Lung diffusing capacity: rebreathing method, applicability in nonuniform ventilation

¹ Department of Epidemiology, Medical Department, and Central Laboratory, Blegdamshospitalet, Copenhagen, Denmark

We have calculated how the carbon monoxide concentration changes when subjects with different distributions of ventilation and lung diffusing capacity (Dl) respire in a small bag. The curve [log_e CO concentration in the bag] versus [time] will sooner or later appear as a straight line. Dl is calculated from the slope of the rectilinear section of the curve and from lung and bag volume. If the curve becomes rectilinear within the period considered, Dl is calculated too low. In some cases the curve will not be rectilinear until more than 45 sec have passed, but will appear to be rectilinear during the period from 30 to 45 sec. If such an experiment is discontinued when 45 sec (the usual duration of experiment) have passed, Dl can be calculated at too high, at correct, or at too low values.

Submitted on February 18, 1964