Fecal continence for solid and liquid stool: The function of the anal-external sphincter continence reflex and the puborectal continence reflex

BACKGROUND: The anal-external sphincter continence reflex and the puborectal continence reflex control fecal continence by involuntary contractions of the external anal sphincter and puborectal muscle. To date it is unknown what the effect of liquid stool is on these reflexes. OBJECTIVE: The purpose of this study was to analyze the consequence of liquid stool on the presence and function of these fecal continence reflexes. DESIGN: This was a prospective, observational study. SETTING: The study was conducted at the Anorectal Physiology Laboratory, University Medical Center Groningen. PATIENTS: Forty-two healthy subjects were included. MAIN OUTCOME MEASURES: Pressure changes at the level of the external anal sphincter and the puborectal muscle during the anorectal pressure test used to measure voluntary contractions, the balloon retention test used to measure involuntary contractions mimicking solid stool, and the rectal infusion test used to investigate the effect of only water mimicking liquid stool were measured. RESULTS: During the test mimicking solid stool, the pressure at the level of the external anal sphincter increased from the start to the end (132 ± 54 vs 198 ± 69 mm Hg; p < 0.001). The pressure at the level of the puborectal muscle increased simultaneously (30 ± 9 vs 176 ± 52 mm Hg; p < 0.001). After injecting water into the rectum, mimicking liquid stool, we observed immediate activation of the anal-external sphincter continence reflex (87 ± 32 vs 145 ± 36 mm Hg; p < 0.001); this was after a median 30 seconds, whereas no activation of the puborectal continence reflex appeared (26 ± 9 vs 26 ± 7 mm Hg; p = 0.655). LIMITATIONS: We only performed anorectal function tests mimicking 2 types of stool consistencies, namely water and solid. CONCLUSIONS: The anal-external sphincter continence reflex controls fecal continence of both solid and liquid stool. Contrarily, the puborectal continence reflex contributes to solid stool continence only. See Video Abstract at http://links.lww.com/DCR/B286.