1. Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, University of Ulsan College of Medicine and Asan Medical Center, Seoul, Korea.
2. Department of Emergency Medicine, University of Ulsan College of Medicine and Asan Medical Center, Seoul, Korea.
3. Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Keimyung University Dongsan Medical Center, Daegu, Korea.