1. From the Division of Pulmonary and Critical Care Medicine (K.M.R., W.G.O., F.S., Z.A., V.D., P.F., J.I.S.), Northwestern University Medical School, Chicago, Ill; Jewish Hospital Heart & Lung Institute and the Departments of Medicine and Pharmacology & Toxicology (S.H.), University of Louisville, Louisville, Ky; and Department of Mathematics (D.H.R.), Northeastern Illinois University, Chicago, Ill.