[1] Qinghai Prov Peoples Hosp, Dept Resp & Crit Care Med, Xining, Qinghai, Peoples R China
[2] Chinese Acad Med Sci, Sch Basic Med, Dept Epidemiol & Biostat, Peking Union Med Coll,Inst Basic Med Sci, Beijing, Peoples R China
[3] Capital Med Univ, Beijing Chao Yang Hosp, Beijing Inst Resp Med, Dept Resp & Crit Care Med, Beijing, Peoples R China
[4] Tianjin Univ, Inst Disaster & Emergency Med, Tianjin, Peoples R China