1. Department of Pulmonary and Critical Care Medicine; Chaoyang Hospital, Capital Medical University; Beijing 100029 P.R. China
2. Department of Respiratory Medicine; Capital Medical University; Beijing 100069 P.R. China
3. Department of Pulmonary and Critical Care Medicine; Xuanwu Hospital, Capital Medical University; Beijing 100053 P.R. China
4. Department of Physiology and Pathophysiology; Capital Medical University; Beijing 100069 P.R. China
5. Institute of Public Health; Peking University; Beijing 100871 P.R. China
6. Department of Pulmonary and Critical Care Medicine; China-Japan Friendship Hospital; Beijing 100029 P.R. China
7. Chinese Academy of Medical Sciences & Peking Union Medical College; Beijing 100730 P.R. China