1. Department of Respiratory and Critical Care Medicine, Chronic Airways Diseases Laboratory, Nanfang Hospital, Southern Medical University, Guangzhou, Guangdong 510515, China
2. School of Nursing, Southern Medical University, Guangzhou, Guangdong 510515, China
3. Department of Respiratory and Critical Care Medicine, The Fifth Affiliated Hospital, Southern Medical University, Guangzhou, Guangdong 510900, China.