Inferior rectal nerve stimulation for anal sphincteric control: experimental study.

The effect of inferior rectal nerve (IRN) stimulation on sphincteric control of the rectal neck was studied in eight dogs. With the dog under anesthesia, the IRN was exposed through para-anal incision, and a bipolar electrode was applied to it. Response of the rectal and rectal neck pressures as well as external and sphincter (EAS) EMG activity to IRN stimulation was determined. IRN stimulation resulted in increase in both the rectal neck pressure (P < 0.01) and the EMG activity of EAS (P < 0.01). Response increased with increasing stimulation frequency up to 50 Hz, above which no more response occurred. Rectal pressure showed no change (P > 0.05). Both the latency and the duration of response decreased with increased stimulation. The response was resumed after an off-time of twice the stimulation phase. Long-term activation has not been associated with an impairment of nerve responsiveness or with electrode migration or break. To conclude, a stimulus of 50 Hz evokes the most adequate EAS contraction and RN pressure elevation. Chronic electrostimulation of the perineal nerve may restore EAS tone.