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I'm aware that deep sea fish don't actually "explode" when brought to the surface but any air sacs in their bodies would expand and cause them possibly fatal damage.

However, what other physiological problems might occur in a creature that had evolved in an environment of extremely high pressure when moved to a low pressure environment?

I'm trying to think of what "survival gear" would be required for a being used to living in pressures in the hundreds of MPa range to be kept alive at the Earth's surface.

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  • $\begingroup$ When I read "environmental pressure" I was thinking of evolutional pressure. And your question didn't make much sense... $\endgroup$ – Bakuriu Dec 2 '14 at 21:04
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    $\begingroup$ Well, we humans die when the atmospheric pressure around us drops too far. Although asphyxiation comes first, and then we suffer from decompression. $\endgroup$ – Philipp Dec 3 '14 at 8:23
  • $\begingroup$ @Bakuriu My question seems to make sense to other people. Their answers have given me precisely the ideas I needed. $\endgroup$ – Matt Jones Dec 4 '14 at 10:14
  • $\begingroup$ You probably didn't get what I meant. Evolutionary pressure from the environment means that the environment basically kills most of the individuals, and hence favorable mutations are selected in short time because they provide a big advantage. Low pressure in this sense means that the environment is full of food and the individuals don't have to compete or have special mutations to survive. Usually an organism that can live in a hard environment is able to live in a non-hard environment. $\endgroup$ – Bakuriu Dec 4 '14 at 10:19
  • $\begingroup$ I got exactly what you meant - you misread my question, but other people understood it and gave me very good answers. $\endgroup$ – Matt Jones Dec 4 '14 at 10:23
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Many of the effects will be similar to what humans encounter when exposed to very low pressures. Here are a few:

It will be harder to breathe

Gas exchange across things like lungs or gills is dependent on the partial pressure of oxygen on those surfaces. In a low pressure environment, any creature that relies on breathing oxygen will be exposed to hypoxia, which could be fatal. This can be survived to some extent through acclimatization, but no humans have lived for extensive periods of time at more than about half of this.

To survive this change, a creature would need to be given either a higher concentration of oxygen or else a pressurized air supply. For long term habitation in an otherwise breathable atmosphere, this could consist of an air compressor. Since the lungs would burst if their pressure was hundreds of times the external air pressure, this would also require a pressurized suit, like what astronauts wear.

Low partial pressure of oxygen is the main issue that mountaineers face, but they only face a pressure around 1/3 of normal air pressure. For lower pressures, other issues will come into play.

Some substances will change phase

This is something that astronauts encounter when going into space. Blood and other fluids in the human body begin to boil at low pressures. For an organism evolved to survive at hundreds of MPa, the body may contain fluids which are only fluid under high pressures. Likewise, some solid structures may become liquid at low pressures.

Astronauts face this problem when they go into space. It requires a pressurized suit to be survivable, since your body can't operate with gas for blood.

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  • $\begingroup$ Brilliant, thank you very much! Certainly I had in mind at the very least that a respirator would be needed - at he other extreme I have in mind something similar to the "tank" that the Guild Navigator inhabits in David Lynch's "Dune". $\endgroup$ – Matt Jones Dec 4 '14 at 10:10
  • $\begingroup$ I selected this one as the answer because it's given me more things to think about than the others, but I wish I could accept all the answers! Thanks to everyone who responded, you've all helped me. $\endgroup$ – Matt Jones Dec 4 '14 at 10:21
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First, check out this article describing how deep-sea fish can be conditioned to live at atmospheric pressure. The depths they talk about are in the tens of MPa (hundreds of atmospheres) range. Basically they find that slowly lowering the environmental pressure allows the fish to survive.

This is similar to the case of scuba divers. If they ascend quickly the expanding gasses in their body can be fatal, but ascending slowly gives the gas enough time to escape the body.

According to wikipedia, A spherical tank to hold 100 MPa of pressure made of, say, a composite material with an ultimate tensile strength of a few GPa would have a radius around 50 times its thickness, not unreasonable. So it would probably be possible for high-pressure beings to undergo a long period of decompression in such a tank, eventually being able to survive at near-atmospheric pressures in a sort of space suit (or even without the suit if they can survive with just 1 atmosphere pressure).

The one problem with a space suit is that any significant pressure tends to inflate the suit like a balloon, making it difficult to move. Even in zero gravity, astronauts tend to be exhausted by spacewalks just from having to bend the joints in their suits.

Note however that things like temperature and oxygen levels are less adjustable. The partial pressure of oxygen is the total pressure times the fraction of the atmosphere that is oxygen. Normal partial pressure is 21 kPa, below a certain value you will suffocate (limit is somewhere around value for the peak of Mont Everest (43 mmHg, or 5,7 kPa) - people can climb there without oxygen bottles, but it is hard and they cannot stay there), and above around 30 kPa the oxygen actually becomes toxic (slowly, diver can still spend 45 min at 160 kPa). Your beings would probably need to breathe a special mix of gasses, like how astronauts breathe a low-pressure, high-oxygen mixture in their space suits.

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  • $\begingroup$ I didn't know that Oxygen could become toxic because of pressure, I know it could cause problems if it was too rich. $\endgroup$ – bowlturner Dec 2 '14 at 18:00
  • $\begingroup$ @bowlturner Essentially it's if the partial pressure goes too high. Increase the % or increase the pressure and you increase the partial pressure. $\endgroup$ – Tim B Dec 2 '14 at 18:10
  • $\begingroup$ @TimB Oh I understand the mechanics, I just never thought of it that way. I knew that some of the diving mixes lowered the % of oxygen. Thanks $\endgroup$ – bowlturner Dec 2 '14 at 18:16
  • $\begingroup$ Many thanks for this information - I hadn't thought of the idea of slow conditioning for making a change from high pressure to low pressure. That's given me a lot of food for thought! $\endgroup$ – Matt Jones Dec 4 '14 at 10:06
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When we humans go to high altitudes we bring extra oxygen to get enough of it in each breath. For deep sea diving we need to bring special air with lower percentages of oxygen and nitrogen so we don't get too much and get poisoned.

At hundreds of MPa, the chemicals we know in their gas form, can exist as liquids or as solutes in strong liquid solution. Carbon dioxide, for example, would not form bubbles.

What survival gear is needed depends on the concentration of these chemicals.

I suggest a creature that lives deep in an ocean where there is about the same concentration of oxygen as at the Earth's surface, but a much higher concentration of carbon dioxide. The creature would want to wear a wetsuit so its skin doesn't dry out and some sort of irrigator to pour oxygen-rich seawater on its gills.

Also, because it is used to a high concentration of carbon dioxide, its blood usually has so much of it that at 100 kPa it would fizz like a shaken Coke. To survive at Earth's surface the creature wears an injector that pumps an acid into its bloodstream to compensate for the carbonic acid that is rapidly lost through the gills at the low pressure. Without the injector, the creature's blood pH would rise and uncontrollably speed up its metabolism. Its muscles would then anaerobically produce carbon dioxide so fast that the creature would get the bends and die violently.

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  • $\begingroup$ You are very right - I hadn't considered dissolved gases within any internal fluids. The creatures would not be worried about dry skin, but certainly keeping any gases dissolved in the "blood" would present interesting problems. Thank you! $\endgroup$ – Matt Jones Dec 4 '14 at 10:08
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One thing to think about is what happens to humans. When we go on top of a mountain we have a much harder time breathing (at least until we get acclimated to it.

On the other hand when we go down into the deep and come back up we have to take precautions because of 'the bends'. I think different air mixes help alleviate this situation but for a long time people had to stay in a pressure tank and be slowly acclimated back to normal pressure the length of time depended on the how long they were down and how deep they went.

The bends for those that don't know is dissolved gasses turn to bubbles in the blood when decompressed to fast causing all sorts of pain and possibly death. These kinds of things would be the most troublesome. Throwing a body out of the space station door wouldn't make it explode, at least not from the difference in pressure, maybe freezing inconsistently might make it look like that.

If the difference was enough, it might be like needing an Oxygen mask at the top of Everest, so that the being could get what it needed, maybe even a pressure mask if the pressure was important in the absorption process.

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  • $\begingroup$ Thanks for the answer - yes, I'd completely forgotten to think about the bends! Some ideas are slowly occurring to me... $\endgroup$ – Matt Jones Dec 4 '14 at 10:09
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I recall hearing of abyssal life that they rely on the pressure to shape enzymes correctly, fold proteins, etc. In general, organic chemistry changes.

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  • $\begingroup$ Any references on this? I'd not heard about this... $\endgroup$ – user3082 Jan 1 '15 at 10:00
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Since this question has been successfully answered, I will only present links for detailed study on the matter:

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

http://www.nature.com/scitable/blog/saltwater-science/do_whales_suffer_from_decompression

http://www.whoi.edu/oceanus/feature/even-sperm-whales-get-the-bends

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