Fig. 1
Studies reporting lung function decline in patients with mild COPD: Chen et al. [58], Bridevaux et al. [29], Brito-Mutunayagam et al. [59], Mohamed Hoesein et al. [60]. Inclusion criteria/study design: Chen et al. [58], subjects aged 45–80 years with a history of smoking or exposure to second-hand smoke for > 10 years; high-risk control group had post-bronchodilator FEV1/FVC > 0.7 and FEV1 < 95% predicted; mild COPD group had post-bronchodilator FEV1/FVC < 0.7 and FEV1 > 80% predicted in the absence of bronchodilator or inhaled corticosteroid; Bridevaux et al. [29], Swiss Study on Air Pollution and Lung Diseases in Adults cohort; considered symptomatic if chronic cough, phlegm or shortness of breath while walking reported at baseline (age range 18–60 years); Brito-Mutunayagam et al. [59], subjects aged ≥18 years from the North West Adelaide Health Study cohort; resolution, persistence or progression of GOLD stage 0 determined at 3.5-year follow-up; Mohamed Hoesin et al. [60], Dutch Belgian Lung Cancer Screening Trial; male heavy smokers (age range 47–80 years). Data shown are calculated from 3-year data described by Mohamed Hoesin et al. [60]. COPD: chronic obstructive pulmonary disease; FEV1: forced expiratory volume in 1 s; FVC: forced vital capacity; GOLD: Global Initiative for Chronic Obstructive Lung Disease; LLN: lower limit of normal