A Method for the Determination of the Volume of AIr in the Lungs: Measurements in Chronic Pulmonary Emphysema*

The present study is concerned with the meas-urement of the functional residual capacity (FRG) in chronic pulmonary emphysema by a gas dilution method, i.e., the washout of nitrogen from the lung during prolonged oxygen breathing. There have been many methods in use to measure the FRC (or the residual volume) since Davy in 1800 measured his own residual volume by rebreathing hydrogen, which he had made himself, from a balloon (1). These methods, both the open circuit (washout) and closed circuit (rebreathing fromn a balloon or spirom-eter), have in general followed a consistent historic trend in that longer and longer periods of washout or rebreathinig have been required in later methods: Davy in 1800 rebreathed for 20 sec-onids (1), Grehant in 1864 for 6 inspirations (2), Van Slyke and Binger in 1923 for 5 minutes (3), Christie and Bates for 7 minutes (4, 5), Darling, Cournand and associates for 7 or 11 minutes (6, 7) and Briscoe, Becklake and Rose for 12 minutes (8, 9). In justice to these earlier workers it should be mentioned that most of those quoted above and others (10, 11) realized that to get the best results in emphysema some-what longer studies were desirable. M\ recent studies of the N2 or helium wash-out in patients with chronic pulmonary emphy-sema have found detectable quantities of these inert gases being washed out of the lungs, dis-tinct from those washed out from tissues, even after 20 to 40 minutes of 02 breathing (12-18). The present study describes a method in which all the N2 eliminated from the lung during 15 minutes, or longer, of oxygen breathing is meas-ured. Moreover, the quantity of N2 which would be eliminated in a longer study is esti-* This investigation was supported by a research grant