1. Department of Geriatrics, Xiangya Hospital of Central South University, Changsha, Hunan 410008, P.R. China
2. Department of Respiratory Medicine, Xiangya Hospital of Central South University, Changsha, Hunan 410008, P.R. China
3. Department of Nephrology Medicine, Huaihe Hospital of Henan University, Kaifeng, Henan 475000, P.R. China