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I'm writing a story about scientifically plausible superhumans ( a new genetically enhanced human species that is mentally and physically superior to ordinary humans ), and one of their main features is the ability to hold your breath for a long enough time ( more than thirty minutes), but without lowering your metabolic rate.

At first glance, the most obvious solution to my problem would be to increase the volume of my superhumans ' lungs so that when they inhale, they can inhale more oxygen. But in this case, I need to improve the ability of their blood to carry oxygen. After all, blood circulation performs one of the most important functions of transferring oxygen from the lungs to the tissues, and carbon dioxide — from the tissues to the lungs. The oxygen consumption of tissue cells can vary significantly, for example, during the transition from a state of rest to physical activity and vice versa. In this regard, the blood must have large reserves necessary to increase its ability to carry oxygen from the lungs to the tissues, and carbon dioxide in the opposite direction.

Hemoglobin is able to capture oxygen from the alveolar air (a compound called oxyhemoglobin) and release the necessary amount of oxygen in the tissues. A feature of the chemical reaction of oxygen with hemoglobin is that the amount of bound oxygen is limited by the number of hemoglobin molecules in red blood cells.

Question: how would it be possible to increase the number of oxygen molecules that could be carried by the blood?

Note: if you have to sacrifice your hemoglobin for something else, I'll be happy to hear an alternative.

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    $\begingroup$ I think you need to broaden the question to include avian lungs (more efficient extraction of O2 from O2-poor air) and a special oxygen-concentrating organ for additional storage of O2 reserves. But anything hard science is not going to work - they will give you equations about speculative stuff, but biology isn't a good match for hard science. Biology is all give and take. $\endgroup$ – DWKraus May 5 at 12:34
  • $\begingroup$ Look up sherpas, humans with genes that allow them to feel more comfortable on great heights. $\endgroup$ – The Square-Cube Law May 5 at 13:06
  • $\begingroup$ Excess hemoglobin is a disease that usually has to be treated by regular blood-letting. Answers that increase it may want to consider that side of things, too. $\endgroup$ – Mary May 5 at 13:14
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    $\begingroup$ I once found a write-up that explained how even mediocre nanotechnology might allow a human to remain underwater for 3 days (70+ hours). Just little storage devices in the bloodstream that would contain (compressed?) oxygen, and when CO2 started to build up, someone would switch over to storing that. I remember it seeming plausible at the time, but it was years ago and my understanding of such things is slightly more sophisticated nowdays. This scheme did rely on micro/nano-mechanical devices however, and I doubt biochemistry alone could achieve the same. $\endgroup$ – John O May 5 at 16:51
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    $\begingroup$ Oxygen isn't the only bottleneck for humans holding their breath. The burning sensation you get if you hold your breath long enough is caused by Carbon Dioxide making the air in your lungs more acidic. To dramatically extend the breathing time, you would also need more resistance to CO2 poisoning. Looking to the current limits for holding your breath should help give some ideas. smithsonianmag.com/smithsonian-institution/… $\endgroup$ – Kyle A May 6 at 14:08
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Swimming Like a Seal:

I'm not sure hard science is the best fit for this question, but I'll give it a go. I think the key element you are looking for is aquatic mammalian myoglobin. There is a good set of review articles here on the subject. The biochemistry gets pretty technical, so dig in deep to the second link to get the hard science.

Basically, cetacean myoglobin is able to reach much higher levels than most mammals, but is structurally a little different to reach these concentrations. It stores oxygen, releasing it in the muscles over time. Seals, for example, can achieve up to two hours of dive time, although this is likely at a much-reduced activity level. But 30 min at a reasonably normal respiration should be achievable. Big brains are also greedy for oxygen, so this will also come into play. Dolphins, for example, get to only about 12 min on dive times.

Biology is all about give and take, and I'm guessing there are consequences to having all that atypical myoglobin. It may function differently in non-diving conditions, it may have a very high energy cost (to make/maintain), it might function best at high pressures (like underwater) but the science of "this-is-better-than-that" is always highly speculative and not a good match for the hard science tag.

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    $\begingroup$ This is solid unweird mammal physiology; +. Now I have to think of something weirder and less plausible for my answer. On it! $\endgroup$ – Willk May 5 at 14:35
  • $\begingroup$ @Willk That's one of the most perfect comments I've ever seen. Good luck! $\endgroup$ – DWKraus May 5 at 15:12
  • $\begingroup$ this is an awesome answer - the downside of cetacean myoglobin is probably just that, well, there's a lot more iron needed to form heme groups - bioavailable iron is a pretty scarce resource. The effects of nutrient starvation are likely to be much more severe, and these humans are likely to need a meat and iron rich diet to be healthy. It'd be pretty solvable in our modern society, but early humans wouldn't have survived the switch from hunting to agriculture $\endgroup$ – lupe May 6 at 13:38
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Circulating peroxisomes carrying O2 as H2O2

synopsis: H2O2 is a concentrated liquid source of O2 gas with available O2 increasing as concentration of H2O2 increases. Stores of oxygen as H2O2 could be tapped during long breath holding.

All hail the peroxisome, ancient armor of our ancestors!

https://en.wikipedia.org/wiki/Peroxisome

Peroxisomes are tiny intracellular organelles, a 50th of the size of a red blood cell. They handle hydrogen peroxide for us - detoxifying it when it accumulates and producing it when needed for oxidative metabolic functions / offensive oxidative attacks against invaders.

So: except for the noneukaryotes in the audience, we all have tiny spaces which are fortified against the corrosive effects of H2O2. In this scenario, H2O2 serves as an oxygen source. Can one produce O2 from H2O2? Yes, and in generous amounts. A 3% solution of H2O2 will produce 10 times its volume of O2 gas. So a liter of 3% solution makes 10L pure O2. I am fairly sure that the internal concentration of H2O2 in a peroxisome is less than 3% but let us use 3% - nothing will burst into flame and these are supersoldiers after all.

Assume O2 consumption for a breath holding supersoldier mediating is 100 ml/minute and a supersoldier doing squats (like they do) is 2000 ml/minute. Average 1000 ml/minute and one would get 10 minutes of O2 demand from 1L of 3% H2O2 solution.

Peroxisomes are the size of platelets. We will fortify the blood with a liter of 3% H2O2 peroxisomes circulating. We will stash another liter in the liver and a third in the tissues. At cost of 3 extra liters volume we get enough O2 for 30 min moderate activity.

The peroxisomes can just dump peroxide into the blood and the oxygen produced by endogenous catalase will be swept up by RBC. These researches injected H2O2 into bags of deoxygenated blood, which perked them right up.

THE OXYGENATION OF BLOOD BY HYDROGEN PEROXIDE: IN VITRO STUDIES

oxygenation by h202

I think these folks were using 30% peroxide and so a tenth the volume of the 3% in my scenario. Peroxide packs a lot of O2!

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  • $\begingroup$ How do you keep this much peroxide stable in the body? And O2 at this level would possibly be toxic and would screw up T cell signaling. Not to mention that three liters of fluid would be really bad for people. pubmed.ncbi.nlm.nih.gov/15133946/…. $\endgroup$ – DWKraus May 5 at 20:07
  • $\begingroup$ @DWKraus - re stable - read up on the noble peroxisome! That is what it does. re 3 liters really bad - maybe if you are a dainty 40kg supersoldier (and there is nothing wrong with that if you are). 3 liters for a big supersoldier is chump change. Back in the day you yourself probably drank 3 liters of beer then went on a 10k jog. Or maybe not the jog. Re O2 toxic - the peroxisomes let it off little by little as O2 saturation in the hemoglobin drops. $\endgroup$ – Willk May 5 at 20:25
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    $\begingroup$ The noble peroxisome breaks down any H2O2 not immediately used because it's so toxic. They contain oxidation reactions to limited organelles to protect the body from oxidative damage (that's why anti-oxidants are so useful). Hypervolemia is a serious problem in transfusions, and no, I've never consumed three liters of beer and gone for a run. But I could see some sort of specialized organ (specialized second liver?) that did something similar (not three liters worth). $\endgroup$ – DWKraus May 5 at 20:37
  • $\begingroup$ I do think that an additional 3 litres of circulatory volume is unfeasible. The stroke volume would need to increase by roughly 50-60%, that’s way too much. It’s also a completely different situation than taking in 3litres of beer orally. // A potential workaround would be the following: Most (maybe all, didn’t check) cells do already have peroxisomes. They could be storing O2 in the form of H2O2 in there and a concentration gradient could facilitate O2 generation during times of hypoxia in each individual cell. Restoring of the peroxisomes would work via the bloodstream. This might get $\endgroup$ – Narusan May 5 at 20:50
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    $\begingroup$ I get the idea of a modified peroxisome organelle, but H2O2 is very labile & toxic, and you'd need to evolve something like hemoglobin to stabilize it in the peroxisome. I'd go with big, fat cells filled with peroxisomes instead of trying to make them into a sub-cell like platelets, to get around the fluid issues and to isolate the oxidative damage. Existing red cells can absorb released O2 from a liver-like organ. $\endgroup$ – DWKraus May 6 at 2:16
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Using a blood substitute you could improve this.

Perfluorochemicals can carry several times more oxygen than red blood cells. They could be adapted for that. Along with other minor efficiency boosts, this could let them survive longer underwater.

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  • $\begingroup$ I think perflourochemicals are largely unstable, and break down fairly quickly under physiological conditions (one of the benefits for transfusion). You might want a special organ, filled with this, which releases the chemicals in times of O2 stress ( I had a character in a story whos breasts were filled with something very close to this for an emergency O2 storage). $\endgroup$ – DWKraus May 5 at 20:01
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    $\begingroup$ @DWKraus perfluorinated organic compounds are not unstable. On the contrary, they are considered persistent organic pollutants and are resistant to chemical and biological degradation: doi.org/10.1186/2190-4715-23-38 This is why perfluorinated compounds have become a major health and environmental concern in some places. $\endgroup$ – WaterMolecule May 6 at 1:23
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There was a good article about this a while back: https://foresight.org/Nanomedicine/Respirocytes.html

Now, this was talking about artificial respirocytes, but the general concept remains.

Long story short: whereas red blood cells mainly store O2 in solution and/or chemically bound, if you store O2 under pressure instead you can achieve a much higher capacity if you have the materials for it (and the nanotech to be able to actually construct the thing).

Major caveats:

  1. The pressures required to actually be helpful require extremely strong materials. The above article was assuming diamond walls.
  2. These would not fulfill the ancillary duties of red blood cells (clotting, notably.)
  3. The complexity required for the control scheme for said respirocytes (when/how to let out/in O2/CO2) is rather high for something that isn't a fully-viable cell.
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