A Non-interventional Study to Investigate the Current Situation of Asthma-COPD Overlap Syndrome in Patients Over Age 40 With Persistent Airflow Limitation in China

Inclusion Criteria: Outpatients, age ≥ 40 years Clinically diagnosed as asthma, COPD/chronic bronchitis/emphysema or ACOS at least 12 months With persistent airflow limitation (post-BD FEV1/FVC\<0.7) Signed informed consent forms Exclusion Criteria: Have been involved in other clinical trial within 3 months Having other respiratory diseases which can influence airflow, such as lung cancer, tuberculosis, pneumonia, bronchiectasis, etc With acute exacerbation Inability to understand the study procedures or inability/reluctance to answer questionnaire judged by the investigator