Brain Tissue Oxygenation In Response To Changes In Arterial Pressure In Patients With Mild Cognitive Impairment

Purpose : To test the hypothesis that brain oxygenation responses to changes in arterial pressure are altered in patients with amnestic mild cognitive impairment (aMCI). Methods : Forty‐five aMCI patients (18 males, 65 ± 6 yr) and 30 age and education matched cognitively normal control subjects (NC, 15 males, 66 ± 6 yr) underwent stepwise changes in mean arterial blood pressure (MAP) induced by intravenous infusion of sodium nitroprusside and phenylephrine. Transcranial Doppler and near‐infrared spectroscopy were used to measure the cerebral blood flow velocity (CBFV) at the middle cerebral artery and cortical tissue oxygenation index (TOI) at the prefrontal lobe, simultaneously. All measurements were normalized as percentage changes from baseline (Δ, %). Random coefficient mixed model was used to estimate the regression slopes of ΔCBFV% and ΔTOI% to changes in ΔMAP%. Results : Drug induced changes in MAP were from ‐26% to 49% (65~143 mmHg) relative to the baseline. The mixed model regression slopes of ∆CBFV% to ∆MAP% showed no differences between aMCI and NC (0.313 ± 0.047 vs. 0.219 ± 0.065, P = 0.238), suggesting the presence of intact cerebral autoregulation in aMCI. However, the slope of ∆TOI% to ∆MAP% was steeper in aMCI than in NC (‐0.253 ± 0.024 vs. ‐0.147 ± 0.032, P = 0.007), indicating an enhanced cortical oxygenation response to changes in blood pressure in aMCI. Conclusion : The enhanced cortical oxygenation responses to changes in blood pressure in patients with aMCI suggest that abnormalities of the cerebral microvasculature in regulation of brain tissue oxygenation may occur early in Alzheimer disease. Grant Funding Source : NIH grant R01AG033106‐01 and R01HL102457