Internal anal sphincter relaxation associated with bisacodyl-induced colonic high amplitude propagating contractions in children with constipation: a colo-anal reflex?

Background Describe the association of internal anal sphincter (IAS) relaxation with colonic high- amplitude peristaltic contractions (HAPCs). Methods Retrospective review of colon manometry tracings of children with constipation to determine the IAS relaxation characteristics associated with HAPCs (HAPC-IASR) events and compare them to the those seen during the performance of the anorectal manometry (ARMRAIR) events. Key Results A total of 70 HAPC- IASRs were observed in 15 patients, 65 after bisacodyl, two during fasting and three after a meal. In 64% of events, the IAS relaxation started when the HAPC reached left colon and in 36% as proximal as the hepatic flexure. High- amplitude peristaltic contraction propagation seems to be important in HAPC-IASR characteristics; those propagating distal to sigmoid colon demonstrated larger and longer IAS relaxation as well as lower residual pressure, but equivalent resting pressure compared with HAPCs ending proximal to sigmoid colon. Although IAS resting pressure was comparable for ARM-RAIRs and HAPC-IASRs, the duration and magnitude of anal relaxation was higher, and the anal residual pressure was lower in HAPC-IASRs. Conclusions & Inferences We demonstrated that IAS relaxation in constipated children is associated with HAPCs migrating in the proximal and distal colon; in most cases, starting when peristalsis is migrating through left colon and in an important proportion while migrating proximally. We also demonstrated that HAPC-IASRs are different from ARM-RAIRs suggesting a neurally mediated reflex. Finally, the IAS relaxation characteristics are highly dependent on the degree of propagation of HAPCs, which could have important implications in the understanding of defecation disorders.