...But what really happens in the body and brain in the moments after cardiac arrest?...
...During cardiac arrest, the electrical signals driving the heart's pumping action are disrupted, the heart ceases beating and death shortly follows, the AHA said.
In the vast majority of terminal cases, physicians medically define death based on when the heart no longer beats, said Dr. Sam Parnia, director of critical care and resuscitation research at NYU Langone School of Medicine in New York City.
"Technically speaking, that's how you get the time of death — it's all based on the moment when the heart stops," he told Live Science.
Once that happens, blood no longer circulates to the brain, which means brain function halts "almost instantaneously," Parnia said. "You lose all your brain stem reflexes — your gag reflex, your pupil reflex, all that is gone."
The brain's cerebral cortex — the so-called "thinking part" of the brain — also slows down instantly, and flatlines, meaning that no brainwaves are visible on an electric monitor, within 2 to 20 seconds. This initiates a chain reaction of cellular processes that eventually result in the death of brain cells, but that can take hours after the heart has stopped, Parnia said.
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