GB2414672A

GB2414672A - Vascular assist prosthesis

Info

Publication number: GB2414672A
Application number: GB0407410A
Authority: GB
Inventors: Nicholas Michael Turner
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-04-01
Filing date: 2004-04-01
Publication date: 2005-12-07
Also published as: GB0407410D0

Abstract

A vascular assist prosthesis comprising a sheet E having multiple electromechanical contractile regions B with discrete electrical control connections C which are individually controlled and connected to a common earth terminal D. The prosthesis is fastened around a fluid-containing vessel F or limb to form a tubular structure and the electromechanical regions B form a series of rings which are activated in sequence to provide a compression wave which pumps fluid in the direction of the wave. A combined power supply and control unit containing a rechargeable battery, battery charger and electronic charge indicator may be either integral with the prosthesis or connected to it by an electrical cable. Alternatively the control unit may have an antenna enabling the battery to be charged by an external charger. The power supply indicator may also be external. The prosthesis may include perforations A for colonisation and anchoring by bodily tissue.

Description

24 1 4672 Minimally Invasive Vascular Assist Prosthesis This surgically

implantable device, would provide augmentation of the often inadequate natural system of venous outflow from a limb, by actively promoting the flow of blood in a vein back towards the heart, in opposition to the pull of gravity.

By doing so it would prevent vascular reflex and stasis of blood in bodily extremities;- problems that may result from existing vascular disorders or from extended periods of immobility, and which may cause further vascular damage or frequently fatal blood clots.

The device could be used therefore to treat Chronic Venous Insufficiency (CVI), which is often the consequence of damage to venous valves caused by Deep Vein Thrombosis (DVT). It could also be used to treat individuals in which there is a congenital absence of valves to begin with.

Valves normally act to allow blood flow in one direction only; back towards the heart. When a person is standing, this mechanism prevents blood from pooling in the calves and feet.

The reflux of blood in individuals with incompetent or absent valves, often causes swelling of the limb, varicose veins, pain, ulceration, skin changes and an elevated risk of future DVT and Pulmonary Embolism.

The vascular prosthesis is not a valve per se, but by introducing preferential flow in one direction, will perform the same vital function for a person into whom it is implanted; resistance against the tendency for blood to fall back towards the feet and promotion of flow back towards the heart.

The device is modelled on biological structures such as the animal oesophagus and intestinal tract, or the insect heart, which achieve active transport of their contents by progressively and sequentially contracting sections along their length to produce a wave of preferential flow in one direction.

The device is not an artificial vein or a conventional vascular prosthesis.

It is designed as a vein massaging device rather than an artificial vessel, valve or pump to be inserted into the natural vascular system.

Existing vascular prostheses are difficult to integrate with biological veins and necessitate the incision of veins and contact between blood and artificial materials, generating precisely those medical risks which this device is designed to avoid.

Current surgical procedures to address reflex of blood seen in CVI, have achieved limited success. Both implanted artificial valves and biological valves transplanted 2.

from elsewhere in the body, often develop blood clots and fail, often as a result of the inherently aggressive and invasive nature of surgical intervention.

Incision of blood vessels in vascular surgery presents a risk of initiating DVT because clotting factors are released from the incised vessel wall, into the vessel lumen. The open design of this device however, allows it to be placed externally around a vein and encourage unidirectional flow in it, by the sequential contraction of separate bands of an artificial analogue of biological muscle. The device and the procedure to implant it, would be of particularly low invasiveness by the usual standards of vascular surgery.

Only the distal deep veins normally possess valves. Valve-less perforator and superficial veins however, are frequently forced to assume some of the capacity of deep veins occluded by DVT; a role for which they are not structurally suited.

In the absence of valves, an increased volume of blood tends to cause these veins to swell, resulting in structural damage to their walls and often triggering various related skin changes.

The ability of the device to confer the function of a valve would enable such veins to be functionally upgraded, in support of their increased post-thrombotic role.

The vascular assist prosthesis could also be used to prevent the collapse of a venous bypass after vascular surgery, by maintaining adequate pressure in the system.

Natural venous valves are passive structures which maintain the direction of blood flow efficiently, only when muscles compress the veins and propel blood through them. The natural mechanism of valves and muscular pump only prevents stasis of blood when a person exercises the relevant muscles of the limb in question. In individuals with CVI, the muscular pump is often insufficient to produce adequate blood flow. Often, it may itself result in reflux problems, because incompetent valves are unable to prevent blood being propelled equally in the wrong direction.

The device would if periodically recharged by electromagnetic induction however, continually and actively regulate the flow of muscle-pumped blood.

Conversely, it would also prevent stasis of blood in the extremities caused by the long periods of immobility necessitated by air travel for example, which may constitute a risk of DVT and frequently fatal Pulmonary Embolism.

In addition to addressing blood flow problems of CVI the device could be implanted with prophylactic benefits therefore, in individuals with a higher risk of DVT such as those who are bedridden or immobile for an extended period, suffer from paralysis of a limb, have suffered a previous DVT or have congenital clotting or valve abnormalities.

As shown in fig. I,the device would be supplied in an open form; a single rectangular sheet (e) comprising a base material of a mechanically compliant, biocompatible and electrically insulating polymeric material, onto which are bonded, concentric bands of a flexible Electroactive Polymer, or E.A.P. (b). Four bands are shown in the diagrams merely as an example. Each of these bands is contained within its own sealed, electrically insulating polymeric film, penetrated only by electrodes to supply power. A sealed f lm is particularly necessary for 3_.

those kinds of EAP that utilise the mechanism of ion exchange, in order to contain the relevant electrolyte solution. EAP's are a varied and growing class of new materials which have the property of contracting in a manner analogous to biological muscle when electrical energy is applied. One example is the Ionomer Polymer-Metal Composite that utilises Nafion09 (perfluorosulphonate) and Flemion(perfluorocaboxylate), as base polymers.

No particular EAP is integral to the design of my device however. What is important are the unique electromechanical properties of EAP's as a class of materials.

Relying on the intrinsic contractile qualities of EAP, conventional moving parts which could incur wear would be unnecessary.

Electrodes (c) for each band are printed onto the base sheet. These conductors connect to the EAP bands at one end, and join a connector (d) at their other end.

For simplicity, one electrical pole could be supplied by a common earth conductor for all Bands (longest electrode in diagram). Separate conductors for each band supply the opposite polarity, to allow them to be activated discretely.

Although the device would operate at low voltage, as with all electrically active medical implants, adequate electrical insulation would be provided.

At either end of the device, an area of base material without EAP bands may include perforations (a) to allow biological connective tissue (fascia) to colonise the device and secure it in place.

As shown in fig.2, the device would be closed around a section of compliant vein (f) sufficiently free of any post thrombotic scarring, organised blood clot or sclerosis, to allow external compression of its walls.

Before placement of the device, the relevant section of vein could be surgically wrapped with a layer of fascia to pack the space between it and the device and ensure an adequate transmission of force. Fasteners or sutures (h) would then be used to maintain the device in closed form around the vein.

Electrical power connections (g) in the form of ribbon cable (shown) or multicore cable, would then be attached, connecting the prosthesis to an implanted electrical battery and electronic control unit, to activate each ring discretely and in sequence.

In order to prevent fluid oscillation and reflux within the device, the power supply/sequencing electronics would be suitably preset to ensure that relaxation of preceding EAP bands could not begin until contraction of the proceeding band was complete or nearing completion.

The contraction signal for each band would be of appropriately low amplitude and sufficiently gradual attack/long slope, to provide a gentle compression.

EAP generates an electrical signal when placed under mechanical stress. An additional band of EAP could therefore be used as a local blood pressure sensor, allowing the rate of the device to be synchronised with blood pressure and keep pace with circulatory demand. Alternatively, those compressor bands momentarily in relaxation could be utilised for the same function.

The compact power unit would comprise a small battery, charger and receiver electronics and a compact antenna coil. The receiver and antenna would allow the battery to be recharged by electromagnetic induction, using an external hand held charger device, without the need for physical connections through the skin.

The power unit electronics would also include telemetry to signal the implanted batteries level of charge to a small external sensor and a charge indicator. This charge sensor and indicator, could either be incorporated into the external hand-held charger, or worn as a small cosmetically discrete external unit.

I argue that the design I have described here, for a minimally invasive vascular assist prosthesis represents an inventive step, which would not be obvious to those skilled in the art, of either materials science or vascular surgery, and has the potential to significantly enhance the treatment of vascular disorders. It occurred to me as a consequence of a personal medical interest in developing solutions to vascular disease that would involve a much lower risk of initiating the body's clotting mechanisms, than conventional treatments. It comprises a complete, practical system, incorporating an implantable, open preparation prosthesis, an integral blood pressure sensor, and a control and power supply with a receiver for inductive charging. External elements are a hand-held inductive charger and a separate device charge status monitor, which could be worn over the site of the implant. Constructed with sufficient reception range for the implant telemetry, the status monitor could alternatively be worn on a wrist strap In addition to its surgical advantages, the device also presents a more efficient alternative to conventional external orthopaedic devices designed to assist circulation.

Presently, compression stockings are sometimes used to administer limited vascular support to limbs. These are however passive devices with only limited capacity to improve blood flow and are still dependent on movement of the muscles to actually pump blood through the valves.

There are also externally applied pneumatic devices used to prevent DVT during surgery, which actively massage the leg. These are too cumbersome and obtrusive for continuous use. They also produce a generalized compression of the lower legs, rather than operating sequentially to produce a progressive wave of compression along the area of application, to induce preferential flow.

They work in a manner analogous to the compression of the veins by leg muscles.

With both the body's natural muscular pump or external compression devices, competent venous valves are required to translate this generalised compression, into a flow of blood in one direction only.

In individuals with absent or incompetent valves however, such generalised compression tends to propel blood back towards the feet as well as towards the heart. The proposed vascular assist device in contrast, incorporates the functions of muscular compression and venous valves.

The prosthetic implant therefore presents a more efficient, permanent and discrete means of vascular support, than conventional orthopaedic prostheses. A larger version of the device however, could be used periodically, to apply external 'smart' is compression to a limb and maintain adequate blood flow more efficiently than currently available compression stockings or pneumatic devices. It would simply be wrapped around the calves and fastened, to provide protection to surgical patients, long-haul air travellers, or other immobilised persons. External application would allow the use of more conventional power supply technologies than the inductive charging of the implant version of the device.

Kevtofi. 1 a) Perforations in base sheet to allow fascia (biological connective tissue to colonize and anchor the device b) Compressor bands of Electroactive Polymer (EAP) enclosed within an electrically insulating film.

c) Discrete printed electrical power conductors and common earth for EAP bands d) Electrical power connector e) Base sheet, acting as a former for the EAP bands Kev to fig.2 a) Perforations in base sheet to allow fascia (biological connective tissue to colonize and anchor the device b) Compressor bands of Electroactive Polymer (EAP) enclosed within an electrically insulating film.

c) Discrete printed electrical power conductors and common earth for EAP bands d) Electrical power connector e) Base sheet, acting as a former for the EAP bands f) Section of compliant vein g) Power/control ribbon cable h) Clips/fasteners to hold the device in cylindrical form Diagrams show spaced EAP bands for clarity. In the working design, they are separated only by a slight gap to allow contraction and prevent binding.

N.B. An alternative construction of the device could be formed by a single sheet of the chosen EAP material, with discrete electrodes at regular intervals to allow sequential activation and compression of regions along its length. The sheet could be manufactured as an adjustable tie arrangement, with a long locking slot along one side edge, through which the other edge would be fed, looping over to form a cylinder around the vein. Another one piece design could take the form of a coil or spring. To place the device, the end turn/coil would be placed over the vein at an angle, and the whole device rotated to bring the vein fully within its length.

Again, electrodes would be arranged along its length to activate different regions. I' At,

Claims

Claims I A minimally invasive vascular assist prosthesis existing in an

open form before use, comprising a flat sheet onto which there is formed a series of discrete electromechanical contractile regions, each with discrete electrical control connections to allow each region to be controlled separately. One electrical polarity for all connections may be supplied by a common 'earth' terminal, with the opposite polarity then being supplied by separate terminals for each contractile region. When the two long edges of the prosthesis are brought together and fastened to form a tube around a bodily limb or fluid containing vessel such as a vein, the contractile regions thereby achieve the form of a series of rings. When each ring is contracted in suitable sequence by connected power supply and control electronics, a wave of compression proceeds along the length of the prosthesis and the vessel or limb it encloses, resulting in any fluid contained within the said limb or vessel, being pumped in the direction of the compression wave.
2 A minimally invasive vascular assist prosthesis as claimed in claim one, where a combined power supply and control unit is supplied in order to activate each contractile region in a sequence suitable to produce a wave of compression and fluid flow in one direction. This unit contains a rechargeable battery, electronics to recharge the battery and electronics to indicate its level of residual charge. In embodiments intended for external compression of a limb, the power supply and control unit may be physically integrated with the prosthesis to form a single construction. In embodiments intended for surgical implantation, the implantable power supply and control unit may be physically separate from the prosthesis but connected to it by suitable electrical cabling.
3 A minimally invasive vascular assist prosthesis as claimed in claim 2, where in an embodiment of the invention intended for surgical implantation, a compact antenna is included with the implanted power supply and control unit, to receive power for recharging the battery inductively from an external charger. Also included in this surgically implantable embodiment of the invention, are receiver electronics for converting power received by the antenna from the external charger, into a useable charging current. Also included in the power supply and control unit of this embodiment, is appropriate telemetry to signal the,,battery charge level, by radio frequency to an external sensor and charge status indicator.
4 A minimally invasive vascular assist prosthesis as claimed in claim 3, where in the embodiment intended for surgical implantation, there is supplied a separate external sensor and charge-status indicator unit, to receive radio frequency charge- status signals from the implanted power supply and control unit telemetry.

A minimally invasive vascular assist prosthesis as claimed in any of the above claims, where the invention would either be retained in place around a limb or vessel, using suitable fasteners, either separate or integral to the base sheet of the device.

Claims (continued) 6 A minimally invasive vascular assist prosthesis as claimed in claim 1, where an embodiment intended for surgical implantation, could incorporate perforations to allow colonization and anchoring of the device, by bodily tissue.