Abnormal defecation dynamics in chronically constipated children with encopresis.

We studied the ability to defecate water-filled balloons in 16 healthy and 37 chronically constipated children with encopresis. The act of bearing down for defecation was evaluated by measuring intra-abdominal pressure, rectal pressure, anal pressure, external anal sphincter EMG activity, and rectal sensation and rectal volume necessary to inhibit the anal sphincters. Fifteen control children and 20 constipated children were able to defecate rectal balloons. External sphincter activity decreased during the act of bearing down for defecation in 100% of controls, in 58% of constipated children able to defecate balloons, and in only 7% of patients unable to defecate balloons. Constipated children unable to defecate balloons were significantly less likely to recover after conventional laxative treatment than constipated children able to defecate balloons (P less than 0.02). Increased external sphincter activity during defecation appears to be the factor that prevents balloon expulsion in constipated children and could be the cause of their chronic fecal retention.