1 Department of Internal Medicine, Division of Pulmonary Medicine, Kangbuk Samsung Hospital, Seoul, Korea.
2 Department of Medicine, Division of Pulmonary and Critical Care Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea; Department of Health Sciences and Technology, SAIHST, Sungkyunkwan University, Seoul, Korea. Electronic address: sangwonum@skku.edu.