Two new pulmonary functional indexes suggested by a simple mathematical model.

We propose a new experiment consisting of several 'single-breath' tests made during different stages of nitrogen (or other inert gas) washouts and then measuring the slope of the alveolar plateau divided by the mean expiratory nitrogen concentration (normalized slope). A simple mathematical analysis predicts that: (a) The normalized slope should grow in function of the breath number n (after the beginning of the washout) chosen to perform the single breath test. It should reach an asymptotic value which is an index of the asynchroism of the expiratory movement (sequential ventilation): Isv. (b) The index of the distribution of the ventilation (IDV) is not the slope of the alveolar plateau as usually considered, but the slope of the normalized slope of the alveolar plateau plotted in function of n and divided by ISV.