Response of external urethral sphincter to high frequency biphasic electrical stimulation of pudendal nerve

Purpose: We optimized the axonal blocking effect of high frequency, biphasic stimulation on neurally evoked contractions of the external urethral sphincter (EUS) and further investigated the repeatability of the blocking effect during relatively long periods to evaluate any acute nerve damage. Materials and Methods: Two stainless steel electrodes were positioned 5 to 10 mm apart on the decentralized pudendal nerve in a-chloralose anesthetized cats. The distal. electrode was first tested at different frequencies (1 to 10 kHz) to search for the effective blocking frequency. At a fixed frequency (4, 6, 8 or 10 kHz) different stimulation intensities were then tested to evaluate their blocking effect. Sine waveform or biphasic pulses of a fixed pulse width were also tested. Finally, the proximal electrode was stimulated at 40 Hz for more than 40 minutes and during the same period the distal electrode (6 to 10 kHz) was repeatedly activated for 1-minute intervals in an attempt to block the EUS contraction induced by the proximal electrode. Results: High frequency, biphasic stimulation (6 to 10 kHz) with a pulse width dependent on frequency is optimal to block EUS contractions compared with sine waveform or biphasic pulses of a fixed pulse width. Acute nerve damage caused by blocking stimulation was not observed on neurally evoked urethral pressure. Conclusions: Reversible block of EUS contractions by high frequency, biphasic stimulation of pudendal nerves is a potential method for suppressing detrusor-sphincter dyssynergia and improving voiding in spinal cord injured patients.