1. Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine and Lung Institute, Seoul National University College of Medicine, Seoul, Korea.
2. Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Seoul Metropolitan Government Seoul National University Boramae Medical Center, Seoul, Korea.
3. Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine and Lung Institute, Seoul National University Bundang Hospital, Seoul National University College of Medicine, Seongnam, Korea.
4. Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Chung-Ang University College of Medicine, Seoul, Korea.