What would increase cerebral blood flow?

Increased levels of carbon dioxide (CO2) in the blood lead to vasodilation of cerebral blood vessels, which ultimately increases cerebral blood flow. This response is a key mechanism of cerebral autoregulation, where the blood vessels in the brain respond to changes in metabolic demand. When CO2 levels rise, the pH of the blood decreases (making it more acidic), which signals the vascular smooth muscle to relax and widen the blood vessels, allowing more blood to flow through. This is particularly important in situations where neuronal activity increases, as heightened metabolic activity generates more CO2, necessitating increased blood flow to deliver oxygen and remove waste products.

In contrast, decreased levels of CO2 would lead to vasoconstriction, thereby reducing cerebral blood flow. Additionally, decreased oxygen (O2) levels can also trigger vasodilation, but the direct and more immediate driver of increased cerebral blood flow in response to metabolic demand is the increase in CO2. Therefore, increased CO2 is a critical factor in manipulating cerebral blood flow effectively in response to the brain's needs.