Figure 1

Framework of the study: a cohort-nested, prospective, randomised controlled trial. Definition of abbreviations: COPD = Chronic Obstructive Pulmonary Disease; RCT = Randomised Controlled Trial; Tiffeneau < 0.6 = Tiffeneau index (FEV₁/VC) < 0.6*; FEV₁ = Forced Expiratory Volume in one second*; FVC = Forced Vital Capacity*; GOLD I = mild COPD, FEV₁/FVC < 0.7 and FEV₁ ≥ 80% of predicted*; GOLD II = moderate COPD, FEV₁/FVC < 0.7 and 50% ≤ FEV₁ < 80% of predicted*; GOLD III = severe COPD, FEV₁/FVC < 0.7 and 30% ≤ FEV₁ < 50% of predicted*; GOLD IV = very severe COPD, FEV₁/FVC < 0.7 and FEV₁ < 30% of predicted or FEV₁ < 50% of predicted* plus chronic respiratory failure. *All lung functions are post-bronchodilator values.