Maximal flow pulsation in the pial arterioles of rats at increased intracranial pressure.

Red cell velocity in the brain pial arterioles ( 12-58 microm in diameter) of rats was measured by a fiber-optic laser-Doppler anemometer microscope to study the effects of intracranial pressure (ICP) on flow pulsation. The amplitude of velocity pulsation in the pial arterioles was 24+/-9% (mean +/- SD) of the temporal mean velocity under normal physiological conditions (ICP = 5 mmHg). It increased gradually up to 40+/-11% with increasing ICP up to 50 mmHg on average. It also increased with the vessel diameter at fixed values of ICP. In each arteriole, the velocity amplitude increased steeply at a critical value of ICP as ICP increased. The critical value of ICP ranged between 20 and 40 mmHg,. increased with the vessel diameter, and decreased downstream along arterial trees. These results suggest a correlation between the critical ICP and the internal pressure of the pial arteriole.