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Severity parameter and global importance factor of non-newtonian models in 3D reconstructed human left coronary artery
This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.The capabilities and limitations of various molecular viscosity models, when testing Left Coronary Artery (LCA) tree, were analyzed via: molecular viscosity, local and global non-Newtonian importance factors, Wall Shear Stress (WSS) and Wall Shear Stress Gradient (WSSG). Seven non-Newtonian molecular viscosity models, plus the Newtonian one, were compared. Dense grid of 620000 nodes located, mostly, at near to low WSS flow regions (endothelium regions) is needed for current LCA application. The WSS
distribution yields a consistent LCA pattern for nearly all non-Newtonian models. High molecular viscosity, low WSS low WSSG values appear at proximal LCA regions at the outer walls of the major bifurcation. The global importance factor for the non-Newtonian power law model yields 76.7% (non-Newtonian flow), while for the Generalized power law model this value is 6.1% (Newtonian flow). The capabilities of the applied non-Newtonian law models appear at low strain rates. The Newtonian blood flow treatment is considered to be a good approximation at mid-and high-strain rates. In general, the non-Newtonian power law and the Generalized power law blood viscosity models are considered to approximate the molecular viscosity and WSS calculations in a more satisfactory way
Investigation of blood pressure waveform using harmonic distortion: implications for cardiovascular risk
Blood pressure waveform (BPW) can be used to characterize changes in the cardiovascular system due to diseases and aging. The BPW morphology is largely determined by both the total mechanical impedance of the vasculature and the flow waveform produced by the left ventricle. The BPW can be further decomposed into its two primary components: the forward and reflected waveforms. It is known that under several conditions, such as aging, arterial wall stiffening, and increased cardiovascular risk, the magnitudes and phases of these waves change and therefore distort the aggregate BPW. Previous studies of the BPW has yielded mixed results, largely due to the insensitivities of the primary wave morphology index, augmentation index (AI). To this end, a new method of morphology characterization was developed which takes into account the overall harmonic content of the BPW.
Harmonic distortion (HD), derived from Fourier-transformed BPW, was first used to characterize changes in the aortic wall. Utilizing mice subjected to normal and high fat, high-sucrose diets, the results demonstrate that HD exhibits a linear relationship with both systolic blood pressure (SBP) and arterial stiffness. Next, a transmission line model of arterial impedance was developed to study physiologically realistic BPWs under various arterial tree sizes and stiffness. Comparison of HD and other indexes reveals that HD correlates strongly with arterial stiffness, surpassing AI in accuracy for higher stiffness values. Finally, HD analysis was applied to BPWs collected clinically on a diverse group of participants. HD emerges as a more sensitive indicator than AI, notably correlating with diabetes and demonstrating stability across heart rate variations. The superior statistical performance of HD over AI in hemodynamic variables underscores its potential as a robust measure for cardiovascular risk assessment. This research offers a comprehensive framework for assessing arterial health, highlighting the potential of HD as a stable, sensitive, and noninvasive measure. This integrated approach contributes to a nuanced understanding of the intricate factors influencing BPW morphology and its implications for cardiovascular health in the context of aging and disease