<i>Apparent Pulmonary Diffusing Capacity for CO at Varying Alveolar O₂ Tensions</i>

Abstract

The apparent pulmonary diffusing capacity for CO (Dl) has been measured at alveolar O2 tensions from 40 to more than 600 mm Hg. Two methods were used: a) in six healthy subjects a steady state method in which the end-expiratory tension of a continuous record of respired CO concentration was considered ‘alveolar’ and b) in seven healthy subjects a breath holding technique. Dl, measured by either method, decreased with increasing alveolar O2 tension in all subjects, varying as much as fivefold over the entire range. All estimates of Dl were corrected for the presence of COHb in the mixed venous blood. Dl (steady state; breathing air) was on the average 0.85 of Dl (breath holding; breathing air). Submitted on February 15, 1957