WO2006067473A1

WO2006067473A1 - A blood circulation assistance device

Info

Publication number: WO2006067473A1
Application number: PCT/GB2005/005018
Authority: WO
Inventors: Christopher Bowles; Charlotte Harris; Asghar Khaghani; Klaus Affeld; Christophe Lederer; Martin Cable
Original assignee: Cardiac Limited
Priority date: 2004-12-23
Filing date: 2005-12-22
Publication date: 2006-06-29
Also published as: CN101124002A; JP2008525077A; AU2005317897A1; MX2007007669A; GB0428257D0; EP1830903A1; CA2634816A1

Abstract

A blood circulation assistance device (1) comprises one or more cuff elements (3) which define a chamber for receiving a blood conduit (6). The chamber is open at both ends of the one or more cuff elements (3) for the blood conduit (6) to extend therethrough. There is an aperture (22) in the side of the one or more cuff elements (3) between each end of the chamber for locating the one or more cuff elements (3) about the blood conduit (6). The one or more cuff elements (3) bear two inwardly expanding inflatable elements (4, 5) for compressing the blood conduit (6). The inflatable elements (4, 5) are disposed diametrically opposite each other across the chamber.

Description

A BLOOD CIRCULATION ASSISTANCE DEVICE

The present invention relates to a blood circulation assistance device and a method of effecting counterpulsation, especially diastolic counterpulsation.

Mechanical circulatory support is being used increasingly for the management of heart failure. In particular, ventricular assist devices (VADs), which are configured in parallel with the native ventricles of the heart, can provide haemodynamic benefit for patients pending heart transplantation (bridge to transplantation)¹ or recovery of the natural heart muscle function (bridge to recovery)². More recently, VADs have been considered as an alternative to heart transplantation (destination therapy, permanent use)³. Total artificial hearts⁴, which are less widely used than VADs, entail removal of the natural heart and have been designed as a bridge to transplantation and for destination therapy. As VADs and total artificial hearts entail blood contact, continuous anticoagulation of the patient is mandatory to minimise the risk of blood clotting (thrombogenesis). ^ *

Intra-aortic balloon counterpulsation (IABC)⁵, is a widely applied treatment which is predominantly used for acute heart failure. Insertion of an intra-aortic balloon (IAB) is relatively non-invasive with respect to a VAD but support duration is typically limited to less than a fe^5V weeks because the patient is non-ambulant, and there is a significant risk of occlusion of the artery through which the IAB catheter is inserted leading to lower limb ischaemia⁶. Like VADs and total artificial hearts, the IAB catheter is in contact with the blood as a result of which the patient is required to receive continuous anticoagulation.

WO-A-02/24254 discloses a novel, totally implantable, extravascular, (non blood contacting) counterpulsator suitable for chronic use in ambulatory patients, comprising a sophisticated electrohydraulic energy converter. The energy converter comprises an impeller which rotates about an axis in order to drive a fluid and which is moved axially, in reciprocating fashion, in order to change the alignment of the impeller. In brief, the operating principle is as follows. As diastole begins, the energy converter pumps hydraulic fluid from an integral intracorporeal reservoir (as described in US-A-5,346,458) into a peri-aortic jacket, thereby compressing the aorta and displacing blood proximally and distally (towards and away from the heart, respectively). This has the effect of raising the diastolic blood pressure thereby improving organ perfusion, particularly that of the heart muscle, which receives the majority of its blood supply during diastole. At the end of diastole, the direction in which the energy converter pumps the hydraulic drive fluid is rapidly reversed, with the result that the peri-aortic jacket deflates leading to a fall in the end-diastolic arterial blood pressure (the pre-systolic dip). This reduces the amount of work that the heart is required to perform during the ejection phase (systole) of the subsequent heartbeat.

One problem with this type of energy converter is that the reciprocating axial movement of the impeller results in a corresponding reaction in the rest of the counterpulsator device. This reaction could conceivably cause movement of the counterpulsator device relative to the aorta leading to aortic trauma.

WO-A-02/24254 also discloses an alternative means of achieving extra-aortic counterpulsation by means of a solid-state actuator coupled directly to the aorta.

It is of paramount importance that the aorta within the peri-aortic jacket can withstand repetitive deformation for prolonged periods without inducing mechanical failure of the aorta or deleterious tissue remodelling. Moreover, it is highly desirable that the configuration of the implantable system is compatible with a minimally traumatic surgical procedure. The current invention seeks to meet one or more of these requirements and it has been found that the performance of embodiments of the present invention exceeds that of the most sophisticated IAB systems currently available in crucial aspects (see Figure 19).

Summary of the Invention

According to one aspect of the present invention, there is provided a blood circulation assistance device comprising: one or more cuff elements defining a chamber for receiving a blood conduit, the chamber being open at both ends of the one or more cuff elements for the blood conduit to extend therethrough, the one or more cuff elements bearing at least one inwardly expanding inflatable element for compressing the blood conduit.

Conveniently, there is an aperture in the side of the one or more cuff elements between each end of the chamber for locating the one or more cuff elements about the blood conduit.

In some embodiments, there is one inflatable element.

Preferably, there are at least or exactly two inwardly expanding inflatable elements. In some embodiments, a set of (e.g. two) inflatable elements act in conjunction to work, in effect, as a single inflatable element. In this specification, the term "inflatable element" includes a set of inflatable elements working in conjunction.

Advantageously, the inflatable elements are disposed diametrically opposite each other across the chamber.

In this specification, the terms "diametrically opposite" and "diametrically opposed" mean that, if the points of the inflatable elements that can come closest to each other, on inflation, are considered, then the respective normals at each point have between. them an angle of at least 135°, preferably 160°, more preferably 170°, more preferably 175° and most preferably 180°.

Conveniently two cuff elements define the chamber, the aperture being between the two cuff elements.

Preferably the two cuff elements, the inflatable elements and the chamber that they define are elongate, such that the chamber can receive the blood conduit longitudinally therethrough, with the cuff elements and the inflatable elements being parallel to the blood conduit.

Advantageously, the blood circulation assistance device further comprises an inlet, leading to the two inwardly expanding inflatable elements. Conveniently, the inlet leads to the centre of each inflatable element, along the longitudinal axis.

Alternatively, the inlet leads to one end of each inflatable element.

Alternatively, the inlet leads to both ends of each inflatable element.

Alternatively, the inlet leads to the side of each inflatable element, along their full length.

Preferably, the inlet is substantially parallel to the longitudinal axis of the inflatable elements.

Alternatively, the inlet is at an acute angle to the longitudinal axis of the inflatable elements.

Alternatively, the inlet leads to the side of each inflatable element, at a point between the centre and the end of the longitudinal axis thereof.

Conveniently the two inflatable elements are inflatable simultaneously.

Preferably, the blood circulation assistance device further comprises a manifold leading to the inflatable elements, the cross-section of the manifold leading to each inflatable element being different,.. ..

Advantageously, at the maximum expansion of the two inflatable elements, opposing sides of a blood conduit received in the chamber do not contact one another.

Conveniently, at the maximum expansion of the inflatable elements, the minimum trans- sectional curvature of a blood conduit received in the chamber is maximised, preferably by having a minimal trans-sectional radius of curvature of at least 30% of the original value, such as for example at least 36.3% of the original value or exactly 36.3% of the original value. It is particularly preferred that the minimal trans-sectional radius of curvature is at least or exactly 40.4% of the original value.

Preferably, at the maximum expansion of the two inflatable elements, a blood conduit received in the chamber has a reduction in its lumenal cross-section to more than 50% of its original value, more preferably to more than 51.5% of the original value. It is preferred that the Iumenal clearance of the blood vessel when compressed is at least 10%, more preferably at least 15% and more preferably at least 20% of the resting diameter. In this regard, it is to be appreciated that a blood circulation assistance device may be set to result in a Iumenal clearance, on compression of the blood vessel, of 20% when initially fitted but this may change to, for example a 15% or 10% clearance over time, as the inflatable elements stretch slightly.

Advantageously, the inflatable elements are made from a material which resists elastic deformation.

Conveniently, the ends of the inflatable elements are rounded.

Preferably, the ends of the inflatable, elements protrude longitudinally from the one or more cuff elements, along the axis of a blood conduit received in the chamber.

Advantageously, the blood circulation assistance device further comprises a pump in fluid communication with the inflatable elements.

Conveniently, the fluid path from the pump to the inflatable elements has an increasing cross-section.

Preferably, the fluid which communicates between the pump and the inflatable elements has a viscosity of between 8 x 10^"4 and 1.2x10^"3 Pa. s (0.8 and 1.2cP), more preferably 1x10^"3 Pa.s (1.0cP).

Advantageously, the fluid which communicates between the pump and the inflatable elements is a fluorocarbon.

Conveniently, the connection provided between the pump and the inflatable elements in order to effect fluid communication therebetween is flexible.

Preferably, the flexible connection comprises a joint having a ball with a passage extending therethrough, connected rotatably at either end to a socket.

Advantageously the flexible connection is concertinaed in order to provide flexibility.

Conveniently the flexible connection is lockable in a particular configuration. Preferably, the pump is adjacent the one or more cuff elements and the aperture is located on the opposite side of the chamber from the cuff.

Advantageously, the pump is adjacent to the one or more cuff elements and the aperture is located on the chamber at 90° with respect to the pump.

Conveniently, the pump comprises an impeller rotatable about an axis to effect pumping, the impeller being axially moveable from a first position to a second position to effect reversal of the direction of pumping.

Preferably, the blood circulation assistance device further comprises a counterbalance, moveable in synchronicity with the impeller but in an opposing direction from the axial movement of the impeller so as to counteract the reaction of the -movement of the impeller.

Advantageously, the counterbalance is movable parallel to the impeller.

Conveniently, the counterbalance comprises a second rotatable impeller, both impellers being rotatable about an axis to effect pumping.

Preferably the blood circulation assistance device further comprises a sensor capable of detecting whether the impeller is in the first or second position; and a control mechanism for shutting down the impeller in response to the sensor detecting that the impeller is locked in a position causing inflation of the inflatable elements.

Advantageously, the pump comprises a rotatable impeller; an inlet port for drawing in fluid; an outlet port for ejecting fluid; and a valve assembly interposed between the rotatable impeller and the inflatable element, the valve assembly being slidable or rotatable from a first position in which the inlet port is in fluid communication with the inflatable element and a second position in which the outlet port is in fluid communication with the inflatable element, such that movement of the valve assembly between the first and second positions effects deflation and inflation of the inflatable elements, respectively.

Conveniently, the pump is beatable in the pleural cavity. Alternatively, the pump is locatable within the pre-peritoneal or intra-peritoneal cavity and is connected to the inflatable elements via a hydraulic tube. The pre-peritoneal cavity would be fashioned by a surgeon.

Alternatively, the pump is locatable extra-corporeally.

Advantageously, flow guides are provided between the pump and the inflatable elements. The flow guides are preferably vanes, swivels and or deswirlers. The flow guides preferably minimise undesirable secondary flow behaviour or create desirable secondary flow features.

Preferably, the blood circulation assistance device further comprises a sleeve provided around the outer circumference of the one or more cuff elements.

Advantageously, the blood circulation assistance device further comprises at least one band about the one or more cuff elements.

Conveniently, one or more cuff elements are movable so as to increase or decrease the size of the chamber.

Preferably, there are provided two or more cuff elements, connected by a lockable hinge.

Advantageously, the blood circulation assistance device further comprises an inner sleeve located between the inflatable elements and the chamber.

Conveniently, the blood circulation assistance device further comprises one or more eyelets for attaching the blood circulation assistance device to a structure.

Preferably, the inflatable elements are between 3 and 15 cm long, more preferably between 5 and 9 cm long.

Advantageously, the inflatable elements are inflatable once in each cardiac cycle of a patient fitted with the device.

Conveniently, the inflatable elements are inflatable in the diastolic phase of each cardiac cycle of a patient fitted with the device or less frequently, such as in alternative cardiac cycles. Preferably the device is locatable in the left paravertebral gutter of a human.

Advantageously, the blood circulation assistance device further comprises an integral ECG electrode or electrodes for detecting the heartbeat of an individual.

Conveniently, the blood circulation assistance device further comprises a position sensor, a pressure sensor or an accelerometer for detecting the heartbeat of an individual.

According to a further aspect of the present invention, there is provided a blood circulation assistance device comprising : one or more cuff elements defining a chamber for receiving a blood conduit, the one or more cuff elements bearing an inwardly expanding inflatable element for compressing the blood conduit received in the chamber, the inflatable element being expandable such that, at its maximum expansion, the minimal trans-sectional radius of curvature of the blood conduit received in the chamber is maximised.

Conveniently, the minimum trans-sectional radius of curvature of the blood conduit is at least 30% of the original value, preferably at least or exactly 36.3%, more preferably at least or exactly 40.4% of the original value.

Preferably, at the maximum expansion of the inflatable-element, the reduction of the lumenal cross-section of the blood conduit is to more than 50%, preferably more than 51.5% of the original value.

Advantageously, the lumenal clearance of the blood vessel when compressed is at least 10%, preferably at least 15% and more preferably at least 20% of the resting diameter.

According to another aspect of the present invention, there is provided a blood circulation assistance device comprising: one or more cuff elements defining a chamber for receiving a blood conduit, the one or more cuff elements bearing an inwardly expanding inflatable element for compressing the blood conduit received in the chamber; and a pump, the pump comprising: a rotatable impeller; an inlet port for drawing in fluid; an outlet port for ejecting fluid; and a valve assembly interposed between the rotatable impeller and the inflatable element, the valve assembly being slidable or rotatable from a first position in which the inlet port is in fluid communication with the inflatable element and a second position in which the outlet port is communication with the inflatable element, such that movement of the valve assembly between the first and second positions effects deflation and inflation of the inflatable element respectively.

According to yet another aspect of the present invention, there is provided a blood circulation assistance device comprising: one or more cuff elements defining a chamber for receiving a blood conduit, the one or more cuff elements bearing an inwardly expanding inflatable element for compressing the blood conduit received in the chamber; and a pump in fluid communication with the inflatable element, the pump comprising an impeller rotatable about an axis to effect pumping, the impeller being axially movable from a first position to a second position to effect reversal of the direction of pumping, there being a counterbalance provided, movable in synchronicity with but in an oppositing direction from the axial movement of the impeller so as to counteract the reaction of the movement of the impeller.

Conveniently, the blood circulation assistance device further comprises a second inwardly expanding inflatable element for compressing a blood conduit received in the chamber.

According to a further aspect of the present invention, there is provided a method of effecting counterpulsation of a blood vessel comprising: introducing an annular stent into the lumen of the blood vessel, at each end of a section of the blood vessel; providing an external band, around the blood vessel at each end of the section of the blood vessel such that a portion of the blood vessel is trapped between each external band and its respective annular stent; and effecting counterpulsation on the blood vessel between the two annular stents.

Preferably, compression of the blood conduit is carried out using a blood circulation assistance device as described above.

Advantageously, each annular stent comprises a circumferential groove about its outer surface, for receiving its respective external band. In this specification, the word "comprising" means "including" or "consisting of and the word "comprises" means "includes" or "consists of.

In this specification, "blood conduit" means a natural blood vessel; a synthetic or artificial blood vessel; or other tubular structure for carrying blood.

In order to minimise the risk of aortic trauma, the design of embodiments of the invention has been influenced by the following considerations:

1. Preventing contralateral contact (in other words, the meeting of opposing sides) of the aortic endothelium when the aorta is fully compressed because this has been -found to be involved in endothelial denuding and atherogenesis.

2. Minimising the maximal trans-sectional curvature of the aorta (i.e. maximising the minimum trans-sectional radius of curvature) during compression in order to minimise the aortic wall stress (Fig.2).

3. Avoidance of an abrupt change in longitudinal section of the aorta at the ends of the jacket thereby minimising stress concentration at the ends of the jacket (Fig.3). .

4. Ensuring that the configuration of the aorta is predictable during deformation, i.e. avoiding aortic wall creasing and resultant wall stress concentration.

5. Minimising the relative motion of the peri-aortic jacket with respect to the aorta to avoid erosion of the aorta.

6. Minimising the transverse reaction on the aorta induced by the operation of the counterpulsator during compression and release phases.

In order that the invention may be more readily understood, and so that further features thereof may be appreciated, embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, which are as follows. Figure 1 is a perspective view of a blood circulation assistance device in accordance with one embodiment of the present invention.

Figure 2 is a cross-sectional view of a peri-aortic cuff, in a deflated state (left), and an inflated state (right) located about an aorta, in accordance with an embodiment of the present invention.

Figure 3 is a longitudinal view of the peri-aortic cuff and aorta of the embodiment of Figure 2 along the lines A-A(left) and B-B (right) respectively, with the inflatable elements being deflated (left) and inflated (right).

Figure 4 is an axial cross-sectional view of a blood circulation assistance device according to another embodiment of the present invention.

Figure 5 is a perspective view of a blood circulation assistance device in accordance with one embodiment of the present invention, superimposed on a computer tomography-derived illustration of a human chest.

Figure 6 is a perspective view of the manifold and inflatable elements of a blood circulation assistance device in accordance with another embodiment of the present invention.

Figure 7 is a perspective view of the manifold and inflatable elements of a blood circulation assistance device in accordance with another embodiment of the present invention.

Figure 8 is a perspective view of the manifold and inflatable elements of a blood circulation assistance device in accordance with another embodiment of the present invention.

Figure 9 is a perspective view of the manifold and inflatable elements of a blood circulation assistance device in accordance with another embodiment of the present invention. Figure 10 is a perspective view of the manifold and inflatable elements of a blood circulation assistance device in accordance with another embodiment of the present invention.

Figure 11 is a perspective view of the manifold and inflatable elements of a blood circulation assistance device in accordance with another embodiment of the present invention.

Figure 12 is a perspective view of a universal coupling, in a first position, between an energy converter and the inflatable elements of a blood circulation assistance device in accordance with another embodiment of the present invention.

Figure 13 is a perspective view of the universal coupling shown in Figure 12, in a second position.

Figure 14 is a perspective view of another universal coupling, in a first position, between an energy converter and the inflatable elements of a blood circulation assistance device in accordance with a further embodiment of the present invention.

Figure 15 is a perspective view of the universal coupling shown in Figure 14, in a second position.

Figure 16 is a perspective view of a blood circulation assistance device in accordance with yet another embodiment of the present invention.

Figure 17 is a perspective view of a blood circulation assistance device in accordance with another embodiment of the present invention.

Figure 18 is a perspective view of the peri-aortic cuff and manifold of a blood circulation assistance device used in the Example 1 of the present invention.

Figure 19 is a graph showing arterial blood pressure versus time from 50mm length periaortic jacket (upper) and (lower) 40 cm³ intra-aortic balloon; Key: A = Assisted beat, U = Unassisted beat. Figure 20 is a graph of : i) an electrocardiogram (ECG), ii) instantaneous coronary artery blood flow (proximal left anterior descending artery), iii) arterial blood pressure with respect to time in a model using a 50 mm length peri-aortic jacket. These traces were obtained simultaneously at an assist ratio of 1 :2. Assisted beats are depicted with an "A" and unassisted with a "U".

Figure 21 is a perspective view of a blood circulation assistance device in accordance with a further embodiment of the present invention, as shown in position within a human torso.

Figure 22 is a schematic representation of a longitudinal sectional view of an energy converter according to one embodiment of the present invention comprising an axially reciprocating valve assembly in the "cuff deflation" state.

Figure 23 is a schematic representation of a longitudinal sectional view of an energy converter according to the embodiment shown in Figure 22 in the "cuff inflation" state.

Figure 24 is a schematic representation of a longitudinal sectional view of an energy converter according to another embodiment of the present invention comprising a rotating valve assembly in the "cuff deflation" state.

Figure 25 is a schematic representation of a cross-sectional view along the line A-A¹ of Figure 24.

Figure 26 is a schematic representation of a cross-sectional view along the line B-B' of Figure 24.

Figure 27 is a schematic representation of a longitudinal sectional view of an energy converter according to the embodiment shown in Figure 24 in the "cuff inflation" state.

Figure 28 is a schematic representation of a cross-sectional view of the energy converter shown in Figure 27 along the line A-A'. Figure 29 is a schematic representation of a cross-sectional view of the energy converter shown in Figure 27 along the line B-B'.

Figure 30 is the result of an investigation, using an experimental model, into the curvature of an aorta when under compression by two inflatable elements.

Figure 31 is the result of an investigation, using an experimental model, into the curvature of an aorta when under compression by two inflatable elements and additional constraints to model the effect of lumenal pressure.

Figure 32 is the result of an investigation, using an experimental model, into the curvature of an aorta when under compression by-three inflatable elements.

Figure 33 is the result of an investigation, using an experimental model, into the curvature of an aorta when under compression by three inflatable elements.

Referring to Figure 1, a blood circulation assistance device 1 comprises a pump or energy converter 2 connected to a hollow peri-aortic jacket or cuff 3. The peri-aortic cuff 3 is rigid or semi-rigid and is curved so as to define a substantially cylindrical chamber within it. In contact with the inner surface of the peri-aortic cuff 3- are provided two elongate inflatable elements 4, 5 which are held in place by the peri-aortic cuff 3, diametrically opposite one another across the chamber. The chamber is sized and shaped to receive (preferentially) the descending aorta 6 (although in alternative embodiments, it is sized and shaped to receive the ascending aorta) and the inflatable elements 4,5 are positioned parallel to the descending aorta 6 and contra-lateral Iy with respect to it. Each end of the chamber is open to allow the aorta 6 to extend through it. A slit (or aperture) 22 is provided in the peri-aortic cuff or jacket 3 which leads between the two inflatable elements into the chamber and which extends from one end of the chamber to the other so that the peri-aortic cuff 3 can be slipped over the aorta 6 in a direction perpendicular to the longitudinal axis of the aorta 6. This permits the device 1 to be emplaced without requiring severing (i.e. surgical division) of the aorta 6. The inflatable elements 4, 5 are filled with a hydraulic drive medium contained within a common manifold 7 of low compliance, in fluid communication with the pump or energy converter.

The hydraulic fluid flow path between the pump and the inflatable elements 4, 5 is designed to allow rapid filling and emptying of the inflatable elements 4, 5 by minimising both flow resistance due to cross sectional changes, as far as is practicable, and undesirable secondary flow features of the hydraulic drive fluid (e.g. contra-rotations associated with abrupt cross-sectional change which may impair filling and emptying of the inflatable elements 4, 5). However, secondary flow characteristics are not invariably detrimental; indeed, it may be desirable to potentiate them by the inclusion of flow guides in order, for example, to create fluid mixing to avoid simultaneous bi-directional flow within the hydraulic fluid path.

The entry of the hydraulic drive medium from the energy converter 2 into the manifold 7 is associated with inflation of the inflatable elements 4, 5. As the outer surfaces of the inflatable elements 4, 5 is constrained by the peri-aortic cuff 3, the inner surfaces of the inflatable elements 4, 5 move together compressing the aorta within the jacket 3. The length of the peri-aortic jacket 3 is preferentially in the range of 3 to 15 cm.

In vitro and animal studies have demonstrated that a relatively short peri-aortic jacket (5cm) is associated with a more pronounced pre-systolic arterial pressure reduction than an intra-aortic balloon (see Figure 19). The extent to which pre-systolic pressure is reduced by counterpulsation devices is a crucial determinant of clinical efficacy, particularly in the setting of heart failure.

There are two conditions which should be avoided during the compression of the aorta: i) contact between contralateral endothelial surfaces and ii) excessively high curvature of the aortic endothelium. Both conditions cause damage or denudation of the endothelium, a process which is believed to be atherogenic. The present inventors' experimental studies have shown that the selection of two inflatable elements 4, 5, in the preferred embodiment, are sized and positioned to ensure that aortic deformation is associated with the formation of a comparatively low maximum trans-sectional aortic curvature (in comparison with a system eliciting the same haemodynamic benefits comprising a greater number of inflatable elements). The present inventors' animal studies have demonstrated that placement of a peri-aortic jacket having two inflatable elements around the aorta is relatively straightforward.

In embodiments where two inflatable elements 4, 5 are provided, it is important that the two elements inflate simultaneously in order to avoid a potentially deleterious reaction on the aorta 6. Simultaneous inflation can be achieved by design of a differential cross section of the manifold branches supplying the individual inflatable elements. When the inflatable elements are fully inflated, there is a gap between the inner surfaces of the inflatable elements as is shown in Figures 2 and 3. The gap is sufficiently great to prevent contralateral contact of the aortic endothelium, in order to minimise the risk of aortic endothelial denuding, a process which is highly atherogenic. This gap is maintained either by using inflatable elements which do not undergo significant elastomeric deformation under prescribed operating conditions or by restricting the volume of hydraulic fluid in the system.

The present inventors' experiments (see Example 2) have demonstrated that the optimal number of inflatable elements is two

The inflatable elements 4, 5 associated with the peri-aortic cuff or jacket 3 are of relatively low compliance and so do not undergo significant elastomeric deformation during inflation in order to maximise their mechanical fatigue life. Nevertheless, a small degree of creep is expected in the inflatable elements as a result of repeated inflation/deflation cycling which is accommodated by the generous lumenal clearance, as described above. An acceptable mechanical fatigue life is achieved by appropriate material and wall thickness selection. Appropriate physical characteristics of the inflatable elements could be achieved by manufacturing them from a reinforced or filled polymer. The drive fluid which is provided is not associated with an adverse change in the physical characteristics of the membrane of inflatable elements with respect to time. Potentially suitable drive fluids include aqueous and non-aqueous liquids with a viscosity of 0.8 and 1.2cP, preferably 1.OcP (8x10^"4 and 1.2x10^"3Pa.s, preferably 1x10^"3Pa.s). The drive medium is a fluorocarbon in some embodiments. In order to further reduce the risk of aortic damage, the ends of the inflatable elements 4, 5 have a rounded geometry and they protrude slightly beyond the rigid peri-aortic cuff or jacket 3, in a longitudinal direction, in order to avoid an abrupt change in aortic section at the ends of the peri-aortic jacket (see Figures 1 and 3).

The present inventors' in vitro experiments have revealed that the use of two elongate inflatable elements 4, 5, parallel to the longitudinal axis of the aorta 6, is associated with more predictable deformation characteristics of the aorta than a circumferential cuff, which the inventors' studies have shown is usually associated with marked aortic creasing and localised stress concentration. Consequently, the preferred embodiment is inherently better-suited to chronic counterpulsation, with respect to aortic durability, than a transverse, circumferential peri-aortic cuff.

Relative position of the energy converter and the cuff

There are a number of advantages associated with ensuring that the distance between the peri-aortic cuff 3 and the energy converter 2 are minimised: - i) The overall size of the device is reduced thereby reducing surgical trauma during implantation. ii) The "dead space" in the hydraulic fluid path, and the flow resistance, are both minimised. This is particularly important in the context of diastolic counterpulsation, which is a very dynamic process. The hydraulic fluid flow resistance and the rate of change of flow with respect to time (dQ/dt) are both adversely affected by the inertial effects of a large dead space.

In the preferred embodiment, the distance between the energy converter 2 and periaortic jacket 3 is minimised thereby minimising the fluid dead space. A particularly preferred embodiment of the blood circulation assistance device is shown in transverse cross-section at the level of the impeller ports 8 which are in fluid communication with the inflatable elements 4, 5, in Figure 4. It can be seen that the hydraulic fluid path has a non uniform cross section in order to avoid excessive flow resistance or changes in flow resistance. In one embodiment of the invention, flow guides are introduced into the hydraulic fluid path to minimise undesirable secondary flow behaviour which could otherwise compromise flow resistance and thus dQ/dt. An example of undesirable secondary flow is the formation of counter-rotation features which can occur if there is an abrupt change in cross section. Conversely, in one embodiment flow guides are included to create desirable secondary flow features; for example, guides that potentiate mixing to reduce simultaneous bi-directional flow may improve the performance characteristics of the device (dQ/dt). The flow guides would be in the form of vanes or swirlers or deswirlers in the fluid path.

In one embodiment, the energy converter 2 and peri-aortic cuff 3 shown are sized and shaped to fit in the left pleural cavity. The device is designed to be located by a surgeon in the left paravertebral gutter after the cuff has been placed around the aorta. The feasibility of this approach has been validated by computer-based fitting studies which entailed superimposition of the boundaries of the preferred embodiment within the Computed Tomography (CT)-derived left pleural cavity boundaries of normal humans (including those of the descending aorta) as illustrated in Figure 5.

The fluid connection between the pump or energy converter 2 and the inflatable elements 4, 5 is varied from embodiment to embodiment.

Referring to Figure 6, an embodiment is shown in which the manifold 7 connects the pump 2 to the inflatable elements 4, 5 at the centre of their longitudinal axis. The manifold 7 is perpendicular to the longitudinal axis of the inflatable elements 4, 5.

Referring to Figure 7, an embodiment is shown in which the manifold 7 connects to the inflatable elements 4, 5 at one of their respective ends 9, 10. The manifold 7 is directed at an acute angle from the elongate inflatable elements 4, 5 so that fluid is reflected back off the far wall 11 of the manifold 7 when it moves from the pump to the inflatable elements 4, 5 or vice versa.

Referring to Figure 8, an embodiment is shown in which the inlet 7 is positioned at the centre of the inflatable elements 4, 5 along their longitudinal axis and perpendicular thereto. The manifold 7 bifurcates into first and second ducts 12, 13. The first duct connects the manifold 7 to the respective first ends 9, 10 of the inflatable elements 4, 5 and the second duct 13 connects the manifold 7 to the respective second ends 13, 14 of the inflatable elements 4, 5. Thus the pump 2 is in fluid communication with both ends of each inflatable element 4, 5.

Referring to Figure 9, an embodiment is shown in which, as in the previous embodiment, the manifold 7 is located at the centre of the longitudinal axis of the inflatable elements 4, 5 and perpendicular thereto. However, in this embodiment, the manifold 7 connects to the sides of the elongate inflatable elements 4, 5, along their full length.

Referring to Figure 10, an embodiment is shown in which the manifold 7 is provided at the first ends 9, 10, respectively of the inflatable elements 4, 5, as in the embodiment depicted in Figure 7. However, in this embodiment, the manifold 7 is substantially parallel to the longitudinal axis of the inflatable elements 4, 5 but is offset so that there is a "dog leg" section 15 of the manifold 7 between the main part of the manifold 7 and the respective first ends 9, 10 of the inflatable elements 4, 5.

In each of the embodiments shown in Figures 6 to 11 , the manifold 7 is located equidistantly between the two inflatable elements 4, 5. However, referring to Figure 11 , an embodiment is shown in which the manifold 7 is located between the centre of the longitudinal axis of the inflatable elements 4, 5 and the respective first ends, 9, 10 of the inflatable elements 4, 5. The manifold 7 is substantially perpendicular to the longitudinal axis of the inflatable elements 4, 5.

In order to cater for minor anatomical variations in patients, some embodiments have a universal coupling between the energy converter 2 and the peri-aortic cuff 3, in order to ensure that misalignment of the cuff is avoided. Misalignment is undesirable for two reasons: the efficacy of counterpulsation may be reduced and the risk of aortic trauma may be increased as a result of increased local aortic wall stress.

Referring to Figures 12 and 13 the universal coupling 16 comprises a "ball and double socket" joint. More specifically, the universal coupling 16 comprises first and second generally cylindrical sections 17, 18 connected by a ball 19 having a bore 20 through it. Each of the first and second sections 17, 18 is swivelable relative to the ball 19 so as to permit their relative movements. Fluid communication between the first and second sections 17, 18 is permitted by the bore 20.

Referring to Figures 14 and 15, in which another embodiment of the invention is shown, the universal coupling 16 comprises first and second generally cylindrical sections 17, 18 connected by a concertinaed section 21 which is sufficiently flexible to permit relative movement of the first and second cylindrical sections 17, 18.

In certain embodiments, the movement of the universal couplings shown in Figures 12 to 15 are restricted, for example by the use of key-ways which only allow adjustment of the position of the cuff 3 relative to the energy converter 2 in one plane.

Such universal couplings must have a low compliance because any change in volume associated with the coupling will reduce the efficacy of the device by delaying filling or emptying of the cuff. In one variant of the preferred embodiment, the coupling can be locked rigidly in a particular configuration, after adjustment by the surgeon at the time of implantation, in a manner most appropriate to the patient anatomy. Locking of the universal coupling is achieved, in some embodiments, by means of a threaded compression ring or grub screw which is tightened by the surgeon during the implantation procedure to maintain the implant in an appropriate configuration.--

In preferred embodiments, the pump 2 is located adjacent and parallel to the peri-aortic cuff 3. In some embodiments, as shown in Figure 16, the slit 22 is located at one side of the plane defined by the pump 2 and the peri-aortic cuff 3. That is to say that the slit 22 is oriented postero-medially. In other embodiments, as shown in Figure 17, the slit 22 is on the far side of the peri-aortic cuff 3 from the pump 2. That is to say that the slit 22 is oriented antero-medially.

Stabilisation of the energy converter peri-aortic-cuff assembly

Positional stability of the peri-aortic cuff 3, with respect to the aorta 6, is of paramount importance if the efficacy of counterpulsation is to be maximised and the risk of aortic trauma minimised. A key advantage of embodiments of the invention is that the slit 22 in the peri-aortic jacket 3 permits the peri-aortic jacket to be placed around the aorta 6 rapidly with neither the need for surgical division of the aorta nor cardiopulmonary bypass. However, having positioned the peri-aortic jacket 3 around the aorta 6, it is essential that subsequently the jacket 3 does not become misaligned. In order to prevent this, the device 1 is, in some embodiments, secured with respect to the aorta 6.

In some embodiments, an inert sleeve of strong synthetic fabric such as woven polyester, Dacron^®, PTFE, with a low distensibility is placed around the outer circumference of the peri-aortic jacket 3, after positioning around the aorta 6. A sheet of such a material is sutured into the form of a sleeve by a surgeon. Additionally, having fashioned this sleeve, the surgeon sutures it to the aorta 6 at the ends, in certain embodiments.

In further embodiments, ratchet plastic bands, such as those made of nylon or a alternative material or materials with a high tensile strength are provided around the outside of the peri-aortic jacket 3. In variants of these embodiments, the bands have an adjustable buckle in order to vary their circumference. In other variants, these bands are of a woven material and can be sewn by the surgeon. In some embodiments both an inert sleeve and plastic bands are provided.

Accommodation of variation in aortic diameter

A key advantage of embodiments of the invention, which are preferentially sized and shaped for placement of the device on the descending aorta, is that the latter is associated with smaller variations in diameter than the ascending aorta and thus the efficacy of the device is more predictable. Nevertheless, it is important that the device can be coupled to the aorta effectively irrespective of its diameter. In one embodiment, the outer edges of the peri-aortic cuff 3, which abut either side of the slit 22 are semirigid and are slightly splayed under normal conditions. This allows the surgeon to approximate the two inflatable elements 4, 5 to the desired degree by means of fashioning the cuff 3 appropriately such that it is under mild circumferential tension under resting conditions, i.e. before the device is switched on. As the aortic diameter can be measured by imaging prior to surgery, or at the time of surgery, if the diameter of the peri-aortic jacket 3 is adjustable in discrete increments, a means exists to ensure that the aorta is compressed optimally whilst avoiding contralateral aortic endothelial contact. This benefit is available in an alternative embodiment in which the peri-aortic cuff 3 comprises one or two hinged jaws on which the inflatable elements 4, 5 are located and which can be locked to an appropriate diameter for the size of the aorta 6.

Reinforcement of the aorta

It is conceivable that the surgeon implanting a device according to the current invention may wish to prevent direct contact between the aortic adventitia (outermost layer) and the inflatable elements 4, 5. In order to achieve this a woven polyester (Dacron^®) or PTFE sleeve, a tissue engineered construct, or mobilised intercostal muscle or other autologous tissue such as pericardium is provided between the inflatable elements 4, 5 and the chamber in which the aorta 6 is received. The adjustable peri-aortic jacket 3 allows for their incorporation in the implantation procedure.

In some circumstances, where there is believed to be an increased risk that the device 1 could cause aortic dissection and/or delamination, in order to prevent the propagation of the dissection/delamination, two annular stents are introduced into the lumen of the aorta 6, at either end of the peri-aortic jacket. External banding is applied around the aorta 6, at the position where each annular stent exists within the aorta 6. Thus the aorta 6 is sandwiched between a stent on the inside and an external band on the outside. This prevents propagation of the dissection.

In preferred embodiments, each annular stent has a circumferential groove around its rim for receiving the aorta 6 when the external band is applied, which presses the aorta 6 into the groove. This assists in maintaining the stent and external band in place.

Stabilisation of the energy converter

In some embodiments, the energy converter 2 is stabilised by the incorporation of eyelets onto its outer surface to allow the device to be sutured, wire-tied, or screwed to rigid or semi rigid structures within the thoracic cavity, such as the vertebrae, ribs, intercostal muscle or cartilage. Energy converter variants

It is preferred that aortic trauma be minimised during operation of blood circulation assistance devices according to the present invention. In embodiments in which the pump 3 comprises an impeller which rotates about an axis and which is moved axially in order to effect reversal of pumping (as described in detail in WO-A-02/24254), it is preferred that features are provided to avoid reaction forces on the aorta 6 during operation of the device. The energy converter 2 is associated with small axial reactions as a result of the bi-directional axial translation that the impeller assembly undergoes during normal operation. It is conceivable that this reaction could be transmitted to the aorta 6 although it is unlikely that this effect would be clinically significant because the mass of the impeller assembly is low in relation to the -remainder of the energy converter/cuff assembly 2,3. However, it is conceivable that this reaction could produce undesirable effects on the aorta 6 or other organs. Consequently, in one embodiment, the energy converter 2 comprises two impeller assemblies which move towards, or away from, each other simultaneously to eliminate the axial reaction.

In another variant, the reaction associated with axial movement of the impeller assembly is eliminated by the simultaneous electromagnetically-driven movement of an equivalent mass in the opposite direction. Of course, the movement of the equivalent mass need not be in exactly the opposite direction provided that its movement has a component in the opposite direction.

An alternative solution to this problem is an energy converter consisting of a rotating impeller which does not undergo a linear translation where change in fluid flow direction is achieved by means of an axially reciprocating or rotating valve assembly.

Referring to Figures 22 and 23, an embodiment of an energy converter with an axially reciprocating valve assembly will now be described.

An energy converter 24 comprises a generally tubular housing 25 which has a first cylindrical connection 26 leading to a cuff (not shown) such as one depicted in Figure 1 and a second cylindrical connection 27 leading to a fluid reservoir (not shown). The tubular housing is sealed at either end. Located within the tubular housing 25 is an axially slidable tubular valve assembly 28 which has a first aperture 29 aligned with the first cylindrical connection 26. Radially opposite the first aperture 29 are second and third apertures 30, 31 located in the tubular valve assembly 28. The second and third apertures 30, 31 are axially aligned and separated such that by moving the tubular valve assembly 28 axially, either the second 30 or the third 31 , but not both (or at least, not both over their entire widths), is aligned with the second cylindrical connection 27.

Within the tubular valve assembly 28 is a tubular manifold 32 which is located coaxially with respect to the tubular valve assembly 28 and the tubular housing 25. The manifold 32 defines a substantially cylindrical interior 33. In one side of the manifold 32 are located a deflation inlet 34 and an inflation outlet 35, which are both aligned with the first cylindrical connection 26. The first aperture 29 of the tubular valve assembly is sized and located such that it may be aligned either with the deflation inlet 34 or the inflation outlet 35 but not both (or at least, not both over their entire widths).

On the opposing side of the manifold 33 are provided an inflation inlet 36 and a deflation outlet 37, aligned with the second cylindrical connection 27. The second and third apertures 30, 31 are sized and located such that when the first aperture 29 is aligned with the deflation inlet 34 then the third aperture 31 is aligned with the deflation outlet 37 but the inflation inl§ U36 is blocked by the valve assembly 28. If, on the other hand, the first aperture 29 is aligned with the inflation outlet 35 then the second aperture 30 is aligned with the inflation inlet 36 and the tubular valve assembly 28 blocks the deflation outlet 37.

A drive fluid is provided in the enclosure defined by the cuff, the energy converter 24 and the fluid reservoir.

Within the cylindrical interior 33 there is a centrifugal impeller 38 which draws in drive fluid at an axial inlet 39 and ejects it at the rim 40 of the impeller 38. The rim 40 of the impeller 38 is aligned with both the deflation outlet 37, on one side, and the inflation outlet 35, on the other side.

In use, the bladder of the cuff is deflated, with the tubular valve assembly in a first position which is shown in Figure 22. In this position, the impeller 38 draws in drive fluid via the first cylindrical connection 26, through the first aperture 29 and the deflation inlet 34 into the impeller 38 at the axial inlet 39 from which it is ejected at its rim 40 out through the deflation outlet 37, the third aperture 31 and through the second cylindrical connection 27 to the drive fluid reservoir as shown by the arrows 41. In this way, the drive fluid is pumped out from the bladders of the cuff and into the drive fluid reservoir.

While the impeller 38 remains pumping in the same direction (i.e. from the axial inlet 39 to the rim 40), the tubular valve assembly 28 is moved axially by an electromagnetic actuator (not shown) to a second position shown in Figure 23, in order to reverse the direction of pumping.

In the second position, drive fluid is drawn from the second cylindrical connection 27, through the second aperture 30 and the inflation inlet 36 into the axial inlet 39 of the impeller 38. From there, it is pumped to the rim 40 of the impeller 38 and out through the inflation outlet 35, through the first aperture 29 and out through the first cylindrical connection 26, which leads to the bladder of the cuff as shown by the arrows 42. In this way, the drive fluid is pumped into the bladder of the cuff as shown by the arrows 42 and thus inflates it.

The tubular valve assembly 28 is subsequently returned to the first position, shown in Figure 22, by the electromagnetic actuator in order to deflate the bladder of the cuff again. Thus the tubular valve assembly 28 axially reciprocates in order alternately to deflate and inflate the cuff bladder.

Referring to Figures 24 to 29, an embodiment of an energy converter comprising a rotating valve assembly will be described. Like reference numerals are used for like components of the embodiment depicted in Figures 22 and 23. As in the previous embodiment, the energy converter 24 comprises a generally tubular housing 25 with first and second cylindrical connectors 26, 27 on opposing sides thereof. Located coaxially within it is a tubular valve assembly 28 which comprises a first aperture 29 which can be aligned with the first cylindrical connector 26 and second and third apertures 30, 31 which can be aligned with the second cylindrical connector 27. However, in this embodiment, the second and third apertures 30, 31 are not axially aligned but are axially and circumferentially offset from one another such that by rotation of the tubular valve assembly 28, either the second 30 or the third aperture 31 is brought into alignment with the second cylindrical connector 27, but not both (or at least not both to their full extent).

Furthermore, a fourth aperture 43 is provided in the tubular valve assembly 28, on the same side as the first aperture 29. Again, the first aperture 29 and the fourth aperture 43 are circumferentially and axially offset from one another so that by rotation of the tubular valve assembly 28, either the first aperture 29 or the fourth aperture 43 is aligned with the first cylindrical connector 26, but not both (or at least not both to their full extent).

The apertures 29, 30, 31, 43, in the tubular valve assembly 28 are arranged such that when the first aperture 29 is aligned with the deflation inlet 34 then the third aperture 31 is aligned with the deflation outlet 37 but the inflation outlet 35 and the inflation inlet 36 are blocked by the tubular valve assembly 28. Conversely, when the second aperture 30 is aligned with the inflation inlet 36 then the fourth aperture 43 is aligned with the inflation outlet 35 but the deflation inlet 34 and the deflation outlet 37 are blocked by the tubular valve assembly 28.

Within the tubular valve assembly 28 and coaxially aligned therewith, is a manifold 32 and an impeller 38 as described in the previous embodiment.

In use, the tubular valve assembly 28 is located in a first position as is shown in Figures 24 to 26. In the first position, the first aperture 29 is aligned with the first cylindrical connector 26 and the deflation inlet 34 and the third aperture 31 is aligned with the deflation outlet 37 and the second cylindrical connector 27. The impeller 38 draws in drive fluid through the first cylindrical connector 26, via the first aperture 29 and the deflation inlet 34 into the axial inlet 39. The impeller 38 then drives the drive fluid to its rim 40 and thus out of the deflation outlet 37, via the third aperture 31 and out through the second cylindrical connector 27, thus following the course of the arrows 41. Thus drive fluid is pumped from the bladder of the cuff which is in fluid communication with the first cylindrical connector 26 and to the reservoir which is in fluid communication with the second cylindrical connector 27.

In order to reverse the direction of pumping of the energy converter 24, but without the need to reverse the direction of pumping of the impeller 38, the tubular valve assembly 28 is rotated by an electromagnetic actuator (not shown) to a second position as shown in Figures 27 to 29. In the second position, the fourth aperture 43 is aligned with the first cylindrical connector 26 and the inflation outlet 35. Similarly, the second aperture 30, 31 is aligned with the inflation inlet 36 and the second cylindrical connector 27. Thus the impeller 38 draws drive fluid through the second cylindrical connector 27, via the second aperture 30 and the inflation inlet 36 into the axial inlet 39 of the impeller 38. From there, it is pumped to the rim 40 of the impeller 38 and thus out through the inflation outlet 35, via the fourth aperture 43, as shown by the arrows 42, and out through the first cylindrical connector 26, as shown by the arrows 42, to the bladder of the cuff (not shown). Thus, in the second position of the tubular valve assembly 28, the impeller 38 has the effect of pumping the drive fluid to the bladder and thus inflating the bladder.

Subsequently, the tubular valve assembly is rotated back to the first position to effect deflation and the process is repeated.

It is to be appreciated that, conceptually, the axial 39 inlet of the impeller 38 can be regarded as an "inlet port" and the rim 40 of the impeller 38 can be considered to be an "outlet port". Thus, the embodiments of Figures 22 to 29 comprise valve assemblies 28 which are movable from a first position in which the inlet port 39 is in fluid communication with the inflatable bladder of the cuff to a second position in which the outlet port 40 is in fluid communication with the inflatable bladder.

Failsafe characteristics of the energy converter

A potentially dangerous failure mode of a blood circulation assistance device 1 of the present invention is one where the aorta 6 remains obstructed for the entire cardiac cycle resulting in an elevated left ventricular stroke work. The embodiments of the present invention whose pump comprises an impeller rotatable about an axis which is axially movable to effect reversal of pumping direction (as described in detail in WO-A- 02/24254) have the advantage of an inherent failsafe characteristic. If the impeller of the energy converter 2 stops rotating then the aortic pressure will drive the hydraulic fluid from the inflatable elements 4, 5 into the energy converter reservoir. However, if the failure mode results in continuous rotation of the impeller, with the impeller assembly lodged in the state associated with aortic compression, the effect would be detrimental to the left ventricle. In order to address this, in some embodiments, there is provided a sensor which detects the axial location of the impeller assembly. A control mechanism is provided which receives input from the sensor. In response to the sensor detecting that the axial movement of the impeller has failed with the impeller, in the position causing the inflatable elements 4, 5 to fill, the control mechanism shuts down power to the impeller. In one embodiment, this sensor is a Hall-effect sensor which detects the proximity of one or more of the magnets of the impeller assembly.

Alternative locations of the energy converter

Referring to Figure 21 an embodiment of the present invention is shown where the periaortic cuff 3 is secured around the descending aorta 6 but the energy converter 2 is located within the peritoneal or a pre-peritoneal cavity with a hydraulic tube 23 linking it to the implanted peri-aortic cuff 3. In further embodiments of the invention, the energy converter 2 is located extracorporeal^.

Alternative locations of the peri-aortic cuff

In the preferred embodiment, the peri-aortic jacket 3 is located around the descending thoracic aorta 6. However, in other embodiments the. peri-aortic jacket 3 is placed in alternative systemic arterial locations.

Power delivery

Electrical power is delivered to the implanted components by one of two means:-

1. A Percutaneous Driveline

In some embodiments, this driveline comprises redundant electrical cables to ensure continuity of power delivery in the event of individual cable failure. Cables with a high tensile strength and high flexibility are provided such as multifilament cadmium/copper types. In certain embodiments the driveline also has a textured outer sleeve in order to promote tissue ingrowth to minimise the infection risk. In addition to power delivery, the percutaneous driveline, in particular embodiments, includes conductors to allow the operator to adjust the operating characteristics of the blood circulation assistance device, namely the counterpulsator, and to convey the heartbeat signal, alarms and data to an external controller/monitor.

2. A Transcutaneous Inductive Coupling System (TETS^

In addition to power delivery, the TETS system also comprises, in some embodiments, a telemetric link to allow the operator to adjust the operating 0 characteristics of the counterpulsator, and to convey the heartbeat signal, alarms and data to an external controller/monitor.

Controller 5

In some embodiments, the blood circulation assistance device 1 comprises an electronic controller which receives electrical power either from the percutaneous driveline or a TETS system. The controller comprises a means of detecting the heartbeat to ensure that the operation of the device is synchronised appropriately. Synchronisation of the CL operation of the device with the heartbeat may entail electrocardiogram (ECG) detection or the use of an alternative method such as a position or pressure sensor or sensors or an accelerometer. The arterial pulse wave may be used for triggering. If the heartbeat detection entails ECG monitoring, at least one of the ECG electrodes are, in some embodiments, integrated in the implanted components. In some embodiments the ECG 5 detector has integral defibrillation protection.

The controller regulates the function of the energy converter 2. The controller may comprise alarms (either audible or vibrational) to alert the patient to a malfunction. The controller may have a data logging facility. If the system comprises a percutaneous 0 driveline, the controller may be intra- or extracorporeal. If the controller is intracorporeal, it may be integrated with either the secondary coil of the TETS system or the energy converter/peri-aortic jacket assembly. Implanted battery

In contrast to ventricular assist device support, short periods of cessation of counterpulsation support should be well tolerated by a patient. Consequently, there is usually no need for the provision for an implanted rechargeable battery to power the system in the event of accidental or intentional disconnection of the external power source. However, in some embodiments an implantable rechargeable battery is provided if, for example, patients wish to take a bath when they have a high dependence on the uninterrupted function of the counterpulsator.

Alternative configuration of the peri-aortic jacket

In some embodiments, in particular to ease manufacture, the peri-aortic jacket 3 comprises a single inflatable element 4. In such an embodiment, the aorta is compressed between the inflatable element and a rigid or semi rigid opposing surface which may be part of the peri-aortic jacket 3.

Examples

The present invention is now-further illustrated by way of the following examples.

Example 1

This data was obtained in an acute porcine (pig) model of counterpulsation using an energy converter as described in WO-A-02/24254 and a prototype cuff of the design illustrated in Figure 18. The efficacy of the prototype device was evaluated with respect to a 40 cm³ intra-aortic balloon in the same animal.

Arterial blood pressure and ultrasonic coronary blood flow in the proximal left anterior descending artery were monitored continuously. A peri-aortic jacket was used as illustrated in Fig 18. Two cuff variants with inflatable elements of 5 and 9 cm length were selected. It was found that for both 5 and 9 cm variants, the diastolic pressure augmentation was comparable to the intra-aortic balloon (see Figure 19). The afterload reduction was found to be comparable, if not better, than the intra-aortic balloon. For example, the peri-aortic jacket of 5 cm length decreased end-diastolic pressure by 10 mmHg more than the intra- aortic balloon. The exemplary device increased diastolic coronary flow by 50 mL/min and induced a larger flow reversal spike at the diastole/systole transition than observed during unassisted beats, providing compelling evidence of effective left ventricular afterload reduction (see Figure 20).

There was no evidence of trauma to the aorta after the acute (one day) experiment at the level of the peri-aortic jacket which concurs with the histological findings of chronic autologous skeletal muscle powered extra-aortic counterpulsation studies (aortomyoplasty)⁷.

Example 2

Experimental modelling studies have been performed with the aim of realising the design specification criteria detailed above. The preferred embodiments of the present invention have a dual inflatable element peri-aortic jacket because it has more symmetrical longitudinal aortic stress and strain characteristics and lower peak cyclical excursion of the aortic wall induced by the counterpulsator. This has theoretical benefits both in terms of rate of change of aortic blood volumetric flow with respect to time (dQ/dt) which is a crucial determinant of the clinical efficacy of counterpulsation, and in terms of mechanical fatigue of the aorta. However, a crucial question was whether there are additional benefits from increasing the number of inflatable elements from two to a greater value. Our investigations suggest otherwise.

Figures 30-33 are cross sectional views of a model representing the aorta in the centre of a peri-aortic jacket (i.e. where aortic deformation is maximal). These were derived by aerosol-spraying a butyl rubber O-ring of 2 mm and 99.1 mm section and inner diameter, respectively, in its resting 44 (circular) and deformed 45 states on A4 size graph paper. Deformation was achieved by compression with rigid discs 46 of 76.1 mm diameter to simulate the action of the inflatable elements in their inflated state. The aortic/ inflatable element diametric ratio was selected on the basis of what appeared pragmatic both in terms of manufacture and placement of the jacket around the aorta. (Subsequent studies revealed that the aortic deformation is relatively insensitive to this diameter ratio).

Figure 30 illustrates the simulated aorta in its resting state and compressed to a degree 5 associated with a clearance at the narrowest part of 20% of the resting internal diameter of the aorta. This deformation was associated with a cross-sectional area reduction to 51.5 % of the original value. The deformed aortic profile was associated with a minimal transsectional radius of curvature of 18 mm (i.e. 36.3% of the rest radius). It was concluded that in this experiment the minimal transsectional radius of curvature was 0 underestimated because the effect of lumenal pressure on the aortic wall profile was neglected. As a consequence, a more elliptical aortic curvature was generated in the model at the positions furthest from contact with the inflatable elements than would have been observed in vivo.

5 In order to attempt to model the effect of lumenal pressure and thereby provide a better realisation of the aortic deformation, the O-ring was constrained with bars 47 in an axis perpendicular to the action of the inflatable elements (see Figure 31) and this was associated with elevated minimum transsectional radius of curvature values of > 20 mm (i.e. >40.4% of the rest radius). _0 _{^ Λ}.

Figures 32 and 33 illustrate the effect of moving to a three-inflatable element design. For Figure 32, where the lumenal clearance was maintained at 20% of the resting diameter, although the reduction in cross-sectional area was to 41% of the original area, this was achieved at the expense of a reduction in the minimum radius of curvature to 10 mm (i.e. 5 20.2% of the rest radius) with a resultant increase in local aortic stress and strain. For Figure 33, where the minimum radius of curvature (during deformation) was similar to that measured in Figure 31 , the reduction in cross-sectional area was less: only to 54% of the original value.

0 These findings indicate that a two-inflatable element design is preferable to one comprising three (or more) elements. A two-inflatable element design is also associated with the added advantage of being easier to place around the aorta than a three (or more) inflatable element system because it is associated with less interference with other anatomical structures. Our fitting studies using clinical computer tomography data substantiate this conclusion.

Our short term animal experimental studies (see Example 1) have demonstrated that placement of a two-inflatable element peri-aortic jacket is relatively easy during the implantation procedure and that such a design is neither associated with visual nor histological evidence of aortic trauma.

References

1. Abou-Awdi NL, Frazier OH. The HeartMate: A left ventricular assist device as a bridge to cardiac transplantation. Transplantation Proceedings 1992;24:2002-2003.

2. Yacoub MH, Tansley P, Birks EJ, Banner NR, Khaghani A, Bowles C. A novel combination therapy to reverse end-stage heart failure. Transplantation Proceedings 2001 33(5):2762-4.

3. Rose EA, Gelijns AC, Moskowitz AJ, et al. Long-term mechanical left ventricular assistance for end-stage heart failure. New England Journal of Medicine.

2001 ;345(20):1435-1443.

4. De Vries WC, Anderson JL et al. Clinical use of the total artificial heart. New England Journal of Medicine. 1984;310: 273-278.

5. Moulopoulos SD, Topaz S, Kolff WJ Diastolic balloon pumping (with carbon dioxide) in the aorta - a mechanical assistance to the failing circulation. American Heart Journal 1962; 63: 669.

6. Arafa, OE, et al. Annals of Thoracic Surgery 1999; 67:645-651.

7. Pattison CW, Cumming DVE, Williamson A et al. Aortic counterpulsation for up to 28 days using autologous latissimus dorsi in sheep. J Thorac Cardiovasc Surg 1991 ;102:766-73.

Claims

CLAiMS

1. A blood circulation assistance device comprising: one or more cuff elements defining a chamber for receiving a blood conduit, the chamber being open at both ends of the one or more cuff elements for the blood conduit to extend therethrough and there being an aperture in the side of the one or more cuff elements between each end of the chamber for locating the one or more cuff elements about the blood conduit, the one or more cuff elements bearing two inwardly expanding inflatable elements for compressing the blood conduit, the inflatable elements being disposed diametrically opposite each other across the chamber.

2. A blood circulation assistance device according to claim 1 wherein two cuff elements define the chamber, the aperture being between the two cuff elements.

3. A blood circulation assistance device according to claim 2 wherein the two cuff elements, the inflatable elements and the chamber that they define are elongate, such that the chamber can receive the blood conduit longitudinally therethrough, with the cuff elements and the inflatable elements being parallel to the blood conduit.

4. A blood circulation assistance device according to claim 3, further comprising an inlet, leading to the two inwardly expanding inflatable elements.

5. A blood circulation assistance device according to claim 4 wherein the inlet leads to the centre of each inflatable element, along the longitudinal axis.

6. A blood circulation assistance device according to claim 4 wherein the inlet leads to one end of each inflatable element.

7. A blood circulation assistance device according to claim 4 wherein the inlet leads to both ends of each inflatable element.

8. A blood circulation assistance device according to claim 4 wherein the inlet leads to the side of each inflatable element, along their full length.

9. A blood circulation assistance device according to claim 6 wherein the inlet is substantially parallel to the longitudinal axis of the inflatable elements.

10. A blood circulation assistance device according to claim 6 wherein the inlet is at an acute angle to the longitudinal axis of the inflatable elements.

11. A blood circulation assistance device according to claim 4 wherein the inlet leads to the side of each inflatable element, at a point between the centre and the end of the longitudinal axis thereof.

12. A blood circulation assistance device according to any one of the preceding claims wherein the two inflatable elements are inflatable simultaneously.

13. A blood circulation assistance device according to claim 12 further comprising a manifold leading to the inflatable elements, the cross-section of the manifold leading to each inflatable element being different.

14. A blood circulation assistance device according to any one of the preceding claims wherein, at the maximum expansion of the two inflatable elements, opposing sides of a blood conduit received in the chamber do not contact one another.

15. A blood circulation assistance device according to any one of the preceding claims wherein, at the maximum expansion of the inflatable elements, the minimised trans-sectional radius of curvature of a blood conduit received in the chamber is maximised, preferably by having a minimal trans-sectional radius of curvature of at least 30% of the original value.

16. A blood circulation assistance device according to any one of the preceding claims wherein, at the maximum expansion of the two inflatable elements, a blood conduit received in the chamber has a reduction in its lumenal cross-section of less than 50% of its original value, preferably less than 51.5% of the original value.

17. A blood circulation assistance device according to any one of the preceding claims wherein the inflatable elements are made from a material which resists elastic deformation.

18. A blood circulation assistance device according to any one of the preceding claims wherein the ends of the inflatable elements are rounded.

19. A blood circulation assistance device according to any one of the preceding claims wherein the ends of the inflatable elements protrude longitudinally from the one or more cuff elements, along the axis of a blood conduit received in the chamber.

20. A blood circulation assistance device according to any one of the preceding claims further comprising a pump in fluid communication with the inflatable elements.

21. A blood circulation assistance device according to claim 20 wherein the fluid path from the pump to the inflatable elements has an increasing cross-section.

22. A blood circulation assistance device according to claim 20 or 21 wherein the fluid which communicates between the pump and the inflatable elements has a viscosity of between 8 x 10^"4 and 1.2x10^-3 Pa.s (0.8 and 1.2cP), preferably 1 x10^"3 Pa.s (1.OcP).

23. A blood circulation assistance device according to any one of claims 20 to 22 wherein the fluid which communicates between the pump and the inflatable elements is a fluorocarbon.

24. A blood circulation assistance device according to any one of claims 20 to 23 wherein the connection provided between the pump and the inflatable elements in order to effect fluid communication therebetween is flexible.

25. A blood circulation assistance device according to claim 24 wherein the flexible connection comprises a joint having a ball with a passage extending therethrough, connected rotatably at either end to a socket.

26. A blood circulation assistance device according to claim 24 wherein the flexible connection is concertinaed in order to provide flexibility.

27. A blood circulation assistance device according to any one of claims 24 to 26 wherein the flexible connection is lockable in a particular configuration.

28. A blood circulation assistance device according to any one of claims 20 to 27 wherein the pump is adjacent the one or more cuff elements and the aperture is located on the opposite side of the chamber from the cuff.

29. A blood circulation assistance device according to any one of claims 20 to 27 wherein the pump is adjacent to the one or more cuff elements and the aperture is located on the chamber at 90° with respect to the pump.

30. A blood circulation assistance device according to any one of claims 20 to 29 wherein the pump comprises an impeller rotatable about an axis to effect pumping, the impeller being axially moveable from a first position to a second position to effect reversal of the direction of pumping.

31. A blood circulation assistance device according to claim 30 further comprising a counterbalance, moveable in synchronicity with the impeller but in an opposing direction from the axial movement of the impeller so as to counteract the reaction of the movement of the impeller.

32. A blood circulation assistance device according to claim 31 wherein the counterbalance is movable parallel to the impeller.

33. A blood circulation assistance device according to claims 31 or 32 wherein the counterbalance comprises a second rotatable impeller, both impellers being rotatable about an axis to effect pumping.

34. A blood circulation assistance device according to any one of claims 30 to 33 further comprising a sensor capable of detecting whether the impeller is in the first or second position; and a control mechanism for shutting down the impeller in response to the sensor detecting that the impeller is locked in a position causing inflation of the inflatable elements.

35. A blood circulation assistance device according to any one of claims 20 to 29 wherein the pump comprises a rotatable impeller; an inlet port for drawing in fluid; an outlet port for ejecting fluid; and a valve assembly interposed between the rotatable impeller and the inflatable element, the valve assembly being slidable or rotatable from a first position in which the inlet port is in fluid communication with the inflatable element and a second position in which the outlet port is in fluid communication with the inflatable element, such that movement of the valve assembly between the first and second positions effects deflation and inflation of the inflatable elements, respectively.

36. A blood circulation assistance device according to any of claims 20 to 29 wherein the pump is beatable within the peritoneal cavity and is connected to the inflatable elements via a hydraulic tube.

37. A blood circulation assistance device according to any one of claims 20 to 36, wherein flow'guides are provided between the pump and the inflatable elements.

38. A blood circulation assistance device according to any one of the preceding claims further comprising a sleeve provided around the outer circumference of the one or more cuff elements.

39. A blood circulation assistance device according to any one of the preceding claims further comprising at least one band about the one or more cuff elements.

40. A blood circulation assistance device according to any one of the preceding claims wherein the one or more cuff elements are movable so as to increase or decrease the size of the chamber.

41. A blood circulation assistance device according to claim 40 wherein there are provided two or more cuff elements, connected by a lockable hinge.

42. A blood circulation assistance device according to any one of the preceding claims further comprising an inner sleeve located between the inflatable elements and the chamber.

43. A blood circulation assistance device according to any one of preceding claims further comprising one or more eyelets for attaching the blood circulation assistance device to a structure.

44. A blood circulation assistance device according to any one of the preceding claims wherein the inflatable elements between 3 and 15 cm long, preferably between 5 and 9 cm long.

45. A blood circulation assistance device according to any one of the preceding claims wherein the inflatable elements are inflatable once in each cardiac cycle of a patient fitted with the device.

46. A blood circulation assistance device according to any one of claims 1 to 44 wherein the inflatable elements are inflatable in the diastolic phase of each cardiac cycle of a patient fitted with the device or less frequently.

47. A blood circulation assistance device according to any one of the preceding claims wherein the device is locatable in the left paravertebral gutter of a human.

48. A blood circulation assistance device according to any one of the preceding claims further comprising an integral ECG electrode or electrodes for detecting the heartbeat of an individual.

49. A blood circulation assistance device according to any one of the preceding claims further comprising a position sensor, a pressure sensor or an accelerometer for detecting the heartbeat of an individual.

50. A blood circulation assistance device comprising : one or more cuff elements defining a chamber for receiving a blood conduit, the one or more cuff elements bearing an inwardly expanding inflatable element for compressing the blood conduit received in the chamber, the inflatable element being expandable such that, at its maximum expansion, the minimal trans-sectional radius of curvature of the blood conduit received in the chamber is maximised.

51. A blood circulation assistance device according to claim 50 wherein the minimal trans-sectional radius of curvature of the blood conduit is at least 30% of the original value.

52. A blood circulation assistance device according to claims 50 or 51 wherein, at the maximum expansion of the inflatable element, the reduction of the lumenal cross-section of the blood conduit is to more than 50% of its original value.

53. A blood circulation assistance device comprising: one or more cuff elements defining a chamber for receiving a blood conduit, the one or more cuff elements bearing an inwardly expanding inflatable element for compressing the blood conduit received in the chamber; and a pump, the pump comprising: a rotatable impeller; an inlet port for drawing in fluid; an outlet port for ejecting fluid; and a valve assembly interposed between the rotatable impeller and the inflatable element, the valve assembly being slidable or rotatable from a first position in which the inlet port is in fluid communication with the inflatable element and a second position in which the outlet port is communication with the inflatable element, such that movement of the valve assembly between the first and second positions effects deflation and inflation of the inflatable element respectively.

54. A blood circulation assistance device comprising: one or more cuff elements defining a chamber for receiving a blood conduit, the one or more cuff elements bearing an inwardly expanding inflatable element for compressing the blood conduit received in the chamber; and a pump in fluid communication with the inflatable element, the pump comprising an impeller rotatable about an axis to effect pumping, the impeller being axially movable from a first position to a second position to effect reversal of the direction of pumping, there being a counterbalance provided, movable in synchronicity with but in an oppositing direction from the axial movement of the impeller so as to counteract the reaction of the movement of the impeller.

55. A blood circulation assistance device according to any one of claims 50 to 54 further comprising a second inwardly expanding inflatable element for compressing a blood conduit received in the chamber.

56. A method of effecting counterpulsation of a blood vessel comprising: introducing an annular stent into the lumen of the blood vessel, at each end of a section of the blood vessel; providing an external band, around the blood vessel at each end of the section of the blood vessel such that a portion of the blood vessel is trapped between each external band and its respective annular stent; and effecting counterpulsation on the blood vessel between the two annular stents.

57. A method according to claim 56 wherein compression of the blood conduit is carried out using a blood circulation assistance device according to any one of claims 1 to 55.

58. A method according to claim 56 or 57 wherein each annular stent comprises a circumferential groove about its outer surface, for receiving its respective external band.