Abstract
The single-breath carbon monoxide diffusing capacity of the lung is based on the washout volume (WV) of 750–1,000 mL and the sampling volume (SV) of 500–1,000 mL. According to the Practical Handbook Respiratory Function Testing of The Japanese Respiratory Society, WV can be reduced to about 500 mL in cases of low vital capacity or forced expiratory volume in one second. In this study, we compared the diffusing capacity of the lung for carbon monoxide (Dlco) in 21 healthy subjects between the standard method (WV 750 mL, SV 1,000 mL) and the WV reducing method in five conditions (only WV was reduced by 100 mL from 500 mL), examined the effects for the measured values and its validity of the methods. No significant differences in measured values were found between the standard method and the WV reducing methods up to 300 mL, and significantly lower values were found for the WV reducing methods below 200 mL. In addition, strong correlations were found between the standard method and the WV reducing methods up to 300 mL. From the above, Dlco could provide reliability results as a reference value in cases of WV reduced to 300 mL. These results suggested measurable cases may be expanded.
