1 Department of Medicine, Division of Pulmonary and Critical Care (Y.K.L.) and Department of Radiology and Thoracic Imaging (P.L., H.H.G.), Stanford University School of Medicine, 300 Pasteur Dr, Room S-074A, Stanford, CA 94305; and Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden (P.L.).