1. D. H. Wagner Associates, 894 Ross Drive, Suite 205, Sunnyvale, CA 94089-1443
2. Biomedical Engineering Department, McCormick School of Engineering and Applied Science, Northwestern University, Evanston, IL 60208
3. Department of Mathematics and Statistics, University of Newcastle upon Tyne, Newcastle upon Tyne, NE1 7RU, U.K.
4. Biomedical Engineering Department, McCormick School of Engineering and Applied Science, Northwestern University, Evanston, IL 60208, Department of Anesthesia, Northwestern University Medical School, 303 E. Chicago Avenue, Chicago, IL 60611