What is the normal global cerebral blood flow (CBF) in mL per 100 g of brain tissue per minute?

What is the normal global cerebral blood flow (CBF) in mL per 100 g of brain tissue per minute?

• A. 25 mL/100 g/min
• B. 50 mL/100 g/min
• C. 75 mL/100 g/min
• D. 100 mL/100 g/min

Answer: (B)

The important idea here is the resting perfusion level of brain tissue. At baseline, the brain receives about 50 mL of blood flow per 100 g of brain tissue each minute. This resting value, when scaled to the whole brain (which weighs roughly 1.3–1.4 kg in adults), corresponds to total cerebral blood flow of about 650–700 mL per minute, which matches the commonly cited total CBF range. This flow is kept fairly constant by cerebral autoregulation, functioning across a wide range of mean arterial pressures (roughly 60–150 mmHg). The brain adjusts cerebral vascular resistance to maintain steady perfusion despite changes in blood pressure. CO2 levels also influence CBF: higher CO2 (hypercapnia) increases flow, while lower CO2 (hypocapnia) decreases it. The other options describe flows that are outside the normal resting baseline, either too low to keep brain tissue adequately perfused or higher than typical resting conditions. Thus the baseline global CBF is about 50 mL per 100 g of brain tissue per minute.

The important idea here is the resting perfusion level of brain tissue. At baseline, the brain receives about 50 mL of blood flow per 100 g of brain tissue each minute. This resting value, when scaled to the whole brain (which weighs roughly 1.3–1.4 kg in adults), corresponds to total cerebral blood flow of about 650–700 mL per minute, which matches the commonly cited total CBF range.

This flow is kept fairly constant by cerebral autoregulation, functioning across a wide range of mean arterial pressures (roughly 60–150 mmHg). The brain adjusts cerebral vascular resistance to maintain steady perfusion despite changes in blood pressure. CO2 levels also influence CBF: higher CO2 (hypercapnia) increases flow, while lower CO2 (hypocapnia) decreases it.

The other options describe flows that are outside the normal resting baseline, either too low to keep brain tissue adequately perfused or higher than typical resting conditions. Thus the baseline global CBF is about 50 mL per 100 g of brain tissue per minute.