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A computational evaluation of sedentary lifestyle effects on carotid hemodynamics and atherosclerotic events incidence

Caruso M. V., Serra R., Perri P., Buffone G., Calio F. G., Franciscis S., Fragomeni G.

Acta of Bioengineering and Biomechanics

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2017

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Vol. 19, no. 3

43--52

EN

Purpose: Hemodynamics has a key role in the atheropathogenesis. Indeed, atherosclerotic phenomena occur in vessels characterized by complex geometry and flow pattern, like the carotid bifurcation. Moreover, the lifestyle is a significant risk factor. The aim of this study is to evaluate the hemodynamic effects due to two sedentary lifestyles -sitting and standing positions- in the carotid bifurcation in order to identify the worst condition and to investigate the atherosclerosis incidence. Methods: The computational fluid dynamics (CFD) was chosen to carry out the analysis, in which in-vivo non-invasive measurements were used as boundary conditions. Furthermore, to compare the two conditions, one patient-specific 3D model of a carotid bifurcation was reconstructed starting from computer tomography. Different mechanical indicators, correlated with atherosclerosis incidence, were calculated in addition to flow pattern and pressure distribution: the time average wall shear stress (TAWSS), the oscillatory shear index (OSI) and the relative residence time (RRT). Results: The results have highlighted that the bulb and the external carotid artery emergence are the most probable regions in which atherosclerotic events could happen. Indeed, low velocity and WSS values, high OSI and, as a consequence, areas with chaotic-swirling flow, with stasis (high RRT), occur. Moreover, the sitting position is the worst condition: considering a cardiac cycle, TAWSS is less than 17.2% and OSI and RRT are greater than 17.5% and 21.2%, respectively. Conclusions: This study suggests that if a person spends much time in the sitting position, a high risk of plaque formation and, consequently, of stenosis could happen.

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Percutaneous double lumen cannula for right ventricle assist device system: A computational fluid dynamics study

Condemi F., Wang D., Fragomeni G., Yang F., Zhao G., Jones C., Ballard-Croft C., Zwischenberger J. B.

Biocybernetics and Biomedical Engineering

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2016

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Vol. 36, no. 3

482--490

EN

Objectives: Our goal is to develop a double lumen cannula (DLC) for a percutaneous right ventricular assist device (pRVAD) in order to eliminate two open chest surgeries for RVAD installation and removal. The objective of this study was to evaluate the performance, flow pattern, blood hemolysis, and thrombosis potential of the pRVAD DLC. Methods: Computational fluid dynamics (CFD), using the finite volume method, was performed on the pRVAD DLC. For Reynolds numbers <4000, the laminar model was used to describe the blood flow behavior, while shear-stress transport k-ω model was used for Reynolds numbers >4000. Bench testing with a 27 Fr prototype was performed to validate the CFD calculations. Results: There was <1.3% difference between the CFD and experimental pressure drop results. The Lagrangian approach revealed a low index of hemolysis (0.012% in drainage lumen and 0.0073% in infusion lumen) at 5 l/min flow rate. Blood stagnancy and recirculation regions were found in the CFD analysis, indicating a potential risk for thrombosis. Conclusions: The pRVAD DLC can handle up to 5 l/min flow with limited potential hemolysis. Further modification of the pRVAD DLC is needed to address blood stagnancy and recirculation.

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Numerical prediction of the effect of aortic Left Ventricular Assist Device outflow-graft anastomosis location

Mazzitelli R., Boyle F., Murphy E., Renzulli A., Fragomeni G.

Biocybernetics and Biomedical Engineering

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2016

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Vol. 36, no. 2

327--343

EN

A Left Ventricular Assist Device (LVAD) is used to provide haemodynamic support to patients with critical cardiac failure. As LVADs generate continuous flow to better understand the haemodynamic effects of these devices under different working conditions, and particularly in relation to possible outflow-graft anastomosis location, we performed 3D one-way-coupled fluid–structure-interaction (FSI) for three different LVAD working conditions and with the anastomosis location in the ascending aorta and in the descending aorta. The anatomical model used in this study is a patient-specific geometry reconstructed from computed tomography images and the mechanical support considered is similar to the Jarvik 2000®Heart LVAD. Endothelial cells can be influenced by wall stress generated from the blood flow in the artery, so they can produce vascular complications. For this reason, the second aim of this study is to evaluate and analyse, using different mechanical indicators, the wall shear distribution upon the luminal surface of the aorta generated by an LVAD. These numerical investigations demonstrate the utility of one-way-coupled FSI models to compare the haemodynamic conditions for the two LVAD outflow-grafts anastomosis locations and how both affect the aorta and its wall stress. Furthermore, the mechanical indicators allow the identification of wall regions at greater risk of atherosclerosis. The results of this study indicate that an LVAD outflow-graft anastomosis location in the ascending aorta is the optimal configuration.

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Computational analysis of aortic hemodynamics during total and partial extra-corporeal membrane oxygenation and intra-aortic balloon pump support

Caruzo M. V., Gramigna V., Renzulli A., Fragomeni G.

Acta of Bioengineering and Biomechanics

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2016

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Vol. 18, no. 3

3--9

EN

Purpose: The extracorporeal membrane oxygenation (ECMO) is a temporary, but prolonged circulatory support for cardiopulmonary failure. Clinical evidence suggests that pulsed flow is healthier than non pulsatile perfusion. The aim of this study was to computationally evaluate the effects of total and partial ECMO assistance and pulsed flow on hemodynamics in a patient-specific aorta model. Methods: The pulsatility was obtained by means of the intra-aortic balloon pump (IABP), and two different cases were investigated, considering a cardiac output (CO) of 5 L/min: Case A – total assistance – the whole flow delivered through the ECMO arterial cannula; Case B – partial assistance – flow delivered half through the cannula and half through the aorta. Computational fluid dynamic (CFD) analysis was carried out using the multiscale approach to couple the 3D aorta model with the lumped parameter model (resistance boundary condition). Results: In case A pulsatility followed the balloon radius change, while in case B it was mostly influenced by the cardiac one. Furthermore, during total assistance, a blood stagnation occurred in the ascending aorta; in the case of partial assistance, the flow was orderly when the IABP was on and was chaotic when the balloon was off. Moreover, the mean arterial pressure (MAP) was higher in case B. The wall shear stress was worse in ascending aorta in case A. Conclusions: Partial support is hemodynamically advisable.