The wave-shaped signal, which was previously dubbed ‘the wave of death’, had already been measured by researchers in Nijmegen in the brains of rats that had just been decapitated. The rats had already had electrodes implanted in their brains before the experiment. Some minimal brain activity continues immediately after the decapitation, but after approximately a minute a strong wave-shaped signal can be measured, after which the brain activity ceases. This has raised the question of whether the wave is a reliable indication of the onset of brain death. If the phenomenon could also be measured in humans, would this give doctors a reliable means of establishing brain death?
The researchers from the University of Twente did not carry out new measurements on rats, but used a computational model to seek an explanation for the occurrence of the wave. And the explanation is relatively simple. To reach this conclusion, PhD student Bas-Jan Zandt carried out calculations based on a single neuron. The human brain is made up of billions of neurons. When they become active, or in other words when they ‘fire’, a voltage peak occurs between the interior of the nerve cell and its external environment. Charged particles – ions – then flow through special channels in the cell wall. These then have to be pumped back in again by the cell.
Neuron ‘fires until empty’
Oxygen and energy are essential for this pumping action. If they are no longer present, then after a time the neuron will fire, but it will keep on firing until no more ions are present in the cell. It is precisely this phenomenon that is seen as a wave in the EEG signal. After the wave there will be no more activity in the cell, unless oxygen is reintroduced and the pumping action can be resumed. According to the researchers the wave is therefore not the start of an irreversible process. In addition, according to Prof. Michel van Putten – a neurologist at the Medisch Spectrum Twente and professor at the University of Twente – a whole range of other factors must be examined before brain death can be unequivocally established. He cites the influence of medication on the process, the functioning of the brain stem and respiration as examples of these factors. “Our research complements that of the researchers from Nijmegen well, but it also shows that ‘wave of death’ is certainly not an appropriate term for this phenomenon”, says Prof. van Putten.
The research was carried out by the Neuroimaging group at the MIRA Institute for Biomedical Technology and Technical Medicine of the University of Twente. The researchers worked in collaboration with neurologists from the Medisch Spectrum Twente hospital (MST) and the Leiden University Medical Centre (LUMC), and with the MIRA Clinical Neurophysiology group.