[Alveolar pressure during forced vital capacity. Method and application (author's transl)]

A method allowing the measurement of mean alveolar pressure (Palv) during forced vital capacity is described. The basis of the method is the calculation of the difference between mouth and chest flows, which are measured with a Fleisch pneumotachograph (PTG) and a volumetric plethysmograph respectively. Metrologic conditions of the calculation are discussed. During the forced expiration, the estimation of Palv is realized in good metrological conditions. During inspiration, the thermal condition of the PTG varies and the measured flow is not accurate; thus, the calculated Palv is only an estimation. Some examples of Palv vs mouth flow loops are shown. The simultaneous recordings of this loop and the usual V/V loop allow us to know if a low mouth flow is due to a high pulmonary impedance with high Palv or to a low Palv. For a given impedance, Palv measurement seems to be a good test of the respiratory muscle function.