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摘要
Middle cerebral artery mean velocity (MCAv(mean)) 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 (Y-T) and 10 considered untrained (Y-UT), and 2) 17 old (O; 66 +/- 4 yr) volunteers of whom 8 and 9 were considered trained (O-T) and untrained (O-UT), respectively. A resting hypercapnic reactivity test was also performed. MCAv(mean) 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 %26lt; 0.01) at rest, independent of aerobic fitness level. The age-related decreases in MCAv(mean) and PaCO2 persisted during exercise. Supplemental CO2 reduced the age-associated decline in MCAv(mean) 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 MCAv(mean) at rest and during exercise; however exercise capacity did not diminish this age effect.
- 出版日期2014-8-15
