Isolated small airways obstruction predicts future chronic airflow obstruction: Preliminary findings

Background: Chronic airflow obstruction is a key characteristic of COPD. We aimed to investigate whether isolated small airways obstruction can predict chronic airflow obstruction later in life. Methods: We used longitudinal data from the multinational Burden of Obstructive Lung Disease study. We recruited a representative sample of adults, aged 40 years or older, and performed spirometry at two time points. We defined isolated small airways obstruction as a pre-bronchodilator mean forced expiratory flow rate between 25% and 75% of the forced vital capacity (FEF_25–75) less than the lower limit of normal (1/FVC). We also used the forced expiratory volume in 3 s to forced vital capacity ratio (FEV₃/FVC) to define small airways obstruction. We defined chronic airflow obstruction as a post-bronchodilator FEV₁/FVC Results: Data on 3,856 participants were analysed (median follow-up 8.4 years). Chronic airflow obstruction was more likely to develop in participants with isolated small airways obstruction at baseline (FEF_25-75 3/FVC 3/FVC predicted chronic airflow obstruction better than FEF_25-75 (AUC: 0.76 vs 0.74; Brier score: 0.08 vs 0.10). Conclusions: Spirometric measurements of small airways function can be used as early markers of future obstructive lung disease.