1. Department of Pulmonary and Critical Care Medicine, the Second Xiangya Hospital, Central South University, Changsha, China
2. Research Unit of Respiratory Disease, Central South University, Changsha, China
3. Diagnosis and Treatment Center of Respiratory Disease, Central South University, Changsha, China
4. Department of Medicine, Division of Pulmonary, Allergy and Critical Care Medicine, University of Alabama at Birmingham, Birmingham, AL, USA