1. the Department of Medicine, Division of Cardiology, Barnes-Jewish Hospital of St Louis (G.M.L., M.J.S., D.H.C., A.M.S., S.A.W.), and the Department of Physics (K.D.W., J.G.M., S.A.W.), Washington University, St Louis, Mo; HemaGen/PFC Inc (W.P.C.), St Louis, Mo; the Department of Medicine, Division of Cardiology, Washington University School of Medicine (D.R.A.), St Louis, Mo; and the Division of Hematology, National Institute for Biological Standards and Control (P.J.G.), Hertfordshire, UK.