Mean arterial pressure during cerebral perfusion MRI: An arterial spin‐labeling study in younger and older adults

Abstract

AbstractBackgroundHigh blood pressure (BP) and low cerebral blood flow (CBF) have been independently related to Alzheimer’s disease (AD) pathophysiology. Increased cerebrovascular resistance index (CVRi), the ratio of mean arterial pressure (MAP) to CBF, has also been linked to AD risk in older adults. Autoregulatory mechanisms maintain steady perfusion across a range of MAP values through changes in cerebrovascular resistance in healthy individuals. Age‐dependent cerebrovascular stiffening can disrupt cerebrovascular resistance, leaving the brain vulnerable to hypoperfusion with increased MAP. No studies have evaluated MAP during perfusion MRI to further evaluate whether high BP may be related to lower CBF, and whether this relationship is age‐dependent. We studied MAP during perfusion MRI in a sample of younger and older adults using an MRI‐compatible device to continuously monitor MAP.MethodCommunity‐dwelling older adults (n=21; age 56‐87) free of dementia or stroke, and healthy younger adults (n=16; age 18‐34) underwent resting pseudo‐continuous arterial spin‐labelling (pCASL)‐MRI to quantify CBF during simultaneous in‐scanner, continuous MAP monitoring. Average MAP and CBF were calculated over the 5 minute scan. Multiple linear regression examined the relationship between MAP and CBF for younger and older adults, controlling for age and sex.ResultOlder adults with higher MAP during perfusion MRI exhibited significantly lower CBF levels (R2 = .49, β = ‐.23, p = .02). MAP showed no significant relationship with CBF in younger adults.ConclusionThis is the first study to evaluate MAP during perfusion MRI. Findings indicate that higher MAP is correlated with lower CBF in real time in older adults only. We hypothesize that higher MAP may cause decreased CBF through chronic increases in cerebrovascular resistance. Our approach utilizes pCASL‐MRI, capturing CBF to capillaries and smaller arterioles that are susceptible to age‐related microvascular injury. It remains unclear whether the relationship between MAP and microvascular perfusion plays a role in the increased dementia risk associated with high CVRi, but increased CVRi and decreased CBF are associated with dementia. Future work will explore the role of BP during perfusion MRI and whether it may contribute to diagnosis, prognosis or treatment decision‐making to help prevent dementia.