1. Department of Otorhinolaryngology—Head and Neck Surgery, Chung-Ang University Gwangmyeong Hospital, Gwangmyeong 14353, Republic of Korea
2. Department of Otorhinolaryngology, Yonsei University College of Medicine, Seoul 03722, Republic of Korea
3. The Airway Mucus Institute, Yonsei University College of Medicine, Seoul 03722, Republic of Korea