1. Division of Pulmonary, Allergy and Critical Care Medicine, Department of Internal Medicine, Korea University Guro Hospital, Korea University College of Medicine, Seoul 08308, Republic of Korea
2. Division of Pulmonary, Allergy and Critical Care Medicine, Department of Internal Medicine, Hanyang University Guri Hospital, Hanyang University College of Medicine, Gyeongchun-ro 153, Guri-si, Gyeonggi-do 11923, Republic of Korea