A model for the regulation of cerebral oxygen delivery

Abstract

On the basis of the assumption that oxygen delivery across the endothelium is proportional to capillary plasma[Formula: see text], a model is presented that links cerebral metabolic rate of oxygen utilization ([Formula: see text]) to cerebral blood flow (CBF) through an effective diffusivity for oxygen (D) of the capillary bed. On the basis of in vivo evidence that the oxygen diffusivity properties of the capillary bed may be altered by changes in capillary[Formula: see text], hematocrit, and/or blood volume, the model allows changes in D with changes in CBF. Choice in the model of the appropriate ratio of Ω ≡ (ΔD/D)/(ΔCBF/CBF) determines the dependence of tissue oxygen delivery on perfusion. Buxton and Frank ( J. Cereb. Blood Flow. Metab. 17: 64–72, 1997) recently presented a limiting case of the present model in which Ω = 0. In contrast to the trends predicted by the model of Buxton and Frank, in the current model when Ω > 0, the proportionality between changes in CBF and[Formula: see text] becomes more linear, and similar degrees of proportionality can exist at different basal values of oxygen extraction fraction. The model is able to fit the observed proportionalities between CBF and[Formula: see text] for a large range of physiological data. Although the model does not validate any particular observed proportionality between CBF and[Formula: see text], generally values of ([Formula: see text]/[Formula: see text])/(ΔCBF/CBF) close to unity have been observed across ranges of graded anesthesia in rats and humans and for particular functional activations in humans. The model’s capacity to fit the wide range of data indicates that the oxygen diffusivity properties of the capillary bed, which can be modified in relation to perfusion, play an important role in regulating cerebral oxygen delivery in vivo.