Abstract 12955: Shear-Dependent Changes in Blood Viscosity Negatively Affect Energetic Efficiency in Patient-Specific Models of the Fontan Circulation

Abstract

Introduction: Since blood flow through the lungs is passive in patients with the Fontan circulation, cardiac output is sensitive to power loss through the pulmonary vasculature. Prior small in vitro studies of how changes in blood viscosity at venous shear rates (“non-Newtonian behavior”) affect power loss have yielded conflicting results. The purpose of this study was to evaluate the extent to which non-Newtonian behavior contributes to power loss in a large number of pediatric patient-specific models of the Fontan circulation. Hypothesis: Shear-dependent changes in blood viscosity cause increased power loss in the low-shear Fontan circulation. Methods: Pulmonary vascular geometry was segmented from clinical cardiac MRI images. Pressure and velocity fields were then calculated using computational fluid dynamic simulations. Cardiac index was set at 2 L/min/m2 to simulate a low cardiac output state. A constant viscosity model (“Newtonian”) was compared to a shear-dependent viscosity model (“non-Newtonian”). Power loss was calculated by simplified power loss (using bulk flow and pressure changes) and viscous dissipation rate (using element-wise shear rates and viscosities). Both metrics were indexed to adjust for cardiac output and body surface area. Wilcoxon signed-rank test was used to compare differences between the two viscosity models. Results: Twenty patients (mean 10.9 years, 35% female) were included. Mean viscosity was nearly 10-fold higher in the non-Newtonian vs. Newtonian simulations (mean non-Newtonian to Newtonian viscosity ratio 9.7, SD 0.6). Accordingly, power loss by both metrics was significantly larger for the non-Newtonian simulations ( Figure ). Conclusions: Shear-dependent increases in blood viscosity cause increased power loss in computational models of the Fontan circulation under low cardiac output conditions. Further studies are needed to evaluate the degree to which this correlates with clinical outcomes.