Hyperventilation lowers carbon dioxide and the blood becomes more alkaline. This typically leads to which effect on cerebral blood flow?

Hyperventilation lowers carbon dioxide and the blood becomes more alkaline. This typically leads to which effect on cerebral blood flow?

• A. Increased cerebral blood flow
• B. Reduced cerebral blood flow
• C. No change in cerebral blood flow
• D. Irregular fluctuations in cerebral blood flow

Answer: (B)

Cerebral blood flow is tightly driven by arterial carbon dioxide levels. CO2 diffuses into brain tissue and acts as a potent vasodilator: higher CO2 dilates cerebral vessels and increases blood flow, while lower CO2 causes vasoconstriction and reduces flow. Hyperventilation lowers CO2 and makes blood more alkaline; the drop in CO2-induced vasodilation plus the alkalemia promote constriction of cerebral arterioles. The result is a decrease in cerebral blood flow. Clinically, this can lower intracranial pressure, but it also risks cerebral ischemia if prolonged.

Cerebral blood flow is tightly driven by arterial carbon dioxide levels. CO2 diffuses into brain tissue and acts as a potent vasodilator: higher CO2 dilates cerebral vessels and increases blood flow, while lower CO2 causes vasoconstriction and reduces flow. Hyperventilation lowers CO2 and makes blood more alkaline; the drop in CO2-induced vasodilation plus the alkalemia promote constriction of cerebral arterioles. The result is a decrease in cerebral blood flow. Clinically, this can lower intracranial pressure, but it also risks cerebral ischemia if prolonged.