Cerebral autoregulation maintains a constant cerebral blood flow (CBF) over a range of mean arterial pressures. What is the normal autoregulatory range, and what mediates this response?
- A MAP 50–150 mmHg; mediated by myogenic response of cerebral arterioles and local metabolic factors (CO2, H+, O2) ✓
- B MAP 80–200 mmHg; mediated exclusively by sympathetic vasoconstriction
- C MAP 60–100 mmHg; mediated by baroreceptor reflex at the carotid sinus
- D MAP 50–150 mmHg; mediated by NO release from endothelium in response to shear stress
Correct answer: A. MAP 50–150 mmHg; mediated by myogenic response of cerebral arterioles and local metabolic factors (CO2, H+, O2)
Explanation
Cerebral autoregulation maintains constant CBF (~50 mL/100g/min) over a MAP range of approximately 50–150 mmHg through the myogenic mechanism (Bayliss effect — arteriolar smooth muscle contracts in response to wall stretch) and local metabolic factors (rising PaCO2, H+, and falling PaO2 cause vasodilation). In chronic hypertension, the autoregulatory curve shifts rightward — patients tolerate higher MAPs but are more vulnerable to low pressure. Below MAP 50, CBF falls passively (ischemia); above MAP 150, breakthrough hyperperfusion occurs.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
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