1. From the Department of Bioengineering, Whitaker Institute for Biomedical Engineering (F.L., G.W.S-S.), and Department of Medicine (M.T.K., D.T.O’C., R.J.P.), University of California at San Diego, La Jolla; and Veterans Administration Medical Center, San Diego, Calif (M.T.K., D.T.O’C., R.J.P.).