Modifying the ICP pulse wave - effects on parenchymal blood flow pulsatility

Pulsation of the cerebral blood flow (CBF) produces intercranial pressure (ICP) waves. The aim of this study is to determine if externally modifying ICP pulsatility alters parenchymal blood flow pulsatility. A cardiac-gated inflatable device was inserted in the lateral epidural space of 12 anaesthetized canines (canis familiaris) and used to cause reduction, inversion and augmentation of the ICP pulse. CBF in each hemisphere was measured using laser doppler velocimetry. A significant increase in both mean CBF and its amplitude was observed for reduction as well as inversion of the ICP pulse, with larger changes observed for the inversion protocol. Significant increases in the mean CBF were also observed ipsilaterally for the augmentation protocol, together with indications of reduction contralaterally. External alteration of the ICP pulse thus caused significant changes in parenchymal blood flow pulsatility. The inverse relationship between the ICP and CBF amplitude suggests the changes did not occur via modification of the intracranial Windkessel mechanism. Thus, the effects likely occurred in the low-pressure vessels, i.e., capillaries and/or venules, rather than the high pressure arteries. Future MRI studies are however required to map and quantify the effects on global cerebral blood flow.