Impaired transit and tolerance of intestinal gas in the irritable bowel syndrome

Abstract

Background: Patients with irritable bowel syndrome (IBS) frequently complain of excessive gas but their fasting volume of intestinal gas is apparently normal. We hypothesised that the pathophysiological mechanism involved may be impairment of intestinal gas transit.

Aim: To investigate intestinal gas transit and tolerance in IBS patients compared with healthy subjects.

Methods: A gas mixture (N(2), O(2), and CO(2) in venous proportions) was infused into the jejunum of 20 patients with IBS and 20 healthy controls at 12 ml/min for four hours. Gas evacuation, initially flatus from the anus (two hours) and then intrarectally (two hours), was continuously recorded. Symptom perception (0-6 scale) and abdominal distension were measured at 10 minute intervals.

Results: After two hours of external gas (flatus) collection, 18 of 20 IBS patients had developed gas retention (>400 ml), increased gastrointestinal symptoms (score >3), or abdominal distension (>3 mm girth increment) compared with only four of 20 control subjects. During intrarectal gas collection, 13 of 17 patients still exhibited abnormal responses.

Conclusion: A large proportion of patients with IBS can be shown to have impaired transit and tolerance of intestinal gas loads. This anomaly may represent a possible mechanism of IBS symptoms, specifically pain and bloating.

Figure 1

Evacuation of intestinal gas in patients with irritable bowel syndrome (IBS) (n=20) and healthy subjects (n=20). Gas was infused into the intestine at a constant rate (represented by the broken line) for two hours and collected via an anal cannula. Note that IBS patients expelled a significantly lower volume of gas. Values are means (SEM). **p<0.01.

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).

Figure 3

Individual abdominal distension and gas retention after a two hour intestinal gas infusion in patients with irritable bowel syndrome (IBS) and healthy subjects. Gas retained is volume infused minus volume evacuated. Note that in contrast with healthy subjects, most IBS patients (17/20) retained gas (>400 ml) and/or developed abdominal distension (>3 mm girth increment).