A STUDY ON ELECTRO-STIMULATION OF THE BLADDER

Abstract

The development of new therapeutic procedures has improved the prognosis for the paraplegic patients with spinal cord injuries, but in a number of cases the use of a urethral catheter remains necessary, Catheterisation increases the risk of recurrent infection, which provokes the development of vesicoureteral reflux, leading to an involvement of the upper urinary tract and renal function.
In the last several years, studies on wireless stimulation of the detrusor muscle of neurogenic bladder in an attempt to evacuate its contents has been reported by Bradley, Boyce, Kantrowitz and others, but there are many discrepancies in the results among the investigators.
Thus, the writer studied basic problems in an attempt to improve the application of this procedure to paraplegic patients.
In the present study fifty mongrel dogs were used. Through a lower abdominal midline incision, the lateral vesical spaces and pelvic nerves were exposed transperitoneally and a pair of electrodes were implanted in the detrusor muscle or hooked to the nerves. In short-term experiments oval disk copper electrodes and in long-term experiments stainless steel wire electrodes were used. The electrodes were connected directly with wires to the output terminals of an electronic stimulator (Nihonkoden) and a train of monophasic square waves was applied. The stimulating current and tissue impedance were observed throughout the experiment by an oscillograph. The effect of stimulation was evaluated by a rise of intravesical pressure meassured through a cystostomy tube with a strain gauge type transducer and a carrier amplifier.
To obtain a neurogenic bladder we transected the spinal cord of dog at various levels under deep ether anesthesia. For wireless stimulation an external oscillator and an internal receiver with a pair of stimulating electrodes were adopted. The external oscillator produces 200KC carrier waves which are modulated with LF square waves. The receiver buried in the subcutaneous tissue in the lower abdomen receives and rectifies the waves and sends the square waves to the electrodes sutured into the detrusor.
I. Wired experiments
A. Preliminary experiments
Parameters of the stimulating current to be adopted in the wireless stimulation were explored. Since deeper anesthesia showed poor response, the dogs were kept in constant light anesthesia by intravenous pentothal. In repeating the stimulation, intervals exceeding five minutes were maintained since too short intervals between each stimulation produced a gradual lowering in response. The volume of intravesical content widely influenced the height of response and it was found important to maintain the intravesical content constant throughout an experiment. A pair of electrodes were implanted at venous points in the detrusor muscle, and it was found that at points near the ureterovesical junction the highest intravesical pressure was obtained. Use of more than one pair of electrodes did not show any better effect.
A higher voltage of stimulating current produced a larger contraction of the detrusor in a range of less than 32V. When the voltage and frequency of pulses was kept constant, the longer duration of one pulse produced a higher effect. When the voltage and product of frequency and duration of a pulse was fixed, the most effective frequency of pulses was 20-50cps.
B. Experiments on dogs with spinal cord lesion
In experiments on dogs with upper motor neuron lesions (acute and chronic) the voltage required to produce a satisfactory rise of intravesical pressure was 5-15V (impedance ca. 300ohm) by detrusor stimulation and only 3V(impedance ca. 700ohm) by pelvic nerve stimulation.
In experiments on the dogs with lower motor neuron lesions, the reactibility of the bladder at the acute stadium was nearly the same as that of the dog with upper motor lesion, but it became lower day by day. Several weeks later the lowest values were seen and intravesical pressure s