STUDIES ON INTRAPULMONARY MIXTURE OF GASES. IV. THE SIGNIFICANCE OF THE PULMONARY EMPTYING RATE AND A SIMPLIFIED OPEN CIRCUIT MEASUREMENT OF RESIDUAL AIR

Abstract

In preceding papers of this series, we have studied (1) the relative effectiveness of mixing or distribution of tidal air into alveolar spaces in normal and abnormal subjects, and have proposed (2) an open circuit method for residual air determination, in which nitrogen in the lungs is washed out by continuous inhalation of pure oxygen. The present paper (a) gives the results of a number of determinations of residual air, by the open circuit method, in normal subjects and patients with chronic cardiac or chronic pulmonary disease; (b) offers certain simplifications of technique in the open circuit method; and (c) suggests further significance of some of the data which this method provides. It will simplify the succeeding discussion if a brief review is given of the theoretical basis of the open circuit method of residual air determination. The principle underlying all residual air methods which employ an inert gas, such as nitrogen or hydrogen, is the measurement of this inert gas before and after its distribution (by means of a period of breathing) between an unknown volume (the lungs) and a known volume (the spirometer). The relationship is described by a simple formula. Let nitrogen be the inert gas measured: (Nitrogen percentage in lungs at start X lung volume) + (nitrogen percentage in spirometer at start X spirometer volume) (nitrogen percentage in lungs at end X lung volume) + (nitrogen percentage in spirometer at end X spirometer volume). For purposes of simplification, the correction factor due to nitrogen excreted from the body (3) is here disregarded.