Abstract
Diurnal variability in airways has most commonly been reported using peak expiratory flow (PEF) and forced expiratory volume in one second (FEV1). Characteristics of variability in small, mid and large airways caliber are expected to be different but have not been studied. The aim of the study was to assess diurnal variation in small mid and large airways caliber using FEF25, FEF50, FEF75 and FEF25-75 along with PEF and FEV1 in healthy subjects. Spirometry was performed in 161 healthy subjects twice in a day. Diurnal variability in FEF25, FEF50, FEF75, FEF25-75, PEF and FEV1 were determined and compared. It revealed that all parameters exhibit significant diurnal variability. Diurnal variability is highest in large airways and lowest in smaller airways. Proximal airways show greater diurnal variation in their caliber than distal airways as reflected by greater variability in PEF as compared to FEV1.
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