[1] Kurume Univ, Sch Med, Dept Publ Hlth, Fukuoka, Japan
[2] Yamaguchiken Saiseikai Shimonoseki Gen Hosp, Shimonoseki COPD Res Grp, Yamaguchi, Japan
[3] Chijimatsu Clin, Yamaguchi, Japan
[4] Hallym Univ, Dongtan Sacred Heart Hosp, Dept Pulm Allergy & Crit Care Med, Chunchon, South Korea
[5] Seoul Natl Univ, Bundang Hosp, Dept Internal Med, Seoul, South Korea
[6] Seoul Natl Univ, Lung Inst Med Res Ctr, Div Pulm & Crit Care Med, Seoul, South Korea