1,721,796 research outputs found
Simulation of wall shear stress-driven in-stent restenosis
No full textIn-stent restenosis is a patho-physiological remodelling process due to the presence of foreign material into the artery which alters several factor (e.g. the Wall Shear Stress). It has been demonstrated that WSS can modulate the endothelial phenotype. In this numerical study the in-stent restenotic process is investigated by considering the alteration of WSS due to the presence of a stent. A simplified axisymmetric geometry of stented vessel is considered for computational fluid dynamic (CFD) analysis. A WSS-based remodelling algorithm is tested to simulate the remodelling of the vessel by changing its geometry after each CFD simulation. The final configuration (i.e. the geometry of the vessel at the last iteration) has the WSS everywhere higher than a threshold (0.5 Pa) and should predict the final lumen geometry the restenotic process should lead. The present model is a necessary step towards a future 3D model which would help to compare different stent designs with respect to the amount of restenosis and maybe provide a virtual tool for preclinical testing
An innovative design of a blood pump actuator device using an artificial left ventricular muscle
No full textBlood pumps assist or take over the pump function of a failing heart. They are essentially activated by a pusher plate, a pneumatic compression of collapsible sacs or they are driven by centrifugal pumps. Blood pumps relying upon one of these actuator mechanisms do not account for realistic wall deformation. In this study, we propose an innovative design of a blood pump actuator device which should be able to mimic fairly well global left ventricular (LV) wall deformation patterns in terms of circumferential and longitudinal contraction, as well as torsion. In order to reproduce these basic wall deformation patterns in our actuator device, we designed a novel kind of artificial LV “muscle” composed of multiple actively contracting cells. Its contraction is based on a mechanism by which pressurized air, inside such a cell, causes contraction in one direction and expansion perpendicular to this direction. The organization and geometry of the contractile cells within one artificial LV muscle, the applied pressure in the cells, and the governing LV loading conditions (preload and afterload) together determine the global deformation of the LV wall. Starting from a simple plastic bag, an experimental model based on the abovementioned principle was built and connected to a lumped hydraulic model of the vascular system (including compliance and resistance). The wall deformation pattern of this device was validated visually and its pump performance was studied in terms of LV volume and pressure and heart rate. Our experimental results revealed (i) a global LV motion resembling a real LV, and (ii) a close correlation between our model and a real LV in terms of end-systolic volume and pressure, end-diastolic volume and pressure, stroke volume, ejection fraction and pressure-volume relationship. Our proposed model appears promising and it can be considered as a step forward when compared to currently applied actuator mechanisms, as it will likely result in more physiological intracavity blood flow patterns
Modelling the arterial input function for blood pool agents in dynamic contrast enhanced-MRI: concepts and validations for P792
No full textRelation between left ventricular relaxation rate and arterial loading
No full textA number of studies suggested a relation between reduced left ventricular (LV) relaxation rate and increased arterial stiffness. In the present study we aimed (i) to investigate whether this association is inherently present in apparently healthy, middle-aged individuals, and (ii) to determine to what extent this association is modulated by age and/or body or heart size.
2239 subjects (1151 M and 1088 F) aged between 35 and 55 years (median 46 years) at the initiation of the study, free from overt cardiovascular disease and participating in the Asklepios study, were included in this study.
Important bivariate correlations were observed between diastolic function and various arterial function parameters. In both men and women a pronounced relation was found between the carotid distensibility coefficient and LV relaxation rate, assessed as mitral annular early diastolic velocity (E').
A multiple linear regression model, however, proved age to be the primary independent determinant of E', followed by LV mass. Inclusion of the remaining arterial function variables only marginally increased the model's predictive capacity. The presumably direct relationship between E' and arterial stiffness is thus largely mediated by age and to a lesser extent by LV mass
Experimental and numerical flow modeling towards refinement of three-dimensional echocardiography for heart valve leakage quantification
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