1. Department of Respiratory and Critical Care Medicine, the Second Xiangya Hospital, Central South University, Changsha, Hunan, China
2. Research Unit of Respiratory Disease, Central South University, Changsha, Hunan, China
3. Diagnosis and Treatment Center of Respiratory Disease, Central South University, Changsha, Hunan, China
4. Department of Pulmonary and Critical Care Medicine, Zhuzhou Central Hospital, Zhuzhou, Hunan, China
5. Division 4 of Occupational Diseases, Hunan Prevention and Treatment Institute for Occupational Diseases, Changsha, Hunan, China