Computational fluid dynamic study on effect of Carreau-Yasuda and Newtonian blood viscosity models on hemodynamic parameters

Pulsatile blood flow through the human carotid artery is studied using Computational Fluid Dynamics (CFD) in order to investigate the effect of blood rheology on the hemodynamic parameters. The carotid artery model used is segmented and reconstructed from the Magnetic Resonance Images (MRI) of a specific patient. The results of a non-Newtonian (Carreau-Yasuda) model and a Newtonian model are studied and compared. The results are represented for each peak systole where it is observed that there is significant variation in the spatial parameters between the two models considered in the study. Comparison of local shear stress magnitude in different branches namely Common Carotid Artery (CCA), Internal Carotid Artery (ICA) and External Carotid Artery (ECA) show that the shear thinning property of blood influences the Wall Shear Stress (WSS) variation. This is observed in branches where there is reduction in diameter and where the diameter reduces due to plaque deposition and also in the region where there is flow recirculation like carotid sinus

Stress analysis in a layered aortic arch model under pulsatile blood flow

BACKGROUND: Many cardiovascular diseases, such as aortic dissection, frequently occur on the aortic arch and fluid-structure interactions play an important role in the cardiovascular system. Mechanical stress is crucial in the functioning of the cardiovascular system; therefore, stress analysis is a useful tool for understanding vascular pathophysiology. The present study is concerned with the stress distribution in a layered aortic arch model with interaction between pulsatile flow and the wall of the blood vessel. METHODS: A three-dimensional (3D) layered aortic arch model was constructed based on the aortic wall structure and arch shape. The complex mechanical interaction between pulsatile blood flow and wall dynamics in the aortic arch model was simulated by means of computational loose coupling fluid-structure interaction analyses. RESULTS: The results showed the variations of mechanical stress along the outer wall of the arch during the cardiac cycle. Variations of circumferential stress are very similar to variations of pressure. Composite stress in the aortic wall plane is high at the ascending portion of the arch and along the top of the arch, and is higher in the media than in the intima and adventitia across the wall thickness. CONCLUSION: Our analysis indicates that circumferential stress in the aortic wall is directly associated with blood pressure, supporting the clinical importance of blood pressure control. High stress in the aortic wall could be a risk factor in aortic dissections. Our numerical layered aortic model may prove useful for biomechanical analyses and for studying the pathogeneses of aortic dissection

Measurement of friction-induced changes in pig aorta fibre organization by non-invasive imaging as a model for detecting the tissue response to endovascular catheters

Alterations in quantity or architecture of elastin and collagen fibres are associated with some blood vessel pathologies. Also some medical interventions such as endovascular catheterization have the potential to damage blood vessels. This study reports the use of porcine aorta as a model system for studying the physical impact of catheters on vasculature, in conjunction with non-invasive imaging techniques to analyse collagen and elastin fibre organization and assess load-induced changes. Porcine aorta was exposed to frictional trauma and elastin and collagen fibre orientation evaluated by destructive, histochemical methods and non-invasive imaging. The latter allowed the immediate impact of force on fibre orientation and fibre recovery to be evaluated longitudinally. In normal aorta, elastin fibres are aligned at the surface, but become less aligned with increasing depth, showing no alignment by ~30 µm. Collagen fibres meanwhile appear aligned down to a depth of 35 µm. Changes in collagen and elastin fibre orientation in healthy pig aorta were detected by conventional destructive histology within 5 minutes of application of a sliding 10N load, while lesser loads had less impact. Good recovery of fibre orientation was observed within 20 minutes. Non-invasive imaging of ex vivo aorta tissue provides a good indication of the extent of fibre re-organization following frictional stress, at loads similar to those encountered during medical interventions such as catheterization. These results indicate that tissue deformation can occur from these procedures, even in healthy tissue, and highlight the potential for the development of an in vivo probe capable of monitoring vascular changes in patients