1. Department of Respiratory Medicine, Anhui Provincial Hospital, Cheeloo College of Medicine, Shandong University, Jinan, Shandong 250021, P.R. China
2. Department of Respiration and Critical Care Medicine, Anhui Provincial Key Laboratory of Clinical Basic Research on Respiratory Disease, The First Affiliated Hospital of Bengbu Medical College, Bengbu, Anhui 233004, P.R. China
3. Department of Epidemiology and Health Statistics, Bengbu Medical College, Bengbu, Anhui 233030, P.R. China