Effect of healthy aging on cerebral blood flow, CO2 reactivity, and neurovascular coupling during exercise

We sought to make the first comparisons of duplex Doppler ultrasonography-derived measures of cerebral blood flow during exercise in young and older individuals and to assess whether healthy aging influences the effect of exercise on neurovascular coupling (NVC) and cerebral vascular reactivity to changes in carbon dioxide (CVRco2). In 10 healthy young (23 ± 2 yr; mean ± SD) and 9 healthy older (66 ± 3 yr) individuals, internal carotid artery (ICA) and vertebral artery (VA) blood flows were concurrently measured, along with middle and posterior cerebral artery mean blood velocity (MCAvmean and PCAvmean). Measures were made at rest and during leg cycling (75 W and 35% maximum aerobic workload). ICA and VA blood flow during dynamic exercise, undertaken at matched absolute (ICA: young 336 ± 95, older 352 ± 155; VA: young 95 ± 43, older 100 ± 30 ml/min) and relative (ICA: young 355 ± 125, older 323 ± 153; VA: young 115 ± 48, older 110 ± 32 ml/min) intensities, were not different between groups (P > 0.670). The PCAvmean responses to visual stimulation (NVC) were blunted in older versus younger group at rest (16 ± 6% vs. 23 ± 7%, P < 0.026) and exercise; however, these responses were not changed from rest to exercise in either group. The ICA and VA CVRco2 were comparable in both groups and unaltered during exercise. Collectively, our findings suggest that 1) ICA and VA blood flow responses to dynamic exercise are similar in healthy young and older individuals, 2) NVC is blunted in healthy older individuals at rest and exercise but is not different between rest to exercise in either group, and 3) CVRco2 is similar during exercise in healthy young and older groups.