequential arrangement of the two pumping stages, combined with a radially acting hydrodynamic bearing and an axially mounted reluctance magnet, enables a miniaturized blood pump. The dimensions of the pump body (excluding the inlet and outlet tubes) can be approximately 2.5 x 2.5 x 2.5 cm or less.

[0026] Alternatively, a magnetic bearing or a mechanical bearing could be used instead of the hydrodynamic bearing.

[0027] Fig. 3 shows a modified embodiment of the blood pump in a schematic partial representation, the design corresponding to that of Figs. 1 and 2. Fig. 3 only shows the axial bearing of the rotor 14 in interaction with the housing surfaces. In the embodiment shown, the rotor 14 is arranged eccentrically in the axial direction in the rest position (left half of Fig. 3), so that the first gap 17 between the first impeller 5 and the housing surface 20 is larger than the second gap 18 between the second impeller 10 and the housing surface 21. The magnetic center line 22 of the permanent magnets 19 of the rotor 14 corresponds to the winding axis 23 of the motor windings 16. During operation, due to the pressure difference between the first pumping stage and the second pumping stage, a resulting axial force acts on the rotor 14, which displaces it into the axial center position and holds it there (right half of Fig. 4).In this central position, the gaps 17 and 18 are essentially the same size and the magnetic center line 22 of the permanent magnets 19 is moved upwards relative to the winding axis 23 of the motor windings 16.

Claims

Patent claims:

1. Blood pump for supporting cardiac output, comprising a housing with a housing inlet (1) and a housing outlet (2), wherein the housing forms a first pump housing (4) and a second pump housing (9), a rotor (14) which is mounted in the housing and is rotatable about an axis (13), wherein the rotor (14) comprises a first pump stage with a first impeller (5) arranged in the first pump housing (4) and a second pump stage with a second impeller (10) arranged in the second pump housing (9), wherein the first and the second pump stage are each configured as radial and radial impellers, respectively.are designed as diagonal pumps and are successively permeable to the blood to be pumped from the housing inlet (1) to the housing outlet (2), characterized in that the first pump housing (4) and the second pump housing (9) are connected via a channel (7) which runs radially outside a central section (15) of the housing arranged between the first and the second pump housing (4,9).

2. Blood pump according to claim 1, characterized in that the channel (7) surrounds the central section (15) of the housing in a helical manner.

3. Blood pump according to claim 1 or 2, characterized in that the first pump housing (4) has an annular area (6) surrounding the first impeller (5), from which the channel (7) leads tangentially away.

4. Blood pump according to claim 1, 2 or 3, characterized in that the second pump housing (9) has an annular area (11) surrounding the second impeller (10) exhibits, from which the housing outlet (2) leads tangentially away.

5. Blood pump according to one of claims 1 to 4, characterized in that the second pump housing (9) has an inlet housing section (8) spaced axially from the second impeller (10), into which the channel (7) opens tangentially.

6. Blood pump according to one of claims 1 to 5, characterized in that the rotor (14) is located in the central section (15) the housing is rotatably mounted.

7. Blood pump according to claim 6, characterized in that the central section (15) of the housing forms a hydrodynamic bearing with the rotor (14).

8. Blood pump according to claim 6 or 7, characterized in that the rotor (14) is provided with permanent magnets and, to form an electric motor, has motor windings surrounding the central section (15) of the housing. (16) stator interacts.

9. Blood pump according to claim 8, characterized in that the motor windings (16) of the stator are formed by a single set of coils arranged one after the other in the circumferential direction, the winding axes of which are aligned radially to the axis of rotation (13) and are arranged in a plane perpendicular to the axis of rotation (13).

10. Blood pump according to claim 8 or 9, characterized in that the axial bearing of the rotor (14) is solely provided by the The reluctance force acting between the stator and the permanent magnets of the rotor (14) is realized.

11. Blood pump according to claim 8, 9 or 10, characterized in that a first axial gap (17) is provided between the first impeller (5) and the first pump housing (4) on the side facing away from the central section (15) of the housing, and a second axial gap (18) is provided between the second impeller (10) and the second pump housing (9) on the side facing away from the central section (15) of the housing, and that the rotor (14) is held in an axial position in its rest position by the reluctance force acting between the motor windings (16) and the permanent magnets of the rotor (14), such that the first gap (17) is larger than the second gap (18).

12. Blood pump according to claim 11, characterized in that the reluctance force is designed such that the rotor (14) assumes a central position due to a pressure difference between the first and the second pump stage of 25-75 mmHg, in which the first gap (17) and the second gap (18) are of equal size.

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