[1] Yanan Univ, Sch Med, Yanan 716000, Shaanxi, Peoples R China
[2] Fourth Mil Med Univ, Xijing Hosp, Dept Gen Practice, Xian 710032, Shaanxi, Peoples R China
[3] First Hosp Yulin, Dept Crit Care Med, Yulin 719000, Shaanxi, Peoples R China
[4] First Hosp Yulin, Dept Resp Med, Yulin 719000, Shaanxi, Peoples R China