1 Department of Respiratory Medicine, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
2 Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Seoul St. Mary's Hospital, College of Medicine, The Catholic University of Korea, Seoul, South Korea.
3 Division of Pulmonary and Critical Care Medicine, Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, South Korea.
4 Department of Respiratory Medicine, Faculty of Medicine, Hokkaido University, Sapporo, Japan.