The Hemodynamic Response of the Cerebral Bridging Veins to Changes in ICP

Background To investigate the hemodynamic response of the cerebral bridging veins to increased intracranial pressure (ICP) during normo- and hyperventilation. Methods Flow velocity (FV m ), diameter ( D ), and pulsatility index (PI) were measured and calculated in the cerebral bridging veins using Color Doppler Ultrasound in seven pigs, and cerebral blood flow (CBF) was measured using 133 Xe clearance in nine pigs, both during normo- and hyperventilation. ICP was increased stepwise from baseline (about 10 mmHg) to 20 and 30 mmHg by infusion of mock CSF into the cisterna magna. Results Moderate elevations of ICP caused venous relative stasis as evidenced by a decrease in FV m and increase in diameter and PI, but no change of volume flow in the veins. CBF was stable indicating autoregulation at ICP of 20 and 30 mmHg. Parallel observations were made during normo- and hyperventilation, but at two different levels of CBF. Conclusions The cerebral bridging veins dilation and blood flow velocity decrease indicate the venous relative stasis in response to the elevated ICP. This response is proposed to be caused by an ICP-dependent increase in resistance to the outflow from the cerebral bridging veins.