Blood flow modeling and mass transport in the human aorta

• Κύριος συγγραφέας: Χατζηκωνσταντή, Αναστασία
• Άλλοι συγγραφείς: Λουκόπουλος, Βασίλειος
• Μορφή: Thesis
• Γλώσσα: English
• Έκδοση: 2013
• Θέματα: Human aorta; Low density lipoproteins; Atherosclerosis; Ανθρώπινη αορτή; Χαμηλής πυκνότητας λιποπρωτεΐνες; Αθηροσκλήρωση; 616.136 071

Atherosclerosis is a disease of cardiovascular system and is usually located within large arteries. It is a major cause of death and mortality and it is related to over 12 million deaths annually affecting nearly all people in the modern world. It is a disease that involves the circulation of low density lipoproteins –LDLs (a main carrier of cholesterol) within the blood stream. These eventually accumulate in the cell wall of large and medium sized arteries to form plaques or atherosclerotic patches gradually narrow the lumen and gradually become the site of bleeding and thrombus formation. It is well known that atherosclerotic lesions in the arterial wall develop at certain sites in the human arterial system such as along the inner walls of curved segments and the outer walls of arterial bifurcations. This phenomenon is called the localization of atherosclerosis. As the early event leading to the genesis of atherosclerosis is the accumulation of atherogenic lipids such as low density lipoproteins (LDLs) within the arterial wall, mass transport between the blood and the artery wall must play an important role in the genesis and development of atherosclerosis. In the present study we investigate the correlation of luminal surface LDL concentration (cw) distribution with the distribution of wall shear stress (WSS) and the effects of both non – Newtonian behavior and pulsation of blood flow on the distributions of luminal surface LDL concentration along the wall of the human aorta. The dependence of viscosity and diffusivity and the local density are incorporated in the single and two phase flow models rendering these quantities position dependent. Then we compared the predictions of a single phase model with those of the two phases one under both steady flow and realistic pulsatile flow conditions using a human aorta model constructed from CT images. Then local hemodynamics studied by using computational fluid-dynamics (CFD) applied to realistic geometric model of the aorta. It is therefore important to solve the problem of accurately reconstructing geometric models from CT image in order to gain accuracy in CFD computations and predictions. The present numerical study revealed an adverse correlation between wall shear stress and the luminal surface LDL concentration in the aorta. The results indicate that the luminal surface LDL concentration depends not only on the local wall shear stress but also on both the global and local flow patterns. Also the results showed that under steady flow conditions, although the shear thinning non – Newtonian nature of blood could elevate wall shear stress (WSS) in most regions of the aorta, especially in areas with low wall shear stress, it had little effect on luminal surface LDL concentration (cw) in most regions of the aorta. Nevertheless, it could significantly enhance cw in areas with high luminal surface LDL concentration through the shear depended diffusivity of LDLs. The pulsation of blood flow could significantly reduce cw in these disturbed places. In conclusion the shear shining non – Newtonian nature of blood has little effect on LDL transport in most regions of the aorta, but in the atherogenic – prone areas where luminal surface LDL concentration is high its effect is apparent. Similar is the effect of pulsatile flow on the transport of LDLs.