Maximal Diffusing Capacity of the Lungs

Abstract

Multiple detns. of diffusing capacity were performed during treadmill exercise on 3 normal subjects, using the low O2 method of Lilienthal et al. The severity of exercise and of hypoxia were both varied over a wide range. In the 2 younger subjects, the diffusing capacity rose sharply at levels of O2 consumption between 600 and 1200 ml./min. There was no further rise when the O2 consumption was increased to more than 2200ml./min. In the older subject, the diffusing capacity rose at values of O2 consumption between 500 and 900 ml./ min. with no further rise at approx. 1200 ml./min. Findings suggest that max. values for diffusing capacity were achieved and that the max. diffusing capacity was lower in the older subject. Data also suggest that the max. diffusing capacity can be reached either by hard physical work or by moderate work in association with severe hypoxia. Technically, both exercise and severe hypoxia facilitate the detn. of diffusing capacity by the method employed. Various physiological mechanisms affecting the behavior of the pulmonary capillary bed during exercise and hypoxia are discussed. The max. diffusing capacity is thought to provide a quantitative estimate of the diffusion characteristics of the entire diffusing surface of the lungs.