1. The Department of Anesthesiology, Cheng-Ching General Hospital, Taichung City, 407, Taiwan
2. Institute of Computer Science and Engineering, College of Computer Science, National Chiao Tung University, Hsinchu City, 330, Taiwan
3. Institute of Biomedical Engineering, College of Computer Science, National Chiao Tung University, Hsinchu City, 330, Taiwan