title: Age, aerobic fitness, and cerebral perfusion during exercise: role of carbon dioxide.
abstract: Middle cerebral artery mean velocity (MCAvmean) is attenuated with increasing age both at rest and during exercise. The aim of this study was to determine the influence of the age-dependent reduction in arterial Pco2 (PaCO2) and physical fitness herein. We administered supplemental CO2 (CO2 trial) or no additional gas (control trial) to the inspired air in a blinded and randomized manner, and assessed middle cerebral artery mean flow velocity during graded exercise in 1) 21 young [Y; age 24 ± 3 yr (±SD)] volunteers of whom 11 were trained (YT) and 10 considered untrained (YUT), and 2) 17 old (O; 66 ± 4 yr) volunteers of whom 8 and 9 were considered trained (OT) and untrained (OUT), respectively. A resting hypercapnic reactivity test was also performed. MCAvmean and PaCO2 were lower in O [44.9 ± 3.1 cm/s and 30 ± 1 mmHg (±SE)] compared with Y (59.3 ± 2.3 cm/s and 34 ± 1 mmHg, P < 0.01) at rest, independent of aerobic fitness level. The age-related decreases in MCAvmean and PaCO2 persisted during exercise. Supplemental CO2 reduced the age-associated decline in MCAvmean by 50%, suggesting that PaCO2 is a major component in the decline. On the other hand, relative hypercapnic reactivity was neither influenced by age (P = 0.46) nor aerobic fitness (P = 0.36). Although supplemental CO2 attenuated exercise-induced reduction in cerebral oxygenation (near-infrared spectroscopy), this did not influence exercise performance. In conclusion, PaCO2 contributes to the age-associated decline in MCAvmean at rest and during exercise; however exercise capacity did not diminish this age effect.
authors.forename: Daniela
authors.initials: D
authors.lastname: Flück
authors.forename: Igor D
authors.initials: ID
authors.lastname: Braz
authors.forename: Stefanie
authors.initials: S
authors.lastname: Keiser
authors.forename: Fabienne
authors.initials: F
authors.lastname: Hüppin
authors.forename: Thomas
authors.initials: T
authors.lastname: Haider
authors.forename: Matthias P
authors.initials: MP
authors.lastname: Hilty
authors.forename: James P
authors.initials: JP
authors.lastname: Fisher
authors.forename: Carsten
authors.initials: C
authors.lastname: Lundby
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D001783:Blood Flow Velocity; D002245:Carbon Dioxide / Q000097:blood* / Q000494:pharmacology; D016022:Case-Control Studies; D015444:Exercise; D006801:Humans; D006935:Hypercapnia / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D020768:Middle Cerebral Artery / Q000187:drug effects / Q000254:growth & development / Q000502:physiology*; D010809:Physical Fitness
chemical_list: D002245:Carbon Dioxide