Diffusing capacity and blood flow in different regions of the lung

¹ Department of Physiology and Pharmacology, Graduate School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania

We have measured the disappearance of CO and, in most instances, acetylene relative to helium from early and late portions of the expired alveolar gas after 1.5–20 sec of breath holding at rest in four normal subjects and seven patients with obstructive emphysema and three with sarcoidosis. In all individuals, except one patient with emphysema, graphs of the logarithm of the relative expired alveolar CO concentrations in early and late expired samples against time of breath holding were parallel, but those for the late expired samples lay below these for the early expired samples. The equality of the slopes of the two curves indicated that net diffusing capacity/alveolar volume for those regions of the lungs contributing to the two samples is similar even in severe obstructive disease. The displacement of the disappearance curves can be explained by errors in estimation of the time the gas spends in the alveoli and by an increased rate of CO disappearance caused by reduced alveolar volume during expiration.