Measurement of lung diffusing capacity by means of C¹⁴O in a closed system

¹ Medical Department and Department of Epidemiology, Blegdamshospitalet, and Institute of Medical Physiology, University of Copenhagen, Copenhagen, Denmark

A method of measuring the lung diffusing capacity (Dl) with radioactive carbon monoxide (C¹⁴O) and nonuniformity of ventilation with nonabsorbable gas in a closed system is described. Treating ventilation as a continuous phenomenon and disregarding dead space, the mathematical equations for uniform and nonuniform ventilation (two lung regions ventilated in parallel) are derived. It is proved that sooner or later the curve for carbon monoxide, plotted on semilogarithmic paper, will be rectilinear. Experiments in six normal subjects and eight patients with chronic lung disease are described. Determinations of the distribution of the ventilation and the Dl are made in separate experiments. Since the method is unreliable at high Dl values, many of the Dl estimations are performed at high oxygen tension, which reduces the apparent Dl. It is shown that the assumption of a uniform distribution of Dl to lung volume explains the experimental findings better than the assumption of a uniform distribution of Dl to alveolar ventilation. Dl was decreased in four of the eight patients.

Submitted on October 15, 1962