DIFFERENCES IN MECHANISMS OF NORMAL AND DISORDERED DEFECATION BETWEEN MEN AND WOMEN

Background and Aims. Among healthy persons (PMID 30957382) and constipated patients (PMID 27891696), anorectal pressures measured in an empty rectum in the lateral position differ between men and women. These studies did not assess rectal evacuation. Our aims were to compare anorectal pressures and rectal evacuation in male and female healthy persons and constipated patients.
Methods: Seated barium proctomanometry was used to simultaneously measure anorectal pressures (HRM) and rectal evacuation (barium defecography) in 25 healthy women (35 [14] y), 27 healthy men (27 [15] y), and 20 male (49 [13] y) and 26 female patients (38 [12] y) with chronic constipation. The seated balloon expulsion time (BET) was also assessed. Wilcoxon’s Rank Sum and two-sample t-tests compared anorectal pressures and motion between men vs women and evacuators vs nonevacuators (i.e., rectal evacuation < 25%). Variables were summarized at baseline, during the preparatory phase, which began after participants were instructed to defecate but ended before evacuation commenced, and rectal evacuation.
Results: 45 of 52 healthy persons (87%) but only 23 of 46 patients (50%) were evacuators (P<.0001). During the preparatory phase, rectal and anal pressures increased simultaneously even in evacuators (Figure 1, Table 1). However, anorectal descent was modest and, by definition, the anal canal was closed. Thereafter, (ie, during evacuation) the anorectum descended further and the anal canal opened. Such descent, anal diameter, and the rectoanal gradient (P<.0002) were smaller in nonevacuators than evacuators. Although the rectal pressure increment was also lower in nonevacuators than evacuators, differences were not significant (P= .1). Differences between male vs female evacuators and separately nonevacuators were as follows. Among evacuators, men had a greater rectal pressure and less perineal descent than women (P=.01). Among nonevacuators, rectal and anal pressures were greater in men than women (P=.02). Evacuation was associated with the BET (P<.0001) (Table 1).
Conclusions: In this large, prospective study of asymptomatic and constipated men and women, normal defecation was characterized by increased rectal and anal pressures during the preparatory phase followed by anorectal descent and anal opening during evacuation. Extending observations with MR proctomanometry among women in the same cohort, these findings demonstrate that the anal sphincter contracts at the start of normal defecation. After rectal pressure exceeds anal pressure, the anal pressure declines and the rectoanal gradient becomes positive. Nonevacuators have less anorectal descent and a lower rectoanal gradient than evacuators. Among evacuators, men have greater rectal pressures but less perineal descent vs women. Increased outlet resistance is bigger contributor to reduced evacuation in men than women.