Anorectal sampling: a comparison of normal and incontinent patients.

It has been suggested that sampling of rectal contents by the anal canal may play a role in the continence mechanism. To investigate this concept we studied 18 patients with faecal incontinence and 18 age and sex matched controls. A microtransducer catheter was positioned so that pressures were recorded from the rectum, the junction of the upper and middle thirds of the anal canal and the lower anal canal. Recordings were taken at rest and while distending the rectum with air in a balloon, and then with air injected freely into the rectum. Sampling (equalization of the rectal and upper anal canal pressures) was seen to occur spontaneously in 16 of the controls and only 6 of the incontinent group (P less than 0.02) and induced sampling occurred at a higher rectal volume in the incontinent group than in controls for freely injected air (P less than 0.002). Defective anorectal sampling may be an important contributory factor in the pathogenesis of anorectal incontinence.