Relationship between anal canal tone and rectal motor activity

The anal sphincters facilitate fecal continence by maintaining a pressure barrier; whether proximal contractile events influence this barrier is unknown. The aim of this study was to determine whether a relationship exists between anal canal pressures and rectal motor activity. A fully ambulatory system for prolonged pressure recording was developed. In 12 healthy subjects (seven males and five females; mean age, 35 years; range, 22-43 years), a flexible transducer catheter (outside diameter, 4.5 mm) was introduced endoscopically such that sensors were 2, 3, 8, 12, 18, and 24 cm from the anal orifice. Twenty-four-hour spontaneous motor activity was stored in a 2.5-megabyte portable recorder for later transfer to a Microvax II for computerized analysis and display. Mean anal canal pressure was calculated, and rectal motor complexes (RMCs) were characterized. Mean anal canal resting pressure was 75±12 mmHg. During sleep, anal pressures displayed cyclic decreases (mean periodicity, 1.6 hours; range, 1-4 hours), during which the mean ±SD pressure trough was 15±4 mmHg (range, 8-21 mmHg). RMCs were identified in all subjects: mean frequency, 16 per 24 hours (range, 12-22 per 24 hours); duration, 15.3 minutes (range, 8-35 minutes); contractile frequency, two to three per minute; mean peak amplitudes, 58±18 mmHg; and periodicity, 78±24 minutes (range, 35-265 minutes). Importantly, an RMC was invariably accompanied by a rise in mean anal canal pressure and contractile activity such that pressure in the anal canal was always greater than pressure in the rectum. Anal canal relaxations never occurred during an RMC. Motor activities of the rectum and of the anal canal may be related; the onset of rectal contractions was accompanied by increased resting pressure and contractile activity of the anal canal. This temporal relationship represents an important mechanism preserving fecal continence.