1. Department of Internal Medicine, Pusan National University School of Medicine, Busan, Korea.
2. Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, College of Medicine, Chungbuk National University, Cheongju, Korea.
3. Department of Biochemistry and Molecular Biology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
4. Department of Pulmonary and Critical Care Medicine, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.