[1] Univ Tsukuba, Mito Med Ctr, Dept Internal Med, Mito, Ibaraki 3100015, Japan
[2] Univ Tsukuba, Div Cardiovasc Thorac Surg, Mito, Ibaraki 3100015, Japan
[3] Univ Tsukuba, Inst Clin Med, Mito, Ibaraki 3100015, Japan
[4] Tsukuba Med Ctr, Div Resp Med, Tsukuba, Ibaraki, Japan