Diurnal variations in human pulmonary function

Abstract

Pulmonary function has circadian modulations. Variations in human pulmonary function during the daytime hours (diurnal variations) remain to be well characterized. Discerning these variations will contribute to better understanding the relationship between biorhythms and lung physiology and to improving clinical management of pulmonary diseases. The aim of this study was to determine the magnitude of pulmonary function variability during the usual daytime hours in a population of patients referred for pulmonary function testing. Diurnal fluctuations of human pulmonary function were examined by studying retrospectively a study population of 4,756 individuals with performed pulmonary function tests. We found the lowest and highest spirometric values in the 12:00-12:59 pm and 3:00-4:59 pm time intervals respectively. The difference in the forced expiratory volume in 1 second (FEV1) between the noon (12:00-12:59 pm) and afternoon (4:00-4:59 pm) intervals was 17.6% (P<0.01). Furthermore, the highest values of diffusing capacity of the lung for carbon monoxide [DLCO] and alveolar volume [Va] were identified in the 8:00-8:59 am time interval. These findings, identifying a model of diurnal variations of pulmonary function in individuals referred for pulmonary function testing, are of interest for better understanding lung physiology and human circadian rhythms and may have clinical value in managing lung disorders.

Keywords: Pulmonary function; diffusing capacity; diurnal variations; pulmonary diseases; pulmonary function tests.

Figure 1

Diurnal changes in PFTs. Results from spirometry tests conducted between 8:00 am and 5:00 pm were analyzed. Tests in the following time intervals were analyzed: 8:00–8:59 am (8 am); 9:00–9:59 am (9 am); 10:00–10:59 (10 am); 11:00–11:59 am (11 am); 12:00–12:59 pm (12 pm); 1:00–1:59 pm (1pm); 2:00–2:59 pm (2 pm); 3:00–3:59 pm (3 pm); and 4:00–4:59 pm (4 pm). The asterisk notes the difference between the lowest and the highest value. For complete statistical analysis please refer to Table 2. (A) Variations in FEV1 (*P<0.01 as compared with 4 pm). (B) Variations in FVC (*P<0.05 as compared with 4 pm). (C) Variations in the peak expiratory flow (PEF) (*P<0.05 as compared with 3 pm). (D) Variations in the FEV1/FVC ratio (*P<0.001 as compared with 3 pm). Data are presented as mean ± SEM.

Figure 2

Variation of FEV1 as a percent of predicted values for the same time intervals as described in the legend to Fig. 1. Data are presented as mean ± SEM (*P<0.001 as compared with 3 pm).

Figure 3

Diurnal variations in the peak diffusing capacity of the lung for carbon monoxide (DLCO). (A) Variations in DLCO from 8:00 am to 5:00 pm. Tests in the same time intervals as described in the legend to Fig. 1 were reviewed. Statistical analysis was performed on the following numbers of tests per each time group: 287 (8:00–8:59 am); 460 (9:00–9:59 am); 409 (10:00–10:59 am); 316 (11:00–11:59 am); 212 (12:00–12:59 pm); 452 (1:00–1:59 pm); 442 (2:00–2:59 pm); 255 (3:00–3:59 pm); 62 (4:00–4:59 pm) (*P<0.001 as compared with the average value of the remaining groups) (B) Variation of DLCO as a percent of predicted values. Data are presented as mean ± SEM (*P<0.001).