1. Department of Pulmonary and Critical Care Medicine, East-West Neo Medical Center, Kyung Hee University College of Medicine, Seoul, Korea.
2. Department of Pulmonary and Critical Care Medicine, Dongguk University College of Medicine, Gyeongju, Korea.
3. Department of Pulmonary and Critical Care Medicine, Kyung Hee Medical Center, Kyung Hee University College of Medicine, Seoul, Korea.