Blood circulation assistance device

A blood circulation assistance device (1), for location around a blood conduit (20). The device comprises: an inflatable bladder (10) moveable between a contracted form and an expanded form, for compressing the blood conduit (20) to provide counterpulsation. Pump means (30) in fluid communication with the bladder (10) move the bladder (10) from the contracted form to the expanded form. The pump means (30) comprises a centrifugal impeller (62) rotatable about an axis (61) to effect pumping. The impeller (62) is moveable axially between first and second positions to effect a reversal of the direction of pumping. Control means (50), in communication with the pump means, is capable of monitoring the cardiac cycle of an individual and triggering the pump means (30) to move the bladder (10) to the expanded form at diastole. An outer cuff, surrounds at least a portion of the bladder (10), providing an outer limiting extent to the movement of the bladder (10).

The present invention relates to a blood circulation assistance device and, in particular, a blood circulation assistance device capable of effecting counterpulsation.

Cardiac assist devices can help relieve the load on the heart and increase cardiac output. One type of cardiac assist device are those that effect counterpulsation. A variety of counterpulsation methods have been described for the treatment of acute and end-stage heart failure. The dual benefits of counterpulsation are improved systemic organ perfusion (notably the myocardium) during diastole and left ventricular afterload reduction. In order for counterpulsation to be effective, it is necessary to displace as large a volume of blood as is practicable from the systemic arteries (notably the aorta) at the beginning of diastole and to reverse this process prior to subsequent systole.

Typical devices include the intra-aortic balloon (IAB) counterpulsator, extra ventricular assist devices and Latissimus dorsi myoplasty. As such they are very useful for a wide range of patients, especially those rated as NYHA (New York Health Authority) Grades III and IV. Aortic counterpulsation was initially conceived by Clauss1(1961) and the intra-aortic balloon introduced in 1962 by Moulopoulos2. Despite its usefulness3the IAB device has a number of shortcomings that reduce its usefulness and long-term viability. The IAB device is highly invasive, requiring trans femoral catheterisation and provides the opportunity for infection and thrombogenic complications. In particular, intra-aortic balloon counterpulsation is associated with significant complications, notably, thromboembolism, infection and leg ischaemia. Moreover the system is non-ambulatory, only suitable for short support periods, and there is a risk of balloon perforation leading to gaseous arterial embolisation. As such, IABs are limited to hospital in-patients, particularly those in intensive care.

Since the development of the IAB, direct mechanical compression of the heart for circulatory assistance has been developed after Hayward4and Fischer5. However these techniques are relatively unproven, highly invasive, expensive and inapplicable to high-risk patients due to the possibly lethal trauma of surgery and the lack of any immediate benefit, despite their need for such an effect.

For almost two decades, mobilised and pulse-train stimulated skeletal muscle has been proposed as a method for effecting counterpulsation either by wrapping it around the aorta (aortomyoplasty) or by fashioning pouches or shunts in communication with the aorta.

For example, WO-A-93/05827 discloses an implantable heart-assist device comprising an extra-aortic balloon pump for insertion into a patient's vascular system. The extra-aortic balloon pump is powered by contraction of a skeletal muscle pouch connected to the balloon. Similarly, U.S. Pat. No. 4,979,936 discloses an autologous biologic pump motor comprising an expanding bladder located around a portion of an individual's aorta. The expanding bladder is powered by contraction of skeletal muscle surrounding a collapsible bladder that is connected to the expanding bladder.

The problem with these arrangements is that, in practice, the devices do not pump a sufficient volume of blood to assist a patient. This is because the devices use stimulated skeletal muscle and there is inadequate sustained power and suboptimal contraction and relaxation times using muscle as an actuator. Furthermore, since the devices rely on stimulated skeletal muscle, there is a requirement for a period of delay before the muscle can be utilised effectively,.

Recently, counterpulsation methods employing indirect electrohydraulic actuation have been disclosed such as in WO-A-99/04833. This document discloses a centrifugal or ferrofluid type pump for the transit of the fluid drive medium. However, this document does not disclose how the flow of hydraulic drive medium is reversed, which is important for providing effective counterpulsation.

The present invention seeks to alleviate one or more of the above problems.

The present inventor has overcome the disadvantages of the prior art, providing an implantable, minimally invasive extravascular aortic counter pulsator device which does not require direct blood contact, may be used for ambulatory purposes, and which provides an immediate benefit whilst minimising the possibility of infection or thrombogenic complications due to the lack of direct blood contact.

According to the present invention there is provided an extravascular aortic counterpulsator device comprising actuator means for compressing a blood vessel and control means for controlling the timing of the compression of the blood vessel by the actuator means.

The counterpulsator device may be an aortic diastolic counterpulsator device.

The actuator means may for example comprise a peri-aortic jacket that surrounds the aorta, or a sutured reinforced open weave vascular graft (for example Dacron™, known generically as polyester or polyethylene tetraphthalate (PET)) to replace or augment or protect diseased aorta, and having an expandable balloon interior and a relatively rigid exterior, and pump means attached to the control means such that upon triggering by the control means, the pump means causes the balloon interior of the peri-aortic jacket to expand and compress the blood vessel, thereby effecting counterpulsation. The pump means may for example pump a gas or liquid (such as sterile water, saline or other suitable fluid with viscosity characteristics 1 Pas to 103Pas) into the interior of the peri-aortic jacket.

The pump means may, for example, be controlled such that the expansion of the balloon interior of the peri-aortic jacket is subsequently followed by a shrinking (e.g. a relaxation, restoration or correction to the original form) of the balloon interior to effect expansion of the blood vessel.

Alternatively, the actuator means may apply a pressure upon only a part of the blood vessel upon triggering by the control means, compression being effected by the blood vessel being attached to a solid support (or adjacent structure) against which the actuator means applies pressure. For example the vessel may be the descending aorta which compresses against the rigid support of the spine (i.e. a vertebra) the actuator applying pressure to the aorta which compresses against the rigid support for the spine.

The control means may comprise a pacemaker device (for example one manufactured by Medtronics, Pacesetter, Telectronics or Vitatron) attached to the heart by sensor means and configured such that upon diastole the actuator means is triggered and diastolic counterpulsation effected.

The actuator means may be readily attached to the blood vessel, for example a peri-aortic jacket may have a relatively rigid exterior which is hinged or sprung such that one face of the exterior may be opened and the jacket placed around the blood vessel and the exterior face closed. Thus a partial opening can be produced and the jacket can be placed around the blood vessel and then subsequently closed and secured using a clip closure, ratcheted circumferential tie, or other suitable means i.e. surgical wire to secure the closure of the peri-aortic jacket

In the case of actuator means applying pressure against the descending aorta attached to the spine a jacket may be attached to the spine, for example by means of stitching or other means, such that the actuator may compress the blood vessel, for example, by means of an expandable balloon (or bladder) or other direct mechanical means.

The use of devices according to the present invention requires a minimally invasive surgical procedure since they do not reside within blood vessels nor require complex surgery or muscular conditioning6and thus cause minimal mechanical damage and trauma to blood vessels. Due to their purely mechanical nature they provide an immediate therapeutic benefit and therefore may be used with a wide range of patients for example (but not exclusively) Grade III and IV NYHA patient, particularly those with end-stage failure in functional grades III and IV, together with unstable angina patients who are not suitable for routine bypass surgery.

According to one aspect of the present invention, there is provided a blood circulation assistance device, for location around a blood conduit, the device comprising:compression means moveable between a contracted form and an expanded form, for compressing the blood conduit to provide counterpulsation;mechanical driving means, associated with the compression means, for moving the compression means from the contracted form to the expanded form;control means in communication with the mechanical driving means, the control means being capable of monitoring the cardiac cycle of an individual and triggering the mechanical driving means to move the compression means to the expanded form at diastole; andan outer cuff, surrounding at least a portion of the compression means, providing an outer limiting extent to the movement of the compression means,the compression means being locatable between the blood conduit and the outer cuff such that, in its expanded form, the compression means presses against the outer limiting extent of the outer cuff to compress the blood conduit.

According to another aspect of the present invention, there is provided a blood circulation assistance device comprising:a compression means, moveable between an expanded and a contracted form; mechanical driving means, associated with the compression means, for moving the compression means from the contracted form to the expanded form; and an outer cuff surrounding at least a portion of the compression means and providing an outer limiting extent to the movement of the compression means, the device being for use in a method of providing counterpulsation to the blood circulation of an individual comprising the steps of:locating the outer cuff about a blood conduit in the individual, the compression means being between the blood conduit and the outer cuff;monitoring the cardiac cycle of the individual; andeffecting counterpulsation on the blood conduit by operating the mechanical driving means to move the compression means from the contracted form to the expanded form at diastole, the compression means thus pressing against the outer limiting extent of the outer cuff and compressing the blood conduit.

Conveniently the compression means comprises at least one inflatable bladder.

Preferably the mechanical driving means comprises a pump in fluid communication with the at least one inflatable bladder, a fluid being provided in the pump and the at least one inflatable bladder.

Advantageously the pump is connected in fluid communication with the at least one inflatable bladder by a substantially rigid tube.

Conveniently the substantially rigid tube is less than 20 mm long.

Alternatively the pump is located adjacent the at least one inflatable bladder such that the pump is directly connected to the at least one inflatable bladder.

Advantageously the fluid is a liquid, preferably having a viscosity of up to 103Pas, more preferably from 1 Pas to 103Pas.

Conveniently the pump comprises a centrifugal impeller rotatable about an axis to effect pumping.

Preferably the impeller is moveable axially between first and second positions to effect a reversal of the direction of pumping.

Advantageously the pump further comprises first and second diffusers for receiving fluid from the impeller, the centrifugal impeller being axially moveable relative to the diffusers between a first position in which the impeller is in fluid communication with the first diffuser and a second position in which the impeller is in fluid communication with the second diffuser to effect a reversal of the direction of pumping.

Conveniently the pump further comprises first and second intakes for supplying fluid to the impeller, the intakes being located such that, in the first position, the centrifugal impeller is in fluid communication with the first intake and in the second position, the impeller is in fluid communication with the second intake.

Conveniently the pump further comprises an electromagnet for sliding the impeller between the first and second positions.

Preferably the pump is an Affeld pump such as is described in U.S. Pat. No. 5,346,458.

Advantageously the compression means comprises a plurality of inflatable bladders.

Conveniently the inflatable bladders are configured to be locatable symmetrically about the axis of the blood conduit.

Preferably the at least one inflatable bladder is made from a material having a tensile strength of from 15 to 35 MPa, preferably 20 to 30 MPa and more preferably 25 MPa.

Advantageously the at least one inflatable bladder is made from a material having a Modulus at 100% elongation of from 2 to 6 MPa, preferably 2.5 to 5 MPa, more preferably 2.64 MPa.

Conveniently the at least one inflatable bladder is made from a material having a modulus at 300% elongation of from 4 to 10 MPa, preferably 6 to 7 MPa, more preferably 6.23 MPa.

Preferably the device further comprises at least one plate connected to the compression means, the at least one plate being locatable adjacent the blood conduit such that when the compression means is in its expanded form the at least one plate compresses the blood conduit.

Advantageously the device comprises two opposing plates, locatable on either side of the blood conduit.

Conveniently the compression means and the mechanical driving means comprise a solid state compression means.

Advantageously the solid state compression means comprises at least one piezoelectric and/or electrostrictive compression elements.

Preferably the solid state compression means comprises an array of compression elements moveable from the contracted to the expanded form.

Conveniently the compression elements in the array are moveable to the expanded form sequentially so as to effect peristaltic compression of the blood conduit.

Preferably the outer cuff has a substantially circular cross-section and is locatable to surround the whole circumference of the blood conduit.

Advantageously the outer cuff is a substantially rigid shell.

Conveniently the outer extent of the outer cuff defines a plane, the outer cuff comprising two portions connected by a hinge perpendicular to the plane such that the outer cuff is moveable from an open configuration for positioning of the device about a blood conduit to a closed configuration for the device to effect counterpulsation of the blood conduit.

Preferably the outer cuff further comprises a clip for locking the two portions of the outer cuff in the closed configuration.

Advantageously the cross section of the outer cuff has an incomplete perimeter bounded by two opposing outer edges along the length of the cuff such that the device is locatable to surround a portion of the circumference of the blood conduit.

Conveniently the device further comprises a substantially rigid panel attachable to the opposing outer edges of the outer cuff such that the rigid panel co-operates with the outer cuff to define the outer limiting extent to the movement of the compression means.

Preferably the opposing outer edges of the outer cuff are attachable to a bone such that the bone co-operates with the outer cuff to define the outer limiting extent to the movement of the compression means.

Advantageously the device further comprises a cushion locatable between the blood conduit and the compression means for cushioning the blood conduit when the compression means moves to the expanded form.

Conveniently the cushion comprises a Teflon™ (known generically as polytetrafluoroethylene (PTFE)) pad.

Preferably the compression means is operable to move from the contracted form to the expanded form in 10 to 200 ms, to remain in the expanded form for between 1 and 300 ms and to return to the contracted form in 10 to 400 ms in order to effect counterpulsation.

Advantageously the device is capable of displacing up to 80 ml of blood from the blood conduit when the compression means moves from the contracted form to the expanded form about a blood conduit, preferably between 15 ml and 40 ml of blood.

Conveniently the blood conduit is an artificial blood conduit.

Preferably the artificial blood conduit is a vascular shunt.

Advantageously the diameter of the vascular shunt tapers from one end of the shunt to the other end.

Conveniently the artificial blood conduit is integral to the blood circulation assistance device.

Preferably the control means comprise a pacemaker.

Alternatively the pump means is powered electrically, the control means comprising means for monitoring the current to the pump means.

Advantageously the device does not comprise means to effect copulsation.

According to another aspect of the present invention there is provided a method of providing counterpulsation to the blood circulation of an individual comprising the steps of:providing a blood circulation assistance device comprising: compression means, moveable between an expanded and a contracted form; mechanical driving means, associated with the compression means, for moving the compression means from the contracted form to the expanded form; and an outer cuff, surrounding at least a portion of the compression means, and providing an outer limiting extent to the movement of the compression means;locating the outer cuff about a blood conduit in the individual, the compression means being between the blood conduit and the outer cuff;monitoring the cardiac cycle of the individual; andeffecting counterpulsation on the blood conduit by operating the mechanical driving means to move the compression means from the contracted form to the expanded form at diastole, the compression means thus pressing against the outer limiting extent of the outer cuff and compressing the blood conduit.

Conveniently the method uses the blood circulation assistance device described above.

Preferably the step of locating the outer cuff about the blood conduit comprises:moving the outer cuff into the open configuration;positioning the outer cuff about the blood conduit; andmoving the outer cuff into the closed configuration.

Advantageously the step of locating the outer cuff about the blood conduit further comprises the step of, after moving the outer cuff into the closed configuration:locking the two portions of the outer cuff with the clip.

Preferably the step of locating the outer cuff about the blood conduit comprises:inserting the blood conduit through the opposing outer edges of the outer cuff; andattaching the substantially rigid panel to the opposing outer edges of the outer cuff so that the whole circumference of the blood conduit is surrounded by the outer limiting extent defined by the outer cuff and the substantially rigid panel.

Advantageously the step of locating the outer cuff about the blood conduit comprises:inserting the blood conduit through the opposing outer edges of the outer cuff; andattaching the opposing outer edges of the outer cuff to a bone in the individual so that the whole circumference of the blood conduit is surrounded by the outer limiting extent defined by the outer cuff and the bone.

Conveniently the bone is a vertebra.

In an alternative, the method further comprises the steps of severing a blood vessel in the individual to provide two ends of the blood vessel and attaching either end of the artificial blood conduit to a respective end of the blood vessel.

Advantageously the method further comprises the step of removing a section of the blood vessel prior to attaching either end of the artificial blood conduit to the respective ends of the blood vessel.

Conveniently the method further comprises the steps of grafting either end of the vascular shunt to a blood vessel in the individual such that blood passes through the vascular shunt in parallel with the blood vessel.

Preferably the blood conduit is a blood vessel in the individual.

Conveniently the method further comprises the step of inserting a synthetic patch into the wall of the blood vessel to increase the diameter of the blood vessel.

Advantageously the blood vessel is the aorta of the individual.

Conveniently the blood vessel is the ascending aorta.

Preferably the blood vessel is the descending aorta.

Advantageously no copulsation is performed.

According to a further aspect of the present invention there is provided the use of a pump means for effecting counterpulsation on an individual, wherein the pump means comprises a centrifugal impeller rotatable about an axis to effect pumping, the impeller being moveable axially between first and second positions to effect a reversal of the direction of pumping.

In this specification, the word “comprising” means “including” or “consisting of” and the word “comprises” means “includes” or “consists of”.

In this specification, “mechanical” means apparatus that is mechanical, electromechanical (including solid-state electromechanical), or a hydraulic apparatus with mechanical components .

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

Referring toFIG. 1, a blood circulation assistance device1, in particular, an extravascular counterpulsator device, according to one embodiment of the present invention is provided. The blood circulation assistance device1comprises an actuator means2comprising a peri-aortic jacket10,11. The peri-aortic jacket10,11comprises an expandable or inflatable balloon or bladder interior10and a relatively rigid hinged exterior cuff11. The inflatable bladder10is of annular cross-section and is located about the outer circumference of the ascending aorta20of an individual. The inflatable bladder10extends parallel to the longitudinal axis of the aorta20. The inflatable bladder10is filled with a fluid12and is moveable between a contracted form (shown inFIG. 1) in which the fluid12is of relatively low pressure and an expanded form in which the fluid12is of relatively high pressure. The fluid is a liquid or a gas. In the embodiments in which the fluid12is a liquid, it may be a mineral oil, water or the like. The viscosity of the fluid is up to 103Pas, preferably between 1 and 103Pas. The viscosity of the fluid12can be increased, if required, by the addition of polysaccharides.

The cuff11is also of annular cross-section and is located about the outer circumference of the bladder10, extending parallel to the longitudinal axis of the aorta20. Consequently, the inflatable bladder10and the cuff11are substantially cylindrical and coaxially surround the aorta20. Furthermore, the inner circumference of the relatively rigid cuff11defines an outer extent to the movement of the inflatable bladder10, the inflatable bladder being unable to move outwardly of the outer extent even when in the expanded form.

The actuator means2also comprises pump means30attached (i.e. connected) to the interior of the bladder10of the peri-aortic jacket by a connecting tube40. Thus the pump means30are in fluid communication with the interior of the bladder10. The pump means30are attached by a lead31to pacemaker control means50,51. The pacemaker control means comprises a pacemaker50and a sensor51, the pacemaker being configured (i.e. programmed) to trigger at diastole so as to effect aortic counterpulsation of the blood vessel20, the sensor51being attached to the heart cardiac tissues (not illustrated) in order to monitor the cardiac cycle.

In use, the peri-aortic jacket is placed around the ascending aorta20such that the bladder10and the cuff11surround the whole circumference of the aorta20. The other components of the blood circulation assistance device are located in suitable positions within the body of the individual which positions will differ from person to person. The sensor51monitors the cardiac cycle of the individual and communicates this information to the pacemaker50. At diastole in the cardiac cycle, the pacemaker50sends a signal to the pump means30. In response to the signal, the pump means30pumps the fluid12through the connecting tube40and into the inflatable bladder10thus increasing the pressure of the fluid12in the inflatable bladder11. Consequently, the inflatable bladder moves from its contracted form to its expanded form. The interior circumference of the cuff11defines an outer limiting extent beyond which the inflatable bladder10cannot expand. Because of this outer limiting extent, the bladder10presses against the interior of the cuff11and expands inwardly, thus compressing the aorta20. In some embodiments the aorta20is completely occluded by the compression whereas in other embodiments, the aorta20is only partially occluded.

After a predetermined period of time, but also during diastole, the pacemaker50sends a further signal to the pump means30. In response to this further signal, the pump means30pumps the fluid12through the connecting tube40out of the inflatable bladder10. This decreases the pressure of the fluid12in the inflatable bladder10and the bladder moves from its expanded form to its contracted form. Because of the inherent resilience of the aorta20, the aorta returns to its initial form, after having been compressed, as the bladder10returns to its contracted form.

The sensor51continues to monitor the cardiac cycle of the individual and, at diastole, the above described process is repeated.

In some embodiments, the pump means30do not actively pump the fluid12out of the inflatable bladder10when the bladder10returns to the contracted form. In these embodiments, the inherent internal pressure of the aorta20automatically returns the bladder10to the contracted form once the pump means30ceases to pump the fluid12into the bladder10.

Referring toFIGS. 2 and 3, another embodiment of blood circulation assistance device1is shown. As in the previous embodiment, the blood circulation assistance device1comprises an inflatable bladder10of annular cross-section surrounded by a cuff11also of annular cross-section. In this embodiment the inflatable bladder10and the cuff11each comprise first and second sections12,13separated by first and second longitudinal breaks14,15. Thus, in fact, each of the first and second sections12,13of the inflatable bladder10and the cuff11comprise a section having a semi-circular cross-section.

The first and second sections12,13are connected by a hinge16attached to either edge of the first and second sections of the cuff11adjacent the first longitudinal break14. A releasable clip17is provided adjacent the second longitudinal break15. The releasable clip17comprises a loop18, one end of which is rotatably attached to the edge of the second section13of the cuff11adjacent the second longitudinal break15. The releasable clip17also comprises a catch19, one end of which is rotatably attached to the edge of the first section12of the cuff11adjacent the second longitudinal break15. The catch19is provided with a series of lugs24in which the other end of the loop18may be engaged.

In this embodiment, an additional pipe (not shown) is provided to connect the first and second sections of the bladder10in order to ensure that the two sections are in fluid communication with one another and can be pressurised.

In use of this embodiment, the clip17is released by rotating the catch19away from the cuff11and rotating the loop18so that it is no longer engaged in any of the lugs24. The clip is then in the released state shown inFIG. 3. The first and second sections12,13of the bladder10and the cuff11are then swung apart about the hinge16. The blood circulation assistance device1is then placed around a blood vessel in an individual and the first and second sections12,13are swung back together to surround the blood vessel. The clip17is then secured by rotating the loop18over the catch19so that the loop18engages in one of the lugs24and then rotating the catch19towards the cuff11to tension the loop18. The clip is then in the closed state shown inFIG. 2. Counterpulsation of the blood vessel is then effected as has been described in relation to the previous embodiment.

The advantage of such embodiments of the invention are that the blood vessel does not need to be severed in order locate the blood circulation assistance device1surrounding the blood vessel.

In some other embodiments, the bladder10and cuff11are also split into first and second sections12,13to allow the blood circulation assistance device1to be located around a blood vessel. However, in these embodiments, other means are provided to secure the two sections in the closed state. For example, in some embodiments of the invention, a circumferential tie such as a nylon band, or surgical wire are used instead of the clip17.

With reference toFIG. 4, another embodiment of the present invention is shown. The blood circulation assistance device1comprises an inflatable bladder10of annular cross-section surrounded by a cuff11also of annular cross-section, as in the previous embodiments. As in the previous embodiment, the bladder10and cuff11are split into first and second sections12,13, connected by a longitudinal hinge16. In this embodiment, first and second plates25,26are provided, attached to the inner circumference of the bladder10. The plates25,26are located opposing each other, each one in the centre of one of the semi-circular cross-sections of the first and second sections12,13. The first and second plates25,26are arcuate, the arc being coaxial with the cross-sections of the bladder10and cuff11and are each connected to their respective section of the bladder10by a short stem27.

In use of this embodiment, the blood circulation assistance device1is located around a blood vessel as described in relation to the previous embodiment. However, in this embodiment, the inner circumference of the bladder10is slightly smaller than the outer circumference of the blood vessel that the device surrounds. Thus the bladder10does not contact the blood vessel directly. Instead, the first and second plates25,26project inwardly so as to grip the exterior of the blood vessel. The blood vessel thus sits between the arcuate first and second plates25,26. When the bladder10is moved into its expanded form, the first and second plates25,26are pushed inwardly by the bladder10so as to compress the blood vessel. In other respects, the working of this embodiment of the invention is similar to the previously described embodiments.

In some alternative embodiments, the bladder10does not have an annular cross-section. For example, in some embodiments, the bladder10is elongate and is wrapped helically around the blood conduit before the outer cuff is secured around the bladder10.

Referring toFIG. 5, a further embodiment of the present invention is shown. In this embodiment, the blood circulation assistance device1comprises an inflatable bladder10surrounded by a cuff11. However, in this embodiment, the bladder10and the cuff11are not of annular cross-section. Instead, the bladder10and the cuff11have a cross-section having the shape of around 270° of arc of a circle. Thus the cross-section of the bladder10and the cuff11has an incomplete perimeter, comprising only around three-quarters of a circle. The incomplete section of the perimeter is bounded by two opposing edges28,29which extend along the length of the blood circulation assistance device1.

In use of this embodiment, the blood circulation assistance device1is located surrounding a blood vessel by sliding the blood vessel through the incomplete section of the bladder10and cuff11, between the two opposing edges28,29. The blood circulation assistance device1is of a size such that the bladder10, in its contracted form, fits snugly around the blood vessel. Thus there is no requirement for the blood circulation assistance device1to be hinged or for there to be additional securing means to hold the blood circulation assistance device1in place since it is held in place by friction alone.

A variation of this embodiment of the invention is shown inFIG. 6. This embodiment is identical to the previous embodiment except that a planar panel31is provided, extending between and attached to the two opposing edges28,29. The blood vessel20is thus surrounded by the inflatable bladder10and cuff11on one side and the panel31on the other side. InFIG. 6, the position of the bladder10in the expanded form is shown by the dashed line10′.

In use of this particular embodiment, the blood vessel20is inserted between the two opposing edges28,29of the blood circulation assistance device1, with the panel31removed. The panel31is then attached to each of the two opposing edges28,29so as to secure the blood vessel20with the blood circulation assistance device1. The panel31is attached to the blood circulation assistance device1by means of stitching, suturing, clips staples or other means. Counterpulsation of the blood vessel20is then effected as has been described in relation to the other embodiments of the invention, the dashed line showing the position of the bladder10in the expanded form. The advantage of this particular embodiment is that it is relatively easy to secure the blood circulation assistance device1around a blood vessel without the need to sever the blood vessel. Furthermore, the whole circumference of the blood vessel is surrounded by the blood circulation assistance device1so that there is a greater efficiency in the compressing of the blood vessel20.

A further variation of the previously described embodiment is shown inFIG. 7. In this embodiment, the blood circulation assistance device1is identical to the device of the previous embodiment except that no panel31is provided. Furthermore, the blood circulation assistance device1comprises two inflatable bladders10whose position in the expanded form is shown by the lines10′. In this embodiment, the blood circulation assistance device1is attached to a vertebra32at the two opposing edges28,29of the cuff11. Thus the vertebra32co-operates with the cuff11to define the outer limiting extent beyond which the bladder10may not expand.

In use of this embodiment, the blood vessel20is inserted between the two opposing edges28,29of the blood circulation assistance device1. The two opposing edges28,29of the cuff11are then attached to the vertebra32, by stitching, suturing, clips, staples or other means. Counterpulsation of the blood vessel20is then effected as has been described in relation to the other embodiments of the invention, the dashed lines showing the position of the bladder10in the expanded form. The vertebra32and the cuff11co-operate to define an outer limiting extent and restrain the outward expansion of the bladder10in order to increase the efficiency of compression on the blood vessel20.

In some alternative embodiments, the blood circulation assistance device1is attached to a thoracic rib of the individual rather than to the vertebra32.

Referring now toFIG. 8, a side view of a further embodiment of the present invention is shown, with the bladder10and cuff11cut away for clarity. In this embodiment, the blood circulation assistance device1comprises the coaxially arranged bladder10and cuff11as described in the previous embodiments. In this embodiment, the blood circulation assistance device1additionally comprises a cushion33wrapped around the blood vessel20. Thus the cushion33interposes between the bladder10and the blood vessel20in order to protect the blood vessel20under repeated compression. The cushion33is a pad made from Teflon™ or Dacron™.

In a variation of this embodiment, instead of the cushion33, a synthetic patch of, for example, Dacron™ is grafted into the wall of a blood vessel in order to increase the diameter of a section of the blood vessel. The blood circulation assistance device1is then located around this section of the blood vessel and counterpulsation is effected in accordance with the previously described embodiments. Because this section of the blood vessel has an increased diameter, it contains an increased volume of blood. Thus when the section of blood vessel is compressed an increased quantity of blood is displaced. Therefore, this procedure enables the blood circulation assistance device1to counterpulsate more effectively. Furthermore, the synthetic patch increases the resilience of the blood vessel which increases the effectiveness of counterpulsation in situations where the blood vessel has suffered hardening.

In certain variations of this embodiment, an entire section of a blood vessel is removed and replaced by a synthetic graft. The blood circulation assistance device1is then located around the synthetic graft in order to effect counterpulsation. Indeed, in certain embodiments, the blood circulation assistance device1is provided with an integral synthetic blood vessel as its innermost layer, which synthetic blood vessel can be grafted into the existing ends of the natural blood vessel. These procedures are particularly useful when the section of natural blood vessel in question is diseased and must, in any case, be removed. In these embodiments, it is not necessary for the bladder10and outer cuff11to have any means of opening (such as the longitudinal hinge16described above) in order to fit over the blood conduit because they are inserted between the ends of a blood vessel. In some embodiments, the synthetic graft has a larger internal diameter than the section of blood vessel that it replaces to increase the volume of blood that is contained in the graft and thus increase the volume of blood displaced by each compression of the blood circulation assistance device1.

In some embodiments of the invention, the outer cuff11comprises a plurality of separate cuff pieces. In some versions of these embodiments the cuff pieces are connected in series by interposing articulated sections. Thus the outer cuff11can be shaped so as not to follow a single straight line but a curve or series of curves. This allows the blood circulation assistance device1to be located on blood conduits which have a substantial curve and thus allows relatively large devices, able to displace large volumes of blood, to be implanted.

Indeed, in some embodiments, no articulated sections are required because the entire outer cuff11is preformed as a shaped unit to fit a particular section of the aorta20. This is achieved, in some embodiments, by having a range of preformed outer cuffs11of differing sizes and shapes, one of which is selected because it fits the blood vessel of a particular individual. In other embodiments, measurement of the individual's blood vessel are made pre-operatively, and a shaped outer cuff11is manufactured (for example, using a computer-numerically-controlled milling machine) specifically to fit around the blood vessel. Thus, in these embodiments, the outer cuff11is uniquely fitted for the blood vessel of the individual.

In other versions, there is no direct connection between the cuff pieces. In use, the bladder10is placed around the blood conduit and a series of cuff pieces are placed around the blood conduit and the bladder10in accordance with any of the procedures described above. Thus a series of sections of the bladder10are surrounded by a respective cuff piece. Although the efficiency of compression of the blood conduit is reduced in sections which are not surrounded by a cuff piece, the overall effect of the cuff pieces is sufficient to enable effective compression of the blood conduit and counterpulsation to take place.

Referring now toFIGS. 9,10and11, the location of the blood circulation assistance device1, in certain embodiments of the invention will be described. The aorta20comprises the ascending aorta21which leads from the heart (not shown) and the descending aorta22leading towards the rest of the body.

Referring toFIG. 10, in some embodiments of the present invention, the blood circulation assistance device1is located surrounding the ascending aorta21. The advantage of locating the blood circulation assistance device1surrounding the ascending aorta21is that the device1is located relatively closely to the heart and it has been found that only a relatively small displacement of blood (such as 20 ml) is required in order to achieve effective counterpulsation in this location. In addition, when the blood circulation assistance device1is located surrounding the ascending aorta21, it is downstream of the blood vessels23which lead to the brain. Therefore when the blood circulation assistance device1is located in this position it is more effective at increasing the supply of blood to the brain. Because the ascending aorta21is relatively short, it is necessary for the blood circulation assistance device1to be around 20 to 40 mm long in order that it fits around the ascending aorta.

In some other embodiments of the invention, shown inFIG. 11, the blood circulation assistance device1is located surrounding the descending aorta22. Because the descending aorta is longer than the ascending aorta21, it is possible for the blood circulation assistance device1to be longer, e.g. up to 60 mm long. Furthermore, calcification of the aorta may occur if the blood circulation assistance device1is located surrounding the ascending aorta21which is avoided if the blood circulation assistance device1is located surrounding the descending aorta22.

A side view of a further embodiment of the present invention is shown inFIG. 12. In this embodiment, a vascular shunt34is provided on the descending aorta22. The vascular shunt34comprises a hollow tube made from, for example, polyurethane or Dacron™, either end of which is grafted onto the wall of the descending aorta22, one end distal to the other. An aperture in the wall of the descending aorta22is provided beneath each graft so that blood passing through the aorta20passes not only through the descending aorta22but also through the vascular shunt34. Accordingly the blood flows through the aorta20in parallel with the blood following through the vascular shunt34.

In this embodiment, the blood circulation assistance device1is located around the vascular shunt34. Thus, in this embodiment, the blood circulation assistance device1is not located around a blood vessel but is instead located around another blood conduit, namely the synthetic vascular shunt34. The blood circulation assistance device1, itself, is substantially the same as in the previous embodiments.

In use, this embodiment operates in a similar manner to the previously described embodiments. Therefore, in response to signals concerning the cardiac rhythm of the individual, the bladder10is moved from its contracted to its expanded form at diastole, pressing against the outer cuff11and compressing the vascular shunt34. This effects counterpulsation by forcing blood out of the vascular shunt34.

The advantage of this particular embodiment is that the vascular shunt34can be made considerably longer than any one section of the aorta20. This allows for easier access to the blood conduit when the blood circulation assistance device1is fitted and allows for the blood circulation assistance device1, itself, to be longer and so displace more blood at each compression. Thus, in some versions of this embodiment, the blood circulation assistance device1is long enough to displace up to 80 ml of blood when the vascular shunt34is compressed.

A further advantage of this embodiment is that the blood circulation assistance device1can be located about the vascular shunt34outside the body under straightforward conditions and then the combination of vascular shunt34and blood circulation assistance device1is implanted into an individual simultaneously. Indeed, in certain embodiments, the blood circulation assistance device1and vascular shunt34are formed as an integral unit.

In some further variations of this embodiment, the vascular shunt34has an interior diameter that tapers from one end to the other. In some embodiments, the distal end of the vascular shunt34has a narrower diameter than the proximal end but in other embodiments the proximal end of the vascular shunt34has a narrower diameter than the distal end. The effect of the tapering of the diameter is that blood is preferentially expelled from the end of the vascular shunt34with the wider diameter when the vascular shunt34is compressed. This can be useful when it is desired to increase the supply of blood to a particular part of the circulation adjacent to the wider end of the vascular shunt34.

Referring now toFIG. 13, a longitudinal cross-sectional view of a blood circulation assistance device1in accordance with a further embodiment of the invention is shown. The blood circulation assistance device1comprises an outer cuff11being generally tubular in form and having a central longitudinal lumen35through which a blood vessel20, or other blood conduit, may extend. The lumen35is narrowest at either end of the cuff11, being of approximately the same diameter as the outer diameter of the blood conduit which it surrounds, thus gripping the blood conduit20. The inner section of the lumen is recessed such that the lumen is widest at the centre of the cuff11. On two opposing sides of the cuff11, at the broadest section of the lumen35, are provided apertures36,37, leading to the pump means30. In some embodiments, the apertures36,37lead to the pump means30via a connecting tube40that bifurcates from the pump means30to connect separately to the two apertures36,37. In other embodiments, no connecting tube40is provided and the two apertures36,37connect directly to the pump means30.

An inflatable bladder10is provided over each of the two apertures36,37, on the interior of the cuff11such that each bladder is in fluid communication with the pump via its respective aperture36,37. Each bladder10is moveable between a contracted form when its internal pressure is relatively low and in which each bladder10resides within the recessed section of the lumen35and an expanded form (as is shown inFIG. 13) when the internal pressure is relatively high and in which each bladder extends into the central lumen of the cuff11, thus compressing the blood vessel20.

In use, the pump means30drives fluid through the apertures36,37at diastole in order to increase the pressure within the two bladders10and move them from their contracted form to their expanded form in order to compress the blood conduit20. Subsequently, the pump drives fluid out from the two bladders10, through the apertures36,37to move the bladders10from their expanded form to their contracted form thus releasing the compression on the blood conduit20. In this way, counterpulsation is effected.

It is to be appreciated that, in this embodiment of the invention, two bladders10are provided, on opposing sides of the blood conduit20that they surround. In alternative embodiments of the invention, more than two bladders10are provided. In particular embodiments, three, four, five or even more bladders10are provided around the blood conduit20. It is preferred, however, when a plurality of bladders10are provided, that the bladders are spaced equidistantly around the blood conduit20so that the bladders are symmetric about the longitudinal axis of the blood conduit20.

In embodiments of this invention, the inflatable bladder or bladders10are fabricated using a flexible, fatigue resistant material suitable for implant applications. In some embodiments, the material is resilient. For example a flexible polymer film such as poly ethethylene terephthalate (PET) is used in some embodiments or resilient classes of polymer such as a linear polyurethanes, silicones or thermoplastic elastomers are used in other embodiments. It is preferred that the material has the following range of material properties. The tensile strength is between 15 and 35 MPa, preferably 20 to 30 MPa more preferably 25 MPa. The Modulus at 100% elongation is between 2 and 6 MPa, preferably 2.5 to 5 MPa, more preferably 2.64 MPa. The Modulus at 300% elongation is between 4 and 10 MPa, preferably between 6 and 7 MPa, more preferably 6.23 MPa.

In some embodiments, the inflatable bladder or bladders10are made from a braided structure or fabric to restrict strain and control when in the expanded form.

Suitable materials which may be selected for the fabrication of the bladder10are listed in the following table.

In embodiments of this invention, the outer cuff11is fabricated using medical plastics or metallic alloys approved for such use. Preferably, the material has the following properties. The tensile strength is from 70 to 80 MPa, more preferably 76 MPa. The Flexural Modulus is from 2 to 4 GPa, more preferably 2.8 to 3.4 GPa, more preferably 3.1 GPa. Examples of suitable materials are listed in the table below.

The properties required for the material from which the cuff11is made depend on factors such as its intended location, and the volume of blood it displaces when the blood conduit is compressed. For example, in the ascending aorta, if a thin, radio opaque construction is required then, a medical alloy such as titanium CP is used for fabrication, or alternatively a rigid polymer such as poly etheretherketone (PEEK) containing a radio opacifying agent is used.

In some embodiments of the invention, the outer cuff11is not made from a rigid material. In these embodiments the outer cuff11is made from a deformable but non-extensible material such as a fabric. In some of these embodiments, the cuff11is partly formed in situ, with a length of fabric being stitched around a blood conduit and the bladder10, in the individual. However, it is particularly important in all of these embodiments that the material be non-extensible such that the cuff11is able to define an outer limiting extent beyond which the bladder10may not extend such that the expansion of the bladder10presses against the cuff11to compress the blood conduit more efficiently.

In embodiments of this invention the pump means30is a mechanical pump powered from a battery. The battery is connected to a coil, which is also implanted within the individual, just beneath the skin such that the battery can be recharged by locating an external coil adjacent the internal coil and transferring energy between the two coils by induction.

InFIGS. 14 and 15a pump means30in accordance with certain embodiments of the invention is shown schematically and will now be described. The pump means30is a radial pump and comprises an electric motor60linked to a rotatable axle61. At one end of the rotatable axle61is attached a circular radial centrifugal impeller62. The impeller has intakes63,64, adjacent its hub65, on each side. One intake63leads from a reservoir66, the other intake64leads from a holding tank67. A washer68,69is provided on each side of the impeller, adjacent a respective intake63,64.

The impeller62is axially slideable from a first position (shown inFIG. 14) in which one of the washers68blocks the intake63from the reservoir66but the intake64from the holding tank67is clear and a second position (shown inFIG. 15) in which the other washer69blocks the intake64from the holding tank67but the intake63from the reservoir66is clear. An electromagnet70is provided to slide the axle61and the impeller62between the first and second positions.

The intakes63,64lead outwardly, through the interior of the impeller62, to discharge ports71at the rim of the impeller62. Adjacent the rim of the impeller62are two diffusers72,73. One diffuser72leads back to the reservoir66. The other diffuser73leads back to the holding tank67. When the impeller62is in the first position the discharge ports71feed into the diffuser72leading to the reservoir66and in the second position the discharge ports71feed into the diffuser73leading to the holding tank67.

The reservoir and holding tank contain the fluid12, as described in the first embodiment. The holding tank67is in fluid communication with the bladder10of the blood circulation assistance device1via the connecting tube40.

In use, the impeller62is rotated on the axle61at high speed by the motor60. The impeller62is maintained in the first position by the electromagnet70so that the intake64from the holding tank and the diffuser72to the reservoir66are open and the intake63from the reservoir66and the diffuser to the holding tank67are closed. Thus the impeller62drives the fluid12from the holding tank67to the reservoir66. Since the holding tank67is in fluid communication with the bladder10, the pressure of fluid12within the bladder10is kept relatively low and so the bladder10is maintained in its contracted form.

At diastole, a signal from the control means50results in the electromagnet70sliding the axle61such that the impeller62moves to the second position. The impeller62continues to be rotated by the axle61in the same direction. Now, however, the intake64from the holding tank67and the diffuser72to the reservoir66are closed and, instead, the intake63from the reservoir66and the diffuser73to the holding tank67are open. Accordingly, the impeller62drives the fluid12from the reservoir66to the holding tank67, increasing the fluid pressure in the holding tank67and, therefore, the fluid pressure in the bladder10. Thus the bladder is moved into its expanded form.

Subsequently, but still during diastole, the control means50signals the electromagnet70to return the impeller to its first position and the process is repeated.

In some alternative embodiments, the pump means30does not comprise the holding tank67. In these embodiments, the diffuser73that would otherwise lead to the holding tank67instead leads directly to the bladder10. Similarly, the intake64that would otherwise lead from the holding tank67instead leads directly from the bladder10. Thus, in these embodiments, the pump means30is integral with the outer cuff11and is directly connected to the bladder10.

It has been determined that, in essence, the efficacy of counterpulsation is a function of the rate of blood displacement and refill flow from the section of the blood vessel in contact with the bladder10. In other words, a high rate of change of blood flow (dQ/dt) and a rapid flow reversal of fluid to and from the bladder10are desirable. This is particularly important under conditions of cardiac failure which is normally characterised by an elevated heart rate (tachycardia) which limits the diastolic period. The advantage of the type of pump means30described above is that the direction of pumping can be reversed very rapidly because the direction of rotation of the impeller62does not have to be changed in order to change the direction of pumping. This is possible because the pump means comprises a radial pump and linear actuator integrated into one moving part. Longitudinal displacement of the radial pump results in alignment with either an inlet or outlet manifold. In this way, high dQ/dt and extremely rapid flow reversal of fluid to and from the bladder10can be achieved with an extremely compact pump means30.

Furthermore, the pressure in the holding tank67, and thus in the bladder10, can be maintained for extended periods of time. This has the effect of causing a powerful, sustained compression of the blood conduit about which the bladder10is located to result in effective counterpulsation. In particular, a pump of this type is capable of causing the bladder10to move from the contracted to the expanded form in between 10 and 200 ms; maintaining the bladder10in the expanded form and the blood conduit compressed for between 1 and 300 ms; and returning the bladder10to the contracted form in 10 to 300 ms.

A further advantage of a pump means30of this type is that the monitoring of the cardiac cycle of the individual to whom the blood circulation assistance device1is fitted can be measured using the pump means. This employs the principle that the current drawn by radial pumps is inversely related to afterload. Thus, for an electrohydraulic pump means30as described above, coupled to an extra-aortic counterpulsator comprising an inflatable bladder10and an outer cuff11, aortic pressure can be determined from the current profile in the motor60for the purposes of synchronisation of the blood circulation assistance device1with the cardiac cycle.

Thus, in some embodiments, a current monitor74is provided, connected to the electrical contacts that power the motor60. The current monitor74measures the current to the motor60over time. In use of the blood circulation assistance device1, the current to the motor60changes cyclically over the same time period as the cardiac cycle of the individual. In particular, as the pressure in the blood vessel of the individual falls at diastole, the electrical current supplied to the motor60also falls. Thus the period of diastole is determined by the current monitor74without the need to monitor the cardiac cycle of the individual directly. When the current monitor74determines that the cardiac cycle has reached diastole, the current monitor74signals the motor60to effect pumping to move the inflatable bladder10to the expanded form to cause counterpulsation.

In some of these embodiments of the invention, the current monitor74is provided in addition to the pacemaker50and sensor51that have been described above in order to serve as an integrated control means. However, in some other embodiments, the pacemaker50and sensor51are not provided and the current monitor74is the sole control means. In these embodiments, when the blood circulation assistance device1is started, the current monitor74does not have any starting data as to what point in the cardiac cycle has been reached. Accordingly the current monitor74initially signals the motor60to effect several test pumps on the blood vessel and measures the current during these test pumps. In response to the variation of the electrical current to the motor60during these test pumps, the current monitor74calculates the position reached in the cardiac cycle and operates as has been described previously. While the initial test pumps may not be at diastole and therefore may not cause counterpulsation, they are relatively few in number and do not cause any undesirable side-effects.

A particularly preferred pump means30is an Affeld pump which is described in greater detail in U.S. Pat. No. 5,346,458, which is incorporated herein by reference.

In order to effect expansion of the inflatable bladder10in the above described time periods, it is important that the connecting tube40between the pump means30and the bladder10be as short and wide as possible. Preferably the connecting tube is less than 20 mm long. This ensures that there is the shortest possible delay between the activation of the pump means and the expansion of the bladder. Furthermore, it is preferred that the connecting tube40be substantially rigid to ensure that it does not expand during an increase in the pressure of the fluid12which would result in reduced efficiency. Indeed, in a particularly preferred embodiment, the pump means30is located so close to the bladder10that no connecting tube40is required, the housing of the pump means30and the outer cuff11forming an integral, rigid unit. In this embodiment the pump means30is directly connected to the bladder10.

It is to be appreciated that the provision of a pump means30having centrifugal impeller62which is axially moveable to effect reversal of the direction of pumping allows the pump means to be relatively small. This, in turn, allows the pump means30to be directly connected to the bladder10relatively easily, thereby minimising dead space and leading to further improvements in the dynamic response.

In some embodiments, a pacemaker50and a sensor51are not provided. Instead, the cardiac cycle of the individual to whom the blood circulation assistance device1is fitted is measured by a pressure sensor attached to the blood vessel on which the device1is located. The pressure sensor is located adjacent to the outer cuff11on the blood vessel and measures the pressure of blood in the blood vessel over time. The pressure sensor is connected to the pump means30and, when the pressure sensor detects that the cardiac cycle is at diastole, the pressure sensor signals the pump means30to effect pumping to cause compression of the blood vessel.

In some embodiments of the present invention, the blood circulation assistance device1does not comprise a bladder10and pump means30. In these embodiments, a solid state compression means and mechanical driving means are provided. In certain embodiments these comprise piezoelectric materials or electrostrictive materials (i.e. materials that contract in response to an electric field) such as electrostrictive polymers.

Referring toFIGS. 21 and 22, one such embodiment will now be described. The blood circulation assistance device1comprises an outer cuff11that is substantially the same as the outer cuff11described in relation to the previous embodiments of the invention. Accordingly, the outer cuff comprises a substantially cylindrical tube. Located around the inner circumference of the outer cuff11are an array of radially inwardly extending compression elements80. The compression elements80are arranged in four axially extending lines, spaced equidistantly about the interior circumference of the outer cuff11, each line comprising six compression elements80. The inner end of each compression element80, distant from the outer cuff11, is adjacent to the exterior of the blood conduit20about which the blood circulation assistance device is located.

Each of the compression elements80comprises a piezoelectric material which expands inwardly when an electric current is applied to the material from a contracted form to an expanded form. Each of the compression elements80is in electrical communication with a pacemaker50which, in turn, is connected to a sensor51as described in previous embodiments.

In use, the blood circulation assistance device1is located around a blood conduit20as has been described in the previous embodiments. Thus in certain embodiments, the outer cuff11comprises two separate hinged sections in order allow fitting of the cuff11about the blood conduit20. Prior to diastole, an electric current is not supplied to the compression elements80and thus each of the compression elements80is in its contracted form as shown inFIG. 21. At diastole the pacemaker50supplies an electric current to each of the compression elements80thus causing the compression elements80to move to their expanded form. As each compression element80moves, it contacts and compresses the blood conduit20. The current is maintained for a predetermined length of time, thus maintaining the blood conduit20in a compressed form. The pacemaker50then stops the electric current to the compression elements80, in response to which compression elements80return to their contracted form and release the blood conduit20from compression. The process is then repeated in order to effect counterpulsation.

The advantage of such solid state compression means is that they are considerably more efficient in compressing the blood conduit than embodiments in which a bladder10and pump means30are used. Therefore, a smaller or longer lasting power supply can be provided. Furthermore, because there is no requirement for a pump or a motor, the blood circulation assistance device1, itself, can be considerably smaller than is otherwise possible. In addition, in these embodiments, there is no requirement for the provision of a fluid12and associated hydraulic equipment and so the blood circulation assistance device1is more reliable.

In some variations of these embodiments, the pacemaker50does not supply an electric current to all of the compression elements80in the array simultaneously. Instead, the electric current is initially supplied to the four compression elements80at one end of the outer cuff11in order that they move to the expanded form and compress the blood conduit20. Subsequently, the adjacent four compression elements80, further along their respective lines in the array, are supplied with current so that they move to the expanded form and compress the blood conduit20. This process is then continued with each set of four compression elements being moved to the expanded form until all of the compression elements80in the array are in the expanded form. Thus the compression elements80are activated sequentially to cause peristaltic compression of the blood conduit20. This provides a pulsatile motion to the blood in the blood conduit20as it is compressed.

It is to be appreciated that, in these embodiments of the invention, it is advantageous that the compression elements80expand as much as possible when they move from the contracted to the expanded form. This ensures that the blood conduit20is compressed as much as possible and a large volume of blood in the blood conduit20is displaced. It is known in the art to provide a flat strip that comprise a layer of piezoelectric material and a layer of another material such that, upon the application of an electric current, the layer of the piezoelectric material expands relative to the other layer causing a bending of the layers and a linear extension of the strip. The distance that the strip extends upon the application of an electric current can be increased if the strip is initially wound into the form of a helix. In this form, when the electric current is supplied to the piezoelectric material, the helix expands axially a distance greater than the linear extension of the flat strip. Furthermore, the helix can, itself, be wound into a larger helix whose axial extension on the application of an electric current is even greater than the axial extension of the initial helix. This process can be repeated many times, with each helix being wound into a larger helix having a greater axial extension than the previous helix. Thus a compression element80having the necessary expansion in order to compress the blood conduit sufficiently can be made by constructing the compression element80from a piezoelectric strip wound into successive helices enough times to create the required axial extension upon the application of an electric current.

Further details of the piezoelectric and electrostrictive materials that can be used in connection with these embodiments of the invention are disclosed in the following documents, each of which is incorporated herein by reference. WO-A-01/47318, GB-A-2322232, WO-A-01/47041, U.S. Pat. Nos. 6,111,818, 5,215,446, 5,136,201, 4,633,120, 6,084,321, 6,249,076, 6,109,852, WO-A-92/10916, and WO-A-99/17929.

In embodiments of the present invention, the blood circulation assistance device1, alone, is generally sufficient to assist an individual's circulation by effecting counterpulsation. Therefore, additional assistance for the individual's blood circulation (such as copulsation) is not usually required once the blood circulation assistance device1has been implanted.

EXAMPLES

Typical early prototype devices described above have been evaluated in a series of in vitro models operating under static and dynamic modes7using a cardiovascular simulator equipped with an artificial aorta8(supplied by Institute of Biomedical Technology Hydraulics Laboratory, University of Ghent, NL). The blood circulation assistance device under test was an extra-aortic counterpulsator having two inflatable bladders. The extra-aortic counterpulsator had a length of 50 mm, internal diameter of 33 mm and a total bladder volume of 15 ml. The extra-aortic counterpulsator was capable of displacing 20 ml blood at each compression. The results summarised in the table below from the static model were compared with the performance of intra aortic balloon counterpulsation (Datascope System 90 equipped with a 40 cc intra aortic balloon: 9.5 French Catheter Scale; cat nos. 0334-00-1377-03 R1).

It is to be noted, with respect to the above results, that the intra-aortic balloon tested displaces 40 ml of blood on each compression whereas the extra-aortic counterpulsator displaces only 20 ml of blood on each compression. Therefore, the extra-aortic counterpulsator actually provides a greater percentage change in perfusion per ml of blood displaced than the intra-aortic balloon.

The pressure output graphs of these experiments are shown asFIG. 16for the intra-aortic balloon (IAB) andFIG. 17for the extra-aortic counterpulsator. As can be seen from the pressure graphs, the extra-aortic counterpulsator causes an increase in pressure at diastole to a similar extent as the intra-aortic balloon.

In this example, the intra-aortic balloon used in Example 1 was compared with a single bladder extra-aortic counterpulsator under dynamic conditions. The extra-aortic counterpulsator had a length of 50 mm, an internal diameter of 33 mm and a total bladder volume of 40 ml. The extra-aortic counterpulsator displaced 40 ml of blood on each compression. The intra-aortic balloon and the extra-aortic counterpulsator were signalled to compress on alternate diastoles of the simulated cardiac cycle. The results of the experiments are shown in the table below. Furthermore, pressure time curves measured on the cardiovascular simulator are shown as follows: without circulation assistance (FIG. 18); with intra-aortic balloon assistance (FIG. 19) and with extra-aortic counterpulsator (EAC) assistance (FIG. 20).

As can be seen on comparison ofFIGS. 19 and 20, the extra-aortic counterpulsator was capable of effecting similar increases in pressure at diastole as the intra-aortic balloon. Accordingly, this example shows that the extra-aortic counterpulsator is able to effect counterpulsation to an extent sufficient to have a positive effect on a patient in need of such treatment.

References

1Clauss R H; J Thorac. Cardiovasc.Surg. 42, p447 (1961)2Moulopoulos S D et al; ‘Diastolic balloon pump assistance and early surgery in cardiogenic shock’ Am.Heart J. 63 p669 (1962)3Mundth3 E D., Assisted Circulation in Gibbon's Surgery of the Chest, Editors Sabiston D C and Spencer F C, Saunders p1490–1514 (1983)4Hayward M P et al; supra WO 92/085005Fischer E I; Ann.Thorac.Surg., 60, p417–421 (1995)6Carpenter et al ‘Myocardial Substitution with a Stimulated Skeletal Muscle: First Successful Clinical Case’ The Lancet p1267 (June 1985)7Segers P, Dubois F, Wachter De, Verdonck P ‘Role and Relevancy of a Cardiovascular Simulator’ Cardiovascular Engineering, 3, p48 (1998)8Verdonck P University of Ghent, Institute of Biomedical Technology Hydraulics Laboratory.