Measurements of the Pulmonary Diffusing Capacity for Oxygen During Exercise1,2,3

The pulmonary diffusing capacity is interpreted to reflect the area and permeability of the alveolar-capillary "membrane" (1, 2). This interpretation, particularly as it applies to changes in area, is based principally on the logic of methods used for measuring diffusing capacity rather than on data either bearing out this interpretation or at variance with it. The present study is an attempt to obtain such data by measuring diffusing capacity under circumstances thought to affect primarily the area or primarily the permeability of the alveolar-capillary "membrane." Selected patients who had resections of lung tissue were among those thought to have abnormalities primarily of area, and others with interstitial fibrosis and sarcoid disease were assumed to have defects primarily of permeability. The question arises among patients with resections whether their anatomic loss is associated with a commensurate physiologic loss, i.e., whether additional capillaries open around remaining alveoli in sufficient profusion to preserve the original dimensions of the gas-exchanging surface. The increase in pulmonary vascular resistance demonstrated following large resections (3, 4) indicates attenuation at some point in the lesser circulation and therefore suggests that such preservation is incomplete. This observation does not, however, localize the site of attenuation to