Rectoanal sensorimotor response in humans during rectal distension

PURPOSE: Rectal perception facilitates maintenance of continence and defecation. Whether perception is associated with motor changes in anorectum is unclear. We examined sensory and motor responses of the anorectum during rectal distention. METHODS: Stepwise graded rectal balloon distensions were performed in 23 healthy subjects by placing a six-sensor probe in the anorectum. Manometric changes, rectoanal reflexes, and sensory thresholds were assessed. Studies were repeated in six subjects. RESULTS: All subjects showed rectoanal inhibitory and contractile reflexes, but rectal perception was associated with an anal contractile response (sensorimotor response). In 4 subjects (17 percent) the sensorimotor response first occurred synchronously with a sensation of fullness (Group 1) and in 19 (83 percent) with a desire to defecate (Group 2). Mean balloon volume for inducing the sensorimotor response in Groups 1 and 2 were 80±14 ml and 96±26 ml (P>0.05). The onset, amplitude, duration, and area under curve of the response were similar in both groups. At higher volumes of balloon distention, all subjects (n=23) reported a desire and an urge to defecate. The sensorimotor response associated with an urge to defecate had higher amplitude (P=0.01) and higher area under curve (P=0.001) compared with that associated with a desire to defecate. Repeat studies showed good reproducibility (intraclass correlation coefficient=0.9; P<0.05). CONCLUSIONS: A desire to defecate is associated with a unique, consistent, and reproducible anal contractile response: the sensorimotor response. This response could play an integral role in regulating anorectal sensation and function.