Patent Description:
Blood pumps of different types are known, such as axial blood pumps, centrifugal blood pumps or mixed type blood pumps, where the blood flow is caused by both axial and radial forces. Blood pumps may be inserted into a patient's vessel such as the aorta by means of a catheter, or may be placed in the thoracic cavity. A blood pump typically comprises a pump casing having a blood flow inlet and a blood flow outlet connected by a passage. In order to cause a blood flow along the passage from the blood flow inlet to the blood flow outlet an impeller is rotatably supported within the pump casing, with the impeller being provided with blades for conveying blood.

The impeller is supported within the pump casing by means of at least one bearing, which may be of different types depending on the intended use of the blood pump, for instance whether the blood pump is intended only for short term use (some hours or some days) or long term use (weeks or years). A variety of bearings are known, such as contact-type bearings and non-contact bearings. In non-contact bearings the bearing surfaces do not contact each other, e.g. in magnetic bearings, in which the bearing surface "levitate" due to repelling magnetic forces. Generally, contact-type bearings may include all types of bearings, in which the bearing surfaces may contact at least partially during operation of the pump at any time (i.e. always or intermittently), e.g. in slide bearings, pivot bearings, hydrodynamic bearings, hydrostatic bearings, ball bearings etc. or any combination thereof. In particular, contact-type bearings may be "blood immersed bearings", where the bearing surfaces have blood contact. Contact-type bearings may heat up during use and are subject to mechanical wear caused by the contact of the rotating bearing surface and the static bearing surface during operating of the pump. It is desirable to supply a cooling fluid to the bearing, such as the blood itself. In non-contact-type bearings, the bearing surfaces do not have physical contact but are spaced by a clearance, which is in fluid connection with the passage or other fluid supply. Likewise, other clearances between the impeller and the pump casing should be washed out to avoid blood clotting and clogging, for instance at the downstream front face of the impeller.

Arrangements for rinsing clearances or bearing surfaces within a blood pump are disclosed for instance in <CIT>. Wash out channels extend through the impeller and are in fluid communication with the passage and the clearance via first and second openings. The pressure distribution in the pump casing, where the pressure increases along the impeller in a downstream direction, gives rise to a blood flow through the clearance and the wash out channel, the blood entering the clearance at a downstream end of the impeller and flowing through the wash out channel towards an area of the passage with lower pressure. This wash out flow has the disadvantage of depending on the rotational speed of the impeller, because a pressure difference must be created to cause the blood flow. Other forces such as centrifugal forces and a counter force due to the backward direction of the wash out flow also have to be overcome. In another embodiment disclosed in <CIT>, in which the impeller is supported in the pump casing by a hydrodynamic bearing, the inlet opening of the wash out channel is disposed at the upstream end of the impeller. Secondary blades at the downstream end of the impeller are provided to cause a wash out flow through the wash out channel and the clearance in a direction from an area of low pressure to an area of higher pressure.

<CIT> discloses a rotary blood pump comprising at least one rotor, a housing and at least one conduit in the rotor for conducting a by-passed portion of the blood into a clearance between the rotor and the housing, the portion of blood consisting mostly of plasma without red blood cells, thus preserving the solid particles and red cells from damage.

<CIT> discloses a sealless centrifugal blood pump in which a rotatable impeller is supported in a pump housing by fluid bearings during operation.

<CIT> discloses a pump for moving blood and other shear-sensitive with a rotor journaled hydraulically and, if necessary, magnetically in a housing and where the rotor has flow-control surfaces for producing centrifugal flow components and flow components directed against the housing, the centrifugal flow components serving mainly for producing the externally effective throughput and the flow components directed against the housing serving mainly for contact-free journaling and stabilizing of the rotor in the housing.

It is therefore a primary object of the present invention to provide a blood pump wherein blood flow stagnation and blood clotting and clogging in clearances between rotating parts and static parts of the blood pump, in particular between the static and rotating parts of the bearing or the impeller and the pump casing, are effectively avoided, in particular independently of the rotational speed or operating conditions of the pump. It is a further object of the present invention to provide a blood pump that allows for effective cooling of a contact-type bearing. It is still a further object of the present invention to provide a blood pump wherein clearances can be effectively washed out.

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

Like known blood pumps, the blood pump according to the invention comprises a pump casing having a blood flow inlet and a blood flow outlet connected by a passage. The pump casing may be understood as comprising all static parts of the blood pump. An impeller or rotor is arranged in said pump casing so as to be rotatable about an axis of rotation, which may be the longitudinal axis of the impeller, wherein the impeller is provided with blades sized and shaped for conveying blood along the passage from the blood flow inlet to the blood flow outlet. The impeller is rotatably supported in the pump casing by at least one contact-type bearing, preferably a pivot bearing, comprising a bearing surface of the impeller facing a bearing surface of the pump casing.

At least one wash out channel extends through the impeller and is in fluid connection with the passage via a first opening and with the bearing via a second opening. In order to cause a wash out flow, which may be denoted as active wash out flow, the wash out channel is operatively associated with a secondary pump for pumping blood through the wash out channel towards the bearing. According to the invention, the secondary pump is formed at least partially by said at least one wash out channel which extends through the impeller along a direction having at least one tangential directional component. In other words, the second pump is particularly formed at least partially by said at least one wash out channel itself which is sized, shaped and arranged so as to pump blood through the wash out channel towards the bearing. By providing a secondary pump that causes an active wash out flow, rinsing of the contact-type bearing and thereby cooling of the bearing can be improved compared to an arrangement without means that actively pump blood towards the bearing. The secondary pump may be supported by a suitable pressure distribution within the pump, which is described in more detail below. It will be appreciated, however, that the secondary pump works independently of the pressure distribution within the pump.

The active wash out flow is particularly useful for cooling a contact-type bearing or a "blood immersed bearing", since the amount of blood that is delivered to the bearing to wash out and cool the bearing is increased compared to a pump without a secondary pump. Cooling of the bearing can be further improved by effectively dissipating the heat from the bearing surfaces. For this purpose, the bearing may comprise a highly conductive material, such as stainless steel, that can dissipate the heat better than e.g. ceramics or titanium. It may be advantageous to provide a bearing with at least two components, in particular where the bearing surface is made of a smooth and resistant material, such as ceramics, e.g. provided in the form of a ceramic cap, while a portion of the bearing facing away from the bearing surface may be made of a highly conductive material, such as stainless steel.

In one embodiment, the wash out channel may extend linearly through the impeller and be offset relative to the axis of rotation. In particular, the wash out channel may extend in a plane that is parallel to the axis of rotation. By providing an arrangement having linear wash out channels that are skew with respect to the axis of rotation, i.e. do not intersect the axis of rotation, it is possible to cause an active wash out flow through the wash out channel.

In another embodiment, the wash out channel may be curved and extend from the first opening in a direction around the axis of rotation, in particular along a spiral shape. A spiral shape is to be understood as any curved, spiral, helical or otherwise curved shape in a direction about the axis of rotation at any length. Such shape is advantageous because it may support an active wash out flow towards the bearing.

Preferably, the wash out channel extends from the first opening at an angle relative to a surface of the impeller in a circumferential direction opposite the direction of rotation. In particular in contrast to a wash channel that extends perpendicularly to the surface of the impeller, an angled inlet opening facilitates the entrance of blood into the wash out channel and increases the flow rate through the wash out channel. This effect may be further improved by choosing an appropriate angle. For instance, the angle may be less than <NUM>°, preferably less than <NUM>°, more preferably less than <NUM>°. The wash out channel may extend from the first opening in a substantially tangential direction relative to a surface of the impeller, in other words at a very small angle with respect to the surface of the impeller. It is important, however, that the angle is in a circumferential direction opposite the direction of rotation, in other words that the first opening opens in the direction of rotation to increase the amount of blood that flows through the wash out channel compared to an arrangement in which the wash out channel extends perpendicularly to the surface of the impeller.

In an embodiment, a distance between the second opening and the axis of rotation may be less than or equal to a distance between the first opening and the axis of rotation. In other words, in a downstream direction, the wash out channel extends in a direction towards the axis of rotation. Preferably, in order to reduce the centrifugal forces that have to be overcome by the wash out flow within the wash out channel, a distance between the first opening and the axis of rotation is as small as possible. In other words, the distance between the first opening and the second opening in a radial inward direction should be as small as possible. It is further preferable if the distance between the axis of rotation and the first opening is significantly smaller than a distance between the axis of rotation and a point where the wash out flow exits to the passage, e.g. half (<NUM>%) or less than half, less than <NUM>% or even less than <NUM>%. This arrangement can be improved, i.e. the distance between the first opening and the point where the wash out flow exits to the passage can be increased, in centrifugal blood pumps compared to axial or mixed-type blood pump.

The impeller may comprise a central opening extending along the axis of rotation and accommodating the bearing, wherein the second opening is in fluid connection with the central opening. Furthermore, the wash out channel may be directed towards the axis of rotation substantially in a radial direction at the second opening. This may improve rinsing of the bearing and thereby cooling of the bearing.

Preferably, the first opening of the wash out channel is disposed adjacent to one of the blades of the impeller on a forward side of the blade with respect to the direction of rotation (generally referred to as the positive pressure side of the blade). In this area, the pressure is higher in particular compared to an area on a backward side of the blade (generally referred to as the negative pressure side of the blade), such that an active wash out flow through the wash out channel towards the bearing can be improved. In an embodiment, the first opening may be disposed on the forward side of the blade, while the second opening may be disposed on the backward side of the blade, that is to say both openings are disposed on a radially outer surface of the impeller and the wash out channel extends underneath and crosses the blade. In another embodiment, the wash out channel may extend within the blade, whereby the first opening is disposed on the forward side of the blade and the second opening is disposed in the blade, in particular on a radially outer edge of the blade. It is to be understood that the wash out channel is in fluid communication with the areas to be washed out.

As explained, the performance or output of the secondary pump can be improved by a specific arrangement of the wash out channel through the impeller, for instance a linear or curved wash out channel, which may extend at an angle relative to the surface of the impeller. The performance of the secondary pump may be further improved by the cross section of the first opening of the wash out channel. The cross section of the first opening may be circular or non-circular. In case the wash out channel has a circular cross section and extends at an angle relative to the surface of the impeller, this will result in a non-circular cross-section, such as an elliptical cross-section. In an embodiment, the first opening may be formed by an end portion of the wash out channel that is at least partially exposed due to an incline of the wash out channel relative to a surface of the impeller. In other words, the first opening may be elongate on the surface of the impeller, which may further increase the amount of blood that enters the wash out channel during operation of the blood pump.

In another embodiment, a protrusion may extend into the first opening of the wash out channel, being sized and shaped to increase a blood flow through the first opening into the wash out channel, in particular compared to a cross section of the first opening without the protrusion. The shape of the first opening without the protrusion may be either circular or non-circular. The protrusion may be disposed on a backward side of the first opening relative to the direction of rotation such that it acts as an "airfoil" to promote inflow of blood into the first opening and thereby improve performance of the secondary pump. Alternatively or additionally, the impeller may comprise a wing extending radially therefrom and being disposed adjacent to and behind the first opening of the wash out channel with respect to the direction of rotation. Preferably, the wing extends over the first opening of the wash out channel and opens in the direction of rotation so as to allow blood to enter the first opening. The wing forms a pocket that collects blood during rotation of the impeller and directs the collected blood into the first opening. In order to achieve a similar effect, the impeller may comprise a nose or protrusion comprising the first opening such that the cross section of the first opening extends at an angle relative to the surface of the impeller, preferably an angle greater than <NUM>°, more preferably an angle of <NUM>°, and opens in the direction of rotation. This may significantly increase the amount of blood that flows into the wash out channel.

Preferably, the blood pump comprises two or more of the above described wash out channels that may be symmetrically arranged with respect to the axis of rotation. In particular, the blood pump may comprise two, three, four, five or six wash out channels.

In addition to the size, shape and arrangement of the wash out channels forming at least part of the secondary pump, the secondary pump may further comprise grooves or blades formed in a surface of the impeller. Such secondary grooves or blades may be disposed at a downstream front face of the impeller to support the blood flow through the wash out channel towards the bearing.

In an embodiment, the impeller may have a portion in a downstream direction extending radially outward, the first opening of the wash out channel being disposed in said portion. In particular, said portion conically tapers radially outward in a downstream direction. The portion may be integrally formed with the impeller or separately formed. The performance of the secondary pump may be further increased by arranging the first opening in a radially extending portion of the impeller such that it is directed in a direction opposite the main direction of the blood flow through the passage. The first opening may then catch more blood and improve the performance of the secondary pump. The blades of the impeller may extend over said portion.

In a preferred embodiment, the first opening of the wash out channel is arranged in an area of the impeller that - during operation of the pump - is under a higher pressure than the second opening so as to cause a blood flow from the first opening through the wash out channel to the bearing. In other words, the wash out flow is directed in a "forward" direction, that is to say, in a direction towards the blood flow outlet of the pump casing, because the first opening of the wash out channel, i.e. an inlet opening of the wash out channel, is in a high pressure area of the impeller, while at the downstream side of the impeller the pressure is lower. Thus, by utilizing this pressure difference, in particular the local pressure gradient within the wash out channel, that occurs during operation of the blood pump, a forward flow wash out is created. This has the advantage that the necessary pressure difference is present at any time during operation of the pump, independent of the rotational speed and operating condition (e.g. preload, afterload, magnitude of primary forward flow), in particular also at a beginning of operation, when the rotation of the impeller starts and the rotational speed is low, in particular below the design speed of the blood pump. In contrast, in known blood pumps, where the wash out flow is directed in a "backward" direction, a pressure difference has to be built up, which takes some time during which the wash out flow is slow or may stagnate. This may lead to blood clotting and clogging in the clearance or the wash out channel or both. Furthermore, a backward flow has to overcome forces caused by the main direction of flow, which may also lead to stagnation of the wash out flow and consequently blood clotting and clogging. According to the present invention, a wash out flow in a "forward" direction is present throughout the time of operation of the blood pump, in particular utilizing the pressure distribution within the pump casing during operation of the pump.

The first opening of the wash out channel may be disposed in a downstream half of the impeller. During operation of the pump, the pressure increases along the length of the impeller, in particular in a region where the blades of the impeller are disposed. Therefore, in the downstream half of the impeller, a higher pressure is present than in the upstream half of the impeller. Since a high pressure at the first opening of the wash out channel is preferred, it is preferable to place the first opening in the downstream half of the impeller. More preferably, the first opening may be placed in a downstream third, a downstream quarter or a downstream fifth of the impeller. In particular, it is advantageous to place the first opening as close as possible to the downstream end of the impeller, for instance within the last <NUM> percent of the length of the impeller in the downstream direction.

In terms of the pressure distribution, the first opening of the wash out channel preferably is disposed in an area of the impeller where - during operation of the pump - the pressure is higher than a median pressure with respect to a pressure distribution along a length of the passage where the impeller is situated, more preferably where the pressure is substantially the maximum pressure. A high pressure difference between the first and second openings of the wash out channel improves the wash out flow from the first opening of the wash out channel to the bearing. In particular, a high pressure difference is advantageous to support the secondary pump.

The foregoing summary, as well as the following detailed description of preferred embodiments, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the present disclosure, reference is made to the drawings. The scope of the disclosure is not limited, however, to the specific embodiments disclosed in the drawings. In the drawings:.

Referring to <FIG>, a cross sectional view of a blood pump <NUM> is illustrated. The blood pump <NUM> is designed for extracorporeal, extracardiac or extraluminal use and comprises a pump casing <NUM> with a blood flow inlet <NUM> and a blood flow outlet <NUM>. During operation, the pump casing <NUM> is placed outside a patient's body and the blood flow inlet <NUM> and the blood flow outlet <NUM> are connected to respective connectors (in particular inflow from the heart and outflow to the aorta). <FIG> shows an embodiment that is similar to that of <FIG> with the difference that it is designed as a catheter pump <NUM>'. The blood flow inlet <NUM>' is at the end of a flexible cannula <NUM> which is placed through a heart valve, such as the aortic valve, during use, while the blood flow outlet <NUM>' is placed in a side of the pump casing <NUM>' and is placed in a heart vessel, such as the aorta. The blood pump <NUM>' is connected to a catheter <NUM>, and an electric wire <NUM> extends through the catheter <NUM> for driving the pump <NUM>'. Both blood pumps <NUM> and <NUM>' function in the same way. It will be appreciated that all features described below are applicable for both embodiments.

The blood is conveyed along a passage <NUM> connecting the blood flow inlet <NUM> and the blood flow outlet <NUM>. An impeller <NUM> is provided for conveying blood along the passage <NUM> and is rotatably mounted about an axis of rotation <NUM> within the pump casing <NUM> by means of a first bearing <NUM> and a second bearing <NUM>. The axis of rotation is preferably the longitudinal axis of the impeller <NUM>. Both bearings <NUM>, <NUM> are contact-type bearings. At least one of the bearings <NUM>, <NUM>, however, could be a non-contact-type bearing, such as a magnetic or hydrodynamic bearing. The second bearing <NUM> is a pivot bearing having spherical bearing surfaces that allow for rotational movement as well as pivoting movement to some degree. The first bearing <NUM> is disposed in a supporting member <NUM> to stabilize the rotation of the impeller <NUM>, the supporting member <NUM> having at least one opening <NUM> for the blood flow. Blades <NUM> are provided on the impeller <NUM> for conveying blood once the impeller <NUM> rotates. Rotation of the impeller <NUM> is caused by an electric motor stator <NUM> magnetically coupled to an end portion <NUM> of the impeller <NUM>. Other suitable driving mechanisms are possible as will be appreciated by a person skilled in the art. The illustrated blood pump <NUM> is a mixed-type blood pump, wherein the major direction of flow is axial. It will be appreciated that the blood pump <NUM> could also be a purely axial blood pump, depending on the arrangement of the impeller <NUM>, in particular the blades <NUM>.

The impeller <NUM> comprises a portion <NUM> that is disposed in a downstream portion of the impeller <NUM> and extends radially outwards. The portion <NUM> can be denoted as a yoke, flange portion or end portion. In this embodiment, the portion <NUM> comprises an outer surface that extends at an angle of <NUM>° with respect to the axis of rotation <NUM>. Other appropriate angles could be chosen, e.g. an angle between <NUM>° and <NUM>° or could be a curved surface. The portion <NUM> may be formed integrally with the impeller <NUM> or separately as shown in this embodiment. At least one wash out channel <NUM>, preferably two or more, such as three, four, five or six wash out channels <NUM>, only one of which is shown in <FIG>, extends through the impeller <NUM>, in particular through the portion <NUM>, so as to allow for washing out or rinsing the pivot bearing <NUM> and the clearance <NUM> between the impeller <NUM> and a static part of the blood pump <NUM>, in particular the pump casing <NUM> or the motor <NUM>, which may be regarded as associated with the pump casing <NUM>. The at least one wash out channel <NUM> may also extend at least partially into the main portion of the impeller <NUM> beyond the portion <NUM>.

The wash out channel <NUM> has a first opening <NUM> or inlet opening and a second opening <NUM> or outlet opening. The first opening <NUM> forms a fluid connection between the passage <NUM> and the wash out channel <NUM>, while the second opening <NUM> is in fluid connection with the clearance <NUM>. In particular, the second opening <NUM> is in fluid connection with a central bore or central opening <NUM> of the portion <NUM> accommodating the second bearing <NUM>. The clearance <NUM> is in fluid connection with the passage <NUM> via a clearance transition point <NUM>, i.e. a location where the clearance <NUM> opens to the passage <NUM>.

The first opening <NUM> of the wash out channel <NUM> is disposed in a downstream half of the impeller <NUM>. In particular, the first opening <NUM> is disposed in an area of the impeller <NUM> that is under a high pressure caused by the rotation of the impeller <NUM> during operation of the blood pump <NUM>. In particular, the first opening <NUM> may be in an area close to or at the maximum pressure within the pump casing <NUM>. The pressure is increased by the blades <NUM> and by the deflection of fluid from an axial flow direction to a radial direction and then decreases downstream of the blades <NUM>. Therefore, a pressure at the clearance transition point <NUM> is lower than at the first opening <NUM> of the wash out channel <NUM> due to an appropriate choice of the position of the first opening <NUM>, which is near the downstream end of the impeller <NUM>. This pressure distribution, which may be enhanced by choosing the shape of the blades <NUM> accordingly, results in a flow direction from the first opening <NUM> through the wash out channel <NUM> and the clearance <NUM> to the clearance transition point <NUM>. Alternatively, a further drop in pressure at point <NUM> could be achieved by creating a local pressure drop by the Venturi effect in the proximity of point <NUM>, e.g. by providing a narrowing <NUM> of the passage <NUM> (see <FIG>). In other words, blood flows through the wash out channel <NUM> in a forward direction towards the blood flow outlet <NUM> of the pump casing <NUM>. Blood clotting can be effectively avoided at any time during operation of the blood pump <NUM>, in particular also during phases with low rotational speed below the design speed of the blood pump <NUM>, because the forward flow wash out occurs at any rotational speed.

Apart from washing out the pivot bearing <NUM> and the clearance <NUM>, the blood flow through the wash out channel <NUM> provides cooling for the pivot bearing <NUM>. The pivot bearing <NUM> is arranged in the central opening <NUM> of the portion <NUM>. Thus, blood is conveyed through the wash out channel <NUM> towards the bearing <NUM>. The pivot bearing <NUM> can be effectively cooled and rinsed. The effect can be further improved by providing a secondary pump that actively pumps blood through the wash out channel <NUM> towards the bearing <NUM> as will be described in detail below. Although a "forward" direction of the wash out flow through the wash out channels <NUM> as described is advantageous, the wash out flow may be directed in any direction.

Now referring to <FIG>, an embodiment of an impeller <NUM> is shown. The impeller has blades <NUM> arranged around a body of the impeller <NUM> and sized and shaped for conveying blood when the impeller <NUM> rotates in a direction of rotation (indicated by an arrow in <FIG>). The impeller <NUM> has a portion <NUM> at its downstream end, wherein the portion <NUM> has at least one wash out channel <NUM> having an inlet opening <NUM>. As explained above, the inlet opening <NUM> is arranged in an area of the impeller <NUM> that is under a high pressure to ensure that the blood flow through the wash out channel <NUM> is directed from the first opening <NUM> or inlet opening to the second opening <NUM>. In this embodiment, the inlet opening <NUM> is disposed on a forward side of one of the blades <NUM> with respect to the direction of rotation (also referred to as the positive pressure side of the blade). In particular compared to a backward side of the blade <NUM> (also referred to as the negative pressure side of the blade), the pressure is higher on the forward side, which supports the direction of flow into the inlet opening <NUM> of the wash out channel <NUM>. Nevertheless, the opening <NUM> may be disposed on the backward side of the blade <NUM>, where the pressure may be sufficiently high because the opening <NUM> is disposed in the portion <NUM> at the downstream end of the impeller <NUM>.

In <FIG> different views of an embodiment of the portion <NUM> are shown. In this embodiment, the wash out channels <NUM> form a secondary pump that pumps the blood through the wash out channels <NUM> from the respective first opening <NUM> to the second opening <NUM> and, thus, to the central opening <NUM> and the bearing <NUM> and further to the clearance transition point <NUM> (see <FIG>). In this embodiment, the wash out channels <NUM> extend linearly through the impeller <NUM> and are offset with respect to the axis of rotation <NUM> (indicated by dashed lines in <FIG>, which is a bottom view of the portion <NUM>). The wash out channels <NUM> extend in planes that are parallel to the axis of rotation <NUM>, such that the wash out channels <NUM> extend along a direction that has a tangential component. This arrangement enforces the blood flow in the direction from the first opening <NUM> towards the second opening <NUM>. Two wash out channels <NUM> are shown in this embodiment. It will be appreciated, however, that three, four or more wash out channel can likewise be provided, which may be symmetrically arranged around the axis of rotation <NUM>. As can be seen particularly in <FIG>, which is a cross sectional view along line B-B in <FIG>, the wash out channels <NUM> are inclined in the downstream direction. The second openings <NUM>, which are downstream relative to the first openings <NUM>, are closer to the axis of rotation <NUM> than the first openings <NUM>. The wash out channels <NUM> open to the central opening <NUM> which at least partially accommodates the second bearing <NUM> as shown in <FIG>.

Further embodiments of an impeller <NUM> having wash out channels <NUM> that form a secondary pump are shown in <FIG>. According to the embodiment of <FIG>, the first opening <NUM> is not circular. More precisely, a protrusion <NUM> extends into the first opening <NUM> for enhancing the amount of blood that flows through the first opening <NUM> into the wash out channel. The protrusion <NUM> is arranged at a backward side of the first opening <NUM> with respect to the direction of rotation. The resulting shape of the first opening <NUM> may be denoted as a kidney shape. It acts like an "airfoil" such that a pull or suction is created upon rotation of the impeller <NUM> to increase the amount of blood that enters the first opening <NUM>, in particular compared to an embodiment without the protrusion <NUM> (such as the embodiment of <FIG>). The shape of the protrusion <NUM> can be chosen according to the desired amount of blood that should flow through the wash out channels <NUM>. The cross section of the first opening <NUM> may be symmetric or asymmetric.

Alternatively or in addition to the protrusion <NUM>, a wing <NUM> can be provided as shown in <FIG>. The wing <NUM> is arranged behind the first opening <NUM> with respect to the direction of rotation and forms a pocket to catch a larger amount of blood upon rotation of the impeller <NUM> in the direction of rotation. The wing <NUM> may have any size and shape that is suitable to increase the amount of blood that enters the first opening <NUM> compared to an embodiment without the wing <NUM> (such as the embodiment of <FIG>). The same effect can be achieved by arranging the first opening <NUM> in a nose or protrusion that extends radially from the impeller <NUM>, with the first opening <NUM> pointing in the direction of rotation.

Referring now to <FIG>, an embodiment of a portion <NUM>' having wash out channels <NUM>' is shown. The direction of rotation is indicated by an arrow. As in the above described embodiments, the wash out channels <NUM>' have a first opening <NUM>' and a second opening <NUM>' facing a central opening <NUM>'. The wash out channels <NUM>' form part of a secondary pump as described in connection with the other embodiment to force a blood flow in a direction from the first openings <NUM>' to the second openings <NUM>' towards the second bearing <NUM>. In this embodiment, the wash out channels <NUM>' are curved and extend around the axis of rotation <NUM> in a spiral shape. It will be appreciated that the term "spiral shape" comprises any curved shape, whether it forms a regular spiral or any other curved shape having at least one tangential component. The wash out channels <NUM>' enter the impeller <NUM> at the first opening at a small angle such that the first opening <NUM>' is formed by an exposed portion of the wash out channel <NUM>' and has an elongate shape. This promotes catching blood and helps to increase the amount of blood that enters the first opening <NUM>', in particular compared to an arrangement in which the wash out channels <NUM> extend to the surface of the impeller <NUM> at a large angle, such as perpendicular or substantially perpendicular. The wash out channels <NUM>' extend in a curved shape towards the central opening <NUM>' and exit at the second openings <NUM>' in a substantially radial direction. Blood is effectively pumped into the central opening <NUM>' and thus to the second bearing <NUM>, such that the second bearing <NUM> is rinsed and cooled. As explained in connection with <FIG>, the blood flow through the wash out channels <NUM>' effectively washes out the clearance <NUM> between the rotating impeller <NUM> and the static pump casing <NUM>. In order to further improve the performance of the secondary pump, the secondary pump may further comprise grooves or blades formed on a surface of the impeller <NUM>, in particular in the clearance <NUM>.

It shall be understood that the secondary pump described above cannot overcome the centrifugal effect of a rotating channel of any shape that extends from a larger diameter to a smaller diameter without the assistance of the centrifugal pumping action at clearance <NUM>.

The performance of the secondary pump may be further improved by the position of at least one of the first opening <NUM> and the clearance transition point <NUM> relative to the rotational axis <NUM> and in particular relative to each other. As shown in <FIG> the first opening has a first distance d<NUM> to the rotational axis <NUM>, while the clearance transition point <NUM> has a second distance d<NUM> to the rotational axis <NUM>. The performance of the secondary pump can be improved if the first opening <NUM> is as close as possible to the rotational axis, that is to say if the distance d<NUM> is as small as possible and the wash out channel <NUM> extends only a little distance towards the rotational axis <NUM>. This reduces centrifugal forces that have to be overcome by the wash out flow flowing in a direction towards the rotational axis. In particular, it is advantageous if the first distance d<NUM> is small compared to the second distance d<NUM>, preferably d<NUM> may be half of d<NUM> or less.

In another embodiment, shown in the cross section perpendicular to the rotational axis <NUM> in <FIG>, the impeller <NUM> includes a wash out channel <NUM> with the first opening <NUM> and the second opening <NUM> being disposed on a radially outward surface of the impeller <NUM>. The first opening <NUM> is disposed on a forward side of one of the blade <NUM> with respect to the direction of rotation (indicated by an arrow in <FIG>), while the second opening <NUM> is disposed on a backward side of the blade <NUM>. This causes a blood flow from the first opening <NUM> to the second opening <NUM>. The wash out channel <NUM> is in fluid communication with the central opening <NUM> to wash out and cool the bearing <NUM>. In the embodiment of <FIG>, a wash out channel <NUM> is provided that has a first opening <NUM> disposed on a forward side of one of the blades <NUM> similar to the embodiment of <FIG>. However, the wash out channel <NUM> extends through the blade <NUM> and exits at the second opening <NUM> which is arranged at an edge of the blade <NUM>. This arrangement allows utilizing centrifugal forces to enforce a wash out flow from the first opening <NUM> to the second opening <NUM>. <FIG> depicts another embodiment similar to that of <FIG>. However, the first opening <NUM>' of the wash out channel <NUM>' is disposed diagonally opposite to the blade <NUM> through which the channel <NUM>' extends and where the channel <NUM>' exits at the second opening <NUM>'. Thus, in this embodiment the wash out channel <NUM>' runs diagonally or radially rather than tangential as in the embodiment of <FIG>, such that it touches all sides of the bearing <NUM>.

An embodiment similar to that of <FIG> is shown in <FIG>. The wash out channel <NUM>' has a first opening <NUM>' disposed on a forward side of one of the blade <NUM> with respect to the direction of rotation, while the second opening <NUM>' is disposed on a backward side of the blade <NUM> (please note that the wash out channel <NUM>' is shown in the cross-sectional view of <FIG> although it does not extend in the plane of the cross section but rather similar to the cross-section shown in <FIG>). The wash out channel <NUM>' extends underneath the blade <NUM>. However, in the embodiment of <FIG> the wash out channel <NUM>' does not extend in one plane that is perpendicular to the longitudinal axis <NUM>, but the second opening <NUM>' is disposed downstream of the first opening <NUM>'. Thus, the second opening <NUM>' is also disposed radially outwards from the first opening <NUM>'. The wash out flow can be increased by this arrangement by centrifugal forces in the exit section of the wash out channel <NUM>' leading to the second opening <NUM>'. Also the pressure difference in the passage <NUM> between the first opening <NUM>' and second opening <NUM>' enhances the wash out flow.

It will be appreciated that at least one of the wash out channels <NUM>, <NUM>', <NUM>, <NUM>' described in connection with <FIG> may be provided alternatively or in addition to the aforementioned wash out channels <NUM>, <NUM>'. Also to be understood, channels <NUM>, <NUM>', <NUM>, <NUM>' are in fluid communication with the central opening <NUM> and the clearance <NUM>, thus allowing for a net washout flow in the same manner described above.

Aspects of the disclosure, which are different than the embodiments claimed, are described in the following:
According to an aspect of the disclosure, a blood pump comprises a pump casing having a blood flow inlet and a blood flow outlet connected by a passage, an impeller arranged in said pump casing so as to be rotatable about an axis of rotation, the impeller being provided with blades sized and shaped for conveying blood along the passage from the blood flow inlet to the blood flow outlet, the impeller being rotatably supported in the pump casing by at least one contact-type bearing comprising a bearing surface of the impeller facing a bearing surface of the pump casing, wherein at least one wash out channel extends through the impeller and is in fluid connection with the passage via a first opening and with the bearing via a second opening, the wash out channel being operatively associated with a secondary pump for pumping blood through the wash out channel towards the bearing, wherein the secondary pump is formed at least partially by said at least one wash out channel extending through the impeller along a direction having at least one tangential directional component.

Preferably, the wash out channel extends linearly through the impeller and is offset relative to the axis of rotation. More preferably, the wash out channel extends in a plane that is parallel to the axis of rotation.

Preferably, the wash out channel is curved and extends from the first opening in a direction around the axis of rotation.

Preferably, the wash out channel extends from the first opening at an angle relative to a surface of the impeller in a circumferential direction opposite the direction of rotation. More preferably, the angle is less than <NUM>°, preferably less than <NUM>°, more preferably less than <NUM>°. Also more preferably, the wash out channel extends from the first opening in a substantially tangential direction relative to a surface of the impeller.

Preferably, a distance between the second opening and the axis of rotation is less than or equal to a distance between the first opening and the axis of rotation.

Preferably, a distance between the axis of rotation and the first opening is less than <NUM>%, more preferably less than <NUM>%, even more preferably less than <NUM>% of a distance between the axis of rotation and a point where the wash out flow exits to the passage.

Preferably, the impeller comprises a central opening extending along the axis of rotation and accommodating the bearing, wherein the second opening is in fluid connection with the central opening.

Preferably, the wash out channel at the second opening is directed towards the axis of rotation substantially in a radial direction.

Preferably, the first opening of the wash out channel is disposed adjacent to one of the blades of the impeller on a forward side of the blade with respect to the direction of rotation.

Preferably, a cross section of the first opening is circular. Alternatively preferably, a cross section of the first opening is non-circular.

Preferably, the first opening is formed by an end portion of the wash out channel that is at least partially exposed due to an incline of the wash out channel relative to a surface of the impeller.

Preferably, a protrusion extends into the first opening of the wash out channel and is sized and shaped to increase a blood flow through the first opening into the wash out channel.

Preferably, the impeller comprises at least one wing extending radially therefrom and being disposed adjacent to and behind the first opening of the wash out channel with respect to the direction of rotation. More preferably, the wing extends over the first opening of the wash out channel and opens in the direction of rotation so as to allow blood to enter the first opening.

Alternatively preferably, the impeller comprises a protrusion extending radially therefrom, the protrusion comprising the first opening such that a cross section of the first opening extends at an angle relative to the surface of the impeller and opens in the direction of rotation, wherein the angle preferably is greater than <NUM>°, more preferably <NUM>°.

Preferably, the blood pump comprises two or more wash out channels that are symmetrically arranged with respect to the axis of rotation.

Preferably, the secondary pump comprises grooves or blades formed in a surface of the impeller.

Preferably, the impeller has a portion in a downstream direction extending radially outward, the first opening of the wash out channel being disposed in said portion. More preferably, said portion conically tapers radially outward in a downstream direction. More preferably, the blades of the impeller extend over said portion. More preferably, More preferably, the portion is integrally formed with the impeller or separately formed.

Preferably, the first opening of the wash out channel is disposed in a downstream half of the impeller.

Preferably, the first opening of the wash out channel is disposed in an area of the impeller that - during operation of the blood pump - is under a higher pressure than an area of the impeller where the bearing is disposed so as to cause a blood flow from the first opening through the wash out channel to the bearing.

Preferably, the blood flow from the first opening through the wash out channel is in a direction towards the blood flow outlet <NUM> of the pump casing.

Preferably, the first opening is disposed on a forward side of the blade, and the second opening is disposed on a backward side of the blade, and the wash out channel extends underneath the blade.

Preferably, the wash out channel extends within the blade, wherein the first opening is disposed on a forward side of the blade and the second opening is disposed in the blade, more preferably on a radially outer edge of the blade.

Preferably, the contact-type bearing is a pivot bearing.

Claim 1:
A blood pump (<NUM>), comprising:
- a pump casing (<NUM>) having a blood flow inlet (<NUM>) and a blood flow outlet (<NUM>) connected by a passage (<NUM>),
- an impeller (<NUM>) arranged in said pump casing (<NUM>) so as to be rotatable about an axis of rotation (<NUM>), the impeller (<NUM>) being provided with blades (<NUM>) sized and shaped for conveying blood along the passage (<NUM>) from the blood flow inlet (<NUM>) to the blood flow outlet (<NUM>), the impeller (<NUM>) being rotatably supported in the pump casing (<NUM>) by at least one contact-type bearing (<NUM>) comprising a bearing surface of the impeller (<NUM>) facing a bearing surface of the pump casing (<NUM>),
- at least one wash out channel (<NUM>') which extends through the impeller (<NUM>) and is in fluid connection with the passage (<NUM>) via a first opening (<NUM>') and with the bearing (<NUM>) via a second opening, the wash out channel (<NUM>') being operatively associated with a secondary pump for pumping blood through the wash out channel (<NUM>') towards the bearing (<NUM>), the secondary pump being formed at least partially by said at least one wash out channel (<NUM>') which extends diagonally or radially through the impeller (<NUM>),
wherein the wash out channel (<NUM>') extends through one of the blades (<NUM>) and exits at an outlet opening (<NUM>') and the first opening (<NUM>') of the wash out channel (<NUM>') is disposed diagonally opposite to said blade (<NUM>) and the outlet opening (<NUM>').