Preservation of faecal continence during rises in intra-abdominal pressure: is there a role for the flap valve?

Studies were carried out in 15 normal subjects and 14 patients with idiopathic faecal incontinence to test whether a rectoanal flap valve could be responsible for maintaining faecal continence in man. Intraluminal pressures were recorded from the rectum and from three sites in the anal canal during serial increases in intra-abdominal pressure, produced by forced expiration into a sphygmomanometer keeping the height of the column of mercury at prescribed levels. The anal pressures in the normal volunteers always remained higher than the intrarectal pressures even when these were as high as 230 cm H2O. This pressure gradient was the reverse of that which would be found if an anterior rectal flap valve maintained continence and suggests instead that continence is normally maintained by a reflex contraction of the external anal sphincter. The anal pressures in patients with idiopathic faecal incontinence, however, fell below the rectal pressure as the intra-abdominal pressure increased, creating the conditions for a flap valve. The valve was incompetent, however, because fluid infused into the rectum leaked from the anus whenever the rectal pressure exceeded the anal pressure.