Effect of aortic taper on patterns of blood flow and wall shear stress in rabbits: Association with age

Abstract

Objective -The distribution of atherosclerotic lesions changes with age in human and rabbit aortas. We investigated if this can be explained by changes in patterns of blood flow and wall shear stress. Methods -The luminal geometry of thoracic aortas from immature and mature rabbits was obtained by micro-CT of vascular corrosion casts. Blood flow was computed and average maps of wall shear stress were derived. Results -The branch anatomy of the aortic arch varied widely between animals. Wall shear was increased downstream and to a lesser extent upstream of intercostal branch ostia, and a stripe of high shear was located on the dorsal descending aortic wall. The stripe was associated with two vortices generated by aortic arch curvature; their persistence into the descending aorta depended on aortic taper and was more pronounced in mature geometries. These results were not sensitive to the modelling assumptions.Conclusions -Blood flow characteristics in the rabbit aorta were affected by the degree of taper, which tends to increase with age in the aortic arch and strengthens secondary flows into the descending aorta. Previouslyobserved lesion distributions correlated better with high than low shear, and age-related changes around branch ostia were not explained by the flow patterns.

A Novel Method for Quantifying Spatial Correlations Between Patterns of Atherosclerosis and Hemodynamic Factors

“…In the regions where a correlation existed, lesions occurred more frequently in zones of high rather than low WSS, in contrast to the current consensus that low or low oscillatory WSS promotes plaque formation [23,24]. Potential explanations for the discrepancy with the consensus theory have been discussed in detail elsewhere [11]. The results confirm the need for further investigation of the relation between the localization of atherosclerosis and blood now, in conjunction with appropriate statistical techniques such as those proposed here.…”

“…Application of the novel methodology to a recent comparative study of early atherosclerosis and WSS in the aorta of immature and mature rabbits [11] enabled us to determine if the original findings were significant. A spatial correlation between lipid-rich lesions and WSS was confirmed in the proximal descending thoracic aorta of both age groups, and a trend for a similar correlation was seen around the intercostal ostia of immature rabbits.…”

“…A linear regression analysis of maps of lesion prevalence [10] and WSS [11] around intercostal branch ostia in immature rabbit aortas were conducted to illustrate the shortcomings of this approach. Figure 5 shows the scatter plot of lesion prevalence versus WSS.…”

“…7 Comparative analysis of lesion prevalence and WSS maps in segments of the descending thoracic aorta. Greyscale and color maps show lesion prevalence [10] and WSS [11], respectively, averaged for immature (a) and mature (d) animals.…”

“…The method is applied to compare maps of lesion prevalence in aortas of immature and mature rabbits, obtained by Cremers et al [10], with corresponding averaged maps of WSS, presented previously in Ref. [11]. Additional experiments to further validate the methodology using simulated images or real-world imagery are discussed in the Appendix.…”