1. Department of Lung Cancer and Gastroenterology, Hunan Cancer Hospital, Affiliated Tumor Hospital of Xiangya Medical School of Central South University, Changsha, Hunan 410008, P.R. China
2. Department of Intensive Care Unit, The First People's Hospital of Changde City, Changde, Hunan 410005, P.R. China
3. Department of Respiratory Medicine, Xiangya Hospital, Central South University, Changsha, Hunan 410008, P.R. China