Function of the internal anal sphincter and rectal sensitivity in idiopathic constipation.

Anal manometry was performed in 8 control individuals (group A) and in 13 patients with idiopathic constipation (group B), 6 of whom were grouped apart (group C) because of an elective delay of the intestinal transit in the rectum. The basal pressure of the internal anal sphincter, the rectal inflation volume necessary to elicit the rectoanal inhibitory reflex, and the duration of the reflex were not significantly different in the three groups, while the maximal amplitude of the reflex was significantly lower in group C at 10 and 100 cm3 of rectal distension. However, the amplitude of the sphincteric relaxation and the rectal inflation volumes were significantly correlated (p less than 0.001) in the three groups. The rectal sensitivity was lower in the patient groups and particularly in group C (p less than 0.05 vs. controls up to 50 cm3 of rectal distension). The results obtained do not support the 'outlet obstruction' hypothesis as a mechanism of idiopathic constipation and point out that rectal hyposensitivity seems to be the only abnormality in these patients, particularly in those with an elective delay of the transit in the rectum.