Uniformity of Alveolar Ventilation at Different Lung Volumes

Abstract

The rate of pulmonary N2 clearance was measured while normal subjects breathed He-O2 at small, natural and large end-expiratory lung volumes. The N2 clearance for the whole lung and its ventilatory subdivisions was progressively slowed as end-expiratory lung volume increased. The fraction of the total effective tidal volume received by the underventilated lung volume, and the extent of uneven ventilation were not significantly different at various lung volumes. The alteration of distribution of a reference gas which occurs during a single inspiration is therefore tentatively attributed to a time-dependent phenomenon, rather than a phenomenon which is volume dependent.