1. 1 Division of General Medicine, Mito Medical Center , University of Tsukuba , Mito-city, Ibaraki , Japan
2. 2 Division of Respiratory Medicine, Mito Medical Center , University of Tsukuba , Mito-city, Ibaraki , Japan
3. 3 Division of Respiratory Medicine, Hitachinaka General Hospital , Hitachinaka-city, Ibaraki , Japan