Abstract
Abstract only Recent research focuses on the cerebrovascular response to vasodilatory stimuli as an index of cerebrovascular health; however, vasoconstrictor responses in the brain are likely equally important. We previously have shown that cerebral vasoconstrictor responses to hypocapnia are not affected by aging; however, this was evaluated in primarily sedentary adults. Therefore, we hypothesized that middle cerebral artery velocity (MCAv) vasoconstrictor responses to hypocapnia are dependent on age and habitual physical activity. We evaluated 13 young physically active (YA; age = 30±5 y; VO 2 max = 45±8 mL/kg/min), 6 young sedentary (YS; age = 29±4 y; VO 2 max = 26±3 mL/kg/min), 10 older physically active (OA; age= 61±6 y; VO 2 max =35±7 mL/kg/min) and 8 older sedentary (OS; age = 65±8 y; VO 2 max 23±2 mL/kg/min) adults during the recovery from inhaled 6% CO 2 to room air. Mean arterial pressure (MAP) end tidal CO 2 (ETCO 2 ) and MCAv were recorded throughout. Using a breath‐by breath analysis, cerebrovascular conductance index (CVCi=MCAv/MAP) reactivity was calculated as a slope of CVCi and ETCO 2 and used to quantify vasoconstrictor responses. CVCi reactivity was higher in YA adults (slope=2.74±0.9 AU) compared with both YS (slope=2.20±1.1 AU) and older groups (OA: slope=2.08±0.5 AU; OS: slope=2.07±0.7 AU; p<0.05 for all). There were no significant differences in CVCi reactivity between YS and either OA or OS (p=0.94, p=0.99 respectively). Additionally, CVCi negatively correlated with age (r=−0.38, p<0.05). Our results indicate that aging attenuates the cerebral vasoconstrictor response to hypocapnia in older adults in comparison to physically‐active young adults, but not compared to sedentary young controls. A sedentary lifestyle resulted in attenuated vasoconstrictor responses in the young sedentary group, as their responses were not different than the older adults. It remains unclear how habitual physical activity preserves the cerebral vasoconstrictor response to hypocapnia in young people, and if a structured exercise training intervention would impact this response in older adults. Support or Funding Information NIH HL118154