Limitations of indirect methods of estimating small bowel transit in man

Abstract

Experiments were carried out in healthy volunteers to explore the utility of a new [¹⁴C]lactulose breath test for measuring small intestinal transit time in man and to use this procedure to test whether two antidiarrheal agents, codeine and clonidine, alter small intestinal transit time during digestion of a liquid meal. In an initial validation study performed in 12 subjects (three studies in each subject), a liquid test meal containing 10 g [¹⁴C]lactulose was administered and the colonic entry time estimated from the time course of¹⁴CO₂ excretion in breath compared with that of H₂ excretion. There was a fair correlation (r=0.77;P14CO₂ output was delayed when compared to H₂ output and was incomplete. The meal also contained xylose and [¹³C]glycine, permitting the duodenal entry time of the meal to be estimated by the appearance of xylose in blood and¹³CO₂ in breath, respectively. The same liquid meal was then used to examine the effect on small intestinal transit time (colonic entry time minus duodenal entry time) of codeine or clonidine.⁹⁹Tc-sulphur colloid was also added to the meal to permit a comparison of small intestinal transit estimated by imaging with that estimated by the¹⁴CO₂-lactulose breath test.⁹⁹Tc radioactivity appeared in the cecum (as assessed using gamma scintigraphy) about 2 hr before¹⁴CO₂ radioactivity appeared in breath; the correlation between transit time estimated by the two methods was moderate (r=0.61;P14C]lactulose data, small intestinal transit time ranged from14C]lactulose breath test, which has only moderate accuracy, may have occasional utility as a convenient, noninvasive method for estimating small intestinal transit time in man. However, this study also suggests that indirect methods of estimating small bowel transit in man have limitations, variability, and possibly may lack the desired sensitivity.