Alterations in cerebral metabolic rate and blood supply across the adult lifespan

With age, the brain undergoes comprehensive changes in its function and physiology. Cerebral metabolism and blood supply are among the key physiologic processes supporting the daily function of the brain and may play an important role in age-related cognitive decline. Using MRI, it is now possible to make quantitative assessment of these parameters in a noninvasive manner. In the present study, we concurrently measured cerebral metabolic rate of oxygen (CMRO₂), cerebral blood flow (CBF), and venous blood oxygenation in a well-characterized healthy adult cohort from 20 to 89 years old (N = 232). Our data showed that CMRO₂ increased significantly with age, while CBF decreased with age. This combination of higher demand and diminished supply resulted in a reduction of venous blood oxygenation with age. Regional CBF was also determined, and it was found that the spatial pattern of CBF decline was heterogeneous across the brain with prefrontal cortex, insular cortex, and caudate being the most affected regions. Aside from the resting state parameters, the blood vessels' ability to dilate, measured by cerebrovascular reactivity to 5% CO₂ inhalation, was assessed and was reduced with age, the extent of which was more prominent than that of the resting state CBF.