Excessive hyperventilation may cause cerebral vasoconstriction that reduces cerebral blood flow; which statement is true?

Excessive hyperventilation may cause cerebral vasoconstriction that reduces cerebral blood flow; which statement is true?

• A. It increases cerebral blood flow
• B. It causes cerebral vasodilation
• C. It causes cerebral vasoconstriction reducing CBF
• D. It has no effect on cerebral blood flow

Answer: (C)

Excessive hyperventilation lowers arterial CO2 (PaCO2). CO2 is a potent cerebral vasodilator; when PaCO2 falls, cerebral arterioles constrict. This vasoconstriction reduces cerebral blood flow. So the statement that hyperventilation causes cerebral vasoconstriction reducing CBF is true. The other options don’t fit because hyperventilation does not increase CBF or cause vasodilation, and it does affect CBF by reducing it when CO2 is driven down. Clinically, this can lower intracranial pressure but risks cerebral ischemia if the flow becomes too reduced.

Excessive hyperventilation lowers arterial CO2 (PaCO2). CO2 is a potent cerebral vasodilator; when PaCO2 falls, cerebral arterioles constrict. This vasoconstriction reduces cerebral blood flow. So the statement that hyperventilation causes cerebral vasoconstriction reducing CBF is true. The other options don’t fit because hyperventilation does not increase CBF or cause vasodilation, and it does affect CBF by reducing it when CO2 is driven down. Clinically, this can lower intracranial pressure but risks cerebral ischemia if the flow becomes too reduced.