Which statement best describes the relationship between BAC and brain concentration of alcohol?

Which statement best describes the relationship between BAC and brain concentration of alcohol?

• A. BAC is not related to brain alcohol levels.
• B. BAC is inversely proportional to brain concentration.
• C. BAC is directly proportional to brain concentration.
• D. BAC only reflects liver metabolism.

Answer: (C)

Alcohol distributes quickly into body water, and the brain is highly perfused, so ethanol moves across the blood–brain barrier readily. Because of this rapid diffusion and equilibrium between blood and brain, the amount of alcohol in the brain tracks what's in the blood. When BAC rises, brain concentration rises proportionally, and as BAC falls due to metabolism, brain levels fall as well. This makes brain alcohol concentration directly related to, and roughly proportional to, blood alcohol concentration during both distribution and elimination phases. It isn’t independent of BAC, it isn’t inversely related, and it isn’t governed solely by liver metabolism—liver metabolism alters BAC over time, but the instantaneous brain level reflects the current BAC.

Alcohol distributes quickly into body water, and the brain is highly perfused, so ethanol moves across the blood–brain barrier readily. Because of this rapid diffusion and equilibrium between blood and brain, the amount of alcohol in the brain tracks what's in the blood. When BAC rises, brain concentration rises proportionally, and as BAC falls due to metabolism, brain levels fall as well. This makes brain alcohol concentration directly related to, and roughly proportional to, blood alcohol concentration during both distribution and elimination phases. It isn’t independent of BAC, it isn’t inversely related, and it isn’t governed solely by liver metabolism—liver metabolism alters BAC over time, but the instantaneous brain level reflects the current BAC.