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Anorectal function in normal human subjects: Effect of gender

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Abstract

Multiport anorectal manometry and external anal sphincter (EAS) and internal anal sphincter (IAS) electromyography were conducted in 15 males (41±3 years) and 20 females (43±2 years; 5 nulliparous) during rest, maximum conscious sphincter contraction, rectal distension and increases in intra-abdominal pressure. The basal pressure declined within 15 minutes of insertion of the manometric probe to a stable plateau, 55±4% of the initial value. The maximum basal (91±5 vs 61±6 cm water; mean±SEM), minimum basal (43±7 vs 27±3 cm water) and the maximum squeeze pressures (257±20 vs 107±13 cm water) were higher (p<0.05) in males than females. Distension of a rectal balloon caused a reduction in pressure in all anal channels, that increased in depth and duration as the distending volume was increased. These anal relaxations were associated with rectal contractions and transient increases in the electrical activity of the EAS. Upon deflating the balloon, the anal pressure increased to values that exceeded the pre-inflation values. The pre-inflation (89±4 vs 49±4 cm water), post-inflation (104±9 vs 62±7 cm water) and residual (47±4 vs 30±2 cm water) pressures during rectal distension were significantly higher in males than in females (p<0.05). The higher residual pressure in males was associated with a higher EAS index during rectal distension (0.94±0.10 vs 0.65±0.10 mv s;p<0.05). The lowest volume required to cause a desire to defaecate was significantly higher in males than in females (76±7 vs 48±6 ml;p<0.05) and only 13% of males compared with 55% females (p<0.01) felt pain during rectal distension with 100 ml. During increases in intra-abdominal pressure, all subjects showed increases in pressures in the outermost anal channels, that were associated with increases in the electrical activity of the EAS and were significantly higher in males compared with females (188±17 vs 98± 9 cm water;p<0.05). In conclusion, the data suggest that males have stronger internal and external anal sphincters than females, while females have greater rectal sensitivity.

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Sun, W.M., Read, N.W. Anorectal function in normal human subjects: Effect of gender. Int J Colorect Dis 4, 188–196 (1989). https://doi.org/10.1007/BF01649702

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