Diurnal Variation of Respiratory Function, Independent of Air Quality

Abstract

Specific airway conductance was determined every four hours, around the clock, on six normal subjects who were confined to an environmentally controlled chamber for two six-day study periods. In the first study period the subjects breathed clean filtered air the first three days and ambient air the last three days. In the second study the order was reversed: ambient air was breathed the first three days, and clean filtered air the last three days. Temperature, relative humidity, and the sleep-awake cycle were rigidly controlled during both study periods. No meaningful difference between the level or variance of respiratory function was observed between the clean and ambient phases of study. Significant cyclic diurnal variations were observed in all subjects in both studies, with lowest conductance values at 0400 and highest values observed at 1200. A similar diurnal pattern was observed in functional residual capacity being lowest at 2400 and highest at 0800.