1. Department of Internal Medicine, The Second Hospital of Shandong University, Jinan, Shandong 250033, P.R. China
2. Department of Surgery, Affiliated Hospital of Shandong Academy of Medical Sciences, Jinan, Shandong 250031, P.R. China
3. Department of Geriatric Medicine, Affiliated Hospital of Shandong University of Traditional Chinese Medicine, Jinan, Shandong 250014, P.R. China