1. From the Division of Nephrology and Hypertension (S.N.K., Q.R., P.C.H., V.E.T., Q.Q.), Department of Physiology and Biomedical Engineering (L.W.H., G.C.S.), Mayo Clinic College of Medicine, Rochester, Minn; and Section of Nephrology (S.S.), Department of Medicine, Yale University School of Medicine, New Haven, Conn.