Jiao Yang1, Xu-Wei Wu2, Xi-Qian Xing3. 1. First Department of Respiratory Medicine, First Affiliated Hospital of Kunming Medical University, Kunming, Yunnan, China. 2. First Department of Respiratory Medicine, Yan'An Hospital Affiliated to Kunming Medical University, Kunming, Yunnan, China. 3. First Department of Respiratory Medicine, Yan'An Hospital Affiliated to Kunming Medical University, Kunming, Yunnan, China. Electronic address: xingxiqianmd@yahoo.com.