title: 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.
authors.affiliation: Neurovascular Research Laboratory, School of Kinesiology, Western University, London, ON, Canada.
authors.forename: Nicole S
authors.initials: NS
authors.lastname: Coverdale
authors.affiliation: Neurovascular Research Laboratory, School of Kinesiology, Western University, London, ON, Canada.
authors.forename: Mark B
authors.initials: MB
authors.lastname: Badrov
authors.affiliation: Neurovascular Research Laboratory, School of Kinesiology, Western University, London, ON, Canada kshoemak@uwo.ca.|Department of Physiology and Pharmacology, Western University, London, ON, Canada.
authors.forename: J Kevin
authors.initials: JK
authors.lastname: Shoemaker
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D062186:Arterial Pressure; D000071937:Cerebral Blood Volume; D002560:Cerebrovascular Circulation; D005260:Female; D066128:Gray Matter; D006801:Humans; D006935:Hypercapnia / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D020768:Middle Cerebral Artery / Q000503:physiopathology; D014664:Vasodilation / Q000502:physiology*; D055815:Young Adult
keywords: Middle cerebral artery; aging; cerebrovascular control; transcranial Doppler ultrasound