Abstract
Pulmonary diffusing capacity for CO (DL), the diffusing capacity of the pulmonary capillary membrane, and pulmonary capillary blood volume were measured for 63 male and female subjects aged 17 to 33 years in both sitting and supine postures. From the relationship of these values to morphological factors, the existence and cause of sexual and ethnic differences in DL were investigated. The average DL values for males in both positions were about 35% larger than those for females; even when corrected by body size, such as body surface area or stature, significant sexual difference was found. This difference disappeared when DL was corrected by difference in alveolar volume. That is, differences between men and women in body size and ratio of lung volume to body size are thought to account for sexual difference in DL. From comparison with other reports, an ethnic difference in DL was recognized between Caucasians and Japanese, and its cause is suggested to be the same as cause which accounts for the difference by sex among Japanese.
