1. School of Medicine, Hunan Normal University, Changsha, Hunan 410013, P.R. China
2. Department of Pulmonary and Critical Care Medicine, The Second Xiangya Hospital, Central South University, Changsha, Hunan 410011, P.R. China
3. Department of Physiology, Xiangya School of Medicine, Central South University at Changsha, Changsha, Hunan 410013, P.R. China