1 Department of Internal Medicine, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences, Beijing, 100730, China.
2 Department of Pulmonary and Critical Care Medicine, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences, Beijing, 100730, China.
3 Department of Pulmonary and Critical Care Medicine, The First Affiliated Hospital, College of Medicine, Xiamen University, Xiamen, 361003, China.
4 Department of Pulmonary and Critical Care Medicine, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences, Beijing, 100730, China. xukf@pumch.cn.