Advantage of expressing the variations in some digestive parameters as a function of gastric emptying instead of time

Gastric emptying is a major cause of variability when studying gastrointestinal parameters as a function of time. Here, we investigate whether the parametric variability could be reduced by running experiments on a gastric emptying basis rather than on a time basis.

Healthy volunteers were intubated with gastric and duodenal tubes and were given a liquid meal containing polyethylene glycol to monitor gastric emptying. Gastric pH and human gastric lipase (HGL) concentrations were measured. Their variations were plotted as a function of either time or gastric emptying (%). In both cases, mean curves of variation were established by polynomial regression.

When time was the variable used, the overall deviation of the experimental values from the values given by the best-fitting curve was high (chi2 = 33 for gastric pH; chi2 = 1,744 for HGL), and the individual deviations increased with time. When gastric emptying was the variable used, the overall deviation of the experimental values from the values given by the best-fitting curve was much lower (chi2 = 10 for gastric pH; chi2 = 642 for HGL).

Expressing gastric pH or HGL concentration as a function of gastric emptying instead of time makes it possible to reduce the individual variability. This new type of data analysis may be of a general interest to observe specific variations of gastrointestinal parameters induced by drugs, hormones, and meals, and that might be masked by the large intrinsic variability induced by gastric emptying.