Abstract

The defaecatory mechanism using a balloon model with simultaneous measurement of intrarectal pressure has been studied in 15 control subjects with normal bowel habit and in 39 patients with chronic constipation; 31 with a normal barium enema and eight with idiopathic megarectum. Fourteen of those with a normal barium enema had prolonged whole gut transit times as measured by radio-opaque shapes. The ability of the patient to expel a rectal balloon containing 50, 100, and 150 ml of water, lying on their side in the left lateral position was tested and if unsuccessful, in the sitting position with the knees raised. All but one of the control subjects could expel balloons in the left lateral position. Only five of 17 constipated patients with normal barium enemas and transit times could expel balloons lying on their side although a further three could do so when sitting. None of 14 patients with slow transit and normal barium enemas could expel balloons in left lateral position although three could do so when sitting. Patients with megarectum could not expel balloons in either position. Levels of intrarectal pressure with straining were not significantly different between controls, who were able to expel balloons, and constipated patients with a normal barium enema, but were greater (p less than 0.01) in patients with megacolon than in control subjects. Using the balloon model a disorder of the defaecatory mechanism is present in patients with constipation of different types, but this is not because of an inability to raise intrarectal pressure.