A mathematical model of overall cerebral blood flow regulation in the rat.

In the present work a mathematical model of the cerebrovascular regulatory system in the rat is presented. The model, a generalization of our previous one, includes the reactivity of proximal segments of the cerebrovascular bed and the neurogenic and myogenic feedback regulatory mechanisms besides the action of chemical regulatory factors. The model is then used to analyze the interaction of mechanisms regulating cerebral blood flow in several conditions of physiological importance. In the first stage of the work we simulated experiments in which the neural fibers are cut and artificially stimulated with external means. According to experimental evidence, simulation results point out the existence of an escape of blood flow from stimulation. The model imputes this escape phenomenon to the antagonistic action of chemical factors working on the distal segments of the cerebrovascular bed. In a second stage, we studied the neurogenic mechanism action in a physiological closed-loop condition. With this general model, autoregulation to arterial pressure changes and postischemic reactive hyperemia have been analyzed. A comparison of simulation results with recent experimental data shows that the model is able to produce 60-70% of the experimental regulatory capacity of the cerebrovascular bed. However, some relevant discrepancies still exist between the model and the experimental results, especially as regards the dilatory capacity of small cerebral arterioles. These discrepancies underline the existence of further regulatory mechanisms working on the cerebrovascular bed, the nature of which must still be clarified.