Introduction

Carotid diseases, especially atherosclerosis, are the predominant risk factor of ischemic stroke¹. Patient age, hypertension, hyperlipidemia, diabetes, smoking, etc, are usually associated with the formation of atherosclerotic plaque², in addition, carotid artery bifurcation is the predilection site for atherosclerotic plaque³. Among these risk factors, patient age and the anatomy of carotid bifurcation are immutable, while the status of hypertension, hyperlipidemia, diabetes can be interfered. Therefore, the relationship between hemodynamic changes and different territories of carotid artery, patient age in healthy subjects can help understand how the hemodynamic states influence carotid incidents.
We use 4D flow MRI, a newly developed complementary method, to detect the changes of multiple hemodynamic parameters in different age and locations. The aim of this study is to demonstrate the hemodynamic distribution of normal carotid arteries and to explore the possible influence of these factors because age and location are intrinsic factors in the development of carotid artery disease. In addition, it may also provide age and location matched control cohorts for the assessment of carotid artery disease.

Method

Sixty-two normal volunteers aging from 20 to 75 were enrolled in our study, A rigorous medical history was taken from the volunteers to exclude those with cardiovascular risk factors (hypertension, hyperlipidemia, diabetes, smoking, drinking et al) or former cardiovascular events. 4D flow MRI examination was performed for each subject and analyzed using CVI42 platform to get hemodynamic parameters. Hemodynamic parameters were then compared in different ages and locations (pro-CCA, dis-CCA, pro-ICA and dis-CCA). The relationship between age and hemodynamic parameters was then qualified by Pearson's correlation coefficient.

Result

Hemodynamics changes in different locations
Hemodynamics changes in different locations of carotid artery were displayed in figure1. Pro-ICA had significant lower velocity, WSS and PG than other parts(P<0.05). Velocity and PG all first showed a downward trend and started rising when it reached the lowest point pro-ICA. Figure 2 visually displayed the MIP and streamline map of velocity/WSS in different age group.
Correlation between age and hemodynamics
Linear correlations between hemodynamic parameters in different locations and age were summarized in figure 3. The velocity, WSS and PG showed significantly inverse correlation with age (P<0.05). The velocity and PG better correlation with the age than the WSS. Moreover, the correlation between age and the velocity/PG at CCA were better than ICA, but for WSS, the correlation at ICA was better than CCA. Only distal ICA showed no correlation with age.

Discussion

The shape of carotid bifurcation has a large impact to the distribution of blood flow and velocity⁴. Previous study found low WSS was mainly distributed on the outer side wall of carotid bifurcation⁵. Pressure was the mechanical force of blood flow acting perpendicular to the luminal surface⁶ and PG reflected the magnitude of the pressure change. One study found that PGmean decreased after the percutaneous transluminal angioplasty and stenting (PTAS) when stenosis existed⁷.
Our research showed that velocity, WSS and PG were all reduced with age, and the same phenomenon were also found in aorta for velocity and WSS^{8, 9}.Vessel diameter can increase with age due to decreased elasticity¹⁰. So the decreased velocity may be driven by diameter expansion. How age affects hemodynamics remains unclear, it may be explained by the change of vascular elasticity and endothelial cell function with age¹¹.
Why does this state of hemodynamic led to the formation of plaques? The decrease of velocity prolonged the blood duration in the vessel, resulting in lasting lipid retention and interaction with vessel wall. WSS is the frictional force on the endothelial cells induced by blood flow and is paralleled to the luminal surface of vessel⁶. Low WSS increased the uptake of oxidized low-density lipoprotein¹², causing increasing lipid components in plaques. Moreover, low WSS altered vascular endothelium flow patterns in molecular and cellular levels. All these reactions promote the development of atherosclerosis¹³.

Conclusion

In conclusion, different locations of the carotid artery showed different hemodynamic changes. Among them, proximal ICA showed significantly lower volume, velocity and WSS. In addition, the hemodynamic parameters in different location were inversely correlated with age. It may imply that low volume, velocity and WSS are more likely to cause atherosclerotic plaques. The multi-parameter analysis of 4D flow MRI identified age and location changes of hemodynamic parameters in carotid artery of healthy adults, indicating that age and location impacted the blood flow. This study offered suggestion for choosing age and location matched control cohorts for the assessment of carotid artery disease in future study.

Acknowledgements

No acknowledgement found.

References

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