Figure 3

Bench simulation of the intra-extracranial flow diversion with increased intracranial pressure: Fluid from the irrigation set with pressure Pa is flowing through the Starling resistor with pressure ICP and external pathway with outflow pressure Pe. Flow is measured with the rotary flowmeters, where flow Q Starling represents CBF in the intracranial compartment and is zero at the start of measurement. Roller clamp before the bifurcation creates fixed inflow resistance with the pressure Pd, distal to it. As outflow pressure in the external bypass pathway Pe is increased by raising the height of the outflow, flow Q external decreases, and Pd increases, reestablishing Q Starling due to the steal reversal. Maximal flow in the Starling resistor coincides with the cessation of flow in the bypass pathway and with maximization of Pd: Rising Pe beyond this point does not increase Pd and does not increase flow through the Starling resistor. Lowering Pe again, induces flow diversion from the Starling resistor, thus simulating intra-extracranial steal: which depends—as shown—from ICP–Pe (outflow pressure) gradient, and thus is reversible by increased Pe.