Project supported by the Shaanxi Science & Technology Co-ordination & Innovation Project (No. 2016KTCQ03-07), Shaanxi Provincial Research Center for the Project of Prevention and Treatment of Respiratory Diseases (No. 2016HXKF03), Xi’an Weiyang District Science and Technology Planning Project (No. 201715), the Foundation for Youth Poject of Xi’an Medical University (No. 2015QN02), and the Foundation for College Student Innovation of Xi'an Medical University (No.2016DXS1-44)