A thermodynamic framework based on O2 and CO2 transport models accurately predicts experimental data regarding cerebral blood flow responses to neural activation, hypercapnia, and hypoxia.
Summary Several current functional neuroimaging methods are sensitive to cerebral metabolism and cerebral blood flow (CBF) rather than the underlying neural activity itself. Empirically, the connections between metabolism, flow and neural activity are complex and somewhat counterintuitive: CBF and glycolysis increase more than seems to be needed to provide oxygen and pyruvate for oxidative metabolism, and the oxygen extraction fraction is relatively low in the brain and decreases when oxygen metabolism increases. This work lays a foundation for the idea that this unexpected pattern of physiological changes is consistent with basic thermodynamic considerations related to metabolism. In the context of this thermodynamic framework, the apparent mismatches in metabolic rates and CBF are related to preserving the entropy change of oxidative metabolism, specifically the O 2 /CO 2 ratio in the mitochondria. However, the mechanism supporting this CBF response is likely not due to feedback from a hypothetical O 2 sensor in tissue, but rather is consistent with feed-forward control by signals from both excitatory and inhibitory neural activity. Quantitative predictions of the thermodynamic framework, based on models of O 2 and CO 2 transport and possible neural drivers of CBF control, are in good agreement with a wide range of experimental data, including responses to neural activation, hypercapnia, hypoxia and high-altitude acclimatization.
Richard B. Buxton (Thu,) conducted a review in Cerebral metabolism and blood flow. A thermodynamic framework based on O2 and CO2 transport models accurately predicts experimental data regarding cerebral blood flow responses to neural activation, hypercapnia, and hypoxia.