1. Department of Pulmonary Medicine, Institute of Medicine, University of Tsukuba, Tsukuba, Ibaraki 305‑8576, Japan
2. Department of Respiratory Medicine, Moriya Daiichi General Hospital, Moriya, Ibaraki 302‑0102, Japan
3. Division of Respiratory Medicine, Mito Medical Center, University of Tsukuba‑Mito Kyodo General Hospital, Mito, Ibaraki 310‑0015, Japan