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 pathophysiolo gy of the irritable bowel syndrome (IBS), we evaluated colonic tone an d visceral perception during intracolonic distension using a flaccid b alloon connected to a computerized barostat and placed in the descendi ng colon of IBS patients and healthy controls. In the first part of th e study, basal colonic tone and response to pharmacological (neostigmi ne and glucagon) and physiological (1000-kcal meal) stimuli were recor ded in nine IBS patients. Colonic tone increased by 72 +/- 27% after i njection of neostigmine and decreased by 88 +/- 62% after glucagon. Af ter 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 sec ond part of the study, symptomatic responses (discomfort and pam thres holds) and pressure variations were evaluated during two different met hods of distension (stepwise and intermittent) in a randomized order i n the nine IBS patients and six healthy controls Each distension metho d 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. T he mean pain threshold volume was 250 +/- 25 ml when using stepwise an d 211 +/- 22 ml when using intermittent distension, this difference be ing statistically significant (P < 0.02). Discomfort and pain threshol d volumes recorded during the first session of the same distension met hod 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 IB S patients versus no control when using intermittent distensions (P < 0.001). Intracolonic pressure-volume curves were similar in patients a nd controls. In conclusion, isovolumic distension of the colon is a re producible method of evaluating viscerosensitivity, which is significa ntly increased in IBS patients. This increased viscerosensitivity is n ot related to abnormal colonic compliance and may, alone or in combina tion with other colonic abnormalities, explain the symptoms of irritab le bowel syndrome.