Small airway function measured using forced expiratory flow between 25% and 75% of vital capacity and its relationship to airflow limitation in symptomatic ever-smokers: A cross-sectional study

Abstract

Background Chronic obstructive pulmonary disease (COPD) is diagnosed and its severity graded by traditional spirometric parameters (forced expiratory volume in 1 s (FEV 1)/forced vital capacity (FVC) and FEV 1, respectively) but these parameters are considered insensitive for identifying early pathology. Measures of small airway function, including forced expiratory flow between 25% and 75% of vital capacity (FEF 25-75), may be more valuable in the earliest phases of COPD. This study aimed to determine the prevalence of low FEF 25-75 in ever-smokers with and without airflow limitation (AL) and to determine whether FEF 25-75 relates to AL severity. Method A retrospective analysis of lung function data of 1458 ever-smokers suspected clinically of having COPD. Low FEF 25-75 was defined by z-score