1. Department of Respiratory Intensive Care Unit, The First Affiliated Hospital of Zhengzhou University, Zhengzhou 450052, P.R. China
2. Department of Anatomy, Nursing College of Zhengzhou University, Zhengzhou 450052, P.R. China
3. Department of Thoracic Surgery, The First Affiliated Hospital of Zhengzhou University, Zhengzhou 450052, P.R. China