Dynamic cerebral autoregulation and tissue oxygenation in amnestic mild cognitive impairment.

BACKGROUND: Vascular disease and dysfunction are associated with the higher risk of Alzheimer's disease hypothetically due to cerebral hypoperfusion. Brain perfusion is protected by cerebral autoregulation, which, under normal conditions, maintains a constant cerebral blood flow and brain tissue oxygenation. OBJECTIVE: To determine whether dynamic regulation of cerebral blood flow and tissue oxygenation is impaired in patients with amnestic mild cognitive impairment (aMCI). METHODS: Twenty-seven patients with aMCI and 15 control subjects with normal cognitive function underwent the measurements of cerebral hemodynamics, brain MR imaging, and neurocognitive assessment. Dynamic regulation of cerebral blood flow and tissue oxygenation were assessed by transfer function analysis of changes in mean blood pressure (MBP), normalized cerebral blood flow velocity (CBFV%), and cerebral tissue oxygenation index (TOI) at baseline and during a sit-stand maneuver. RESULTS: Patients with aMCI demonstrated lower cognitive performance in memory and executive function, accompanied by smaller entorhinal cortex volumes. At baseline, cerebral TOI was lower in patients with aMCI than in control subjects. Lower cerebral TOI was also correlated with lower cognitive performance in memory and executive function in all subjects. Transfer function gain and phase between MBP and CBFV% and between CBFV% and cerebral TOI were not different between the groups. Within aMCI patients, greater oscillations of cerebral TOI and higher transfer function gain between cerebral TOI and CBFV% were associated with the lower scores on delayed recall. CONCLUSION: Dynamic regulation of cerebral tissue oxygenation is associated with neurocognitive dysfunction in aMCI patients.