The coupling of cerebral blood flow (CBF) and metabolic rate of oxygen (CMRO2) during physiological and pathological conditions remains a subject of debate. We have developed a physiological model for oxygen delivery and metabolism, which allows the estimation of net oxygen diffusibility at the capillary level, termed “effective oxygen diffusibility (EOD).” The results of PET in monkeys showed dynamic changes in EOD in response to changes in oxygen delivery and consumption. EOD is defined as capillary volume and permeability product, but its change mainly reflects the pericapillary oxygen gradient as long as capillary architecture is preserved. EOD may have sufficient predictability to represent the tissue oxygen demand and application of the model to PET data. In the future, EOD may give us further insight to understand the physiological regulatory system for oxygen demand in the brain.
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