Correlating in-vivo hemodynamics with vascular responses
Hoi, Yie Meng
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The roles of hemodynamics in the natural history of vascular diseases remain unclear due to a lack of understanding of the cellular and molecular responses under various hemodynamic stimuli. In vivo quantitative hemodynamics, when combined with vascular lesion assessment, can yield important cause-and-effect relationships between hemodynamic and vascular responses. The integrated information advance our understanding on vascular functions and potentially improving clinical outcomes. This study aims to correlate the subject-specific in vivo hemodynamics with vascular responses in experimental animal models. A new mapping methodology that utilized subject-specific image-based computational fluid dynamics (CFD) analysis and histology examination was proposed and applied to examine the vascular responses in canine surgically created bifurcation model. The aneurysm-like destructive remodeling events found in this model are localized in vascular regions exposed to high wall shear stress and high positive wall shear stress gradient. Using Doppler ultrasound to quantify the in vivo basilar artery flow in rabbits subjected to common carotid artery ligation, this study also found that increased flow can lead to nascent aneurysm formation at rabbit basilar terminus. This nascent aneurysm is dose-dependent on basilar artery (BA) flow-rate increase. In addition, the increased BA flow also resulted in adaptive BA diameter increases until the wall shear stress returns to baseline level. Tortuous BA can rapidly form following flow alteration. Image-based CFD has surpassed other techniques in quantifying the in vivo hemodynamics. However, CFD result is very sensitive to geometrical variations. Medical-image-based, patient-specific CFD results, which are very sensitive to geometric uncertainties, must be carefully scrutinized before providing clinical feedback.