Direct vasopressin-induced cerebral vasoconstriction tends to decrease cerebral blood flow.

Direct vasopressin-induced cerebral vasoconstriction tends to decrease cerebral blood flow.

• A. False
• B. It has no effect on CBF
• C. It always increases CBF
• D. True

Answer: (D)

Direct vasopressin-induced constriction of cerebral arteries raises local vascular resistance. Cerebral blood flow is highly sensitive to vessel radius (flow changes with radius to a large power), so narrowing those vessels reduces the amount of blood reaching brain tissue. While vasopressin can increase systemic blood pressure, the brain relies on autoregulation to keep CBF steady across MAP changes; when vasopressin directly constricts cerebral vessels, the local decrease in radius tends to dominate, lowering cerebral blood flow. That’s why the statement is true. In practice, high-dose vasopressors can compromise CBF and risk ischemia, especially if autoregulatory capacity is impaired.

Direct vasopressin-induced constriction of cerebral arteries raises local vascular resistance. Cerebral blood flow is highly sensitive to vessel radius (flow changes with radius to a large power), so narrowing those vessels reduces the amount of blood reaching brain tissue. While vasopressin can increase systemic blood pressure, the brain relies on autoregulation to keep CBF steady across MAP changes; when vasopressin directly constricts cerebral vessels, the local decrease in radius tends to dominate, lowering cerebral blood flow. That’s why the statement is true. In practice, high-dose vasopressors can compromise CBF and risk ischemia, especially if autoregulatory capacity is impaired.