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

Abstract

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 (r=-0.47, 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 (r=0.3, P<0.05); and a shorter (r=-0.4, 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 (r=-0.51, 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.

Figures

Figure 1

Representative examples of HRM study in asymptomatic younger women with normal (upper panel, 23 s, 39 y) and abnormal rectal BET (lower panel, 360 s, 36 y). Compared to the upper panel, the lower panel reveals higher anal resting and squeeze pressures and also higher anal pressures during simulated evacuation before rectal distention. Rectal distention, which is accompanied by increased pressure in the rectal balloon, induced anal relaxation in both women. During simulated evacuation thereafter, anal pressures increased to a greater extent in the lower than upper panel. Rectal sensory thresholds for first sensation (1), urgency (2), and maximum discomfort (3) were recorded during rectal balloon distention up to 60 mL (upper panel) and 90 mL (lower panel).

Figure 2

Representative example of HRM study in an asymptomatic older woman (80 y) with normal rectal balloon expulsion time (2 s). Compared to the younger women in Figure 1, anal resting pressure was lower and the HPZ was shorter. However, the squeeze response was preserved. Before rectal distention, simulated evacuation was accompanied by increased pressure in the rectal balloon and anal relaxation; the gradient was normal. Rectal sensory thresholds for first sensation (1), urgency (2), and maximum discomfort (3) were recorded during rectal balloon distention up to 90 mL.

Figure 3

Relationship between rectoanal gradient during simulated evacuation and rank-transformed rectal BET in asymptomatic subjects. A more negative gradient was associated with longer rectal BET (r = −0.51, p