Steady-State Cerebral Autoregulation in Older Adults with Amnestic Mild Cognitive Impairment: Linear Mixed Model Analysis.

We examined whether steady-state cerebral autoregulation (CA) is impaired in older adults with amnestic mild cognitive impairment (aMCI), a prodromal stage of clinical Alzheimer disease (AD). Forty-two patients with aMCI and 27 cognitively normal older adults (NC) of similar age, sex, and education underwent stepwise decreases and increases in mean arterial pressure (MAP) induced by intravenous infusion of sodium nitroprusside and phenylephrine, respectively. Changes in cerebral blood flow (CBF) were measured in the internal carotid and vertebral artery. Linear mixed modelling, including random effects of both individual intercept and regression slope, was used to quantify the MAP-CBF relationship accounting for the non-independent CBF measures. Changes in end-tidal CO2 (ETCO2 ) associated with changes in MAP were also included in the model to account for their effects on CBF. Marginal mean values of MAP were reduced by 13-14 mmHg during sodium nitroprusside and increased by 20-24 mmHg during phenylephrine infusion in both groups with similar doses of drug infusion. A steeper slope of changes in CBF in response to changes in MAP was observed in aMCI relative to NC, indicating impaired CA (MAP*Group, P < 0.05). These findings indicate CA was impaired in older adults with aMCI, suggesting that cerebrovascular dysfunction may occur early in the development of AD.