It is now nearly 25 years since Ritchie1 first reported that compared with control subjects, patients with irritable bowel syndrome (IBS) exhibit decreased pain thresholds to balloon distension of the pelvic colon. However, the concept that disordered gastrointestinal perception might have a significant pathophysiological role in IBS has only become fashionable during the past decade.

Gastrointestinal sensitivity can be assessed using a number of different stimuli, but the one most commonly used is balloon distension, which can be applied to the gut progressively either in the form of volume or pressure increments (ascending series). The latter involves the use of a barostat which is a computer controlled pump able to inject or withdraw air rapidly from the balloon, thus maintaining a constant pressure irrespective of changes in contractility or tone of the area concerned. In most areas of the gut, a measure of visceral perception is taken as the distension threshold (volume or pressure) to induce discomfort; however, in the rectum, similar thresholds can be obtained for the sensations of gas, call to stool and urgency.

There are a number of technical points that have to be taken into consideration when making comparisons between laboratories. These include whether the distension is applied in a ramp (steady increase), intermittent (returning to baseline between inflations) or stepwise (incremental …