Division of Internal Medicine, Japan Agricultural Cooperatives Kochi Hospital, 526-1 Myoken-aza-Nakano, Nankoku, Kochi 783-8509, Japan; Department of Community Medicine for Respirology, Graduate School of Biomedical Sciences, Tokushima University, 3-18-15 Kuramoto-cho, Tokushima 770-8503, Japan. Electronic address: