Fig. 1.

Graphical explanation of the computation of parameters used in the paper based on an example of a methane breath concentration curve. The basal concentration is subtracted from the original curve (open squares) at every time point to produce a curve of the net increment over baseline (solid squares), from which a maximum net increment over baseline is determined (arrow); subsequently the area under the curve of the net increments over baseline is computed according to the trapezoidal rule (shaded area), with the occasional negative values set to 0.