Surgery – Means for introducing or removing material from body for... – Treating material introduced into or removed from body...
Reexamination Certificate
1999-04-23
2001-11-20
Seidel, Richard K. (Department: 3762)
Surgery
Means for introducing or removing material from body for...
Treating material introduced into or removed from body...
C128S887000, C128SDIG008
Reexamination Certificate
active
06319237
ABSTRACT:
BACKGROUND TO THE INVENTION
This invention relates to a urinary sphincter control device for application to a urethra to control flow of fluid through the urethra.
Known devices for controlling incontinence comprise a cuff which can be fitted around a patient's urethra. The cuff comprises at least one chamber which extends around the urethra. A pressurised control fluid can be supplied to the cuff to inflate it, causing the cuff to exert compressive pressure onto the urethra so that flow of fluid along the urethra is prevented. The fluid that is used in such devices might be for example a saline solution. The device will generally include a reservoir for the fluid, and a pump by which pressurised fluid can be supplied to the cuff and withdrawn from the cuff. Known devices include an elastic balloon reservoir by which the pressure of the fluid in the cuff can be controlled within predetermined limits.
A cuff which extends around the urethra has been found to close a urethra satisfactorily against flow of fluid. However, the cuff can also restrict the flow of blood along the urethra, leading to tissue damage and the subsequent need to remove the device from the patient.
SUMMARY OF THE INVENTION
The present invention provides a urinary sphincter control device in which the cuff comprises a plurality of chambers which are discontinuous around the vessel so that blood is able to flow along the vessel in its wall even when the vessel is closed against fluid flow, which can be inflated to cause the configuration of the cuff to change so as to alter the resistance that is provided by the cuff to flow of fluid along the urethra.
The device of the invention has the advantage that it is able to close a urethra against flow of fluid through its bore by closing the vessel transversely. However, the chambers by which the closing force is applied to the vessel are discontinuous around the vessel so that blood is able to flow along the vessel in its wall even when the vessel is closed against fluid flow. The chambers might for example extend generally parallel to the axis of the cuff. The device of the invention can therefore be more comfortable for a patient to use, with reduced likelihood of urethra tissue damage than with existing devices. As a consequence, the device of the invention minimises the need for surgical procedures after implantation to address problems of tissue damage following use of the device.
The advantage that is provided by the present invention in terms of reduced resistance to flow of blood in the urethra arises from the fact that the chambers in the cuff by which force can be applied to the urethra extend generally parallel to the axis of the cuff so as to be aligned with the blood flow in the urethra. In some cases, the orientation of the chambers might be such that they do not extend parallel to the cuff axis provided that the angle between the axes of the chambers and the direction of blood flow is small. Preferably the angle between the axis of the cuff and the axis of the chambers is less than about 20°, more preferably less than about 10°. It will generally be preferred for the chambers to be orientated as close as possible to the cuff axis.
The device of the invention can be arranged so that flow of fluid along the urethra is restricted by the cuff when it is in its inflated configuration. Flow of fluid along the urethra is then allowed by deflation of the cuff, with pressure of fluid within the urethra enhancing the cuff deflation. A device which operates in this way can include a pump for changing the pressure of the control fluid within the cuff, and preferably also means for controlling the pressure of the control fluid so that (a) it is sufficient to close the urethra against fluid flow, but (b) not so great as to cause damage to the cuff or to the patient's tissue. Devices for changing and for controlling the pressure in the cuff in this way are known.
It will be preferred for the device to be arranged so that flow of fluid along the urethra is restricted by the cuff when it is in its uninflated configuration, and in which the effective internal perimeter (which will be a circumference when the cross-section of the device is circular) dimension of the cuff is increased when it is in its inflated configuration so that the pressure imposed by the cuff on the urethra is reduced and so that the urethra is opened to flow of fluid therethrough. Inflation of the chambers of the device increases the internal transverse dimension of the cuff, and can therefore reduce the pressure exerted by the cuff on the urethra. In this arrangement, the maximum force that is imposed on the urethra can be pre-determined. The force that is imposed can then be controlled to suit the requirements of a particular patient by controlling the pressure of fluid that is supplied to the cuff. It is an advantage of this arrangement that the application of the closure force to the urethra can be adjusted externally by controlling the pressure and volume of fluid in the cuff. The device therefore enables the closure force imposed on the urethra to be adjusted after implantation of the device.
Preferably, the device includes, in at least one of the chambers, an element for biassing the configuration of the chamber towards the uninflated configuration. The element can be designed to provide a desired closing force to a urethra on which the cuff is to be used when it operates. Preferred biassing elements are formed from shape memory alloys, especially which exhibit enhanced elastic properties. Articles formed from shape memory alloys can exhibit shape memory properties associated with transformations between martensite and austenite phases of the alloys. These properties include thermally induced changes in configuration in which an article is first deformed from a heat-stable configuration to a heat-unstable configuration while the alloy is in its martensite phase. Subsequent exposure to increased temperature results in a change in configuration from the heat-unstable configuration towards the original heat-stable configuration as the alloy reverts from its martensite phase to its austenite phase.
Shape memory alloys can exhibit enhanced elastic properties compared with materials which do not exhibit martensite-austenite transformations and it is these properties that make the alloys attractive for use in the device of the present invention. The nature of the enhanced elastic transformations of shape memory alloys is discussed in “Engineering Aspects of Shape Memory Alloys”, T W Duerig et al, on page 370, Butterworth-Heinemann (1990). Subject matter disclosed in that document is incorporated in this specification by this reference to the document. A principal transformation of shape memory alloys involves an initial increase in strain approximately linearly with stress. This behaviour is sometimes referred to as non-linear superelasticity. It is reversible, and corresponds to conventional elastic deformation. Subsequent increases in strain are accompanied by little or no increase in stress over a limited range of strain to the end of the “loading plateau”. The loading plateau stress is defined by the inflection point on the stress/strain graph. Subsequent increases in strain are accompanied by increases in stress. On unloading, there is a decline in stress with reducing strain to the start of the “unloading plateau” evidenced by the existence of an inflection point along which stress changes little with reducing strain. At the end of the unloading plateau, stress reduces with reducing strain. The unloading plateau stress is also defined by the inflection point on the stress/strain graph. Any residual strain after unloading to zero stress represents the permanent set of the sample. Characteristics of this deformation, the loading plateau, the unloading plateau, the elastic modulus, the plateau length and the permanent set (defined with respect to a specific total deformation) are established, and are defined in, for example, “Engineering Aspects of Shape Memory Alloys”, on page 376.
ICD Labs, Inc.
Madson & Metcalf
Seidel Richard K.
Sirmons Kevin C.
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