What effect does increased CO2 have on cerebral vessels?

What effect does increased CO2 have on cerebral vessels?

• A. Vasoconstriction and decreased cerebral blood flow.
• B. No change in vessel diameter.
• C. Cerebral edema.
• D. Vasodilation and increased cerebral blood flow.

Answer: (D)

Increased CO2 directly dilates cerebral vessels, boosting cerebral blood flow. CO2 freely crosses into the brain and, inside smooth muscle cells, forms carbonic acid that dissociates to bicarbonate and hydrogen ions, lowering the local pH. This acidosis in the vascular smooth muscle relaxes the vessels, causing vasodilation. The result is higher blood flow to help wash out CO2 and meet the brain’s oxygen needs. Conversely, low CO2 (hypocapnia) narrows vessels and reduces blood flow. Cerebral edema isn’t a direct, primary effect of CO2 changes.

Increased CO2 directly dilates cerebral vessels, boosting cerebral blood flow. CO2 freely crosses into the brain and, inside smooth muscle cells, forms carbonic acid that dissociates to bicarbonate and hydrogen ions, lowering the local pH. This acidosis in the vascular smooth muscle relaxes the vessels, causing vasodilation. The result is higher blood flow to help wash out CO2 and meet the brain’s oxygen needs. Conversely, low CO2 (hypocapnia) narrows vessels and reduces blood flow. Cerebral edema isn’t a direct, primary effect of CO2 changes.