Cerebral Blood Flow in Mild Cognitive Impairment and Dementia: A Systematic Review and Meta- Analysis of Transcranial Doppler Studies

Introduction

Reduced cerebral blood flow has been associated with cognitive decline and incident dementia, with oxidative stress and reduced beta-amyloid clearance as possible mechanisms for neurodegeneration. Transcranial doppler sonography is a non-invasive tool for measuring cerebrovascular hemodynamics, including mean cerebral blood flow velocity. A systematic review and meta-analysis was performed to study mean cerebral blood flow velocity in the middle cerebral artery in persons with mild cognitive impairment and dementia compared to cognitively normal elderly.

Methods

We searched Pubmed, Embase, Cochrane Library, Epistemonikos, PsychINFO, and CINAHL according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. In total, 33439 titles and abstracts were screened, 86 articles were reviewed in full text, and 35 were included.

Results

Mean cerebral blood flow velocity in the middle cerebral artery was significantly lower in Alzheimer's disease (mean difference = 8.42; 95% confidence interval, -10.56 to -6.28), vascular dementia (mean difference = 11.75; 95% confidence interval, -14.68 to -8.82) and mild cognitive impairment (mean difference = 4.19; 95% confidence interval, -5.52 to -2.85) compared to cognitively normal elderly, see figures 1 – 3. Reduction in blood flow was equally pronounced in Alzheimer's disease and vascular dementia (mean difference = 2.79; 95% confidence interval, -0.78 to 6.35).

Discussion

Cerebral blood flow velocity is reduced in Alzheimer's disease, vascular dementia and MCI, with more pronounced disturbances in dementia.