Rectal wall contractility in response to an evoked urge to defecate in patients with obstructed defecation

The aim of this study was to examine rectal sensory perception and rectal wall contractility in response to an evoked urge to defecate and to identify differences between control subjects and patients with obstructed defecation.

Twenty control patients (10 men; median age, 47 (range, 17-78) years) and 29 female patients with disabling obstructed defecation (median age, 48 (range, 18-70) years) entered the study. Under radiologic control, an infinitely compliant barostat balloon was inserted over a guide wire into the proximal part of the rectum. Additionally, a latex balloon was introduced into the distal part of the rectum. This latex balloon was inflated until an urge to defecate was experienced. Simultaneously, rectal wall contractility was assessed by measuring the variations in barostat balloon volume. These variations were expressed as percentage changes from baseline volume.

By comparing controls and patients with obstructed defecation, a significant difference was found regarding mean distending volume required to elicit an urge to defecate (135 +/- 38 vs. 214 +/- 87 ml of air; P < 0.001, Mann-Whitney U-test). In all controls, the evocation of an urge to defecate induced a pronounced increase in rectal tone, proximal to the distal stimulating balloon. By comparing controls and patients, the increase in rectal tone was found to be significantly higher in control subjects (35 +/- 10 vs. 9 +/- 10 percent; P < 0.001). Twenty-five patients (86 percent) showed no or only minimum (<20 percent) increase in rectal tone during the perception of an urge to defecate. In 14 of these patients, the threshold for this perception was increased. Only four patients (14 percent) showed a relatively normal increase (>20 percent) in rectal tone. However, their threshold for perception was greatly increased.

The assembly used in this study provides a useful tool for investigation of rectal evacuation. In all of our patients, obstructed defecation was associated with abnormal rectal sensory perception and/or altered rectal wall contractility.