Abstract
BACKGROUND & AIMS: High-resolution anorectal manometry (HR-ARM) and fluoroscopic defecography, which are used to diagnose dyssynergic defecation (DD), are performed asynchronously and in different positions. This limits our understanding of the relationship between anorectal pressures and rectal evacuation and the diagnostic utility of HR-ARM. We aimed to assess anorectal pressures in isolation and synchronously with defecography. METHODS: We evaluated anorectal pressures during evacuation with left lateral HR-ARM, seated HR-ARM, and seated, concurrent fluoroscopic barium proctography/manometry (proctomanometry). Rectal evacuation was assessed with proctomanometry and rectal balloon expulsion time (BET). RESULTS: Forty-two (86%) of 49 healthy (22 women) vs 25 of 55 (45%) constipated participants (28 women) evacuated ≥25% barium ("evacuators") (P < .001). During the preparatory phase of defecation, rectal and anal pressures increased concurrently; anorectal descent followed. During evacuation, the anal canal opened and evacuation occurred. During preparatory and evacuation phases, rectal pressure, anorectal descent, and widening of anorectal angle independently predicted evacuation (P < .05). During evacuation, the rectoanal gradient was (1) lower in participants with a prolonged BET and/or reduced rectal evacuation (P ≤ .001) and (2) greatest with proctomanometry, lower during seated HR-ARM, and lowest during left lateral HR-ARM (P < .001). Four clusters based on pressure and motion were associated with evacuator status and BET (P < .001). CONCLUSIONS: Early events-increased rectal pressure (propulsive force), anorectal angle (puborectalis relaxation), and anorectal descent (perineal relaxation)-determine evacuation. Body position and rectal filling affect the rectoanal gradient. Most DD patients have both impaired propulsion and relaxation. Constipated patients with a prolonged BET and/or reduced evacuation have DD.