Normal values for high-resolution anorectal manometry in healthy women: Effects of age and significance of rectoanal gradient

Objectives: High-resolution manometry (HRM) is used to measure anal pressures in clinical practice but normal values have not been available. Although rectal evacuation is assessed by the rectoanal gradient during simulated evacuation, there is substantial overlap between healthy people and defecatory disorders, and the effects of age are unknown. We evaluated the effects of age on anorectal pressures and rectal balloon expulsion in healthy women. Methods: Anorectal pressures (HRM), rectal sensation, and balloon expulsion time (BET) were evaluated in 62 asymptomatic women ranging in age from 21 to 80 years (median age 44 years) without risk factors for anorectal trauma. In total, 30 women were aged 50 years. Results: Age is associated with lower (r0.47, P<0.01) anal resting (63 (5) (50 years), 88 (3) (50 years), mean (s.e.m.)) but not squeeze pressures; higher rectal pressure and rectoanal gradient during simulated evacuation (r0.3, P<0.05); and a shorter (r0.4, P<0.01) rectal BET (17 (9) s (50 years) vs. 31 (10) s (50 years)). Only 5 women had a prolonged (>60 s) rectal BET but 52 had higher anal than rectal pressures (i.e., negative gradient) during simulated evacuation. The gradient was more negative in younger (41 (6) mm Hg) than older (12 (6) mm Hg) women and negatively (r0.51, P<0.0001) correlated with rectal BET but only explained 16% of the variation in rectal BET. Conclusions: These observations provide normal values for anorectal pressures by HRM. Increasing age is associated with lower anal resting pressure, a more positive rectoanal gradient during simulated evacuation, and a shorter BET in asymptomatic women. Although the rectoanal gradient is negatively correlated with rectal BET, this gradient is negative even in a majority of asymptomatic women, undermining the utility of a negative gradient for diagnosing defecatory disorders by HRM.