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Impaired Middle Cerebral Artery and Cerebrovascular Vasodilation in Healthy Aging

This study quantified the effect of age on cerebrovascular reactivity (CVR) and cerebrovascular conductance. Cerebral blood flow velocity (CBFV; transcranial Doppler (TCD)) and cross‐sectional area (CSA) of the middle cerebral artery (MCA; 3T Magnetic Resonance Imaging (MRI)) to measure cerebral blood flow (CBF) (HC; 6% CO2) were measured in healthy populations of young (YA: n=6, 24 ± 2 years, 3 males) and older adults (OA: n=6, 66 ± 6 years, 1 male) during hypercapnia (HC). CVR was calculated as the percent change (%Δ) in CBF per change in end tidal carbon dioxide where the end tidal carbon dioxide was the average of the change during TCD and the MRI studies which were performed on separate days. Cerebrovascular conductance was calculated as the quotient of CBF and mean arterial pressure. CVR was not different between YA (2.0 ± 0.9 at minute one to 3.1 ± 0.9 %/mmHg at minute four) and OA (2.6 ± 1.2 at minute one to 4.0 ± 1.6 %/mmHg at minute four) over the four minutes of HC. The CSA in YA increased from 6.29 ± 0.71 at baseline to 7.16 ± 1.00 mm2 at minute four while OA increased from 6.36 ± 0.92 at baseline to 6.75 ± 1.27 mm2 at minute four (p=0.5). The %ΔCBF was not different between the YA and OA yet the %Δ in CBFV was greater during HC in the OA (p=0.01). However, when %ΔCBFV was normalized to the change in mean arterial pressure there was no longer a difference between YA and OA. Also, cerebrovascular conductance was greater in the YA (p=0.03). Therefore, a greater blood pressure response in the OA may be responsible for their preserved CVR despite evidence for an age‐related impairment in MCA dilation and vascular conductance. Supported by the Canadian Institutes of Health Research.