1. Department of Respiratory Medicine, Shandong Provincial Hospital Affiliated to Shandong University, Jinan, Shandong 250021, P.R. China
2. Department of Respiratory Medicine, Beijing Tsinghua Changgung Hospital, Beijing 102218, P.R. China
3. Department of Respiratory Medicine, Qianfo Mountain Hospital, School of Medicine, Shandong University, Jinan, Shandong 250014, P.R. China