1. Swallowing Center, The University of Tokyo Hospital, Tokyo 113-8655, Japan
2. Department of Otolaryngology and Head and Neck Surgery, Faculty of Medicine, The University of Tokyo, Tokyo 113-8655, Japan
3. Ear Nose Throat Head and Neck Surgery Institute, The Medical City, Metro Manila 1600, Philippines
4. Tokyo Teishin Hospital, Tokyo 102-0071, Japan