Extensive studies suggest composition of microbiome of respiratory samples or lung tissues in COPD patients is different from the composition of healthy smokers. Aim of this study is to analyze composition of microbiome of various samples (e.g. feces, sputum, and urine) and to describe difference of composition between COPD patients and healthy smokers.

After the introduction of the Gut-Lung axis theory, extensive studies revealed diversity of microbiomes among healthy smokers and COPD patients form the respiratory samples or lung tissues. In the previous study, distinct difference in composition of microbiome in lung tissue between healthy smokers and COPD patients was reported. This is a cross sectional study to analyze composition of microbiome of various samples (e.g. feces, sputum, and urine) and to compare difference of composition between COPD patients and healthy smokers. This study would help establishing gut-lung axis model in humans.

Inclusion Criteria:

• Patients with smoking history at least 10 pack-year
• Patients with persistent airflow limitation that was not fully reversible (e.g. post-bronchodilator forced expiratory volume in 1 second/forced vital capacity ( FEV1/FVC) <0.7)

Exclusion Criteria:

• Patients with co-existing illness that would interfere with study results (e.g., malignancy, congestive heart failure, cerebrovascular disorders, chronic renal failure, diabetes with severe complications, or uncontrolled hypertension)
• Patients with respiratory disease other than obstructive lung disease (e.g., previous pulmonary resection, tuberculosis-destroyed lung, and bronchiectasis)
• Patients with recent (8 weeks prior to screening) exacerbation or other respiratory illness

COPD group

- Same as above

Healthy smokers

• Participants with smoking history
• Participants with normal spirometry results