Diurnal variation in spirometry parameters of patients with chronic obstructive pulmonary disease: A systematic review and meta‑analysis

Diurnal variation in pulmonary function is a key physiological phenomenon, with potential clinical significance in chronic obstructive pulmonary disease (COPD). The reduced diurnal fluctuation of forced vital capacity (FVC) and forced expiratory volume in 1 sec (FEV1) in patients with COPD may be attributed to airway inflammation, autonomic dysregulation and impaired lung compliance, with potential influence from altered cortisol rhythms. These fluctuations are clinically significant as they highlight the importance of optimizing bronchodilator timing and interpreting spirometry results within a diurnal context. The present systematic review and meta‑analysis examined the diurnal fluctuations in FVC and FEV1) among healthy individuals and patients with COPD. A total of 8 studies, including 595 for FVC (or 725 for FEV1) healthy individuals and 172 patients with COPD, were analyzed. In healthy adults, the mean diurnal FVC difference was 1.92 (P<0.01), with morning values significantly higher than nighttime values. Patients with COPD also exhibited a morning increase in FVC values, but with a smaller, non‑significant difference of 1.04 (P=0.06). The mean difference in diurnal FVC variation between the two groups was 1.46 (P<0.01), indicating a significantly greater variation in healthy individuals. For FEV1, healthy individuals exhibited a mean diurnal difference of 4.94 (P<0.01), whereas patients with COPD showed a smaller but significant difference of 0.82 (P<0.01). However, the between‑group difference in diurnal FEV1 variation was 3.07 (P=0.17), which was not statistically significant. Heterogeneity was moderate to high (I²=57‑59%), suggesting variability across the included studies. The reduced diurnal fluctuation of FVC and FEV1 in patients with COPD may be attributed to airway inflammation, autonomic dysregulation and impaired lung compliance, with potential influence from altered cortisol rhythms. These findings underscore the importance of personalized treatment approaches, optimizing bronchodilator timing and considering diurnal patterns in spirometry interpretation for improved COPD management. Future research should explore longitudinal home spirometry to refine therapeutic strategies.