1. Departments of Physiology and Medicine, Medical College of Virginia at Virginia Commonwealth University, and Hunter Holmes McGuire Department of Veteran Affairs Medical Center, Richmond, Virginia 23249;
2. Department of Cardiology and Cardiovascular Sciences, Fundación Cardiovascular del Oriente Columbiano, AA 1143 Bucaramanga, Santander, Columbia;
3. Department of Anesthesia, Mayo Clinic and Foundation, Rochester, Minnesota 55905;
4. Department of Clinical Physiology, Kuopio University Hospital, FIN-70211 Kuopio; and
5. Department of Applied Mathematics, University of Turku, FIN-20014 Turku, Finland