Influence of pudendal block on the function of the anal sphincters.

TLDR

The anal sphincter function has been studied by continuous recordings of anal canal pressure and striated sphincter electromyography during rectal distension with an air balloon. Ten healthy subjects were examined before and after bilateral pudendal block that paralyzed the striated sphincter, allowing isolation of internal sphincter activity. The internal sphincter accounts for about 85 % of resting anal canal pressure, drops to roughly 40 % after sudden rectal distension, and rises to about 65 % during sustained distension, indicating it is the primary contributor to continence at rest while the striated sphincter maintains continence during sudden distension and both systems play roles during constant distension.

Abstract

The function of the anal sphincters has been studied by obtaining continuous recordings of the pressure in the anal canal and the electromyographic activity in the striated sphincter muscles during expansion of the ampulla recti by means of an air balloon. Ten healthy subjects were examined before and after the striated muscles had been entirely paralysed by bilateral pudendal block, making it possible to record the activity from the internal sphincter alone. The results show that the internal sphincter contributes about 85% of the pressure in the anal canal at rest but only about 40% after a sudden substantial distension of the rectum. During constant substantial rectal distension, the internal sphincter accounts for about 65% of the anal pressure. It is concluded that the internal sphincter in the adult is chiefly responsible for anal continence at rest. In the event of sudden substantial distension of the rectum, continence is maintained by the striated sphincter muscles, whereas both sphincter systems probably have an important function during constant distension of the rectum.