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Background: cerebral autoregulation (CA) is the ability to control cerebral blood flow during fluctuations in arterial blood pressure (ABP). It is impaired in a number of conditions including acute stroke, though studies so far have not found a decline in CA with age. CA is very sensitive to changes in pCO₂., Objective: this study investigates the effect of ageing on CA using a moving-window autoregressive moving average (MW-ARMA) to calculate CA as autoregulatory index (ARMA-ARI) during hypercapnia and hypocapnia, to ascertain whether this method would detect age-related differences in CA due to change in pCO₂., Method: ECG was used to measure R-R interval, Finapres to measure ABP and capnography to measure end-tidal CO₂. Transcranial Doppler ultrasonography was used to measure left and right middle cerebral artery cerebral blood flow velocity (CBFV). Hypercapnia was induced by a breath-hold, hypocapnia by hyperventilation., Results: thirty volunteers of mean age 25 ± 6 years and 30 volunteers of mean age 64 ± 4 years were recruited. CBFV was higher and change in CBFV due to respiratory manoeuvre was significantly greater in the younger group compared with the older group. However, no difference in ARMA-ARI was found between the groups., Conclusion: these findings suggest that CA is not affected by healthy ageing.