Modern medicine has proven so adept at saving victims of cardiac arrest that a good number of people are walking around today who at one time or another were considered clinically dead. While this is a good thing in and of itself, it has the side benefit of having generated numerous reports of the shadowy psychological condition that people experience when they’re close to “the other side.” So consistent are these reports — combining the sensation of floating, seeing oneself from an outside perspective, and moving through a tunnel towards light — that they have earned an official moniker, “Near Death Experiences,” or NDEs.
Just what is behind these eerily similar reports? To those of a certain mindset, they are a supernatural phenomenon, an early glimpse of the afterlife that awaits. To those of a more materialist persuasion, these sensations must be generated by some common brain architecture that gets activated under intense stress. As it happens, this latter view has just received some intriguing scientific backing, in the form of a paper in the latest issue of the journal Critical Care. A key component of NDEs, it appears, is carbon dioxide in the blood. Yes, the same thing that makes Cokes fizzy also makes your life flash in front of your eyes.
According to the report, written by a team of Slovenian doctors led by Zalika Klemenc-Ketis, as many as one-quarter of patients who suffer heart attacks experience NDEs. After examining solutes in the blood of 52 such patients admitted for emergency treatment in Slovenia, they found that those with a higher concentration of carbon dioxide also experienced a higher rate of near-death experiences. (Also significant, though less strongly correlated, was the concentration of potassium ions in the blood).
Klemenc-Ketis and her team did not hazard a guess at a mechanism behind the link. But it’s not entirely surprising that high concentrations of carbon dioxide might be linked to an extreme stress response like NDE. If we stop breathing in fresh air, the level of oxygen in our blood goes down, and the level of dissolved carbon dioxide goes up. These changes are sensed by receptors in the brainstem, the heart, and the carotid artery, which together help trigger the urge to breathe. Though we have no awareness of it, this monitoring is constantly going on at a subconscious level. High carbon dioxide levels stimulate the amygdala, and have been implicated in panic attacks.
That is to say, high concentrations of CO2 are fun in your soft drink, but not in your brain.
Suspicion had already centered on carbon dioxide as playing a role in NDEs, the team leader told a British news station, because “it has been known that in other cases, for example in people at higher altitudes, carbon dioxide might provoke some sort of hallucinations and visions, that could be described as NDE-like experiences.”
Have you ever been in a situation so terrifying, or felt yourself so close to death, that you felt your life flash in front of your eyes? If so, I’d love to hear about it. I’ve never had such an experience myself — at least I don’t think I have — and I would be extremely curious to know what the sensation is like. Do you see your whole life in order, or in snatches? Do you feel great emotion? As far as I know, this phenomenon remains one of the great mysteries of extreme fear.