Table 1.

Definition of Mild COPD and Early COPD

Mild COPD	Early COPD
1) FEV1/FVC<70% (post–bronchodilators) 2) FEV1>80% predicted value	1)>50 year of age and smoking>10 packs/year 2) Meet any of the following: FEV1/FVC<LLN (post–bronchodilators); Chest CT showed small airway obstruction or thickened airway walls; Lung function reduced rapidly; with the decline in FEV1>60mL/year

Note: Other known chronic lung diseases were excluded except for asthma.

Abbreviations: FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; LLN, lower limit of normal; COPD, chronic obstructive pulmonary disease; CT, computer tomography.