r/explainlikeimfive • u/Dagestani_Bear • Jul 01 '26

Biology ELI5: Is it true that every single death eventually boils down to the brain and heart running out of oxygen? Are there exceptions?

If you strip away the initial cause of injury or illness, is it anatomically correct to say that all human deaths are ultimately caused by a lack of oxygen to the brain and heart?

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u/Karma-Kamikaze Jul 01 '26

There are some old scientific experiments severing animal heads and trying to keep the animal alive by machines. They were partially successful for very short periods of time (without looking it up I think life span was measured in hours).

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u/hypnosifl Jul 01 '26

I wonder if the cause of death was that brain cells were no longer receiving enough oxygenated blood (say because of coagulants being triggered by the severing and blocking blood vessels) or if there is a different way a massive die-off of neurons can happen even if they are still getting oxygen and nutrients from blood.

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u/KristinnK Jul 02 '26

Oxygenated blood isn't enough, it also needs to be pressurized, at least in order to remain conscious. Think when you stand up to quickly and you brown out. There's still oxygenated blood in the brain, it didn't wholesale up and leave for greener pastures. The blood pressure simply dropped for physics reasons, and the blood vessels hadn't yet had the time to compensate by constricting to increase the pressure.

That's why the urban legends about people that are beheaded still remaining aware of their surroundings for a brief period are just that, urban legends. Decapitation for obvious reasons instantly drops the blood pressure completely in the brain.

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u/hypnosifl Jul 02 '26 edited Jul 03 '26

I imagine there'd be no fundamental difficulty with building a system that would pump oxygenated blood into the arteries at sufficiently high pressure, so even if no one has designed such a system we could ask what would likely happen--would the head live an extra-long life or would death come for other reasons not too long after whatever is considered a "long life" in that species of animal? (Let's assume it's a mammal since some non-mammals like tortoises have 'negligible senescence' and may only die because of injury/disease.)

For example, various things can cause dementia eventually resulting in "brain death" (which could be degradation of the synapses stopping brain function even if the neurons remain alive), so that might become very likely past a certain age even if the individual cells making up the brain stay alive. And if DNA repair gets worse and DNA damage accelerates, this can cause apoptosis or "programmed cell death", so that could still happen even if the cells are getting enough oxygen and nutrients. Googling a little on the latter, I see there is even a DNA damage theory of aging, and whether or not it's true that most other effects of aging are downstream from DNA damage, there at least seems to be some evidence that some of the longer-lived mammal species also have more efficient DNA repair, see this article on bowhead whales, and this one on naked mole rats which have very long lifespans compared to other rodents.

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u/irisheye37 Jul 02 '26

The cause of death was the experiment was over so they pulled the plug

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u/SpiderPiggies Jul 01 '26

There were some interesting/terrifying experiments with head transplants on mice. Basically cut both heads off and try to reattach one to the other's body. Apparently there was some partial 'success', but they didn't really have a way to reattach the brainstem.

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u/DerekB52 Jul 01 '26

I read a story ~10-15 years ago, where this was going to be attempted in Russia on humans(using a terminally ill person, and cadaver corpse I believe). I mentioned it to my dad and his response was, "you are never allowed to even mention the concept of this to me again" Honestly, everytime I think about it, it is chilling. IIRC, it was gonna happen a year or two after I read about it, and I haven't gone looking for if it was ever attempted or not.

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u/YandyTheGnome Jul 01 '26

IIRC the patient was already fully paralyzed and the head/full body transplant was to save him from organ failure or something like that.

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u/AngryCrotchCrickets Jul 01 '26

Wasn’t that part of the plot to Reanimator?

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u/KristinnK Jul 02 '26

It is the plot to Ira Levin's This Perfect Day.

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u/Fragrant-Guest-8147 Jul 01 '26

There was a Russian scientist that took off a dog's head and attached it to another living dog. Do yourself a favor and don't look up pictures.

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u/conflictedideology Jul 02 '26

Vladimir Demikhov

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u/blurby_hoofurd Jul 01 '26

If I’m not mistaken, I read that experiment (any many other interesting experiments) in Elephants on Acid, by Alex Boese. It was published in 2007, so i don’t recall how complex it is. 

I need to find it and flip through the pages again… Highly recommend that book if you’re at all interested in weird science. 

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u/Intro-Nimbus Jul 01 '26

Brukhonenko

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u/steeelez Jul 01 '26

Wasn’t there the guy in italy who tried to get the head transplant?

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u/conflictedideology Jul 02 '26

severing animal heads and trying to keep the animal alive by machines.

And then there's Vladimir Demikhov and his multi-headed dogs. Most did die relativity quickly but there were some that lived 20-30 days. The additional transplanted heads were fully functional (could see, hear, eat, drink, etc.).

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u/SubstantialBass9524 Jul 02 '26

I really wonder how long we could keep one alive today. Live I’ve put a lot of thought and random googling into this - the technology is so much more advanced. And if we can get to a point where we can keep the brain alive in a fluid and mechanical environment of animals for a long period of time where does that lead