Circadian Rhythm and Variability of Large and Small Airway Spirometric Variables in Healthy Individuals

<bold>Background:</bold>While numerous studies have focused on lung function dynamics in healthy individuals, there is a notable gap in clinical research regarding variability of small-airway variables. <bold>Objective:</bold>To assess the diurnal rhythm and variability in lung function, encompassing both large and small airways. <bold>Methods:</bold>We enrolled 35 healthy adults without a history of smoking. Initial spirometry and a bronchodilation test were performed using the Jaeger spirometer, followed by a 7-day of continuous home monitoring using the GOSPT2000. We evaluate its repeatability and agreement, and analyse circadian rhythm and variability in spirometric measurements. <bold>Results:</bold>The GOSPT2000 demonstrated strong repeatability and high agreement with the Jaeger spirometer. We found a decrease in nocturnal forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC), and FEV3 by 44mL, 59mL, and 53mL, respectively. In contrast, peak expiratory flow (PEF) at noon showed an increase of 0.143L/min. Small-airway variables, including forced expiratory flow at 50% and 75% of the FVC and maximum mid-expiratory flow, showed no significant diurnal variation. The nocturnal CV for large-airway variables was ≤ 4%, while for small-airway variables, it was ≤ 11.89%. <bold>Conclusion:</bold>This study has established a spectrum of variability for both large and small airways in healthy populations. The variability of small-airway variables is higher than that of large-airway variables. The investigation into the diurnal rhythms and variability characteristics of both large and small airway variables in the healthy population can serve as a foundation for diagnosing asthma or assessing the efficacy of asthma treatments.