Image-Based Simulations Show Important Flow Fluctuations in a Normal Left Ventricle: What Could be the Implications?

Abstract

Intra-cardiac flow has been explored for decades but there is still no consensus on whether or not healthy left ventricles (LV) may harbour turbulent-like flow despite its potential physiological and clinical relevance. The purpose of this study is to elucidate if a healthy LV could harbour flow instabilities, using image-based computational fluid dynamics (CFD). 35 cardiac cycles were simulated in a patient-specific left heart model obtained from cardiovascular magnetic resonance (CMR). The model includes the valves, atrium, ventricle, papillary muscles and ascending aorta. We computed phase-averaged flow patterns, fluctuating kinetic energy (FKE) and associated frequency components. The LV harbours disturbed flow during diastole with cycle-to-cycle variations. However, phase-averaged velocity fields much resemble those of CMR measurements and usually reported CFD results. The peak FKE value occurs during the E wave deceleration and reaches 25% of the maximum phase-averaged flow kinetic energy. Highest FKE values are predominantly located in the basal region and their frequency content reach more than 200 Hz. This study suggests that high-frequency flow fluctuations in normal LV may be common, implying deficiencies in the hypothesis usually made when computing cardiac flows and highlighting biases when deriving quantities from velocity fields measured with CMR.

Fluid‐structure interaction of a pulsatile flow with an aortic valve model: A combined experimental and numerical study

“…Large eddy simulation (LES) is used to account for possible turbulence in the flow. Large eddy simulation has the ability to predict intermittent flows . In particular, the so‐called Sigma subgrid model is well adapted to configurations with weak turbulence, as it has been designed not to add subgrid viscosity in a number of laminar canonical cases.…”

“…Large eddy simulation has the ability to predict intermittent flows. 40,42 In particular, the so-called Sigma subgrid model 43,44 is well adapted to configurations with weak turbulence, as it has been designed not to add subgrid viscosity in a number of laminar canonical cases. The present fluid solver was validated on the benchmark of idealized cardiovascular device proposed by the US Food and Drug Administration (FDA), 45 as well as on a variety of test cases.…”

Augmented resistive immersed surfaces valve model for the simulation of cardiac hemodynamics with isovolumetric phases

“…To assess the sensitivity of the efficiency of the pressure correction with respect to the parameter R i and to confirm our previous choice, the same analysis, as the one described in Section , is carried on here. The set of values used for the resistive parameter R i are still Eventually, as the structure of the flow dynamics inside the ventricle can be used as a predictor of diseases or malfunction, it is crucial to ensure that the new pressure correction does not perturb the velocity field. A comparative study of the velocity and pressure fields obtained during the first isovolumetric phase, with and without the pressure correction, is undertaken in order to highlight the absence of disruption.…”

Impact of Pulmonary Venous Inflow on Cardiac Flow Simulations: Comparison with In Vivo 4D Flow MRI

“…Complementary to in vivo flow measurements, computational flow models based on high-resolution computed tomography (CT) can provide detailed information on blood flow characteristics, such as flow instabilities, pressure distribution, or blood residence time 4,5,23,28. Current CT technology is able to acquire time-resolved anatomy on a sub-millimeter level, making CT-based computational models ideal for flow studies of cardiac geometry.…”

“…The total inflow rate through all four pulmonary veins can be calculated a priori from medical image data as the time-rate-of-change of the cardiac blood pool volume, but individual PV flow rates cannot be determined directly, and some sort of assumption must be made. One approach is to prescribe 25% of the total pulmonary flow rate on each PV 4,5. In absence of in vivo measurements this is a straight-forward but rather simplistic approach, as virtually any other flow combination is possible.…”