1. Department of Anaesthesiology, Niigata University, School of Medicine, Niigata 951‐8510, Japan
2. Department of Anesthesiology, College of Physicians and Surgeons, Columbia University, New York, NY 10032‐3784, USA
3. Department of Physiology, Kurume University School of Medicine, Kurume 830‐0011, Japan
4. Department of Physiology, Saga Medical School, Saga 849‐8501, Japan