1. Department of Respiratory Medicine, Mudanjiang Medical University Affiliated Hongqi Hospital, Mudanjiang, Heilongjiang 157000, P.R. China
2. Community Health Service Center, Mudanjiang Medical University Affiliated Hongqi Hospital, Mudanjiang, Heilongjiang 157000, P.R. China
3. Department of Respiratory Medicine, Kangan Hospital, Mudanjiang, Heilongjiang 157000, P.R. China