The relationship of electroencephalograph fluctuations to intracranial pressure B waves

Introduction

Lundberg B waves, characterized as repetitive changes in intracranial pressure occurring at frequencies of 8–33 mHz, have been attributed to cerebral blood flow fluctuations induced by central nervous system pacemakers and cerebral pressure autoregulation.

Methods

Simultaneous measurements of mean arterial pressure (MAP), intracranial pressure (ICP), mean flow velocity (MFV) of the middle cerebral artery (transcranial Doppler WAKI™) and left and right spectral edge frequency (SEFl, SEFr) of continuous EEG recording (Philips™ technologies) obtained 10 ± 4 days after injury in six patients with a closed head injury were recorded and digitalized at a frequency rate of 50 Hz (AcqKnowledge™ software). All patients were mechanically ventilated and sedated using a combination of sufentanil and midazolam.

Results

Cerebral electric activity (oscillations at a mean frequency of 26 ± 9 mHz) and MFV fluctuations were synchronous and in phase with the B waves (mean frequency 23 ± 7 mHz). Figure 1 illustrates simultaneous recording of (from the top to the bottom) MAP, MFV, ICP and SEFr on one characteristic patient.

Discussion

The change in cerebral electrical activity observed by the use of continuous EEG recording resulting from cerebral pace-makers could increase CMRO₂, leading to an increase in cerebral blood flow and secondarily of ICP through a change in cerebral blood volume.

Figure 1