New method for the dynamic assessment of anorectal function in constipation.

A new dynamic technique for the investigation of anorectal function has been developed. This involves radiological visualization of the rectum during voiding of a semisolid radio-opaque contrast medium, and simultaneous measurement of the intrarectal pressure and electrical activity of the external anal sphincter. The method has been used to study patients (n = 16) with profound difficulty passing formed stool. It has demonstrated an abnormal increase in the activity of the puborectalis and superficial and sphincter muscles during voiding in these patients, compared with normal subjects (n = 6). The inability to void was associated with failure to widen the anorectal angle on straining.