Figure 2  .

Individual perception scores and gas retention after a two hour intestinal gas infusion in patients with irritable bowel syndrome (IBS) and healthy subjects. Perception of abdominal symptoms was scored on a seven point scale (0-6). Gas retained is volume infused minus volume evacuated. Broken lines represent the upper limits for perception (score 3—that is, mild to moderate) and gas retention (400 ml, see text) in healthy subjects. Only 4/20 healthy subjects progressively retained gas exceeding 400 ml. In contrast, most IBS patients (18/20) retained gas (>400 ml) and/or developed moderate to severe symptoms (>3 perception score).