Impact of age on cerebrovascular dilation versus reactivity to hypercapnia

Abstract

This study quantified the effect of age on cerebrovascular reactivity and cerebrovascular conductance while accounting for differences in grey matter volume in younger (YA: n = 12; 24 ± 4 years, six females) and older adults (OA: n = 10; 66 ± 7 years; five females). Cerebral blood flow velocity (CBFV; transcranial Doppler) in the middle cerebral artery (MCA), MCA cross-sectional area (CSA), intracranial volumes (magnetic resonance imaging), and mean arterial pressure (MAP; Finometer), were measured under normocapnic and hypercapnic (6% carbon dioxide) conditions. Cerebral blood flow (CBF) was quantified from CBFV and MCA CSA and normalized to grey matter volume. Grey matter volume was 719 ± 98 mL in YA and 622 ± 50 mL in OA (P = 0.009). Cerebrovascular reactivity (%ΔCBF/ΔPETCO2) was not different between YA and OA. In contrast, cerebrovascular conductance (CBF/MAP) in response to hypercapnia was reduced in OA (P = 0.02). Of note, MAP increased more with hypercapnia in OA compared with YA. Therefore, the central hemodynamic response to hypercapnia compensated for a diminished dilatory response downstream from the MCA so that the CBF response to hypercapnia per unit of brain mass was not affected by age. This impairment was not detected by traditional measures of cerebrovascular reactivity.

Keywords: Middle cerebral artery; aging; cerebrovascular control; transcranial Doppler ultrasound.

© The Author(s) 2016.

Figures

Figure 1.

The relationship between baseline cerebral blood flow (CBF) and grey matter volume (GM) in young adults (YA) and older adults (OA). For YA, the equation of the regression line is CBF = −89.21 + 0.49 × GM and for OA CBF = −176.67 + 0.64 × GM.

Figure 2.

Middle cerebral artery cross-sectional area (CSA) during hypercapnia in young adults (YA; a) and older adults (OA; b) expressed as absolute values (c), absolute change (d) and percent change CSA (e). *P < 0.05 versus YA.

Figure 3.

Cerebral blood flow velocity (CBFVGM; a) and cerebral blood flow (CBFGM; b) at baseline and during hypercapnia in young adults (YA) and older adults (OA) expressed as absolute values and percent change (c). *P < 0.05 versus CBFVGM.

Figure 4.

Cerebrovascular conductance (CVCGM; a) at baseline and hypercapnia and the absolute (b) and percent change (c) from baseline to hypercapnia in young adults (YA) and older adults (OA). *P < 0.05 versus baseline; †P < 0.05 versus YA.

Figure 5.

Absolute (a) and relative (b) cerebrovascular reactivity (CVRGM) at baseline and hypercapnia in young adults (YA) and older adults (OA) and the error in calculating CVRGM when CBFVGM was used instead of CBFGM for YA and OA (c). *P < 0.05 versus CBFVGM; †P < 0.05 versus YA.