Cerebrovascular Hemodynamics in Cognitive Impairment and Dementia: A Systematic Review and Meta-Analysis of Transcranial Doppler Studies

Introduction: Transcranial Doppler sonography (TCD) is a non-invasive tool for measuring cerebrovascular hemodynamics. Studies have reported alterations in cerebrovascular hemodynamics in normal aging, mild cognitive impairment (MCI) and dementia, as well as in different etiologies of dementia. This systematic review and meta-analysis was designed to investigate the relationship between cerebral blood velocity (CBv) and pulsatility index (PI) in the middle cerebral artery (MCA) in persons with MCI and dementia. Methods: A systematic literature search was conducted in Pubmed, Embase, Cochrane Library, Epistemonikos, PsychINFO, and CINAHL. The search was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. After screening of 33439 articles, 86 were reviewed in full-text, and 35 fulfilled the inclusion criteria. Results: CBv was significantly lower and PI significantly higher in MCA in vascular dementia (VaD) and Alzheimer's disease (AD) compared to cognitively normal (CN) older persons. Also, CBv was lower in MCI compared to CN. There were no significant differences in CBv in MCA in AD compared with VaD, although PI was higher in VaD compared to AD. Conclusion: Alterations in cerebrovascular hemodynamics are seen in AD, VaD and MCI. While PI was slightly higher in VaD compared to AD, the reduction in CBv appears to be equally pronounced across neurodegenerative and vascular etiologies of dementia.