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What needs to be improved or added to the human body for a human to be able to hold one’s breath for more than 4 hours? please take into account external conditions that can significantly affect the absorption of oxygen: pressure (in the case of being under water or high altitude ), changes in temperature and humidity.

Supplement: this person must be conscious (see, hear) While holding their breath.

Warning: please offer science-based responses, so do not offer solutions about symbiotic bacteria and photosynthesis, and do not talk about a complete transition to an aerobic lifestyle , this is not possible.

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    $\begingroup$ Look into whales, they can slow their heart rate down and can store excess oxygen in a protien in their muscles called myoglobin. $\endgroup$
    – user69935
    Feb 25, 2020 at 16:39
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    $\begingroup$ Do they need to exert themselves while holding their breath? $\endgroup$
    – David
    Feb 25, 2020 at 16:52
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    $\begingroup$ If you want a hard science answer, I think you need to provide a lot more clarifying detail. What does the human need to do for those four hours? What kind of environment is he/she acting in? Do we need to account for pressure changes (e.g. deep ocean diving and/or vacuum)? Do we need to account for temperature changes? A Hard Science answer requires a Hard Science question. $\endgroup$ Feb 25, 2020 at 16:56
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    $\begingroup$ It has been pointed out to you on most, if not all of your previous questions, that requiring hard science for stuff that has little grounding in reality or research is going to make it very hard or even outright impossible for anyone to answer, especially when your questions are as underspecified as this. I'm certainly not going to try. $\endgroup$ Feb 25, 2020 at 17:14
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    $\begingroup$ I don't see how this can be answered by the standards of hard science. "A few hours" is so far out there that it places any answer, no matter how well thought out, firmly in the ream of speculation. $\endgroup$
    – Gene
    Feb 25, 2020 at 17:48

3 Answers 3

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There are no equations in this answer, just arithmetic, because that's all that's necessary for a basic estimate using conservation of mass.

How much oxygen do we need?

A resting adult human breathes in and out 7-8 litres of air per minute, which is about 2000 litres in four hours. About 5% of that volume is oxygen that is taken into the bloodstream, recombined as carbon dioxide and exhaled again. So that's 100 litres of oxygen that becomes 100 litres of carbon dioxide. To hold your breath for four hours while resting, you need to be able to:

  • Have that much oxygen stored, and release it effectively.
  • Be able to scavenge that much carbon dioxide and store it securely.
  • When you have access to a breathable atmosphere, dump the carbon dioxide and replenish the oxygen.
  • Pay the energy costs of all this extra metabolic work, which will require more oxygen and carbon dioxide storage.

Your time holding your breath will be reduced by exertion, mental stress, and almost anything else other than calm rest, often by quite sizeable factors. If you want to be able to hold your breath for four hours whatever the circumstances, allow a factor of 5.

So you need to be able to store the equivalent of 500 litres of oxygen at atmospheric pressure and temperature. The density of oxygen under those circumstances is 1.429 g/L, so that's about 715g of oxygen. That turns into 985g of carbon dioxide. You need storage for both, and to keep them separate.

This is going to require some major changes to human anatomy and biochemistry.

Managing the job?

To be able to recharge your four hours of breath-holding in four hours in a normal atmosphere, you're going to need to double your rate of gas exchange, by doubling lung volume, which will have obvious effects on the shape of the body.

As for storage, humans use Hemoglobin to transport oxygen. It has a molecular weight of about 64,000, and can store four oxygen molecules, with a total molecular weight of (2*4*16 = 128). So the hemoglobin needed to store oxygen is about 500 times the weight of the oxygen.

Myoglobin can only store one oxygen molecule per myoglobin molecule. It has a molecular weight of about 17,800, and the oxygen molecule has a weight of 32, so the myoglobin has about 560 times the weight of the oxygen, a bit less efficient than haemoglobin.

We need about 358Kg of hemoglobin or somewhat more myoglobin as an oxygen store. That won't fit into a human body, by a long way. There are more compact ways of storing oxygen chemically, but they need much more energy to combine the oxygen, release it, or both.

Conclusion: not practical

This is not possible by genetic engineering if you want the resulting creature to be able to pass for human. You'd probably do better with a cyborg.

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  • $\begingroup$ That's some nice math. $\endgroup$ Feb 25, 2020 at 18:01
  • $\begingroup$ @MorrisTheCat: The mathematics is easy: spotting the way to do the estimate was the trick. $\endgroup$ Feb 25, 2020 at 18:10
  • $\begingroup$ Right. Focusing specifically on the mass of the oxygen required and thus the hemoglobin to store it is a very elegant way to frame the problem. Kudos. $\endgroup$ Feb 25, 2020 at 18:15
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    $\begingroup$ What about myoglobin ( like seals and whales)? Is it possible to create special fibrous plates where myoglobin will be stored, just as it is stored in the muscles. But if the myoglobin content in human muscles is 2%, and in seals-20%. The content in these plates (resembling muscle fibers ) is more than 60-85% ( and possibly more ) $\endgroup$
    – user71408
    Feb 25, 2020 at 18:51
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    $\begingroup$ I don't know enough about respiration to make this a decent answer, but you might be able to push these numbers a lot more utilizing the mammalian dive reflex. $\endgroup$
    – Meridian
    Feb 25, 2020 at 22:31
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Chemical reservoir (pouch) that stores an oxygen rich substance, to be used as a source of oxygen when the diving reflex kicks in. Once under normal condition, the substance slowly regenerates.
Place that pouch close to the kidneys and liver.

Probably the closest to human metabolites to use in oxygen storage would be an adduct of hydrogen peroxide and urea. Yes, hydrogen peroxide can be synthesized by human body (it's only two deradicalized hydroxil radicals put together, what the big deal?) and actually more exotic hydrogen peroxides are used by the body when needed (ozone and dihydrogen trioxide aren't unusual).

Yes, if the mammalian body managed to use hydrochloric acid (which is quite strong, stronger, in fact, than the sulfuric acid) and find biological tissues to contain it, I'm quite confident there are biological ways to contain hydrogen peroxide.

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  • $\begingroup$ It's worth noting for those people who keep saying "hydrochloric acid is stronger than sulfuric acid" that molarity is important. While hydrochloric acid dissociates more easily than sulfuric, a hydrochloric acid solution at 0.1 mol/L is going to be weaker than a sulfuric acid solution at 1 mol/L. Without concentration, "stronger" is meaningless. $\endgroup$
    – jdunlop
    Feb 26, 2020 at 18:45
  • $\begingroup$ Can you describe in more detail the device (structure ) of these "bags" and the chemical reactions occurring in them (preferably with formulas)? $\endgroup$
    – user71408
    Feb 29, 2020 at 20:05
  • $\begingroup$ You have the reaction/formula in the Wiki page linked inside my answer. For your convenience, once again here. About that pouch - imagine another stomach or bladder and make it as large as rationally possible. Handwave a protein lining that's mildly resistant to oxidation - maybe similar with the stomach lining with a larger proportion of keratin - with glands that secretes the adduct and cilia that absorbs the oxygen when needed and some other structure that drain the excess urea. $\endgroup$ Mar 1, 2020 at 3:14
  • $\begingroup$ I'm sorry, did you write an answer earlier about the processing of carbon dioxide in the kidneys and liver, and also gave there the formulas of chemical reactions? $\endgroup$
    – user71408
    Mar 1, 2020 at 13:26
  • $\begingroup$ @FrenchThompson nope, I didn't address the evacuation of CO2 in here. You can still use the lungs to evacuate it (exhaling it after in small bubbles) and/or you may want to handwave a gill-like extra organ. The lungs solution would suffer for longer immersion terms - since the lungs will be filled exclusively with CO2 after a while and there's no other gas to wash it away. $\endgroup$ Mar 3, 2020 at 5:55
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Don’t use genetic engineering. Use nanotechnology instead.

Respirocytes are a hypothetical form of nanotechnology capable of allowing an individual to hold their breath for 3.8 hours if their blood is completely replaced with a 50% respirocyte/50% blood plasma mixture. They’re essentially tiny oxygen storage tanks that hold oxygen and carbon dioxide at 1000 atmospheres of pressure (at a safety factor of about 100 since they could safely withstand much higher pressures in theory, but a failure at high pressure might cause damage to the body). This is compared to the pressure that red blood cells store oxygen at of about .5 atmospheres of pressure.

If you want them to be hereditary, it’s not too hard to imagine a civilisation capable of making them to also be capable of making the bone marrow into nanofactories capable of making them, and altering the womb to include nanotechnology that can pass on these nanoaugmentations to their children.

Here’s a page on Ray Kurzweil’s website talking about them as a reference, and explaining where these numbers come from:

https://www.kurzweilai.net/respirocytes

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  • $\begingroup$ This does not meet the requirements of the hard science tag $\endgroup$ Feb 26, 2020 at 10:21
  • $\begingroup$ Is it possible to create a biological analogue of these respirocytes, that is, to create more advanced red blood cells-respirocytes ? $\endgroup$
    – user71408
    Feb 26, 2020 at 10:52
  • $\begingroup$ @StarfishPrime Did you read the link I posted? I'm pretty sure it does. "Based on an article by Robert A. Freitas Jr. written in 2001." $\endgroup$
    – nick012000
    Feb 26, 2020 at 11:41
  • $\begingroup$ @FrenchThompson Probably not, no, considering that they're relying on molecularly-perfect diamond or sapphire structures to build the pressure chambers. $\endgroup$
    – nick012000
    Feb 26, 2020 at 11:42
  • $\begingroup$ @nick012000 I could suggest magic and give you a reference by Aleister Crowley, but that wouldn't make my answer hard science ;-) Nanomechanisms of the sort you've linked may as well be magic, given the barriers that must be overcome to get anything even a fraction of their complexity and vaunted abilities. $\endgroup$ Feb 26, 2020 at 13:12