What physiological change occurs with hypercapnia in the brain?

Hypercapnia, which is characterized by elevated levels of carbon dioxide (CO2) in the blood, leads to various physiological responses in the body, particularly in the brain. One significant response is vasodilation. When CO2 levels rise, it causes the blood vessels in the brain to dilate to enhance blood flow and facilitate the removal of CO2 and other metabolic wastes.

This vasodilation is a direct response to increased levels of carbon dioxide, which acts as a potent vasodilator. It helps to ensure adequate oxygen delivery to the brain, despite the increased levels of CO2. As a result, cerebral blood flow is increased, which can be a critical compensatory mechanism in situations of respiratory failure or other conditions that lead to hypercapnia.

The other choices do not align with the physiological effects of hypercapnia. Vasoconstriction would reduce blood flow, which is not what occurs in this scenario. Increased intracranial pressure and decreased perfusion are also not direct outcomes of hypercapnia; instead, they may be the result of specific pathologies rather than hypercapnia itself. Thus, vasodilation stands as the correct physiological change associated with hypercapnia in the brain.