Quantitative evaluation of intra-aortic flow disturbance by the fluid momentum index: Effect of the left ventricular systolic function on the hemodynamics in the aorta

Abstract

The combined hemodynamics in the left ventricle and aorta were analyzed numerically to investigate how the hemodynamics in the aorta varies with changes in left ventricular systolic function quantified as the ejection fraction (EF). EFs of 0.3, 0.5, and 0.7 were defined by controlling the total volume ejected during systole, while maintaining the ventricular volume at the end of diastole. The results showed that although the variation in left ventricular systolic function resulted in a change in the magnitude of the flow velocity, the intraventricular and aortic flows, including the secondary flows at the aortic valve orifice, were essentially the same regardless of the EF. To evaluate the strength of the secondary flow relative to the axial flow, the flow momentum index, FMI, was proposed. Spatiotemporal maps of the FMI obtained with different EFs had similar topological patterns, suggesting that the left ventricular systolic function contributed less to the efficiency of conveying blood in the axial direction in the aorta. Systolic function had a minimal effect on the spatiotemporal distribution of the maximum wall shear stress (WSS). A comparison of the spatiotemporal maps of the FMI and WSS revealed that the spatiotemporal maximum of WSS that occur in peak systole did not correspond to that of the FMI, demonstrating that the spatiotemporal maximum WSS was not induced by the helical flow. These results demonstrated that the left ventricular systolic function is not reflected in the global hemodynamics in the aorta and addressed potential of the FMI as an index to quantify the aortic flow disturbances.