1. Division of Pulmonary Medicine, Department of Internal Medicine, Chonnam National University Hospital, Gwangju, Korea.
2. Department of Internal Medicine, The Catholic University of Korea, Seoul St. Mary's Hospital, Seoul, Korea.
3. Department of Internal Medicine, Yonsei University Wonju College of Medicine, Wonju, Korea.
4. Division of Pulmonary and Critical Care Medicine, Department of Medicine, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul, Korea.
5. Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine and the Clinical Research Center for Chronic Obstructive Airway Diseases, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
6. Division of Pulmonary Medicine, Department of Internal Medicine, Hallym University Sacred Heart Hospital, Hallym University Medical School, Anyang, Korea.
7. Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Konkuk University Medical Center, Konkuk University School of Medicine, Seoul, Korea.
8. Division of Pulmonary, Allergy, and Critical Care Medicine, Department of Internal Medicine, Chonbuk National University Medical School, Jeonju, Korea.