With regard to regulation of blood flow, the correct order of vascular responsiveness to PaCO2 from most to least sensitive is

With regard to regulation of blood flow, the correct order of vascular responsiveness to PaCO2 from most to least sensitive is

• A. Cerebrum > spinal cord > cerebellum
• B. Cerebrum > cerebellum > spinal cord
• C. Cerebellum > cerebrum > spinal cord
• D. Cerebellum > spinal cord > cerebrum

Answer: (B)

PaCO2 is the strongest regulator of cerebral blood flow, and different CNS vascular beds respond to CO2 level changes with varying sensitivity. When CO2 rises, cerebral arterioles dilate to increase blood flow and wash out the excess CO2, a response driven by pH changes in the brain tissue and CSF. Among CNS regions, the cerebrum shows the greatest CO2 reactivity, the cerebellum less so, and the spinal cord the least. Therefore, the order from most to least sensitive is the cerebrum, then the cerebellum, and finally the spinal cord. This pattern explains why hypercapnia tends to raise cerebral blood flow—and potentially intracranial pressure—more in the cerebral vessels than in the spinal vasculature.

PaCO2 is the strongest regulator of cerebral blood flow, and different CNS vascular beds respond to CO2 level changes with varying sensitivity. When CO2 rises, cerebral arterioles dilate to increase blood flow and wash out the excess CO2, a response driven by pH changes in the brain tissue and CSF. Among CNS regions, the cerebrum shows the greatest CO2 reactivity, the cerebellum less so, and the spinal cord the least. Therefore, the order from most to least sensitive is the cerebrum, then the cerebellum, and finally the spinal cord. This pattern explains why hypercapnia tends to raise cerebral blood flow—and potentially intracranial pressure—more in the cerebral vessels than in the spinal vasculature.