Department of Internal Medicine, Seoul National University College of Medicine, Respiratory Center, Seoul National University Bundang Hospital, Korea.
Address for correspondence: Choon Taek Lee, M.D. Respiratory Center, Seoul National University Bundang Hospital 300, Gumi-Dong, Seongnam, Gyeonggi-Do, 463-707, Korea. Phone: 031-787-7002, Fax: 031-787-4052, ctlee@snu.ac.kr