1. From Cardiovascular Engineering, Inc (G.F.M., E.W.), Holliston, Mass; Department of Mathematics and Statistics (H.P.), Evans Department of Medicine (J.A.V., J.F.K., R.S.V., E.J.B.), Whitaker Cardiovascular Institute (J.A.V., J.F.K., R.S.V., E.J.B.), and Section of Preventive Medicine (M.G.L., R.S.V., E.J.B.), Boston University School of Medicine, Mass; and the National Heart, Lung, and Blood Institute Framingham Study (M.G.L., M.J.K., D.L., R.S.V., E.J.B.), Mass.