Dynamic cerebral autoregulation in people with mild cognitive impairment

Altered cerebrovascular hemodynamics and low cerebral perfusion contribute to the development and progression of dementia. Dynamic cerebral autoregulation (dCA), a measure of the cerebral vasculature's ability to buffer abrupt changes in mean arterial pressure and prevent hypoperfusion, such as during a supine-to-standing transition, have mixed results in people clinically diagnosed with mild cognitive impairment (MCI, people with objective cognitive impairment but maintained functional independence). Therefore, in 30 people with MCI, we tested the hypothesis that participants with a higher standing middle cerebral artery velocity (MCAv) at diastole (higher-velocity group) would have lower dCA values, to confer better cerebrovascular outcomes and enhanced cognitive function compared to participants with a lower MCAv at diastole (lower-velocity group). This study separated people with MCI into different diastolic MCAv groups. dCA was calculated as (MCAv_nadir-MCAv_supine/MCAv_supine)/(MAP_MCAnadir-MAP_MCAsupine/MAP_MCAsupine). This work led to the identification of a dysregulated dCA in the higher-velocity group (p = 0.009) compared to the lower-velocity group despite having greater cognitive scores (p = 0.008). Elevated levels of cerebral oxygen tissue saturation (p = 0.039) and lower end-tidal carbon dioxide (p = 0.042) suggest that a favourable dCA value may be a compensatory mechanism in the neurodegenerative disease processes. The unexpected results highlight the importance of uncovering hemodynamic pathways in clinical populations.