Spontaneous variation of anal "resting" pressure in healthy humans.

To investigate anal sphincter performance during sleep and after a meal, a two-channel micro-transducer probe was used for 12-h stationary recording of basal anal pressure overnight in eight healthy male volunteers. It was shown that the basal anal pressure ("resting" pressure) exhibits three distinct patterns of cyclic activity changes in all subjects: a long-term rhythm with a prominent decrease of pressure during which sleep was approximately circadian, an ultradian rhythm of approximately 20 to 40 min in length that was more prominent at night, and spontaneous relaxations of the sphincter tone occurring between 3 and 20 times per hour with the maximum frequency after breakfast. These data indicate that the anal sphincter is a dynamic structure not often at rest. Long-term anorectal manometry may be supplementary to short-term clinical evaluation of anal sphincter performance in healthy subjects as well as in patients with defecation disorders.