Cerebral venous blood outflow: A theoretical model based on laboratory simulation

OBJECTIVE: The cerebrovascular bed and cerebrospinal fluid circulation have been modeled extensively except for the cerebral venous outflow, which is the object of this study. METHODS: A hydraulic experiment was designed for perfusion of a collapsible tube in a pressurized chamber to simulate the venous outflow from the cran ial cavity. CONCEPT: The laboratory measurements demonstrate that the majority of chang e in venous flow can be attributed to either inflow pressure when the outfl ow is open, or the upstream transmural pressure when outflow is collapsed. On this basis, we propose a mathematical model for pressure distribution al ong the venous outflow pathway depending on cerebral blood flow and intracr anial pressure. The model explains the physiological strong coupling betwee n intracranial pressure and venous pressure in the bridging veins, and we d iscuss the limits of applicability of the Starling resistor formula to the venous flow rates. The model provides a complementary explanation for ventr icular collapse and origin of subdural hematomas resulting from overshuntin g in hydrocephalus. The noncontinuous pressure flow characteristic of the v enous outflow is pinpointed as a possible source of the spontaneous generat ion of intracranial slow waves. CONCLUSION: A new conceptual mathematical model can be used to explain the relationship between pressures and flow at the venous outflow from the cran ium.