Functional pattern of sacral root stimulation in dogs. II. Urethral closure.

Ten dogs were used for electrostimulation of the sacral roots to improve urethral sphincter closure. To induce and maintain urethral closure in longstanding stimulation, a variety of stimulation patterns was investigated systematically. With continuous stimulation, the induced sphincteric response faded corresponding with the increase in frequency of stimulation applied, but in phasic stimulation with a stimulation/rest ratio of 1:2, strong sphincteric contractions were reproducible after each rest interval. If the stimulation bursts were shortened to 30-60 msec., interrupted by an off-time of again twice the duration of the stimulation, unfused sphincteric tetani were induced, resulting in a sinusoidal oscillating closure pressure that did not drop in the prestimulus baseline during the off-time. A sufficient sphincteric closure pressure could thus be sustained over 1 hour of uninterrupted stimulation.