Hypercapnia-induced shear-mediated dilation in the internal carotid artery is blunted in healthy older adults

Abstract

This study aimed to elucidate the effect of aging on shear-mediated dilation of the common and internal carotid arteries (CCA and ICA, respectively). Hypercapnia-induced shear-mediated dilation in the CCA and ICA were assessed in ten young (5F/5M, 23±1 years) and ten older (6F/4M, 68±1 years) healthy adults. Shear-mediated dilation was induced by two levels of hypercapnia (target end-tidal carbon dioxide; +5 and +10mmHg from individual baseline value) and was calculated as the percent rise in peak diameter from baseline diameter. There were no differences in shear-mediated dilation between young and older adults in either artery under lower level of hypercapnia (CCA; 2.8±0.6 vs. 2.0±0.3%, P=0.35, ICA; 4.6±0.8 vs 3.6±0.4%, P=0.37). However, the shear-mediated dilation in response to the higher levels of hypercapnia was attenuated in older compared to young adults in the ICA (4.5±0.5 vs. 7.9±1.2%, P<0.01), but not in the CCA (3.7±0.6 vs. 4.5±0.8%, P=0.35). Shear-mediated dilation was significantly correlated to the percent change in shear rate in the ICA (Young; r=0.55, P=0.01, Older; r=0.49, P=0.03), but not in the CCA in both young and older adults (Young; r=-0.30, P=0.90, Older; r=0.16, P=0.50). These data indicate that aging attenuates shear-mediated dilation of the ICA in response to higher levels of hypercapnia, and shear rate is an important stimulus for hypercapnic vasodilation of the ICA in both young and older adults. The current results may provide insight into age-related changes in the regulation of cerebral circulation in healthy adults.

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

“…Although CVR tests are often interpreted as assays of cerebrovascular endothelial function (e.g. Ainslie et al 2007;Lavi et al 2006) and measurement of ICA diameter change during steady-state CVR tests taken to be representative of shear-mediated dilatation (Iwamoto et al 2018a(Iwamoto et al ,b, 2020Suzuki et al 2020), the current study found no relationship between CVR of Q ICA and cFMD diameter change (r 2 = 0.06; P = 0.46, Fig. 4C).…”

“…Studies by Iwamoto et al . (2018a, 2020) also indicate that there may be no sex differences in ICA vasodilator responses to steady‐state hypercapnia, although differences in methods between those studies and the current study make comparison difficult. Given that the effect of menstrual cycle on vascular function in general remains controversial (e.g.…”

“…2006) and measurement of ICA diameter change during steady‐state CVR tests taken to be representative of shear‐mediated dilatation (Iwamoto et al. 2018a, b , 2020; Suzuki et al . 2020), the current study found no relationship between CVR of Q ICA and cFMD diameter change ( r 2 = 0.06; P = 0.46, Fig.…”

Habitual cigarette smoking attenuates shear‐mediated dilation in the brachial artery but not in the carotid artery in young adults

“…We averaged continuously measured hemodynamic variables of the initial 2 min (baseline) and of the 10 s before peak ICA diameter during the hypercapnia condition. We then analyzed the diameter and mean blood velocity (V mean ) during FMD tests at 30 Hz using custom-designed edge-detecting and wall-tracking software (version 2.0.1, S-13037, Takei Kiki Kogyo) (Iwamoto, Bock, & Casey, 2018b). We detected brachial artery data using an algorithm reported previously (Black, Cable, Thijssen, & Green, 2008).…”

“…We detected brachial artery data using an algorithm reported previously (Black, Cable, Thijssen, & Green, 2008). We interpolated ICA data to 1 Hz and filtered them using the two-stage filtering process (median filter and Savitzky-Golay finite impulse response smoothing filter) (Iwamoto et al, 2018b) with custom software (Python version 3.6.1, Python Software Foundation). We calculated SR in the brachial artery and ICA by the equation; 4 × V mean / arterial diameter.…”