1. Department of Respiratory Medicine, Xi'an Central Hospital, The Affiliated Hospital of Xi'an Jiaotong University, Xi'an, Shaanxi 710003, P.R. China
2. Department of Pathology, Xi'an No. 3 Hospital, The Affiliated Hospital of Northwest University, Xi'an, Shaanxi 710018, P.R. China
3. Department of Emergency, Xi'an Central Hospital, The Affiliated Hospital of Xi'an Jiaotong University, Xi'an, Shaanxi 710003, P.R. China