A group of researchers has monitored the neuronal activity of several patients in the previous moments and during their brain death. The data can be very useful to know the reaction times in cases of ischemia or cerebral infarction.
Death reaches the brain like when the lights of a party go out. Only that what goes off in this case are not bulbs, but neurons that suddenly stop working.
It is one of the information that can be deduced from the study carried out by a team of researchers that has registered for the first time in real time what happens in neuronal activity during the moments before and after death. For the work, published this week in the Annals of Neurology, the authors recorded the data of nine patients who already had subdural electrodes installed in their brains and who died from different causes in hospitals in Berlin and Cincinatti with a non-resuscitation protocol. . The results are especially useful to know the reaction times in cases of massive damage or ischemia and when the point of no return occurs.
Each neuron retains the energy it has left "waiting for the return of a blood flow that will never return"
In the work done with animals in the 1940s, the biologist Aristides Leão had already recorded a massive and spontaneous silence of the neurons within five minutes of the brain damage and a kind of wave that was 'eclipsing' successively the areas of the brain. brain until you reach the most distant of the injury. In the cases studied on this occasion the damage had occurred previously and only the final moments of the electrical activity in the cerebral cortex and the behavior of the neurons were seen. These cells must maintain a delicate metabolic and electrical balance to survive and be able to send the electrochemical impulses that constitute brain activity. Therefore, at the moment when the blood flow stops and, therefore, the oxygen supply, the cell ceases its activity and tries to conserve those resources, according to the authors, in case the flow returns. As they explain in Livescience, sending signals would make them lose valuable resources, so that the neuron conserves the energy it has left "waiting for the return of a blood flow that will never return".
With these results, the authors observed that this first event is not like a "wave of darkness" that is spreading through the brain, but happens everywhere at the same time, when the neurons stop their activity due to lack of resources. The second 'surge' - technically called "terminal expansive depolarization" - takes place a few minutes after the first and occurs when the cells deplete their chemical stores and the ions are lost in the surrounding tissue. At that time it is as if 86,000 million tiny batteries were discharged at the same time and the brain is suddenly turned off, when it begins to produce a cascade of toxic reactions in the tissue that no longer allow recovery. "The brain is the most vulnerable organ to hypoxia and ischemia," the authors write. "Irreversible damage to these cells occurs within ten minutes after the cessation of circulation, the same as in a cardiac arrest." This cascade of reactions has been studied for more than half a century, but until now the encephalograms (EEG) gave an inaccurate information about what happened in these last moments. Some interpretations affirmed that brain activity ended when the signal recorded on the EEG ceased, while others interpreted that neurons remain polarized several minutes after that electrical silence, granting an extra recovery time.
Irreversible damage to these cells occurs within the next ten minutes after cessation of circulation
These new data, the researchers argue, provide useful information not only for the treatment of ischemias, but to establish the time of death declaration in cases of organ donation. As seen in animals, in the time after the first wave of cessation of neuronal activity, if the oxygen flow is restored, the neurons can recover their activity and survive.