title: Subject-specific model estimation of cardiac output and blood volume during hemorrhage.
abstract: We have developed a novel method for estimating subject-specific hemodynamics during hemorrhage. First, a mathematical model representing a closed-loop circulation and baroreceptor feedback system was parameterized to match the baseline physiology of individual experimental subjects by fitting model results to 1 min of pre-injury data. This automated parameterization process matched pre-injury measurements within 1.4 +/- 1.3% SD. Tuned parameters were then used in similar open-loop models to simulate dynamics post-injury. Cardiac output (CO) estimates were obtained continuously using post-injury measurements of arterial blood pressure (ABP) and heart rate (HR) as inputs to the first open-loop model. Secondarily, total blood volume (TBV) estimates were obtained by summing the blood volumes in all the circulatory segments of a second open-loop model that used measured CO as an additional input. We validated the estimation method by comparing model CO results to flowprobe measurements in 14 pigs. Overall, CO estimates had a Bland-Altman bias of -0.30 l/min with upper and lower limits of agreement 0.80 and -1.40 l/min. The negative bias is likely due to overestimation of the peripheral resistance response to hemorrhage. There was no reference measurement of TBV; however, the estimates appeared reasonable and clearly predicted survival versus death during the post-hemorrhage period. Both open-loop models ran in real time on a computer with a 2.4 GHz processor, and their clinical applicability in emergency care scenarios is discussed.
authors.affiliation: Department of Medical Education and Biomedical Informatics, University of Washington, Seattle, WA 98195, USA. mneal@u.washington.edu
authors.forename: Maxwell Lewis
authors.initials: ML
authors.lastname: Neal
authors.forename: James B
authors.initials: JB
authors.lastname: Bassingthwaighte
mesh_terms: D000818:Animals; D001810:Blood Volume; D002302:Cardiac Output; D002303:Cardiac Output, Low / Q000503:physiopathology*; D003198:Computer Simulation; D003936:Diagnosis, Computer-Assisted / Q000379:methods; D006470:Hemorrhage / Q000150:complications* / Q000503:physiopathology*; D008954:Models, Biological; D013552:Swine