Inadequate Rectal Pressure and Insufficient Relaxation and Abdominopelvic Coordination in Defecatory Disorders

BACKGROUND & AIMS: Diagnostic tests for defecatory disorders (DDs) asynchronously measure anorectal pressures and evacuation and show limited agreement; thus, abdominopelvic-rectoanal coordination in normal defecation and DDs is poorly characterized. We aimed to investigate anorectal pressures, anorectal and abdominal motion, and evacuation simultaneously in healthy and constipated women. METHODS: Abdominal wall and anorectal motion, anorectal pressures, and rectal evacuation were measured simultaneously with supine magnetic resonance defecography and anorectal manometry. Evacuators were defined as those who attained at least 25% rectal evacuation. Supervised (logistic regression and random forest algorithm) and unsupervised (k- means cluster) analyses identified abdominal and anorectal variables that predicted evacuation. RESULTS: We evaluated 28 healthy and 26 constipated women (evacuators comprised 19 healthy participants and 8 patients). Defecation was initiated by abdominal wall expansion that was coordinated with anorectal descent, increased rectal and anal pressure, and then anal relaxation and rectal evacuation. Compared with evacuators, nonevacuators had lower anal diameters during simulated defecation, rectal pressure, anorectal junction descent, and abdominopelvic-rectoanal coordination ( P <.05). Unsupervised cluster analysis identified 3 clusters that were associated with evacuator status (P <.01), that is, 10 evacuators ( 83%), 16 evacuators (73%), and 1 evacuator (5%) in clusters 1, 2, and 3, respectively. Each cluster had distinct characteristics (eg, maximum abdominosacral distance, rectal pressure, anorectal junction descent, anal diameter) and correlates that were more (clusters 1-2) or less ( cluster 3) conducive to evacuation. Cluster 2 had 16 evacuators ( 73%) and intermediate characteristics (eg, lower anal resting pressure and relaxation during evacuation; P <.05). CONCLUSIONS: Women with DDs and a modest proportion of healthy women had specific patterns of anorectal dysfunction, including inadequate rectal pressurization, anal relaxation, and abdominopelvic-rectoanal coordination. These observations may guide individualized therapy for DDs in the future.