Comparison of Bipolar Lead Electrodes for High-Frequency Blocking of the Pudendal Nerve

Aims: High-frequency (HF) pudendal-nerve blocking that includes lead electrodes on the nerve are needed for spinal cord injury (SCI) patients to manage detrusor sphincter dyssynergia (DSD) that causes high urethral resistance. Several bipolar lead electrodes were compared using HF blocking stimulation parameters. Methods: Seven swine were anesthetized and urethral and anal sphincter pressures recorded. The left pudendal nerve adjacent to the sacral spine was exposed and proximal electrode used to induce intermittent contractions of urethral and anal sphincters. Blocking of sphincter contractions with electrodes at a distal location on the pudendal nerve with HF was evaluated. Initial HF tests used bipolar TECA electrodes at 1.2, 10 and 40 kHz; then, different electrodes and stimulating parameters were evaluated.Results: Initial results with HF demonstrated blocking of intermittent sphincter contractions induced by the proximal nerve electrode. Sphincter contraction blocking was greatest at 1.2 and 10 kHz at currents above 0.25 mA and was reduced at 40 kHz. Sphincter pressures, however, were elevated at the end of the 15 seconds of HF stimulation. These unwanted stimulatory effects on sphincter contraction were greatest at 1.2 kHz, reduced at 10 kHz, and least at 40 kHz. Further tests showed reduced nerve blocking effects using electrodes separated from the nerve or small helical Permaloc electrodes. Cutting the pudendal nerve centrally had no effect indicating that afferent fibers were not involved in the HF blocking effects. Conclusions: Bipolar TECA lead electrodes on the pudendal nerve stimulated at 10 kHz with1 to 5 mA of current were most effective in their nerve blocking effects with least unwanted stimulator effects. Nerve blocking without unwanted nerve stimulation was not observed with the variables tested. Therefore, unwanted stimulatory side effects should be anticipated in SCI patients when HF nerve blocking of the pudendal nerve with lead electrodes is implemented for urethral resistance. Thus, further testing is needed.