Lung Health of Early COPD: A Multi-center Cohort Study

Inclusion Criteria: 1. Gender: male or female 2. Age: 35-75 years old 3. post-bronchodilator spirometry: FEV1/FVC \< 0.8 and FEV1%pred ≥80% Exclusion Criteria: 1. Other diseases may affect lung function, like lung cancer, bronchiectasis, interstitial lung disease or chest surgery. 2. BMI \> 35 kg/m2 3. Dementia or other severe neurological disease 4. Pregnancy 5. Conditions that contraindicated lung function test