Role of tissue hypoxia in cerebrovascular regulation: a mathematical modeling study

This paper presents a mathematical model of cerebrovascular regulation, in which emphasis is given to the role of tissue hypoxia on cerebral blood flow (CBF). In the model. three different mechanisms are assumed to work on smooth muscle tension at the level of large and small pial arteries: CO2 reactivity, tissue hypoxia, and a third mechanism necessary to provide good reproduction of autoregulation to cerebral perfusion pressure (CPP) changes. Using a single set of parameters for the mechanism gains, assigned via a best fitting procedure, the model is able to reproduce the pattern of pial artery caliber and CBF under a large variety of physiological stimuli, either acting separately (hypoxia, CPP changes, CO2 pressure changes) or combination (hypercapnia+hypoxia; hypercapnia+hypotension). Furthermore, the model can explain the increase in CBF and the vasoconstriction of small pial arteries observed experimentally during hemodilution, ascribing it to the decrease in blood viscosity and to the antagonistic action of the flow-dependent mechanism (responsible for vasoconstriction) and of hypoxia (responsible for vasodilation). Finally, the interaction between hypoxia and intracranial pressure (ICP) has been analyzed. This interaction turns out quite complex, leading to different ICP time patterns depending on the status of the cerebrospinal fluid outflow pathways and of intracranial compliance.