The internal anal sphincter response: manometric studies on its normal physiology, neural pathways, and alteration in bowel disorders.

Manometric recordings of lower bowel motility have been difficult to interpret because 1) this segment frequently displays no spontaneous activity for periods as long as 6 hours (1), 2) attempts to stimulate normal activity have been met with inconsistent results (2-4), and 3) the activity observed has not been clearly related to this segment's primary function, defecation (2-7). We have described previously (8) an internal anal sphincteric response that can be elicited at will, is regularly reproducible, and is analogous to the physiological concomitants of defecation. This response is essentially that reported in 1877 by Gowers, who found that insufflation of air into the rectum produces relaxation of the internal anal sphincter (9). Very few investigations of this response, however, have subsequently been carried out. This investigation was designed to define in the human 1) the normal physiology of the sphincter response, 2) the neural pathways involved, and 3) the effect of various disorders of bowel function upon this response.