Investigation of small bowel transit time in man utilizing pulmonary hydrogen (H₂) measurements

Pulmonary H₂ excretion was used to quantitate the small bowel transit time in man. This technique is based on the observation that H₂ is produced when carbohydrate is fermented by colonic bacteria and that this H₂ production is reflected by a concomitant increase in breath H₂ excretion. The time, therefore, between ingestion of the unabsorbable disaccharide, lactulose, and the rise in breath H₂ represents the small intestinal transit time of the head of the lactulose load as it passes through the gut. Following ingestion of a mixture of polyethylene glycol (PEG) and lactulose by 9 subjects, transit time measured by H₂ excretion correlated closely with the simultaneously determined time for PEG to reach the distal ileum (r = 0.97). The ileal appearance of PEG preceded the rise in H₂ excretion by a mean of 7.6 minutes. Transit time of 10 Gm. of lactulose in 40 healthy subjects averaged 72 minutes (range 25 to 118). Studies repeated 3 to 5 times in 6 subjects showed good individual reproducibility with subsequent measurements differing from initial by a mean of ±14 per cent. There was an inverse relation between transit time and dose of lactulose ingested by 9 subjects with 5, 10, and 20 Gm. of lactulose having mean transit times of 128 ± 19, 94 ± 15, and 40 ± 8 (S.E.M.) minutes, respectively. This technique appears to provide a simple, safe, and noninvasive means of studying small bowel transit time in man.