1. From the Division of Pulmonary, Critical Care, and Sleep Medicine, Department of Medicine, Tufts—New England Medical Center, Tufts University School of Medicine, Boston, Mass (R.B.), and Division of Cardiopulmonary Pathology, Department of Pathology (R.M.T.), and Division of Pulmonary and Critical Care Medicine (P.M.H.), Department of Medicine, Johns Hopkins Hospital and Johns Hopkins University School of Medicine, Baltimore, Md.