A Prospective Cohort Study of Asthma and COPD Overlap in Japanese COPD Patients Using the Diagnostic Criteria of The Japanese Respiratory Society

Inclusion Criteria: 1. Patients from whom written consent to participate in this study has been obtained 2. Patients ≥40 years old 3. Patients with FEV1/FVC ratio \<70% after bronchodilator inhalation within the past year or on the registrationa 4. Patients who satisfy any one of the following items: 1\) Smoking history (≥10 pack-years) or comparable air pollution exposure on the registrationa 2) Presence of the low attenuation area on chest CT demonstrating emphysematous alteration within the past year or on the registration a,b, 3) Impaired pulmonary diffusing capacity (%DLCO \<80% or %DLCO/VA \<80%) within the past year or on the registrationa 4) Patients deemed capable of visiting their study center in Japan at least once a year on an outpatient basis Exclusion Criteria: 1. Patients who participated in other interventional studies such as clinical trial within the last 8 weeks. 2. Patients who are unsuitable for their enrollment in this study, judged by the participating physician, because they cannot comply with the procedures, restrictions, and requirements of this study (e.g., patients with dementia). 3. Patients with exacerbationsa of COPD or asthma within the last 8 weeks. a COPD exacerbation: State of increased shortness of breathing, increased cough and sputum, and occurrence or exacerbation of chest discomfort that requires a change of treatment during the stable phase. However, exacerbation preceded by other disorders (e.g., heart failure, pneumothorax, pulmonary thromboembolism) is excluded. Asthma exacerbation: Occurrence of paroxysmal/variable cough/sputum/wheezing/dyspnea caused by various factors including respiratory infection. 4. Patients carrying following disorders that should be distinguished from COPD or asthma: Diffuse panbronchiolitis, congenital sinobronchial syndrome, occlusive panbronchiolitis, bronchiectasis, pulmonary tuberculosis, pneumoconiosis, lymphangioleiomyomatosis, congestive heart failure, interstitial lung disease, lung cancer, laryngitis, epiglottitis, vocal cord dysfunction, intratracheal tumor, airway foreign substance, tracheomalacia, bronchial tuberculosis, pulmonary thromboembolism, cough induced by drug such as angiotensin-converting enzyme inhibitor, spontaneous pneumothorax, hyperventilation syndrome, psychogenic cough