Circadian Rhythms of the Indices in the Diffusing Function of the Lung in Healthy Men

Diurnal variation in the lung diffusing function can influence the results of clinical evaluations. We investigated circadian rhythms from diurnal variations of the indices in the diffusing function of the lung. We measured the single breath lung diffusing capacity for carbon monoxide (DLCO) and alveolar volume (VA) in 13 healthy men, and also measured pulse rate at 7:00, 11:00, 15:00, 19:00 and 23:00. To identify the presence of a circadian rhythm from daily variations, data were analyzed by the group mean cosinor method. Significant circadian rhythms were apparent for DLCO/VA, VA and pulse rate. The acrophases for these parameters occurred at 20:15, 5:26 and 18:08, respectively. The double amplitude of DLCO/VA was statistically 4.72%. Our results suggest that diurnal variations in VA and pulse rate may contribute to the variation in DLCO/VA. Although DLCO/VA showed only a small change throughout the day, our findings suggest that the examination of DLCO/VA should be performed preferably at the same time of day in an individual.