In Vitro Assessment of Non-Newtonian Hemodynamics in Aorta Phantom with Particle Image Velocimetry

International audienceArterial hemodynamics are essential in the development of cardiovascular pathologies, such as aneurysms or aortic dissection where vessel walls can be torn and weakened. Surgical or endovascular procedures are performed to treat these diseases. However, these procedures often result in complications (aortic rupture, malperfusion, etc.) [1] partly due to difficulties in visualizing and analyzing the flow to prevent them. In vitro studies can provide more precise flow visualizations than traditional medical imaging [2-3] and thus, a better understanding of disease progression, and treatment. In this work, an aortic flow simulator was designed to study non-Newtonian hemodynamics in pathologic aortic replicas. Experiments were conducted on a patient-specific compliant silicon model of the human aorta. A circulatory mock loop was set up to control and monitor pulsatile flow and pressure (fig. 1). To address blood rheology, a non-Newtonian blood mimicking fluid was designed with Xanthan gum polymers and glycerol solutions. Particle Image Velocimetry (PIV) technique was implemented to describe and map non-Newtonian flow fields in the phantom (fig. 2). Velocities were calculated for 12 different times in the cardiac cycle and averaged on 500 cycles. The current results are limited to a specific geometry of the aorta with aneurysm but the experimental set-up can accommodate various shapes of model. Pathological aorta models with aortic dissection will be tested with similar PIV evaluations. It will be compared with in vivo data for validation and numerical simulations for complementary analysi

In vitro flow study in a compliant abdominal aorta phantom with a non-Newtonian blood-mimicking fluid

International audienceIn vitro aortic flow simulators allow studying hemodynamics with a wider range of flow visualization techniques compared to in vivo medical imaging and without the limitations of invasive examinations. This work aims to develop an experimental bench to emulate the pulsatile circulation in a realistic aortic phantom. To mimic the blood shear thinning behavior, a non-Newtonian aqueous solution is prepared with glycerin and xanthan gum polymer. The flow is compared to a reference flow of Newtonian fluid. Particle image velocimetry is carried out to visualize 2D velocity fields in a phantom section. The experimental loop accurately recreates flowrates and pressure conditions and preserves the shear-thinning properties of the non-Newtonian fluid. Velocity profiles, shear rate, and shear stress distribution maps show that the Newtonian fluid tends to dampen the observed velocities. Preferential asymmetrical flow paths are observed in a diameter narrowing region and amplified in the non-Newtonian case. Wall shear stresses are about twice higher in the non-Newtonian case. This study shows new insights on flow patterns, velocity and shear stress distributions compared to rigid and simplified geometry aorta phantom with Newtonian fluid flows studies. The use of a non-Newtonian blood analog shows clear differences in flows compared to the Newtonian one in this compliant patient-specific geometry. The development of this aortic simulator is a promising tool to better analyze and understand aortic hemodynamics and to aid in clinical decision-making

Particle Image Velocimetry to Evaluate Pulse Wave Velocity in Aorta Phantom with the lnD–U Method

International audiencePurpose: Pulse Wave Velocity (PWV) is an indicator of arterial stiffness used in the prediction of cardiovascular disease such as atherosclerosis. Non-invasive methods performed with ultrasound probes allow one to compute PWV and aortic stiffness through the measurement of the aortic diameter (D) and blood flow velocity (U) with the lnD-U method. This technique based on in vivo acquisitions lacks validation since the aortic elasticity modulus cannot be verified with mechanical strength tests.Method: In the present study, an alternative validation is carried out on an aorta phantom hosted in an aortic flow simulator which mimics pulsatile inflow conditions. This in vitro setup included a Particle Image Velocimetry device to visualize flow in a 2D longitudinal section of the phantom, compute velocity fields (U), and track wall displacements in the aorta phantom to measure the apparent diameter (AD) variations throughout cycles.Results: The lnD-U method was then applied to evaluate PWV (5.92 ± 0.32 m/s) and calculate the Young's's modulus of the aorta phantom (0.66 ± 0.08 MPa). This last value was compared to the elasticity modulus (0.53 ± 0.07 MPa) evaluated with tensile strength tests on samples cut from the silicone phantom.Conclusion: Considering the uncertainties from the two methods, the measured elasticities are consistent and close to a 50-60 years old male aortic behavior. A comparison with in vivo data shows that the choice of silicone for the phantom material is a relevant and promising option to mimic the human aorta on in vitro systems

In vitro assessment of abdominal aortic dissection hemodynamics based on particle image velocimetry

International audienceAortic Dissection (AD) is a condition in which the inner layer of the vessel tears causing separation between the inner and middle layers of the aorta. Blood surges into the tears, resulting in vulnerable secondary blood flow channel. Surgery consists in positioning a stent graft in the damaged area to reinforce vessel walls and redirect flow [1]. Tears, surgical tools insertion and stent graft positioning generate flow field disturbances that may influence the evolution of the disease. Many studies have investigated flow disturbances in Abdominal Aorta (AA) under healthy, dissection and post-surgical conditions with the use of AA phantom [2-4]. However, non-Newtonian behaviour is rarely investigated in such aorta phantom. The current study focuses on replicating AA non-Newtonian flow patterns in pathological and stented AA compliant phantoms.La dissection aortique est une pathologie initiée par une déchirure de la couche interne du vaisseau causant une séparation entre les couches composant la paroi de l’aorte. La pénétration du sang dans la déchirure engendre la formation d’un chenal secondaire et fragilise la paroi. Une technique de chirurgie consiste à déployer une endoprothèse au niveau de la zone endommagée afin de renforcer la paroi et de rediriger l’écoulement sanguin [1]. La déchirure, l’insertion d’outils chirurgicaux et le positionnement de l’endoprothèse sont des sources de perturbations de l’écoulement qui peuvent influencer l’évolution de la maladie. De nombreuse études ont investigué la perturbation des écoulements dans l’aorte saine, disséquée et post-chirurgie sur des fantômes vaisseaux sanguins. Néanmoins, la problématique non-newtonienne de l’écoulement est rarement traitée dans de tels modèles. Cette étude porte sur la reproduction d’écoulements non-newtoniens dans un fantôme d’aorte pathologique pré et post déploiement d’endoprothèse

IN VITRO ASSESSMENT OF ABDOMINAL AORTA NON-NEWTONIAN HEMODYNAMICS BASED ON PARTICLE IMAGE VELOCIMETRY

International audienc