1. Department of Otorhinolaryngology-Head and Neck Surgery, Suwon St. Vincent's Hospital
2. Stanford University Sleep Medicine Division, Redwood City, CA
3. Yeouido St. Mary's Hospital
4. Bucheon St. Mary's Hospital, College of Medicine, The Catholic University of Korea, 222 Banpo-daero, Seocho-gu, Seoul 137-701, Republic of Korea