1. From the Division of Cardiovascular Medicine (P.D.S., A.P., M.E.A.), Department of Internal Medicine, Carver College of Medicine, University of Iowa, Iowa City, IA; Department of Biomedical Engineering (T.J.H.), The Ohio State University, Columbus, OH; Department of Molecular Physiology and Biophysics (M.E.A.), Carver College of Medicine, University of Iowa, Iowa City, IA.