[Intracranial pressure. IV - Relationships with post capillary vascular pressures (author's transl)].

The authors have demonstrated experimentally in dogs that, in all cases, the cortical venous pressure (Pvco) is higher than the intracranial pressure (PIC), which always remains higher than the sagittal sinus venous pressure (PSLS). The difference between Pvco and PIC remains statistically equal to 8 mm Hg and can be explained by the "Vascular Waterfall" phenomenon; during Queckenstedt's test, the intracranial venous volume does not change, and is not the cause for the increase of PIC; this increase is due to the constancy of the difference between PIC and PSLS, which is induced by the resorption of CSF through the arachnoïd villi. Increases in Pvco and PIC are shown to be equal to 70% and &2% respectively of the change in PSLS. Any other factor that increases PIC (injections in the cisterna magna, pharmacological effects) does not change PSLS, which remains equal to zero. As long as the cerebral blood flow is constant, the increase in cerebro-vascular resistance of the veins at the site of their junction to the sagittal sinus must be compensated upstream by a vasodilatation, which leads to a new distribution of the pressures along the cerebro-vascular bed.