RECTAL ADAPTATION TO DISTENSION - IMPLICATIONS FOR THE DETERMINATION OF PERCEPTION THRESHOLDS

Chronic changes in rectal compliance and perception are often associat ed with constipation, but the mechanisms responsible for these changes are not known. These studies evaluated the dynamic response of the re ctal wall to distention and, in a separate investigation, the influenc e of adaptive relaxation on perception thresholds. In Study 1, seven h ealthy volunteers were evaluated using a computer-controlled barostat to maintain continuous isobaric distention of the rectum at urge thres hold over a 25-min period. Changes in intrabag volume were evaluated a t minutes 1, 5, and 25. Study 2 investigated changes in perception thr esholds with different interstimulus intervals (30 s vs. 60 s) in 16 h ealthy subjects. Pressure was incremented in steps of 2 mmHg up to dis comfort threshold. The mean intrabag volume, pressure, and the complia nce index for the first and second 5-s intervals were compared to the last 5 s interval. Statistical analyses were performed using the Wilco xon Sign-Rank test with Bonferonni corrections. Study 1 showed a signi ficant relaxation of the rectal wall in response to balloon distention with volumes consistently increasing from minute 1 to minute 25. Stud y 2 showed a significant change in the compliance index at the thresho ld for moderate urge and intense urge during the 60-s distention that resulted from progressive relaxation of the rectal wall. Study 1 showe d an adaptive response of the rectum to distention. Study 2 confirmed these findings and implied a role for this adaptive response in the de termination of rectal sensory thresholds.