Division of Pulmonary and Critical Care Medicine, Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine Seoul, Korea.
Address for correspondence: O Jung Kwon, MD. Division of Pulmonary and Critical Care Medicine, Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, 50 Ilwon-dong, Kangnam-ku, Seoul 135-710, South Korea. Phone: 82-2-3410-3429, Fax: 82-2-3410-3849, ojkwon@smc.samsung.co.kr