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My question: What is it that needs to be improved or added to the human body so that it can withstand critically (fatally) low and high (if, my genetically modified person is underwater or a very dense atmosphere, like Venus) pressure for a person? Relative to survival at low atmospheric pressure:

At these low pressures, adaptation is not possible. The key is your observation that "with water boiling at 25-30*C". Since normal body temperature is 37 C, while blood does not boil, saliva and all the fluid in the lungs which lubricate the alveoli will instantly boil off. Not to mention your eyes losing all lubrication from tears, which will shortly produce blindness due to friction with the eyelids.

This is an example of the Armstrong Limit, and this limits minimum pressure to just about 10% of sea level, even with pure oxygen.

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    $\begingroup$ The quote is wrong. Water boils at a discrete rate, not instantly. Take a look here - youtu.be/glLPMXq6yc0 $\endgroup$ Jan 12 '20 at 17:41
  • $\begingroup$ There are two separate questions here. I'll see about answering the low pressure one, but you should spin the high pressure adaptation into a separate question. $\endgroup$ Jan 12 '20 at 17:56
  • $\begingroup$ please, you can show links to articles (maybe, I use a translator it is inconvenient for me to translate the video) or write everything as an answer. $\endgroup$
    – user71408
    Jan 12 '20 at 18:05
  • $\begingroup$ Also please read the hard-science tag guideline, and take special note of the bit that says "this tag should never be the only tag on a question". $\endgroup$ Jan 12 '20 at 18:11
  • $\begingroup$ You are never surviving on Venus with just a human body. I don't care what you do, short of making an exoskeleton which is basically an Iron Man suit, you are not surviving on Venus. $\endgroup$
    – Halfthawed
    Jan 12 '20 at 18:24
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To be adapted to (and be able to work freely), as opposed to endure; I think you have to re-write biology from scratch using the only known materials that are mostly stable fluids in vacuum, which we use as lubricants for satellites. These are perflouropolyalkylethers (or equivalents). There is actually a whole family of similar-propertied materials. Some material like this would need to be your medium in which biology happens, in my opinion.

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19940024896.pdf

We are mostly liquid (~70%) creatures, and our how our cells and the micro flora and fauna all interact is built on this.

You will also need to dispense with respiration, which might be possible if you eat foods that contains everything you need (rich in enriched uranium) or can be combined with electro-magnetic light to produce everything essential. You could eliminate waste material the same way we excrete, but it would need to be a system that traps respiration byproduct also.

For high pressures, however, water is a pretty good stuff to be mostly made out of. Sharks have been tagged diving to depths as high as 1,200 meters (3,937 ft $ 1 \over 20$ ft per atmosphere ~ 196.8 atmospheres) which is more than double the 90 atmospheres on the surface of Venus.

You'll need to adapt a form of respiration that works in such high pressure (sharks filter oxygen out of the water with gills).

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  • $\begingroup$ Sorry, you can paint your answer in detail. I need to create a genetically engineered person (who should look like a person externally) able to survive with deadly low or high pressure (you can specify numbers when answering) $\endgroup$
    – user71408
    Jan 12 '20 at 18:24
  • $\begingroup$ I agree you basically need to reinvent biology especially multicellular biology. which is no such a scope and scale that I doubt a meaningful detailed answer can be given. $\endgroup$
    – John
    Jan 13 '20 at 0:25
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    $\begingroup$ @FrenchThompson I added some extra text for more detailed. In summary: I believe you could genetically engineer a person to hit the high-pressure mark on Earth, but to hit the low-pressure mark you'll need to re-invent biology using a different substance than the water we're about 70% all made of. Can't do that with hard science, yet. There do exist materials (space lubricants) that fit the bill, however. $\endgroup$ Jan 13 '20 at 11:02
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To alter a human in an way that could survive both incredibly high as well as low pressure, would be impossible. There are to many processes that would need to exist to protect in one state, that would work against it in the other. It's like taking a submarine that's made to keep the water pressure out, and using it in space.

However it might be possible to adapt a human to exist in one, of either of those cases. (Though transition between into or out of those states can be a problem)

High pressure isn't really much of a problem in of itself. Just need to equalize the pressure with the surroundings. The reasons why we usually talk about problems with high pressure, is because we need to transition from normal to high and back again, within a reasonable time (We only have so much air, before we need to get back to the surface). Animals that live at the bottom of the sea today, has no problems using the same physics and chemistry that we do at the surface, as long as they stay at their level.

At high enough levels of pressure, we can run into gasses becoming liquids, that will of course require changes to the body to deal with it (lungs can't breathe liquid oxygen, but they could be changed to do so) It all depends on the environment.

Low pressure is a bit more of a problem, primarily due to sublimation (liquids and solids becomes gases a little at a time, so you sort of slowly dissolve)

First up, you would need to adapt the skin to act more like a wet-suit, that's 2-3 sizes to small. That'll create an artificial pressure inside the body, working well enough. The skin will still sublimate, but can be regrown from the inside (think oister in acid, that regrows it's shell faster than it's disolved).

Second is the eyes, here you would need something like some snakes have (https://en.wikipedia.org/wiki/Brille) that'll contain the needed pressure and protect the eyes (no tear ducts or crying of course)

Finally we need lungs (here we're talking a low pressure environment, with the necessary gasses to live (oxygen for humans) just a lot less of it. The lungs themselves can't be coated like the skin, as that would prevent absorption of oxygen. However a tiered system, where a large amount of gas is inhaled, and then compressed through a series of valves before finally ending up in the lungs. Would create a normal level in the lungs themselves, allowing them to absorb oxygen. An exit valve will then slowly drain any excess through a separate exit, at a rate equal to the intake.

For a complete no pressure environment, you would of course have to completely change energy production. Storing enough oxygen for any extended time is just not viable in a human. (A side note here, we already have anaerobic respiration, though it produces lactic acid. If you were to alter your human to give it a way to effectively deal with it, it shouldn't be necessary to breathe at all :))

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  • $\begingroup$ Perfectly! That's what I need! $\endgroup$
    – user71408
    Jan 13 '20 at 17:42
  • $\begingroup$ tell as much as possible about this! More in detail regarding: lungs and skin, how exactly should they be improved and with what? (for example. the skin needs to be strengthened. What structure will it have?) $\endgroup$
    – user71408
    Jan 13 '20 at 17:45
  • $\begingroup$ There would be a bit more problems with the skin at low pressures. It also has to act as a thermal insulator, and, unless the outer layer is more sturdy, the loss rate maybe too high for any regrowth process to compensate. $\endgroup$
    – Alexander
    Jan 13 '20 at 18:13
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I don't think the changes are incompatible.

As it stands we have not found any indication of a pressure that is too high for humans, although there are limits for other reasons. We are vulnerable to too-rapid pressure changes, this is probably quite hard to engineer around as it is going to be basically impossible to stop gases from going into solution under pressure. You didn't specify a need for quick adaption so this isn't a showstopper, though. The actual limit on what a human can survive is based on breathing--at sufficient pressure all gases mess with the brain too much. That's where I would be looking for a change--what can be done to protect the brain & nervous system from nitrogen narcosis. (We call it that because that's the first one that was encountered, but every gas we can breathe causes trouble if the pressure is high enough.)

On the low end the point where body temperature goes above boiling will be awfully hard to overcome. You might be able to live a short time outside that, though:

Modify our oxygen transport system so the body can store a much larger supply of oxygen and carbon dioxide--note that I am not talking about larger lungs, but stored in a bound form. Modify the throat to be able to clamp down hard on the airway, likewise the urinary and anal sphincters, and add another one around the vagina. Add a bunch of strong fibers to the skin to address swelling. (Note that vacuum on bare skin is drying but not otherwise harmful apart from the swelling. I have seen proposals for spacesuits that leave the arms and legs in vacuum, protected only by a compression layer. This probably isn't adequate for EVA use {no heating, cooling only by sweating, won't fare well against micrometeoriates} but the ease of use could be of great help in a sheltered environment--say inside some sort of structure that's in vacuum.)

The air leaves the lungs and then the body clamps down, the sphincters are strong enough to have minimal leakage at the vapor pressure of water at body temperature. I see no way to protect the eyes completely, they'll lose mobility but you can still turn your head--awkward but not impossible. Obviously you have to get back to pressure before your stored oxygen runs out or your stored CO2 builds up too much.

I see nothing about these changes that are incompatible with each other so your engineered human should be able to take both high and low pressure.

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(Only a partial answer)

It takes one hell of a change to screw with liquid pressure within the body. The struggle basically comes with the pressurised gas.

Large diving aquatic mammals have compartmentalised lungs where one half can entirely collapse around its blood vessels as a means of limiting the gas released into the bloodstream.

Hope I got that right, or at least sent you in the right direction.

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When it comes to biological changes, it's hard to say what qualifies as a large or small change. Everything is in such complicated balance. However, we can talk about mechanical approaches to these environments. These should be applicable in exploring the biological world.

In both cases, the key issue is breathing pressure. Our lungs need to maintain a sufficiently high partial pressure of oxygen or we fail to oxygenate blood. In the extreme case of someone suddenly exposed to pure vacuum, we have about 15 seconds before we lose consciousness. This is because the blood flowing in the lungs is actually stripped of the oxygen it has left by the vacuum. 15 seconds later, that completely deoxygentated blood reaches the brain, and we're out.

All solutions I am aware of involve raising the partial pressure of oxygen enough. You could evolve to need less pressure, such as the biological adaptations sherpas have. But approaching vacuum pressures is going to almost certainly call for pressurizing oxygen. We'll assume you have one.

Of course, you still have to worry about the idea of the water evaporating off your skin, right? Actually, it turns out that's not as big of an issue as we might think. There are very real thermodynamic limits which prevent all of the water from snap-evaporating, turning you into an icicle. This is fundamental to the bio-suit, one of the many technologies in development seeking to revolutionize the space suit. The outside of the suit is actually porous. Human skin can withstand pure vacuum on the millimeter scale without any trouble. Its only as you get to larger unprotected areas that you have issues with fluids pooling under the skin. Their suit actually exposes the skin to pure vacuum, covered in layers of material which handle the gross pressures without issue. In fact, this is deemed an advantage. Evaporation is an excellent way to cool the body. We call it sweat, and we've been doing it for millions of years. The exposed skin actually operates in the same way, letting our body's own sweat-based regulation handle temperature balances which require substantial equipment in modern EVA suits.

Going the other way is much harder. While a pure vacuum will never "pull" on you harder than 1 atmosphere more than you're used to, there's no limit to how high pressures can go.

Once again, the key is breathing. Modern divers rely on SCUBA apparatus, which deliver gasses at roughly the same pressure at the water around us. Breathing creates roughly a 1/10th of an atmosphere differential at most, so as long as the gasses remain within 1/10th of an atmosphere of the water around you, you can breathe. (practically, we use regulators which get much closer than 1/10th for comfort).

The killer problem we are still working on is gas mixtures. Strange things get toxic at high pressures. At high enough partial pressures of oxygen, oxygen itself becomes toxic. (as a recreational diver, I was taught that 1.4 atmospheres of oxygen is the threshold, though the real threshold is almost certainly higher). Deep divers often tune down the fraction of the oxygen in the gasses they breathe as they go deeper in order to avoid this. It gets replaced with other gasses. Nitrogen is a common one because it's very cheap. However, in deep dives there is an effect called nitrogen narcosis which leaves one feeling drunk and sleepy. These are bad effects to feel, which can lead to mistakes that leaves one dead. The depth (and thus pressure) where this takes effect varies from individual to individual, but its generally somewhere around the 30m range.

The typical solution is to use helium to fill in the gaps. For deep dives, heliox is a common gas mix, containing helium and oxygen in whatever concentrations are correct for that depth. This works great until tremendously deep dives, on the order of 150m (15 atmospheres!), where helium starts to have bad effects on the central nervous system, an effect called High-pressure nervous syndrome (HPNS). These effects become significant around 300m. Some mixes, such as Tri-mix, exist to resolve this. Adding in other gasses seems to mitigate the effect of HPNS, so trimix adds a little nitrogen into the mix.

There is a depth where the body is simply not meant to operate. It seems to be below 1000m, based on deep divers, but there is a point where our chemistry simply cannot keep up with the pressure. Adaptations to fix this would be fundamental re-designing of the body.

All of the solutions described above are mechanical ones we have used to explore space and the oceans. Any biological solution will likely have to resolve the issues we have found in our mechanical solutions.

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  • $\begingroup$ great answer! you can tell more about triple mixing $\endgroup$
    – user71408
    Jan 14 '20 at 5:58
  • $\begingroup$ I am not a commercial diver, so the nuances of that are beyond me. From the research I have seen, they're still in the nebulous region for researchers themselves. If you're interested in trimix, it's probably worth reading scholarly works about HPNS. This is one of the sources provided by Wikipedia. It's an overview from '76. I'm certain more research has been done on this, but its limited in that very few individuals seek to dive that far down, so the market for that information is small. $\endgroup$
    – Cort Ammon
    Jan 14 '20 at 15:14
  • $\begingroup$ can you give me some links to related articles? $\endgroup$
    – user71408
    Jan 14 '20 at 16:34

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