Anorectal angle enhances faecal continence

This study was performed with an in vitro model to assess the relative importance of sphincter pressure and anorectal angulation in maintaining faecal continence. Water and semisolid material were infused separately into porcine intestine compressed by an inflatable cuff until leakage was observed. Angulation of the bowel with respect to the cuff was 180 degrees and then 90 degrees. With water, holdback pressure was independent of angulation. In contrast, when semisolid material was used, angling the bowel to 90 degrees increased holdback pressure by at least 100 per cent. Measurements taken in solid tubes demonstrated that both a restriction in the tube and an unconstricted 90 degrees bend produced a resistance to flow of the semisolid material which was dependent on flow rate. These data suggest that liquid is retained in the rectum by occlusion pressure alone, whereas the retention of semisolid material is enhanced by angulation.