1. Department of Respiratory Medicine, Second Affiliated Hospital of Guangxi Medical University, Nanning, Guangxi 530007, P.R. China
2. School of Medicine, Qinghai University, Xining, Qinghai 810000, P.R. China
3. Department of Respiratory Medicine, Beihai People's Hospital, Beihai, Guangxi 536000, P.R. China