Maintenance of cerebral blood flow depends on keeping what two forces in balance?

• A. Mean arterial pressure and intracranial pressure
• B. Cerebral perfusion pressure and intracranial pressure
• C. Cerebral spinal fluid pressure and mean arterial pressure
• D. Heart rate and cerebral blood flow velocity

Answer: (B)

Cerebral blood flow hinges on the pressure gradient that drives blood into the brain being balanced against the pressure inside the skull that resists that flow. The two forces to keep in balance are the cerebral perfusion pressure (the driving force for blood flow) and the intracranial pressure (the opposing force). In other words, maintaining adequate flow depends on keeping the cerebral perfusion pressure in a safe range relative to the intracranial pressure. Cerebral perfusion pressure is roughly the mean arterial pressure minus the intracranial pressure, so changes in either can tip the balance: higher ICP lowers CPP and reduces blood flow, while too low CPP from low MAP or very high ICP can risk ischemia; autoregulation works to adjust resistance within limits, but the fundamental balance remains between CPP and ICP.