HUANG Lu-ying is now working at Department of Respiratory Diseases, People's Hospital of Guangxi Zhuang Autonomous Region, Nanning, Guangxi 530021, China. Correspondence to: Dr. SHI Huan-zhong, Institute of Respiratory Diseases, First Affiliated Hospital, Guangxi Medical University, Nanning, Guangxi 530021, China (Tel: 86-771-5359226. Fax: 86-771-5359226. Email: shihuanzhong@sina.com)