The present invention concerns centrifugal pumps, and particularly, but not exclusively, miniaturised pumps suitable for implantation into the human heart or vascular system. The present invention will now be described primarily with reference to pumps for use in the cardiac system, but it will be appreciated that the pumps according to the invention are suitable for use in other applications.

Heart Failure is a global health problem resulting in many thousands of deaths each year. Until recently the only way to curatively treat advanced heart failure has been by heart transplant or the implantation of a total mechanical heart. Unfortunately donor hearts are only able to meet a tiny fraction of the demand and total mechanical hearts have yet to gain widespread acceptance due to the technical difficulties involved with these devices.

Ventricular assist devices (VADs) have been gaining increased acceptance over the last decade primarily as a bridge to transplant devices. The devices are implanted long term and work alongside a diseased heart to boost its output and keep the patient alive and/or give a better quality of life whilst awaiting transplant.

The use of these devices has shown that, in most cases, once the device has been implanted the heart failure does not progress any further and the patient recovers a good quality of life. In cases where a heart transplant has not been available, patients have lived for several years with a VAD fitted without major complications.

Therefore a VAD can be considered a viable alternative to heart transplantation and offers hope to the many thousands of heart failure patients for whom a donor heart will not be available.

At present, the main reasons preventing VADs from being fitted on a more routine basis is the invasive surgical procedure required to fit the devices, and the high cost of the devices themselves.

With regard to the surgery, typically a sternotomy, full heart lung bypass, and major procedures to the heart, thoracic aorta and abdominal cavity are required to fit a VAD. Presently the risk of such an operation cannot be justified except in the case of those in the most advanced stages of Heart Failure. Current commercial devices are typically of complex construction and require specialised and expensive manufacturing processes for their construction. They are therefore costly and the surgery required to fit them is also expensive because they requires a long and intensive operation.

If the long term implantation of a VAD or an equivalent circulatory assist device could be achieved with a less invasive surgical procedure, certainly eliminating any procedures to the abdominal cavity and ideally eliminating the need for a sternotomy and heart lung bypass, and the cost of the devices could be significantly reduced then the use of VADs to treat heart failure could become far more widespread and routine.

The key to a less invasive implantation procedure for a VAD is to make the device as small as possible so that it can be implanted entirely within the pericardial space eliminating the need for any procedures to abdominal cavity. Furthermore, a device small enough to be implanted via a thoracotomy as opposed to a full sternotomy would be beneficial for those cases where this approach is suitable.

It is also important to minimise surgical risks so it is beneficial to use existing proven techniques, improving on them where possible. A well proven method of implanting current VADs is attaching the devices directly to the apex of the left ventricle, with an inlet to the device residing within the ventricle and the outlet of the device sitting outside of the heart. This eliminates the need for a separate inflow cannula reducing the potential for complications. The workings of the pump (impeller, motor, etc) may reside mostly within the ventricle, across the ventricle wall, or mostly outside of the ventricle depending on the design of the device.

The operational efficiency of a VAD should be as high as possible, by an appropriate combination of motor efficiency and pump efficiency. High efficiencies provide benefits such as extended battery life, smaller power cables and the possibility for transcutaneous powering of the pump via an implantable inductive coil.

There is a continuing need to develop improved miniaturised cardiac pumps suitable for implantation into the human heart or vascular system, using known low risk surgical procedures for their fitment. The bearings of the pump should be well washed with blood to minimise the chances of thrombus formation in operation and the pump should be small enough to be implanted entirely within the pericardial space without surgery to the abdominal cavity.

In general terms a centrifugal pump, such as one suitable for implantation into a ventricle of a human heart, is known which comprises

a) a housing comprising a fluid inlet, a fluid outlet and a flow path which extends between the inlet and the outlet; and

(b) a rotatable pump member including an impeller disposed axially within the housing for causing fluid to flow along the flow path from the inlet to the outlet, the pump member being rotatably coupled to the housing about an upstream bearing, and a downstream bearing comprising a bearing member on the pump member and a complementary bearing seat formation on the housing.

In such known devices, the pump member is rotatably coupled to the housing about the respective upstream and downstream bearings; the rotatable member includes an impeller which may have an impeller shroud defining a secondary flow path between the pump member and the housing.

We have found that in such a centrifugal pump, there are sometimes problems in setting the rotatable pump member accurately in the upstream and downstream bearings. Specifically, if the longitudinal separation between the upstream and downstream bearings (hereinafter referred to as "the setting length") is too long, the rotatable pump member tends to vibrate and rattle in use, whereas if the setting length is too short, the pump member tends to stick in rotation. Neither is desirable because they can potentially cause shortening of the bearing life and, in extreme cases, pump failure. Because the respective parts are all so small, it is difficult to achieve sufficient precision so that the setting length is "just right".

According to the invention, the centrifugal pump of the type described above is further provided with a mechanical adjuster (such as one or more threaded screws) for fine adjustment of the position of the bearing formation along an axis of the pump member. The mechanical adjuster may be for adjustable movement of the bearing formation along an axis of the pump member either towards the bearing member along that axis, or away from the bearing member along that axis. In a preferred embodiment, the adjustable movement is permitted by flexure of a plate member forming part of the housing; flexure arising as the relevant mechanical adjuster is tightened.

Preferably the bearing seat is integral with the plate member forming part of the housing and, in preferred embodiments, the bearing seat is provided in a boss which is integral with the plate member. As used herein, the term "boss" means a rounded protuberance, which typically has a circular sectional shape, and which protuberance is thicker and therefore stiffer than the surrounding parts with which it is integral.

As used herein, the term "downstream" is defined with reference to the direction of flow in a primary flow path. That is, any part which is nearer in the primary flow path to the inlet of the housing (specifically, closer to the source of blood flow through the pump in the case of a cardiac pump) is considered to be upstream, and any part (such as the downstream bearing as described) to which the fluid flows on its path between the inlet and the outlet is considered to be "downstream".

The plate member forming part of the housing in a preferred embodiment of the invention is preferably an integral part of the volute forming part of the pump.

When the pump according to the invention is a cardiac pump, it is preferably to be implanted by attachment to the apex of the heart, and advantageously it can be small enough to be implanted wholly within the pericardial cavity.

Preferred features of embodiments of the invention are set out in the subsidiary claims, described in the following description and illustrated in the accompanying drawings, as will subsequently be described in more detail.

As indicated above, the pump member is rotatably coupled to the housing by an upstream bearing and a downstream bearing. Preferably at least the downstream bearing comprises a recess and a complementarily shaped projection to seat in the recess.

A preferred example of such a bearing is a ball and socket (ball and cup) bearing in which a convex or domed projection (the ball) is seated in a complementarily shaped concave socket (the cup). It is particularly preferred that the downstream bearing has the ball or equivalent projection on the rotatable pump member, and the socket in the boss. On the other hand, it is preferred that the upstream bearing has the socket in the rotatable pump member and the ball or equivalent projection in the housing.

The pump preferably has, subject to the constraints of manufacturing tolerances, smooth continuous contours in the surfaces of the rotatable pump member and the housing adjacent the transition between the rotational bearing member and the stationary bearing seat of the downstream bearing, which as indicated is preferably in the form of a ball and socket.

It is preferred in a cardiac pump according to the invention that the impeller comprises an impeller shroud defining a secondary blood flow path between the pump member and the housing, the secondary blood flow path comprising an entrance and an exit; the entrance and exit being in fluid communication with a primary blood flow path, with the exit upstream in the primary flow path relative to the entrance, such that blood flow along the primary flow path results in reduction of pressure at the exit relative to that at the entrance and flow of blood along the secondary flow path.

In the latter embodiment, the blood exiting from the secondary flow path is preferably arranged to pass back into the primary flow path and the secondary flow path exit is preferably arranged to direct a flow of blood into the primary flow path in a direction which is substantially coincident with a direction of blood flow along the primary flow path adjacent the exit.

The disposition of the secondary flow entrance relative to the secondary flow exit within the primary flow path avoids the need for a junction in the primary flow path for splitting the flow of blood, and the subsequent complexities to the impeller design this might otherwise introduce.

In a preferred embodiment of the invention, the pump comprises an impeller and outlet that both reside outside of the heart, in combination with a combined motor and inlet cannula section that straddles the wall of the ventricle and extends into the ventricle itself. The motor rotor components may be attached to the impeller and extend into the inlet cannula. The motor stator components may be integrated into the inlet cannula adjacent to the rotor components.

The layout of the pump according to the invention provides significant advantages and allows the earlier discussed considerations to be achieved, for example, in the case of a cardiac pump, the positioning of the impeller outside of the heart (where there is a space available) advantageously allows a larger diameter of impeller to be used in order to enhance efficiency. Integrating the motor components into the inlet cannula provides a convenient position for the motor without increasing the overall size of the pump.

Embodiments of the invention and preferred features thereof will now be described in more detail, with reference to accompanying drawings, in which:

Figure 1 is a cutaway view of a first embodiment of a pump according to the invention implanted into the human heart;

Figure 2 is a perspective cutaway view of the pump of Figure 1 , prior to final adjustment of the setting length (the longitudinal spacing between the upstream bearing and the downstream bearing), which is initially too long and is then corrected by fine adjustment to the desired setting length when the rotor is assembled);;

Figure 3 is a full sectional view of the pump of Figure 2, again prior to final adjustment;

Figure 4 is a full sectional view of the pump of Figure 2, similar to the view of Figure 3, but after adjustment of the setting length, such that the pump is ready for use;

Figure 5 is a full sectional view of a further embodiment of pump according to the invention (this embodiment having a setting length that is initially too short and is then corrected by fine adjutment to the desired setting length when the rotor is assembled); and

Figure 6 is a full sectional view of the pump of Figure 5, but after fine adjustment of the setting length, such that the pump is ready for use.

Referring first to Figure 1 of the accompanying drawings, there is shown a centrifugal cardiac pump, comprising an outer casing 1 which has therein a single rotating member having an impeller (not shown in Figure 1 ). The outer casing 1 has an inlet 2 for blood, and a centrifugal or radial outlet 3 for blood, creating a blood flow path between the inlet 2 and the outlet 3. Part of the outer casing 1 (which includes a volute or pumping chamber 10) resides outside of the heart on the apex 4 of the ventricle 5 with the outlet 3 connected to an outflow cannula 6 which is in turn grafted to the descending aorta 7. It is also possible to graft the outflow cannula 6 to the ascending aorta 8 (graft not shown). The positioning of the pumping chamber outside of the heart allows the overall pump to be significantly larger than would be possible if it were to be fully implanted into the heart.

An inflow cannula 9 (shown externally in Figure 1 ) extends between the pumping chamber, through the wall 14 of the ventricle 5 into the chamber of the ventricle, so that the inlet 2 is completely within the chamber of the ventricle 5.

The pump is to be attached to the heart by a sewing ring 12 which would typically be attached to the outside of the apex 4 of the ventricle 5 by means of sutures, a tissue compatible adhesive, a combination of the two, or any other suitable attachment method. A sealing felt (not shown) may be trapped between the sewing ring 12 and the apex 4 to form a bloodtight seal around the emergence of the inflow cannula from the apex 4.

Electrical power is provided to the pump by an electrical cable 17. The electrical cable 17 can either be routed percutaneously to an external console and power supply or to an implanted inductive coil for trans-cutaneous power transfer.

Referring now to Figures 2 to 4, in which like parts to those in Figure 1 are denoted by like reference numerals, the casing includes a pumping chamber within which is an impeller 20 that is an integral part of a single rotating member 21 . The impeller 20 as shown is arranged to provide a radial flow (such that the pump is a radial flow type, or centrifugal pump) and the impeller is surrounded by a volute 22, which aids the conversion of kinetic energy to pressure energy thus improving efficiency. The impeller 20 comprises a series of impeller blades 23 that are surrounded by a shroud 24.

As indicated, positioning of the pumping chamber 10 outside the heart enables both the impeller 20 and volute 22 to be of an optimised design to the benefit of both pumping capacity and efficiency. The motor that powers the pump in the illustrated embodiment of Figures 1 to 4 is integrated into the inflow cannula 9. The motor rotor 28 is integral to the single rotating member 21 that also comprises the impeller 20 and extends from the pumping chamber 10 through the length of the inflow cannula 9 to the pump inlet 2. The static motor components of a coil 30 and laminations 31 are incorporated into the wall of the inflow cannula 9.

The single rotating member 21 is rotationally suspended relative to the casing by an upstream bearing 32 at the inlet 2 end of the pump and a downstream bearing 33 at the outlet 3 end of the pump, the downstream bearing 33 being in the form of respective ball 34 and cup 35 members (see Figure 3). As illustrated, the cup member 35 is provided in a boss 40 which is integral with a plate member or diaphragm 41 ; the plate member or diaphragm is of thinner and more flexible material than the boss and the boss protrudes from the body of the plate member.

The part of the boss 40 which is closest to the rotating member (that is, the "face" of the boss) is shaped so as to incorporate the cup member 35, which as indicated is to receive the corresponding ball bearing member 34 so as to form the downstream bearing.

The obverse of the boss is arranged to engage with an externally threaded grubscrew 42 which is provided on a separate internally threaded mounting plate 50 having a complementary internal screw thread 47, in which the mounting plate is itself mounted to the pumping chamber 10. In the preferred embodiment illustrated, both the mounting plate 50 and the grubscrew are symmetrical about the axis of the rotating member 21.

Figures 2 and 3 show the arrangement during assembly (that is, before the assembled apparatus is to be implanted into a patient) when the grubscrew 42 is at its most distant from the obverse of the boss 40. The grubscrew 42 is then screwed in (tightened) in the direction of arrow A using a driving head (not shown) such that the grubscrew engages with the obverse of the boss 40 until the bearing seat is at optimum position (as determined empirically) for smooth rotation of the rotating member 21 while the ball member 34 is securely received in the cup member 35. It will therefore be understood that the grubscrew 42 accordingly permits fine adjustment of the setting length between the respective upstream and downstream bearings. Typically, the mounting plate 50 is substantially more rigid than the diaphragm 41 such that only the latter moves in response to tightening of the grubscrew 42 against the boss 40. The driving head in the grubscrew may be any of the well known types, such as a slot, a cross-head, a hexagonal recess (operable by an "Allen key") or the like.

It should be noted that the respective ball 34 and cup 35 features can be reversed in orientation, i.e. the ball 34 could be in the stationary casing 1 of the pump instead of being part of the single rotating member 21 , whilst the cup 35 could be part of the single rotating member 21 of the pump instead of being part of the casing 1.

It should also be appreciated that other bearing types, for example V bearings, could be utilised in the pump according to the invention instead of the ball and cup bearings shown in the illustrated embodiments of the invention described herein.

A clearance within the impeller shroud 24 allows a secondary blood flow path 37 between the two parts that washes over the downstream bearing 33.

The surfaces of the impeller shroud 24, the casing 1 and the downstream bearing 33 provide a smooth continuous face over which the blood is caused to flow. The pathway is with minimal discontinuity so as to provide for smooth, unhindered flow that is free from areas that could undesirably cause flow statis and consequently thrombus.

In the embodiment of Figs 2 to 4, the setting length is initially too long but it is fine tuned to the required amount when the grubscrew is driven inwardly, in the direction of arrow A.

Reference will now be made to Figs 5 and 6 of the accompanying drawings, in which many parts correspond to those in Figs 2 to 4; the parts that correspond are given the same reference numerals as in Figures 2 to 4, and will therefore not be described again in full detail. In the embodiment of Figs 5 and 6, however, the setting length is initially too short and is then extended by flexing of the diaphragm 41 when the rotor 21 is assembled into the pump and the relevant adjustment screws are tightened..

In the embodiment of Figs 5 and 6, the pumping chamber 10 is in two parts, namely an upstream part 10a and a downstream part 10b with respective circumferential faces 60a and 60b which are arranged to be connected one to the other so as to form a liquid tight seal, with a smooth transition from one to the other. Specifically, upstream part 10a includes the majority of the length of the casing and includes the coil 30 and laminations

31 which are incorporated into the wall of the inflow cannula 9. Downstream part 10b includes the remainder of the casing, including the diaphragm 41 which has integral therewith the boss 40 defining a cup bearing member 35 which is arranged for complementary engagement with the ball member 34.

Figure 5 shows the arrangement prior to assembly of the upstream part 10a and the downstream part 10b before ball member 34 is seated into complementary engagement with cup bearing member 35. The diaphragm 41 is undeflected and if the pump were assembled without the rotor 21 present the setting length between the upstream bearing

32 and the downstream bearing 33 would be less than the length of the rotor between the respective upstream and downstream bearings on the rotor 10.

With reference specifically to Figure 6, when the upstream part 10a and the downstream part 10b are assembled with the rotor 21 contained within the pump, the diaphragm 41 is forced to deflect in order to achieve the correct setting length between the upstream bearing 32 and downstream bearing 33.

In this second exemplary embodiment of the invention, the diaphragm 41 is engineered such that its flexibility allows the required deflection to be achieved at a force between the bearings (typically referred to as 'preload') that is within the operational load capacity of the bearings. It will therefore be appreciated that this preload is maintained throughout the operating life of the pump.

In the second embodiment of the invention as illustrated, the connection between the upstream part 10a and the downstream part 10b is achieved by tightening of a series of threaded screws 65 (each having a slotted screw head 65a) into complementary threaded blind bores 64 so as to ensure a secure and permanent connection. However, it should be appreciated that the connection could be achieved by other means such as bonding or welding.