Assessment of dynamic cerebral autoregulation and cerebrovascular CO2 reactivity in ageing by measurements of cerebral blood flow and cortical oxygenation

New Findings What is the central question in this study? It is unknown to what extent increasing age influences the dynamic adaptations of cerebral blood flow velocity and cortical oxygenation in response to changes in blood pressure (cerebral autoregulation) and to changes in carbon dioxide (cerebrovascular CO2 reactivity). What is the main finding and its importance? We have shown that ageing up to 86years is associated with an overall preservation of dynamic cerebral autoregulation and cerebrovascular CO2 reactivity, leading to a sufficiency of cerebral cortical oxygenation during daily life activities, despite the decrease in absolute cerebral blood flow velocity and increase in cerebrovascular resistance with advancing age. With ageing, cerebral blood flow velocity (CBFV) decreases; however, to what extent dynamic cerebral autoregulation and cerebrovascular CO2 reactivity are influenced by ageing is unknown. The aim was to examine the dynamic responses of CBFV and cortical oxygenation to changes in blood pressure (BP) and arterial CO2 across different ages. Fifty-eight participants in three age groups were included, as follows: young (n=20, 24 +/- 2years old), elderly (n=20, 66 +/- 1years old), and older elderly (n=18, 78 +/- 3years old). The CBFV was measured using transcranial Doppler ultrasound, simultaneously with oxyhaemoglobin (O(2)Hb) using near-infrared spectroscopy and beat-to-beat BP measurements using Finapres. Postural manoeuvres were performed to induce haemodynamic fluctuations. Cerebrovascular CO2 reactivity was tested with hyperventilation and CO2 inhalation. With age, CBFV decreased (young 59 +/- 12cms(-1), elderly 48 +/- 7cms(-1) and older elderly 42 +/- 9cms(-1), P<0.05) and cerebrovascular resistance increased (1.46 +/- 0.58, 1.81 +/- 0.36 and 1.98 +/- 0.52mmHgcm(-1)s(-1), respectively, P<0.05). Normalized gain (autoregulatory damping) increased with age for BP-CBFV (0.88 +/- 0.18, 1.31 +/- 0.30 and 1.06 +/- 0.34, respectively, P<0.05) and CBFV-O(2)Hb (0.10 +/- 0.09, 0.12 +/- 0.04 and 0.17 +/- 0.08, respectively, P<0.05) during the repeated sit-stand manoeuvre at 0.05Hz. Even though the absolute changes in CBFV and cerebrovascular resistance index during the cerebrovascular CO2 reactivity were higher in the young group, the percentage changes in CBFV, cerebrovascular resistance index and O(2)Hb were similar in all age groups. In conclusion, there was no decline in dynamic cerebral autoregulation and cerebrovascular CO2 reactivity with increasing age up to 86years. Despite the decrease in cerebral blood flow velocity and increase in cerebrovascular resistance with advancing age, CBFV and cortical oxygenation were not compromised in these elderly humans during manoeuvres that mimic daily life activities.