[1] Yonsei Univ, Wonju Coll Med, Dept Internal Med, Wonju, South Korea
[2] Kyung Hee Univ, Dept Pulm & Crit Care Med, Kyung Hee Univ Hosp Gangdong, Sch Med, Seoul, South Korea
[3] Sungkyunkwan Univ, Sch Med, Div Pulm & Crit Care Med, Dept Internal Med,Samsung Med Ctr, 81 Irwon Ro, Seoul 06351, South Korea