1. Department of Internal Medicine, Chung-Ang University College of Medicine, Seoul, Korea
2. Department of Occupational & Environmental Medicine, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul, Korea
3. Aeromedical Center, Korean Air, Seoul, Korea
4. Department of Otolaryngology-Head & Neck Surgery, Inha University Hospital, Incheon, Korea