EVALUATION OF COLONIC SENSORY THRESHOLDS IN IBS PATIENTS USING A BAROSTAT - DEFINITION OF OPTIMAL CONDITIONS AND COMPARISON WITH HEALTHY-SUBJECTS

To study the role of abnormal visceral perception in the pathophysiology of the irritable bowel syndrome (IBS), we evaluated colonic tone and visceral perception during intracolonic distension using a flaccid balloon connected to a computerized barostat and placed in the descending colon of IBS patients and healthy controls. In the first part of the study, basal colonic tone and response to pharmacological (neostigmine and glucagon) and physiological (1000-kcal meal) stimuli were recorded in nine IBS patients. Colonic tone increased by 72 +/- 27% after injection of neostigmine and decreased by 88 +/- 62% after glucagon. After the meal, the maximal increase in colonic tone was 76 +/- 31% with the total response to the meal lasting 109.7 +/- 32.0 min. In the second part of the study, symptomatic responses (discomfort and pam thresholds) and pressure variations were evaluated during two different methods of distension (stepwise and intermittent) in a randomized order in the nine IBS patients and six healthy controls Each distension method was repeated twice in IBS patients to study reproducibility. In IBS patients, the mean discomfort threshold volume was 172 +/- 76 ml when using stepwise and 167 +/- 43 ml when using intermittent distension. The mean pain threshold volume was 250 +/- 25 ml when using stepwise and 211 +/- 22 ml when using intermittent distension, this difference being statistically significant (P < 0.02). Discomfort and pain threshold volumes recorded during the first session of the same distension method were not different from those recorded during the second one. When comparing IBS patients to controls, the pain threshold was reached at a volume less-than-or-equal-to 300 ml in all IBS patients versus only one control when using stepwise distensions (P < 0.001) and in all IBS patients versus no control when using intermittent distensions (P < 0.001). Intracolonic pressure-volume curves were similar in patients and controls. In conclusion, isovolumic distension of the colon is a reproducible method of evaluating viscerosensitivity, which is significantly increased in IBS patients. This increased viscerosensitivity is not related to abnormal colonic compliance and may, alone or in combination with other colonic abnormalities, explain the symptoms of irritable bowel syndrome.