A method for matching the refractive index and kinematic viscosity of a blood analog for flow visualization in hydraulic cardiovascular models.

In this work, we propose a simple method to simultaneously match the refractive index and kinematic viscosity of a circulating blood analog in hydraulic models for optical flow measurement techniques (PIV, PMFV, LDA, and LIF). The method is based on the determination of the volumetric proportions and temperature at which two transparent miscible liquids should be mixed to reproduce the targeted fluid characteristics. The temperature dependence models are a linear relation for the refractive index and an Arrhenius relation for the dynamic viscosity of each liquid. Then the dynamic viscosity of the mixture is represented with a Grunberg-Nissan model of type 1. Experimental tests for acrylic and blood viscosity were found to be in very good agreement with the targeted values (measured refractive index of 1.486 and kinematic viscosity of 3.454 milli-m2/s with targeted values of 1.47 and 3.300 milli-m2/s).

Large-displacement 3D structural analysis of an aortic valve model with nonlinear material properties.

Grafts used in aortic valve-sparing procedures should ideally not only reproduce the geometry of the natural aortic root but also its material properties. Indeed, a number of studies using the finite element method have shown the importance of the natural sinus shape of the root in the functioning of the normal aortic valve, and the relative increase in stresses due to the replacement of the valve by a stiffer synthetic graft. Because of the wide range in experimentally measured values of aortic wall and leaflet material properties, studies by different research groups have incorporated very different material properties in their models. The aim of the present study was to investigate the influence of material properties on aortic wall displacements, and to determine which material properties would most closely match reported experimental data. Two geometrically accurate 3D models corresponding to the closed and open valve configurations were created in Pro/Engineer CAD software. Loads corresponding to systolic and diastolic pressures were specified and large-displacement structural analyses were carried out using the ANSYS package. Results have indicated that the closest match to experiments using isotropic material properties occurred for a Young's modulus of about 2000 KPa. Nonlinear models based on experimental stress-strain curves have shown similar displacements, but altered strain distribution patterns and significantly lower stresses. These results suggest that an accurate comparison of potential new graft models would have to be made with natural aortic valve models incorporating nonlinear material behavior.