5. Qualifications of Investigators: Dr. Arthur Wallace, M.D., Ph.D. has done medical research since 1978 including large animal, human clinical trials, and human physiological measurement. He has a Ph.D. in biomedical engineering and completed a medical internship, anesthesia residency, and a fellowship in cardiac anesthesiology. He has been a faculty member of anesthesiology at UCSF since 1992 during this time he has been the PI on several clinical trials in high risk patients including the Afterload, Warm Cardioplegia, Atenolol, Clonidine, EDRF Intraop, L-ARG, AVD Study, PCRRT, and Aneurysm Trials. Dr. Wallace has worked with impedance devices since 1991 and has been the chief scientific advisor on the ECOM projects since their inception in 1996. He has been responsible for the tube design, algorithm development, electronic design, in-vivo experiments, as well as the animal and human trials.