Even five minutes after a person's heart stops beating, their brain cells may still function, according to new findings published Thursday in Annals of Neurology.
For the study, nine people in Berlin, Germany, and Cincinnati, Ohio, had the electrical signals in their brain monitored as they died. (All the patients had suffered from some serious kind of brain injury, and all had "do not resuscitate" orders.)
The basics of what happens when cells die is pretty well established. When blood stops flowing, there's no oxygen. Oxygen is necessary for cells to produce the energy they need to keep functioning. If they're deprived of this energy, then they die.
"Brain Tsunami"
In the study, oxygen levels in the brain decreased and the heart stopped after life support was stopped. But when a person's blood pressure plummets, their brain cells can still draw on energy reserves for a few minutes.
"Within about 3 minutes," lead author Jens Dreier, professor at the Center for Stroke Research Berlin, wrote to Newsweek in an email, "the brain's fuel reserves have become depleted." When that happens, the mechanisms that brain cells use to keep ions separated, something that's necessary for them to function at all, starts to fail. That creates what is sometimes called a "brain tsunami," said Dreier.
The breakdown of ion gradients releases a massive wave of electrochemical energy in the form of heat, Dreier explained. "This energy loss spreads through the cortex and other areas of the brain." The technical name for this loss is spreading depolarization.
But this loss does not necessarily signify the end. Like a battery that's lost its charge, this loss of polarization may be reversible, at least for a while, Jed Hartings, a neuroscientist at the University of Cincinnati College of Medicine and a member of the UC Gardner Neuroscience, noted. But how long a brain can exist like that is still an open question.
"The chemical changes that lead to death begin with depolarization," Hartings said. That change begins the countdown to irreversible damage.
That finding is new. Previously researchers believed that irreversible damage occurred when brain activity flatlines. The current study shows that's not the case. "And that's really the fundamental insight here," said Hartings.
In theory, understanding exactly what happens in the brain when the heart stops might help us hone protocols around organ donation. Because even after a person's heart stops, cellular activity may linger. Brain waves may, too.
Diagnosing Brain Death
When it comes to medical certainties, brain death has proved challenging. "We've never had a method to diagnose brain death," Hartings noted, "and we don't have a way to be certain when all capacity for awareness is lost." Clinical guidelines can help, but they aren't definitive.
Some organ donation protocols allow surgeons to begin removing organs five minutes after a person's heart stops or their blood pressure plunges. (A Canadian review paper supports this approach.) The thinking behind that timeframe is that after five minutes, a person's brain can't be restored.
Dreier thinks that cutoff may be inaccurate. "The nerve cells are not dead at five minutes," he wrote, citing experiments done with animals.
According to his data and other experimental evidence from animals, if circulation resumes after five minutes, then it is "very likely," Dreier said, "that the person will recover."
Though whether their brains are ever the same, said Dreier, is still far less certain.
