Diffusing capacity of the lung in pulmonary emphysema

¹ Department of Medicine and Cardiopulmonary Laboratory, St. Vincent's Hospital, New York City, and Department of Medicine, Seton Hall College of Medicine and Dentistry, Jersey City, New Jersey

Steady-state CO and O₂ methods for measuring pulmonary diffusing capacity may be affected by abnormal distribution of inspired gas relative to perfusion. These methods frequently fail to separate abnormalities in diffusion from abnormalities in distribution in patients with obstructive emphysema. A rebreathing CO method has been developed which, in theory, is less sensitive to inequalities in distribution. The Dl_CO by this method in 41 normal subjects averaged 20.8 ± 8.6 ml/min mm Hg and was closely correlated with body size and lung volume. Only 3 of 25 patients with obstructive emphysema had a Dl_CO less than the 95% confidence level although the mean value for all of the patients (16.8 ml/min mm Hg) was significantly lower than that of the normal group. It is concluded that loss of diffusing surface is not a common cause of oxyhemoglobin desaturation in obstructive emphysema.

Submitted on December 27, 1963