GB2459481A

GB2459481A - Expanding medical collet

Info

Publication number: GB2459481A
Application number: GB0807438A
Authority: GB
Inventors: Steven Fawcett
Original assignee: INVIVO TECHNOLOGY Ltd
Current assignee: INVIVO TECHNOLOGY Ltd
Priority date: 2008-04-23
Filing date: 2008-04-23
Publication date: 2009-10-28
Also published as: WO2009130457A1; GB0807438D0

Abstract

A medical device for opening occluded fluid conduits of a mammalian body comprises a collet 12 having a nose 14 for attachment of one element 11 of a Bowden cable, and an expanding tail 15 having an internal recess 17 adapted to receive the other element 13 of the Bowden cable. The attachment may be by a weld 10 or by a sheath crimped into a groove 18 on the nose. Relative axial movement of the Bowden cable elements causes fingers 16 of the collet to expand. A resilient sheath and/or expandable stent may cover the fingers. Multiple collets may be used together (figures 4 and 5), with just the first and last in contact with the Bowden cable. The expanding collet may be used to fracture calcified plaque deposits on the insides of arteries; the Bowden cable may be a catheter and guide wire.

Description

Expanding Medical Collet This invention relates to an expanding collet for use in medical procedures, and is particularly concerned with the treatment of blocked fluid conduits, such as arteries.

It is known that over time the fluid conduits of a mammalian body may become partially blocked due to the deposit of material on the inner wall. The reasons for such deposits are many, and the consequences for health may be very serious.

Narrowing tends to be localized, and a standard method of treatment is balloon angioplasty whereby an uninflated balloon is placed within the fluid conduit in the affected region. The balloon is expanded by introducing therein fluid under pressure, typically by injecting liquid from a syringe, and the fluid conduit is consequently expanded.

A stent may be inserted during or after balloon angioplasty in order to maintain the fluid conduit at the desired cross-sectional area.

Balloon angioplasty is appropriate for larger fluid conduits and for relatively soft occlusions. However some conduits, are very small, and it is consequently difficult to place an uninflated balloon therein especially where the cross-sectional area is much reduced by a calcified deposit or a fibrotic in-growth.

Hard occlusions are also problematic because the balloon may be unable to generate the required force to expand the deposit; in such instances the balloon may merely adopt a hour-glass shape in the conduit whereby the fluid conduit is expanded on either side of calcified material. In some circumstances the operator may burst the balloon in an attempt to force open the conduit, or may burst the conduit itself Furthermore hard edges of the deposit may puncture the balloon.

What is required is a device capable of being introduced into a range of mammalian fluid conduits and adapted to generate sufficient radial force to dilate or crack hard calcified aridlor fibrotic occlusions.

According to the invention there is provided a medical collet assembly comprising a rotationally symmetrical collet having a non-expanding nose and an expanding tail comprising a plurality of fingers, the fingers defining an internal recess, and the assembly further comprising a Bowden cable having internal and external elements, one of the internal and external elements being operatively connected to said nose, and the other of said internal and external elements being adapted to enter said recess upon relative axial movement of said elements, to expand said tail.

The force generated by the collet fingers is localized and in use is applied directly, for example, to a calcified region. Greater radial force can be developed by the device of the invention, without risk of over-expansion of the fluid conduit, as will become apparent. Preferably the inner element is operatively connected to the nose, and the outer element enters the recess in use.

In addition to directly expanding a fluid duct, the invention permits progressive dilatation of an occlusion by repeated expansion, contraction and longitudinal movement, in a nibbling' fashion. Furthermore the device may be used to correct failed balloon angioplasty, for example where a stent has failed to expand in the desired manner.

In a preferred embodiment a screw-threaded adjuster is provided for progressive relative movement of the Bowden cable elements, so as to urge the collet fingers radially outwardly.

Preferably the collet has a bullet shaped nose so as to be more easily introduced into a fluid conduit. The collet is preferably tubular so as to permit introduction over a guide wire; in such circumstances the guide wire may comprise the inner element of the Bowden cable, and include a stop thereon adapted to engage the nose of the collet.

Alternatively the guide wire may be fixed to the nose of the collet, and act as the inner element of the Bowden cable.

In a preferred embodiment, the internal recess may be tapered axially inwardly of the collet, and the outer element of the Bowden cable comprise an arcuate solid tip adapted to expand said tail on relative axial movement, Said tip preferably comprises a radio-opaque marker.

The collet may be of any suitable medically acceptable material, for example a metal such as stainless steel or a hard plastic. In the preferred embodiment the collet is one piece and of resilient material so that the fingers tend to return to the unexpanded condition upon relaxation of the Bowden cable. Alternatively, a resilient device may be additionally provided to urge apart the collet and the element of the Bowden cable which in use is associated with said tail.

In the preferred embodiment, the inner element of the Bowden cable is also a catheter guide wire, and is substantially inextensible in use so that relative movement at the proximal end of the Bowden cable produces equivalent movement at the distal end.

The guide wire is typically of stainless steel.

The outer element of the Bowden cable should be flexible so as to substantially follow the path of the conduit into which it is inserted, yet be sufficiently resistant to axial compression in use. These two requirements are somewhat opposed, but the skilled man will select a suitable design dependant on factors such as material type, wall thickness, wall type, maximum compression load, diameter of the fluid conduit, and depth of insertion within the mammalian body. A suitable wall type may be for example a braid of plastics material, being both flexible and resistant to compressive forces.

In an alternative embodiment, several collets may be arranged nose to tail, each collet being arranged for operative expansion by a neighbouring collet, and the end most collets being operatively connected to one or other of the inner and outer elements of the Bowden cable.

The device may further include a resilient sheath, typically a silicone tube to bridge the collet fingers in use. The sheath has the further advantage of developing a return force on the collet upon radial expansion thereof by the collet, and distributing the expansion force.

In an alternative embodiment the device may include a stent around the periphery thereof in unexpanded form. A resilient sheath may lie between the device and the stent. In use the stent is expanded uni-directionally by the device to hold the vessel at the required cross-sectional area. The device has the advantage that expansion of the stent is precise, and that over-expansion is obviated.

Other features of the invention will be apparent from the following description of a preferred embodiment shown by way of example only in the accompanying drawings, in which:-Fig. I is an elevation of the distal portion of a collet assembly according to one embodiment of the invention.

Fig. 2 corresponds to Fig. I and illustrates the assembly in operative (expanded) condition.

Fig. 3 illustrates the distal portion of a first alternative embodiment of the invention.

Fig. 4 illustrates in elevation a second embodiment of the invention in the unexpanded condition, and Fig. 5 illustrates the embodiment of Fig. 4 in the expanded condition.

With reference to Fig. 1 a stainless steel guide wire 11 for insertion within a mammalian fluid conduit has mounted thereon a collet 12 and a tubular sleeve 13.

The conduit may for example be a human blood vessel, a heart valve or the urethra.

In the embodiment of Fig. I the guide wire 11 is firmly secured to the nose of the collet 12. In the case of compatible materials a weld 10 is suitable, but other joining methods such as mechanical crimping or adhesive may be suitable.

The collet 12 is a one-piece component of resilient metal or plastic, and comprises a nose portion 14 and an expandable tail portion 15 having a plurality of close-fitting fingers 16, typically four or more. The fingers 16 narrow towards the tail and define an internal recess 17 which narrows towards the nose, as illustrated in dotted outline.

As illustrated in Fig. 1, the collet 12 is in an unstressed state and may be machined or moulded as a single component. If of metal, the fingers may be formed by e.g. wire eroding, but moulding and slitting techniques may also be suitable.

A continuous groove 18 is provided around the periphery at about mid-length, and whose purpose will be described below.

The tubular sleeve 13 is flexible and resistive to compression loads in use. An aimular nosepiece 19 of the metal terminates the distal end. As illustrated, the nosepiece 19 and collet 12 are separated so as to show the components clearly, but in preparation for use the nosepiece is in light contact with the fingers 16. The guide wire 11 and sleeve 13 together comprise a Bowden cable.

At the proximal end, not illustrated, a mechanism is provided to reversibly draw the guide wire 11 axially through the sleeve 13. Any suitable and preferably progressive mechanism may be used, for example a screw-thread on the guide wire 11, and an associated nut bearing on the proximal end of the sleeve 13.

In use the assembly is introduced into the occluded fluid conduit, and the tail portion positioned adjacent the region to be expanded. The bullet shaped nose portion 14 assists placement, and either the collet 12 or the nosepiece 19 are preferably of metal to permit visualization by medical imaging techniques.

By drawing the guide wire 12 proximally the fingers 16 are resiliently expanded by the nosepiece 19, as illustrated in Fig. 2, thereby mechanically expanding the occluded region and opening up the fluid conduit. Upon release of the guide wire, the natural resilient of the fingers 16 tends to urge the collet 12 axially away from the nosepiece 19, so as to reduce the diameter thereof for withdrawal.

The expansion procedure can be repeated along the length of the fluid conduit by small distal or proximal movements of the assembly in the unexpanded condition.

The diameter ratio of the collet is typically in the range 3:1 to 4:1. Most importantly the maximum diameter of the collet is restricted by bottoming of the nosepiece 19 in the recess 17, and can be pre-selected by the manufacturer of the assembly. Thus over-expansion of the fluid conduit is obviated.

The external profile of the collet 12 is selected to suit the intended use, and the shape and angle of the fingers in the expanded condition is chosen similarly. The external surface of the fingers may be smooth, or may have projections adapted to assist in breaking or splitting a calcified deposit.

In a modification of the invention, a flexible sheath of e.g. silicone rubber may closely overlie the collet 12 and sleeve 13 so as to spread the load exerted by the fingers 16, and to bridge the inter-finger gaps which are created in use.

Such a sheath is resiliently stretched in use, and assists in returning the collet to the unexpanded condition. Such a sheath may be crimped or moulded onto the collet 12 in the region of the groove 18 and against relative axial movement. The sheath is preferably lubricated on the inside to ensure free relative movement of the sleeve 13.

A ftirther advantage of the sheath is that entry of material into the collet is prevented, so that inadvertent jamming thereof is not a risk.

The proximally situated external mechanism for actuating the Bowden cable preferably includes graduations which permit the close-fitting but unexpanded state to be recognized, and further to show the maximum state of expansion of the collet and stages therebetween. A screw-threaded mechanism may for example be in the form of a micrometer type adjustment relating rotational angle directly to the expanded diameter of the fingers 16.

Typically the device is intended to focus expansion force on a length of conduit in the range 2-5mm. A collet for renal use may be 1.25 -1.50mm in diameter in the unexpanded state. However it will be understood that the collet will be sized for example to suit the fluid conduit, the likely nature of the occlusion, the required expansion ratio and the radial force to be developed. The collet illustrated in the accompanying drawings is illustrative of many different sizes and shapes comprising a generally bullet-like nose and a multi-finger expandable tail.

An alternative embodiment is illustrated in Fig. 3, in which the inner element 21 of the Bowden cable is tubular; other components are the same save for the need to accommodate the larger diameter of this inner element 21. This embodiment permits a plain guide wire to remain with a patient after removal of the collet assembly in case a subsequent medical procedure, for example stent placement, is required.

Figs. 4 and 5 show another alternative in which two or more collets 22 are arranged nose to tail, each nose being adapted to expand the adjacent tail. Such a multiple collet arrangement can expand a greater length of fluid conduit in one operation. The return force of the collet fingers increases progressively as the diameter increases, and accordingly the overall diameter of the succession of collets will also tend to increase progressively. An outer silicone sheath may also be provided, fixed relative to one of the collets and having an internal lubricant to ensure free sliding of the remainder.

Claims

Claims 1. A medical collet assembly comprising a rotationally symmetrical collet having a non-expanding nose and an expanding tail comprising a plurality of fingers, the fingers defining an internal recess, and the assembly further comprising a Bowden cable having internal and external elements, one of the internal and external elements being operatively connected to said nose, and the other of said internal and external elements being adapted to enter said recess upon relative axial movement of said elements, to expand said tail.
2. An assembly according to claim 1 and further including a screw-threaded adjuster for progressive relative movement of the Bowden cable elements.
3. An assembly according to claim 1 or claim 2 wherein said inner element is operatively connected to the nose, and said outer element enters the recess in use.
4. An assembly according to any preceding claim wherein said collet has a bullet shaped nose.
5. An assembly according to any preceding claim wherein said collet is tubular.
6. An assembly according to any preceding claim wherein said internal recess is tapered axially inwardly of the collet, and the associated element of the Bowden cable comprise an arcuate solid tip adapted to expand said tail on relative axial movement.
7. An assembly according to claim 6 wherein said tip comprises a radio-opaque marker.
8. An assembly according to any preceding claim wherein said collet is one piece and of resilient material.
9. An assembly according to any preceding claim wherein the inner element of said Bowden cable is also a catheter guide wire.
10. An assembly according to any preceding claim and further comprising a plurality of said collets arranged nose to tail, each collet being arranged for operative expansion by a neighbouring collet, and the end most collets being operatively connected to one or other of the inner and outer elements of the Bowderi cable.
11. An assembly according to any preceding claim and further including a resilient sheath to bridge said fingers in use.