Fig. 3

Perfusional pressure dynamics during transition to ortostathic position in conditions of preserved intracranial compliance vs. exhausted intracranial compliance. Dural sinus stenosis increases dural sinus pressure reducing CSF absorption rate and expanding the CSF volume at IC expense. (A) An intact IC allows the physiologic, gravity-dependent, pressure drop in cortical vein upon standing up. This compensates the correspondent arterial pressure drop and guaranties the maintaining of perfusion pressure constancy (AP-VP) despite postural changes. (B) A reduced IC prevents the ICP reduction and the strictly coupled cortical venous pressure drop required to balance the simultaneous gravity-dependent arterial pressure drop. This leads to the transient CPP reduction up to promote a syncope in predisposed individuals (IC: intracranial compliance; AP: arterial pressure; VP: cortical venous pressure; PP: perfusional pressure)