In subjects with CTT < or =70 h, CTT does not follow a normal distribution but is clustered in subgroups that can be distinguished only by measuring segmental colonic transit. Within these subgroups, there is a marked difference in transit times between IBS patients and normal subjects, suggesting that IBS patients with "normal" CTT are not "normal". The Rome II criteria do not reflect differences in segmental transit times in IBS patients with "normal" CTT. We therefore propose to evaluate segmental transit times in IBS patients with "normal" CTT, before and after treatment, in order to correctly interpretate variations in signs and symptoms. These findings have important implications in evaluating the effect of drugs on bowel function and should help define better inclusion criteria for studies evaluating new drugs for the treatment of IBS.

Abnormal colonic response to food is frequently found in constipated patients, with different patterns according to the type of constipation.

Constipated patients have lower threshold sensation volume, lower constant sensation volume, and lower maximum tolerable volume than controls. Thirty-seven patients (40%) were found to have anismus, based on anorectal manometry. No significant difference was found between constipated patients with anismus and constipated patients without anismus, using anorectal manometry. Constipated patients had longer colorectal transit time than controls, but neither total nor segmental colonic transit time was correlated with the presence or absence of anismus. In patients with anismus, a higher frequency of oesophageal symptoms, dysmotility-like dyspepsia, aerophagia, functional bowel disorders, functional abdominal pain, soiling, and dyschezia was found. In addition, a higher frequency of urinary complaints, sexual complaints, and depression was found. Anismus was associated with increased awareness of constipation, abdominal bloating, and abdominal pain, but not with diarrhoea.