Relationship between viscoelastic properties of the rectum and anal pressure in man.

Viscoelastic properties of the rectal wall and anal sphincter pressure were studied simultaneously in 25 normal children. During rectal distension for 60 s, with varying volumes of air, the rectal pressure varied as the sum of two exponential functions of the time plus an asymptotic constant. A rectoanal inhibitory reflex was elicited during these distensions. The exponential decrease of the rectal pressure corresponded exactly to the return of the upper anal canal pressure to the resting value in some subjects. In others, the upper anal canal remained relaxed as long as the rectal ampulla was distended, except with smaller volumes. The results obtained may be explained by an analogical rheological linear model.