FIELD OF THE INVENTION
This invention relates to prosthetic devices for the treatment of urinary incontinence and, in particular, to prosthetic devices employing transplanted tissue.
BACKGROUND OF THE INVENTION
The present invention is concerned with forms of incontinence caused wholly or partly by inadequate sphincter function. This may include forms of stress incontinence, urge incontinence and total incontinence. The invention has been developed initially for use in treating male incontinence and will be described principally with respect to that application. However, it will be appreciated by those skilled in the art that the invention is also applicable for use in treating female incontinence.
Incontinence is a major health problem, particularly with the ageing population, for which there is no well-accepted medical treatment. For females, surgically constructed slings are increasingly being used for stress incontinence and with increasing success. However, here is no low risk and reliably effective treatment for moderate to severe male stress incontinence particularly after treatment of prostate cancer. As the incidence of prostate cancer is increasing, this is a growing health issue.
The internal sphincter of the urethra consists of smooth muscle cells interposed with elastic tissue and is located in the proximal urethra. Its constant tone is crucial to maintaining mechanical resistance in the proximal urethra sufficient to hold back the passive pressure exerted by urine in the bladder. Weakness in this area is a common cause of urinary incontinence, for example after treatment for prostate cancer.
Prosthetic sphincter valves have been proposed in numerous forms, including mechanical, hydraulic and electrical devices which replace or supplement the defective damaged internal sphincter of the urethra (e.g. PT 101841, SE 931516, GB 2266844, FR 2638964, WO97/01309 and U.S. Pat. No. 4,619,245). Electrical stimulation of the muscles of the sphincter has also been proposed (DE 29614895). Other approaches have proposed the use of external or implanted electrodes to stimulate existing sphincter function.
A variety of approaches have been proposed in relation to the electrical stimulation of the muscles of the sphincter, most of which are directed towards stimulating an existing sphincter and/or muscles disposed about, for example, a bladder(DE 29614895).
Another group of prior art proposals for the treatment of incontinence are directed towards the stimulation of sacral nerves and the like. Such proposals again seek to use the existing muscle structures. (U.S. Pat. No. 4,771,779, U.S. Pat. No. 4,703,775, U.S. Pat. No. 4,607,639, U.S. Pat. No. 3,870,051, U.S. Pat. No. 4,688,575, U.S. Pat. No. 4,389,719 and U.S. Pat. No. 5,702,428).
Other stimulation means have been proposed, for example U.S. Pat. No. 5,562,717, wherein stimulating electrodes are disposed on the skin of a person to externally stimulate existing muscles to control incontinence. This method is disadvantageous in that it requires electrodes to be disposed in a predetermined location of the person and be electrically connected to a power source therefore not allowing complete freedom.
It has also been proposed to implant part of a small skeletal muscle from the thigh around the patient's urethra, and then to electrically stimulate the muscle to “retrain” it to function as a replacement sphincter (New Scientist, 29 Jun. 1996). However, this approach, even if successful, would require relatively high levels of electrical stimulation to allow sufficient contracture of the replacement sphincter.
It is an object of the present invention to provide an improved prosthetic device for use in treating incontinence.
SUMMARY OF THE INVENTION
Broadly, the present invention utilises innervated smooth muscle to provide an auxiliary sphincter. This is stimulated by a suitable device in order to provide a functional sphincter in the patient. As a consequence, the stimulator device can operate with lower power consumption, and produce a superior sphincter action.
According to a first aspect of the invention there is provided an implantable sphincter stimulator configured for operatively providing electrical stimulation to a surgically implanted innervated smooth muscle sphincter disposed about a urethra so as to control the flow of urine therethrough, the stimulator including:
a stimulus generating unit in electrical communication with a receiver, the stimulus generating unit operatively configured to provide a first predetermined electrical stimulation signal adapted to contract said sphincter, and a second predetermined signal adapted to allow said sphincter to relax, one of said predetermined signals being selected in response to a signal received at the receiver from a remote controller.
In preferred embodiments, the stimulator applies the first stimulation signal, unless a signal is received indicating that the patient wishes to empty the bladder. The second stimulation signal may be simply the absence of a stimulation, a lower level signal or an alternative signal.
Preferably, the stimulation signal is one which will maintain a continuous tone in the innervated sphincter. In other preferred embodiments of the invention the stimulation signal is pulsatile. Preferably, the stimulator provides multiple channel pulse generation. Preferably also, the stimulation pulse frequency is in the range of 0.25 to 2.5 Hz and having a width in the range of 0.05 to 0.20 milliseconds.
Preferably the stimuli applied have a current less than or equal to 30 mA.
More preferably, the stimulation signal is generally rectangular and symmetrical biphasic, although alternative biphasic pulses may be used.
Preferably, the sphincter stimulator includes a replaceable or rechargeable battery power source, preferably one which is in-situ rechargeable, for example inductively.
Preferably, the signal to the receiver is communicated by microwave or radio means, optically or by magnetic energy and the receiver respectively is a microwave, radio, photon or magnetic energy receiver.
Preferably, the stimulus generating unit includes a demodulator responsive to the received signal for providing a modulated signal to a stimulus encoder which in turn provides a signal to a stimulus driver. The stimulator preferably includes two or more electrodes for operatively delivering the stimuli to the sphincter. The stimuli may differ between electrodes, or may be the same at each.
Preferably, after the sphincter has been relaxed, the stimulator is adapted to supply the first stimulation signal to contract the sphincter when a predetermined signal to contract the sphincter is not received by the receiver after a predetermined period.
Preferably, the sphincter stimulator includes a transmitter for transmitting sphincter stimulator telemetry information indicative of one or more parameters of the stimulator for detection remotely. Preferably, the information is transmitted by means of radio waves, microwaves, optically or by magnetic energy. More preferably, the parameters include one or more of the stimulation signal frequency, current, width and/or shape, and/or of the received signal strength and battery status. Preferably, the stimulus generating unit includes a processing device with non-volatile memory.
Preferably, the receiver is configured to accept a remotely generated sphincter stimulator calibration signal and in response, the stimulus generation unit selectively varies one or more of the stimulation signals. More preferably, the calibration signal is transmitted in response to received sphincter stimulator telemetry information, for example the telemetry signals from the stimulator.
Preferably, the stimulator is in electrical communication with the sphincter by at least one electrical lead having two or more electrodes which are operatively implanted into the sphincter at a predetermined location. More preferably, the lead includes three electrodes disposed in an epimysal, cuff or tripolar configuration about the sphincter.
Preferably, the smooth muscle is taken from the smooth muscle of the bladder and transplanted about the urethra and having its circulation intact. Alternatively, the muscle is venous smooth, anococcygeus smooth muscle, terminal ileum transplanted as a segment devoid of mucosa and having its circulation intact. A further alternative is the dartos smooth muscle from the scrotum or labia. In each case, the long axes of the muscle cells are disposed substantially circumferentially about the sphincter. Depending upon the muscle selected, the circulation may or may not be transplanted intact. If the circulation is not transplanted intact, new vessels will need to be regrown, or otherwise provided.
According to a second aspect of the invention there is provided a system for use in treating bladder incontinence in a person, the system including:
a portion of innervated smooth muscle tissue configured to define a sphincter and implanted substantially circumferentially about the urethra of the person;
an implanted sphincter stimulator arranged so as to allow electrical stimuli to be applied to the sphincter; and
a non-implanted controller in communication with the sphincter stimulator for selectively triggering the generation of predetermined electrical stimulation signals to respectively contract the sphincter or allow the sphincter to relax.
Preferably, the smooth muscle is in the form of a strip and is generally rectangular. More preferably, the strip has dimensions in the range from 4.5 cm to 7.5 cm by 1.25 cm to 2.25 cm. Also preferable, the muscle is disposed substantially fully around the urethra in a generally cylindrical arrangement such that the long axes of the muscle cells are substantially circumferentially aligned.
Preferably, the smooth muscle is selected from those described above.
Preferably, the system includes a sphincter as described above.
Preferably, the controller includes:
means for generating a predetermined signal at the transmitter;
a power source; and
actuation means for selectively generating a signal such that on receipt of the signal, the sphincter stimulator provides the stimulation signal at its output for contracting the sphincter or allowing it to relax. The signals for selecting relaxation or contracture may be different, or the same signal may trigger alternation of states.
One form of the controller, particularly for use by a physician, may include a receiver for receiving the sphincter stimulator telemetry information signal from the sphincter stimulator. Preferably, the signal is transmitted by radio waves, microwaves, optically or by magnetic energy and receiver respectively is a radio, microwave, photon or magnetic energy receiver.
Preferably, the system includes a remote sphincter stimulator programming unit for selectively programming the sphincter stimulator to provide a predetermined output. Preferably, one or more of the stimulation signal current, shape, frequency and width is variable in response to the calibration signal provided by the programming unit. More preferably, the programming unit includes a transceiver for providing the programming signal to the stimulator. The programming unit may conveniently be the physician controller.
According to a third aspect of the invention there is provided a method of using an implantable sphincter stimulator for treating bladder incontinence, the method including the steps of disposing an innervated smooth muscle sphincter about a urethra, arranging one or more electrodes so as to allow stimulation of the neural structures of said sphincter, said electrodes being connected to the sphincter stimulator, so that post implantation, a predetermined stimulation signal may be applied by a stimulus generating unit to selectively contract the sphincter or allow it to relax.
Preferably, the method includes the step of transmitting the signal to the sphincter stimulator by radio signals, microwaves, optically or by magnetic energy.
Preferably, three electrodes are arranged in the sphincter in an epimysal, cuff or tripolar configuration.
Preferably, the sphincter is smooth muscle selected from those previously described.
According to a fourth aspect of the invention there is provided a method of treating incontinence including the steps of:
disposing an innervated smooth muscle sphincter around a urethra;
locating a plurality of electrodes in predetermined locations in the sphincter and electrically connecting the electrodes with an implanted sphincter stimulator; and
selectively actuating the sphincter stimulator to provide a predetermined stimulation signal to either contract the sphincter or allow it to relax in response to a remotely generated signal.
According to another aspect of the invention there is provided a method of surgically implanting a sphincter stimulator in a system for treating urinary incontinence, including the steps of:
implanting the innervated smooth muscle sphincter about the urethra in a person;
implanting the electrodes into the sphincter at predetermined locations; and
implanting the sphincter stimulator, the arrangement being such that the electrodes are electrically connected to the sphincter controller to permit stimulation signals from said sphincter stimulator to stimulate the neural structures of said smooth muscle.
Implanting in this context includes transplanting from the same or another person, or the use of externally prepared smooth muscle tissue. In each aspect, it is preferred that the implanted sphincter function so as to substantially prevent leakage of urine when contracted. In general, the main function of the innervated muscle prosthesis is to augment function in the internal sphincter. It should not be used to override any natural sphincter function that may be preserved. The sphincteric pressure exerted by the prosthesis should be sufficient to restore the net sphincteric resistance to its normal level of operation. Unnecessarily high pressure would not only be wasteful of internal stimulator energy but could also cause dangerous overfilling of the bladder. On the other hand, the pressure must be sufficiently high to prevent the leakage of urine.
The smooth muscle tissue may be selected from those described above, or any other suitable smooth muscle tissue. It will be appreciated by those skilled in the art that other types of smooth muscle may potentially be employed as the implantable sphincter including alpha-adrenergic excitatory innervation, cholinergenic excitatory or, inter alia, circular intestinal muscle.
One advantage of using smooth muscle tissue is that it physiologically performs a sphincteric-like function and the muscle layer should be able to be transplanted whilst maintaining its innervation, or allowing for its reinnervation, and blood supply. Moreover, smooth muscle of the types described is readily reinnervated by sympathetic nerves should the existing innervation be damaged during surgery. Reinnervation may take some time, for example, two to three weeks, after surgery.
Another advantages associated with the use of an innervated smooth muscle sphincter in accordance with the present invention is that in smooth muscle, a long-lasting contracture (2-3 seconds) results from a single neural stimulation. Accordingly, only a low frequency of stimulation is required to produce a tetanic contraction especially where it is moderated by neurotransmitter release.
The tension generated per unit cross-sectional area of smooth muscle is greater than for skeletal muscle. Smooth muscle generates tension over a wide length/tension relationship, that is, it continues to generate tension even when partially contracted. Smooth muscle is able to maintain high tension with relatively low energy expenditure. Smooth muscle tissue generally displays a persistent generation of tone during low frequency repetitive nerve stimulation.
A further advantage of the use of smooth muscle according to the present invention is that low frequency nerve stimulation causes the release of a chemical transmitter. Stimulating the nerves within smooth muscle invariably triggers a contraction because the neurotransmitter interacts with a receptor. The activated transmitter/receptor complex then activates a second messenger pathway and releases calcium ions from internal stores. It is relevant that calcium is the final trigger in the contraction of both skeletal, smooth or cardiac muscle. When stores release calcium they do so for extended periods of time, typically in the order of several seconds. Therefore, if the exciting pathway is triggered repeatedly at low frequencies a sustained rise in calcium occurs and the smooth muscle develops a contracture. That is, it does not relax between stimuli. In some smooth muscles, a few stimuli delivered every two seconds, for example, will lead to a sustained contraction.
An alternative way to excite smooth muscle is to stimulate it directly which produces quite long lasting contractions but only on application of very high stimulating voltages. Nerves have low thresholds for activation, compared with muscles, and this, together with the low frequencies of activation required, means that stimulus spread will be avoided. Importantly, an electrical device can reasonably be expected to survive untouched for many years with such low usage demands.