Internal carotid and brachial artery shear‐dependent vasodilator function in young healthy humans

Abstract

Brachial artery (BA) shear-mediated dilatation is a widely used assessment of vascular function with links to coronary artery health and cardiovascular risk. r Cerebral vascular health is often interrogated using cerebrovascular (middle cerebral artery velocity) reactivity to carbon dioxide. r We show that endothelium-dependent diameter (dilator) responses are not significantly related between the internal carotid artery (ICA) and BA; nor are endothelium-independent responses. r Additionally, ICA endothelium-dependent responses are not related to middle cerebral artery velocity or ICA blood flow reactivity responses to carbon dioxide. r Therefore, assessment of large extracranial cerebral artery vascular health should be quantified via methods specific to the vessel, not via peripheral endothelial function or cerebrovascular reactivity to carbon dioxide.

Cerebral Hemodynamic and Neurotrophic Factor Responses Are Dependent on the Type of Exercise

“…The importance of the total shear stimulus in comparison to peak changes has been demonstrated over short time periods (up to 60 s) in brachial artery flow mediated dilatory (FMD) responses ( Pyke and Tschakovsky, 2007 ), but to the best of our knowledge has not been investigated over longer time periods, such as that represented here. While Hoiland et al (2017) demonstrated the capacity for transient periods of hypercapnia (30 s) to induce an FMD response within the cerebrovasculature, a recent comparison of brachial and internal carotid artery FMD showed that the magnitude and pattern of dilatory responses was distinctly different between the two vessels ( Carr et al, 2020 ) and as such the impact of peak and total shear stimulus within the cerebrovasculature may be distinct from that seen within the periphery. Therefore, whether exercise-induced observations, both acute and chronic, based on FMD responses in the periphery are translated to FMD responses in the cerebrovasculature remain to be determined.…”

“To measure is to know”: no relationship between cerebrovascular and peripheral shear‐mediated dilation in young adults

“…Before we can consider cFMD a true cerebral-equivalent of FMD, essential data on the underpinning mechanisms of this response, alongside its reliability, sensitivity to cerebrovascular disease risk, prognostic power and association with cerebral microvascular function is essential to determine. Overall, these novel findings from Carr et al (2020) address an important research gap and demonstrate vessel-specific endothelium-dependent function in healthy young adults. This work is instrumental in informing valuable future research to better measure and understand both cerebrovascular function and dysfunction.…”

“…In a recent issue of The Journal of Physiology , Carr et al . (2020) explored the relationships between ICA and brachial artery shear‐mediated dilation in 19 healthy adults (23±6 years). They also explored the endothelium‐ independent responses of these arteries, through glyceryl trinitrate (GTN) administration.…”

“…Given the above, the cerebral‐FMD challenge used by Hoiland et al ., (2017) and Carr et al, (2020) appears to be a more appropriate test of cerebrovascular function that better measures predominantly shear‐mediated dilation, compared to “traditional” CVR tests. However, Carr et al, (2020) did not report the relationship between SRAUC and dilation in neither the brachial nor internal carotid artery, though previous work has reported an r 2 = 0.44 for the cFMD test (Hoiland et al ., 2017). Continuing to report these relationships is an important consideration for future work studying shear‐mediated responses of the cerebrovasculature, particularly when comparisons are being made between groups (for example, in the context of ageing).…”

“…Overall, these novel findings from Carr et al . (2020) address an important research gap and demonstrate vessel‐specific endothelium‐dependent function in healthy young adults. This work is instrumental in informing valuable future research to better measure and understand both cerebrovascular function and dysfunction.…”