Block of external urethral sphincter contraction by high frequency electrical stimulation of pudendal nerve

Purpose: High frequency electrical stimulation (1 to 10 kHz) of the pudendal nerve was evaluated as a method to block the external urethral sphincter contractions and increases in intraurethral pressure induced by electrical stimulation of pudendal nerve efferent axons. Materials and Methods: Two stainless steel electrodes were positioned 5 to 10 mm apart on the decentralized pudendal nerve in alpha-chloralose anesthetized cats. The most central electrode was electrically stimulated (40 Hz) to activate the efferent input to the external urethral sphincter. The change in the neurally evoked urethral responses by high frequency electrical stimulation of the distal electrode using a sinusoidal waveform or biphasic charge balanced pulses was examined. Results: For the 2 waveforms stimulation frequencies between 6 and 10 kHz were most effective in blocking external urethral sphincter activation. Intraurethral pressures caused by contractions of the external urethral sphincter were decreased more than 90% by high frequency stimulation using effective frequencies. When high frequency stimulation was turned off, external urethral sphincter responses recovered rapidly. Conclusions: Reversible block of the external urethral sphincter contractions by high frequency electrical stimulation of the pudendal nerves is a potential method for suppressing detrusor-sphincter dyssynergia and improving voiding in spinal cord injured patients.