Evaluation of Bipolar Permaloc™ Electrodes for Direct Bladder Stimulation

Abstract

Purpose: A bladder control system for spinal cord injured (SCI) patients is needed that can be implanted with minimally invasive methods. New Permaloc bipolar electrodes consisting of 6 mm helical, wire, stimulating surfaces separated by 3 mm and a polypropylene securing barb (Synapse Biomedical Inc) were developed for this application. They are implanted on the bladder wall with a 16 gauge needle, a minimally invasive method. Methods: Seven swines were anesthetized, the lower urinary tract exposed and instrumented with pressure transducers. Four Permaloc™ electrodes were implanted following identification of effective bladder wall stimulation sites next to the ureters and dorsal neurovascular bundle. Bladder stimulation to induce high pressures was conducted at 40 Hz, 400 µs pulses, 5 s stimulation periods and a high stimulating current of 40 mA. Results: At the high stimulating current peak bladder pressures were low, ranging from 12±2 to15±3 cm H20, insufficient to induce urination. Urethral sphincter contractions occurred during high bladder pressure. A spinal reflex role for high sphincter pressures during stimulation was shown by similar high pressures recorded during a bladder squeeze test without stimulation. Conclusions: Stimulation with Permaloc™ bipolar electrodes at high currents produced insufficient bladder pressures for urination. Further modifications of the electrode such as greater separation of the bipolar stimulating surfaces or changes in the testing methods such as alternative animal models are needed to induce high bladder pressures without side effects.