The brain is a metabolically demanding organ. Although it accounts for only 2% of the total mass of the body, ~15% of cardiac output, ~20% of O₂ consumption, and ~25% of glucose utilization is devoted to nourishing the brain. Many mechanisms have evolved to ensure that the brain receives adequate O₂ and glucose to feed its neurons. When systemic blood pressure varies, autoregulatory mechanisms adjust the tone of brain blood vessels so that perfusion within the brain remains constant (Payne 2016). Also, as blood O₂ and CO₂ changes, perfusion to the brain is varied accordingly to ensure that appropriate tissue gas levels are maintained (Rudzinski and others 2007). Neuronal projections from subcortical areas contribute to cortical blood flow regulation on a large spatial scale (Bekar and others 2012; Cohen and others 1996). At the local level, when brain activity increases, blood flow to that region rises, supplying active neurons with sufficient nutrients. This increase in local blood flow in response to neuronal activity is termed functional hyperemia.

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介导脑功能性充血的机制

大脑是需要代谢的器官。尽管它仅占人体总质量的2％，但约占心输出量的15％，O ₂消耗量的约20％，以及葡萄糖利用量的约25％专门用于营养大脑。已经发展出许多机制来确保大脑接受足够的O ₂和葡萄糖来喂养其神经元。当全身性血压变化时，自动调节机制会调节脑血管的张力，从而使脑内的灌注保持恒定（Payne 2016）。另外，作为血液O ₂和CO ₂改变后，对大脑的灌注也会相应变化，以确保维持适当的组织气体水平（Rudzinski等2007）。皮层下区域的神经元投射有助于大范围的皮层血流调节（Bekar等人，2012； Cohen等人，1996）。在局部水平上，当大脑活动增加时，流向该区域的血液就会增加，从而为活跃的神经元提供足够的营养。这种响应神经元活动的局部血流量增加被称为功能性充血。