Left Ventricular Fluid Mechanics: the long way from theoretical models to clinical applications

\u2014The flow inside the left ventricle is characterized by the formation of vortices that smoothly accompany blood from the mitral inlet to the aortic outlet. Computational fluid dynamics permitted to shed some light on the fundamental processes involved with vortex motion. More recently, patient-specific numerical simulations are becoming an increasingly feasible tool that can be integrated with the developing imaging technologies. The existing computational methods are reviewed in the perspective of their potential role as a novel aid for advanced clinical analysis. The current results obtained by simulation methods either alone or in combination with medical imaging are summarized. Open problems are highlighted and perspective clinical applications are discussed

High Frame Rate Ultrasound Particle Image Velocimetry for Estimating High Velocity Flow Patterns in the Left Ventricle

Echocardiographic determination of multi-component blood flow dynamics in the left ventricle remains a challenge. In this study we compare contrast enhanced, high frame rate (1000 fps) echo particle image velocimetry (ePIV) against optical particle image velocimetry (oPIV, gold standard), in a realistic left ventricular phantom. We find that ePIV compares well to oPIV, even for the high velocity inflow jet (normalized RMSE = 9 ±1%). Additionally, we perform the method of Proper Orthogonal Decomposition, to better qualify and quantify the differences between the two modalities. We show that ePIV and oPIV resolve very similar flow structures, especially for the lowest order mode with a cosine similarity index of 86%. The co

Flow Dynamics in Cardiovascular Devices: A Comprehensive Review

This review explores flow dynamics in cardiovascular devices, focusing on fundamental fluid mechanics principles and normal blood flow patterns. It discusses the role of different structures in maintaining flow dynamics and the importance of stents, heart valves, artificial hearts, and ventricular assist devices in cardiovascular interventions. The review emphasizes the need for optimized designs and further research to enhance knowledge of flow dynamics in cardiovascular devices, advancing the field and improving patient care in cardiovascular interventions

Extraction and Analysis of Vector Flow Imaging Data in a Pediatric Population

Vector flow imaging (VFI) is a new ultrasound technology that provides real time, angle-independent visualization of flow velocities in the heart and great vessels. Thus far, VFI has been used for superficial applications due to the limited penetration depth of available transducer probes; however, this depth in smaller pediatric patients enables adequate aortic views. In this project, VFI was used to study pediatric aortic stenosis (PAS)—a congenital heart defect that results in the narrowing of the aorta and/or aortic valve. The decision to refer PAS patients for surgical or catheter-based intervention is initially based on Doppler ultrasound. VFI is potentially more precise, and avoids many of the pitfalls of conventional Doppler ultrasound, namely in the under- or overestimation of pressure differences in the aorta leading to less than ideal treatment timelines. Our goal was to create a method for quantitatively analyzing vectors produced by the VFI machine and to validate VFI technology by attaching an aortic arch phantom to a customized flow loop. This research will set the foundation for the creation of patient-specific aortic arch phantoms

Measuring blood flow and pro-inflammatory changes in the rabbit aorta

Atherosclerosis is a chronic inflammatory disease that develops as a consequence of progressive entrapment of low density lipoprotein, fibrous proteins and inflammatory cells in the arterial intima. Once triggered, a myriad of inflammatory and atherogenic factors mediate disease progression. However, the role of pro-inflammatory activity in the initiation of atherogenesis and its relation to altered mechanical stresses acting on the arterial wall is unclear. Estimation of wall shear stress (WSS) and the inflammatory mediator NF-κB is consequently useful. In this thesis novel ultrasound tools for accurate measurement of spatiotemporally varying 2D and 3D blood flow, with and without the use of contrast agents, have been developed. This allowed for the first time accurate, broad-view quantification of WSS around branches of the rabbit abdominal aorta. A thorough review of the evidence for a relationship between flow, NF-κB and disease was performed which highlighted discrepancies in the current literature and was used to guide the study design. Subsequently, methods for the measurement and colocalization of the spatial distribution of NF-κB, arterial permeability and nuclear morphology in the aorta of New Zealand White rabbits were developed. It was demonstrated that endothelial pro-inflammatory changes are spatially correlated with patterns of WSS, nuclear morphology and arterial permeability in vivo in the rabbit descending and abdominal aorta. The data are consistent with a causal chain between WSS, macromolecule uptake, inflammation and disease, and with the hypothesis that lipids are deposited first, through flow-mediated naturally occurring transmigration that, in excessive amounts, leads to subsequent inflammation and disease.Open Acces

Parasternal versus apical view in cardiac natural mechanical wave speed measurements

Shear wave speed measurements can potentially be used to noninvasively measure myocardial stiffness to assess the myocardial function. Several studies showed the feasibility of tracking naturalmechanical waves induced by aortic valve closure in the interventricular septum, but different echocardiographic views have been used. This article systematically studied the wave propagation speedsmeasured in a parasternal long-axis and in an apical four-chamber view in ten healthy volunteers. The apical and parasternal views are predominantly sensitive to longitudinal or transversal tissue motion, respectively, and could, therefore, theoreticallymeasure the speed of different wave modes. We found higher propagation speeds in apical than in the parasternal view (median of 5.1 m/s versus 3.8 m/s, p < 0.01, n = 9). The results in the different views were not correlated (r = 0.26, p = 0.49) and an unexpectedly large variability among healthy volunteers was found in apical view compared with the parasternal view (3.5-8.7 versus 3.2-4.3 m/s, respectively). Complementary finite element simulations of Lamb waves in an elastic plate showed that different propagation speeds can be measured for different particlemotion componentswhen differentwavemodes are induced simultaneously. The in vivo results cannot be fully explained with the theory of Lamb wave modes. Nonetheless, the results suggest that the parasternal long-axis view is amore suitable candidate for clinical diagnosis due to the lower variability in wave speeds

Assessing the performance of ultrafast vector flow imaging in the neonatal heart via multiphysics modeling and In vitro experiments

Ultrafast vector flow imaging would benefit newborn patients with congenital heart disorders, but still requires thorough validation before translation to clinical practice. This paper investigates 2-D speckle tracking (ST) of intraventricular blood flow in neonates when transmitting diverging waves at ultrafast frame rate. Computational and in vitro studies enabled us to quantify the performance and identify artifacts related to the flow and the imaging sequence. First, synthetic ultrasound images of a neonate's left ventricular flow pattern were obtained with the ultrasound simulator Field II by propagating point scatterers according to 3-D intraventricular flow fields obtained with computational fluid dynamics (CFD). Noncompounded diverging waves (opening angle of 60 degrees) were transmitted at a pulse repetition frequency of 9 kHz. ST of the B-mode data provided 2-D flow estimates at 180 Hz, which were compared with the CFD flow field. We demonstrated that the diastolic inflow jet showed a strong bias in the lateral velocity estimates at the edges of the jet, as confirmed by additional in vitro tests on a jet flow phantom. Furthermore, ST performance was highly dependent on the cardiac phase with low flows (< 5 cm/s), high spatial flow gradients, and out-of-plane flow as deteriorating factors. Despite the observed artifacts, a good overall performance of 2-D ST was obtained with a median magnitude underestimation and angular deviation of, respectively, 28% and 13.5 degrees during systole and 16% and 10.5 degrees during diastole

Hybrid system for ex vivo hemorheological and hemodynamic analysis: a feasibility study

Precise measurement of biophysical properties is important to understand the relation between these properties and the outbreak of cardiovascular diseases (CVDs). However, a systematic measurement for these biophysical parameters under in vivo conditions is nearly impossible because of complex vessel shape and limited practicality. In vitro measurements can provide more biophysical information, but in vitro exposure changes hemorheological properties. In this study, a hybrid system composed of an ultrasound system and microfluidic device is proposed for monitoring hemorheological and hemodynamic properties under more reasonable experimental conditions. Biophysical properties including RBC aggregation, viscosity, velocity, and pressure of blood flows are simultaneously measured under various conditions to demonstrate the feasibility and performance of this measurement system. The proposed technique is applied to a rat extracorporeal loop which connects the aorta and jugular vein directly. As a result, the proposed system is found to measure biophysical parameters reasonably without blood collection from the rat and provided more detailed information. This hybrid system, combining ultrasound imaging and microfluidic techniques to ex vivo animal models, would be useful for monitoring the variations of biophysical properties induced by chemical agents. It can be used to understand the relation between biophysical parameters and CVDs.1196Ysciescopu