1 Department of Respiratory and Critical Care Medicine, The First Affiliated Hospital of Chongqing Medical University, Chongqing 400016, China.
2 Department of Respiratory and Critical Care Medicine, West China Hospital, Sichuan University, Chengdu, China.
3 Department of Respiratory and Critical Care Medicine, The First Affiliated Hospital of Chongqing Medical University, Chongqing 400016, China. Electronic address: guosl999@sina.com.