Detection of attenuated dynamic cerebrovascular function in aging and cognitive decline using a novel neuroimaging approach: Neuroimaging / New imaging methods.

Background: Cerebrovascular contributions to aging and cognitive decline have been increasingly recognized, yet the impact of changes in dynamic cerebrovascular function remain unclear. Breath holding and hyperventilation elicit alterations in end‐tidal carbon dioxide (etCO2) and cerebrovascular functions underlying cerebral blood flow (CBF). Manipulation of breathing during neuroimaging may therefore enable assessment of dynamic cerebrovascular changes implicated in cognitive decline. Method: Community‐dwelling younger (n=15) and older (n=40) adults performed guided 15‐second breath holds to induce hypercapnia and paced breathing (alternating between 5‐second inhalation and exhalation) to induce hypocapnia, while undergoing pseudo‐continuous arterial spin labelling (pCASL) MRI. Continuous blood pressure and end‐tidal carbon dioxide (etCO2) were simultaneously collected. Cerebrovascular resistance index (CVRi), was estimated by dividing mean arterial blood pressure by pCASL‐derived CBF. Carbon dioxide reactivity (CO2R) was calculated by dividing change in CBF by change in etCO2. Older adults also underwent neuropsychological assessment of global and domain‐specific cognition. Relationships between dynamic cerebrovascular function, aging, and cognition were analyzed, controlling for hypertension and education. Result: Across age groups, paced breathing decreased etCO2, CBF, and CO2R, while increasing CVR. Breath‐holding increased etCO2, CBF, and CO2R, while decreasing CVR. Older adults demonstrated attenuated cerebrovascular autoregulation (i.e. changes in CBF, CO2R, and CVR) in response to hypo‐ and hypercapnia, despite equivalent changes in etCO2 and blood pressure. Among older adults, weaker cerebrovascular response was associated with worse performance on measures of global cognition, memory, and executive function. Effects were preserved even after controlling for hypertension. Conclusion: Through instigation of mild hypercapnia and hypocapnia during MRI, cerebrovascular reactivity deficits were detected in community‐dwelling older adults. Hemodynamic response was attenuated in older relative to younger individuals, suggesting that acute autoregulatory capacity may diminish with aging, above and beyond changes associated with hypertension. Reduced hemodynamic response was also associated with poorer global cognition and performance on tests of executive function and memory. Results suggest that age‐related vascular changes may hamper the proficiency with which changes in blood pressure and CO2 are met with cerebrovascular responses, potentially compromising CBF and neuronal function. This noninvasive method may therefore enable detection of cerebrovascular changes characterizing the earliest stages of cognitive decline. [ABSTRACT FROM AUTHOR]