Ventriculojugular shunt against the direction of blood flow. I. Role of the internal jugular vein as an antisiphonage device.

The internal jugular vein (IJV) of an adult human cadaver was used to study the effect of its behavior as a collapsible tube in regulating its upstream pressure. The results suggested that the resistance to flow in the IJV varies according to changes in its contour, which occur as a result of changes in its transmural pressure. This suggested that, in vivo, during change of posture from recumbent to erect, collapse of the IJV occurs and increases the resistance to blood flow in it. The increase in the resistance to blood flow acts as a natural self-regulating antisiphon device, which counteracts the effect of gravity and regulates the pressure above the vein, i.e., in the sigmoid sinus and, consequently, the intracranial pressure, within narrow limits, regardless of the position of the individual.