Pulmonary diffusion capacity for Co at varying alveolar oxygen tensions and different alveolar volumes

In six healthy nonsmoker volunteers pulmonary diffusion capacity for Co (DLCO) was determined by single breath holding technique. Multiple measurements of DLCO were taken with PAO2 from 70 to 610 mm Hg, out of which at least 10 tests were performed between 100 to 140 mm Hg. A wide and non uniform inverse relationship was found between DLCO and PAO2 from 70 to 610 mm Hg. In narrow range of 100-140 mm Hg, a highly significant linear negative correlation was found. To find out corrected DLCO at PAO2 120 mm Hg, expressed as DLCO120, a correction factor of 0.45% for each mm Hg change in PAO2 should be applied to measured DLCO inversely. By regulating inspiratory volume, DLCO was studied at different alveolar volumes and there was a direct positive correlation between them. DLCO should be measured at maximum alveolar volume, as with one percent fall in VA there is 0.69% decrease in DLCO. This new method of expressing DLCO as DLCO120 at maximal effective alveolar volume will be more useful in studying the effects of factors affecting DLCO and for interlaboratory comparison.