On the Evaluation of Pulmonary Diffusing Capacity during Exercise

The purpose of this study is to examine the linearity and the uniformity of increase in pulmonary diffusing capacity for carbon monoxide during exercise. The subjects were four healthy volunteers (22 yr old) who were studied at rest and during exercise. Exercise was performed in duplicate with an electronically braked bicycle ergometer at a load of 50, 70, 90, 110 or 130 watts for about 15 min. Diffusing capacity increased in a linear fashion with increasing oxygen intake as shown in a highly correlation coefficient above 0.98 in each subject. Both slopes of diffusing capacity on oxygen intake and on pulmonary capillary blood volume were uniform among subjects and also among subject groups which was indicated by a comparison with other previous reports. This suggests that increase in diffusing capacity necessary for a unit increase in oxygen intake is not different between individuals and between subject groups and that this increase reflects the uniform change in pulmonary capillary blood volume. In addition, it is implied that diffusing capacity might be a significant factor to determine the over-all oxygen transport capacity. On the other hand, the elevation of regression of diffusing capacity on oxygen intake was different significantly between subjects, which was caused by the difference in diffusing capacity at rest. It was thought that diffusing capacity during exercise expressed as a percent of resting value could not be evaluated adequately.