Hemodynamics and stresses in numerical simulations of the thoracic aorta: Stochastic sensitivity analysis to inlet flow-rate waveform

Numerical simulations of the blood flow inside a patient-specific thoracic aorta in presence of an aneurysm are considered. We focus on the impact on the numerical predictions of the inlet flow-rate waveform. First, the results obtained by using an idealized and a MRI-measured flow-rate waveform are compared. The measured boundary condition produces significantly higher wall shear stresses than those obtained in the idealized case. Discrepancies are reduced but they are still present even if the idealized inlet waveform is rescaled in order to match the stroke volume. This motivates a systematic sensitivity analysis of numerical predictions to the shape of the inlet flow-rate waveform that is carried out in the second part of the paper. Two parameters are selected to describe the inlet waveform: the stroke volume and the period of the cardiac cycle. A stochastic approach based on the generalized Polynomial Chaos (gPC) approach, in which continuous response surfaces of the quantities of interest in the parameter space can be obtained from a limited number of simulations, is used. For both selected uncertain parameters, we use beta PDFs reproducing clinical data. The two selected input parameters appear to have a significant influence on wall shear stresses as well as on the velocity distribution in vessel regions characterized by large curvature. This confirms the need of using patient-specific inlet conditions to obtain reliable hemodynamic predictions.