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Thread: Artificial gills - how?

  1. #1 Artificial gills - how? 
    Forum Bachelors Degree CEngelbrecht's Avatar
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    Found a website some time ago, that claimed to have figured out how to make a gismo that allowed you to breathe oxygen from the surrounding water, and they were seeking crowd funding to get it on the market. Sounded very exciting, however, a quick readthrough of the claimed principle showed it as a massive hoax, trying to steal mo money from the gulliple of the world.



    But... just out of curiosity... could it be made to work? Like, you put on some kind of stormtrooper helmet, which then diffuses oxygen in and diffuses excess carbon dioxide out into the surrounding water, allowing you to breathe inside an air bubble constantly being automatically kept at set levels of O2 and CO2 (and N2?), and then you could be under water as long as you like, with limited bulky equipment and no gas limit from a SCUBA tank.

    Would there still be issues of decompression sickness and nitrogen narcosis, is what I can't figure out right now. And how deep would you be able to go before physics would still kill you? Tens of meters? Hundreds? Thousands? Provided that the diffusion issue could even be solved.


    (A game I played recently, where your character wore a helmet and could stay under water indefinitely.)


    Last edited by CEngelbrecht; December 21st, 2017 at 08:22 AM.
    "The suppression of uncomfortable ideas may be common in religion or in politics, but it is not the path to knowledge, and there's no place for it in the endeavor of science. (History) shows us clearly that accepted and conventional ideas are often wrong, and that fundamental insights can arise from the most unexpected sources."
    - Carl Sagan, 1980


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  3. #2  
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    https://en.wikipedia.org/wiki/Deep_diving

    with scuba world record it at 332m

    the problem of external pressure is significant and even if you can breathe under water, water pressure around 103 meters will be 10 times the atmospheric at sea level which will feel like someones choking you


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  4. #3  
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    Quote Originally Posted by gdpvk View Post
    https://en.wikipedia.org/wiki/Deep_diving

    with scuba world record it at 332m

    the problem of external pressure is significant and even if you can breathe under water, water pressure around 103 meters will be 10 times the atmospheric at sea level which will feel like someones choking you
    This is nonsense.

    The whole principle of SCUBA diving is that the air, or other breathing mixture, is delivered to the diver at the ambient water pressure. If it were not, it would be impossible to inflate the lungs at a depth of more than about 3 metres.

    The problems of deep diving are to do with the effects of dissolved gases on the body.
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    no its more than that , underwater pressure has serious effects structurally, it is actually tough to go deep underwater without something to weigh you down, air in your lungs will have buoyancy effect, you will feel the pressure on your chest.
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  6. #5  
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    Quote Originally Posted by gdpvk View Post
    no its more than that , underwater pressure has serious effects structurally, it is actually tough to go deep underwater without something to weigh you down, air in your lungs will have buoyancy effect, you will feel the pressure on your chest.
    The buoyancy effect of your lungs does not change as you go lower, if you are breathing from a SCUBA apparatus. The pressure inside and outside remains the same, the volume of your lungs does not change, and so the amount of water you displace does not change.

    The buoyancy of any trapped air in, for instance, a dry suit, reduces as you descend, because as it gets compressed by the increasing pressure, it takes up less volume. Same with a buoyancy compensator (stabiliser jacket). So you have to watch it carefully, especially during ascent to avoid rocketing to the surface as the buoyancy increases with reduction in pressure.
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    yes correct air in you lungs get compressed which means the compressed air in your lungs will exert equal amount of pressure when you try to hold air in, which is what i meant by choking
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    Genius Duck Moderator Dywyddyr's Avatar
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    Quote Originally Posted by gdpvk View Post
    yes correct air in you lungs get compressed which means the compressed air in your lungs will exert equal amount of pressure when you try to hold air in, which is what i meant by choking
    1) Having compressed air in your lungs is nothing like choking.
    2) The "compressed air" is at ambient pressure, therefore it isn't actually compressed per se.
    "[Dywyddyr] makes a grumpy bastard like me seem like a happy go lucky scamp" - PhDemon
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    https://en.wikipedia.org/wiki/Barotrauma



    after air compression in lungs, the air cylinders actually compensate for the pressure difference, which should happen gradually. also there will be a structural limit to how much air pressure your body can handle,
    Last edited by gdpvk; January 24th, 2018 at 08:20 AM.
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    Quote Originally Posted by gdpvk View Post
    yes correct air in you lungs get compressed which means the compressed air in your lungs will exert equal amount of pressure when you try to hold air in, which is what i meant by choking
    This is a completely unscientific statement. "Holding air in" is neither here nor there.

    You breathe compressed air just as if you were on the surface, if its pressure equals the exterior pressure which is being applied all over your body by the water. The air tank has air at very high pressure, the pressure reduction valve drops this to equal that of the water around you. Equal pressure means the pressure exerted by the compressed air is exactly balanced by the ambient water pressure, There is no pressure difference, provided to remember to keep clearing your ears as you descend, to stop a pressure difference building up between your middle ear and the water on the other side of your eardrum. (I had trouble with this, which is why I gave up). All this stuff about choking is rubbish.
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    Quote Originally Posted by gdpvk View Post
    Yes, this is what happens if you do not equalise the pressure, for example in your middle ear. What I have been telling you however is that SCUBA gear automatically equalises the pressure of the air you breathe so there is no risk of problems with your lungs, so long as you carry on breathing normally as you descend or ascend.

    If you do a free ascent, i.e. with no SCUBA gear and with just one lungful of breath to last you as you go up, then you do have to ensure you exhale slowly, to compensate for the expanison of the air in your lungs as the pressure drops. If under these circumstances you were to "hold your breath", you would risk bursting your lungs.
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  12. #11  
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    Quote Originally Posted by gdpvk View Post
    https://en.wikipedia.org/wiki/Barotrauma



    after air compression in lungs, the air cylinders actually compensate for the pressure difference, which should happen gradually. also there will be a structural limit to how much air pressure your body can handle,
    I see that you added these explanatory sentences AFTER I had made my two posts. But yes indeed, that is why this should not be an issue if you know what you are doing as a diver.

    As for a "structural limit" to the pressure your body can handle that is quite untrue.

    The limit is biochemistry, due to phenomena such as nitrogen narcosis when the dissolved concentration of nitrogen in the blood gets too high. Plus of course the physics of the "bends" if you ascend too fast after a prolonged period at great depth, causing gas to come out of solution as bubbles in the blood.
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    i understand the biochemistry problems nitrogen narcosis and oxygen toxicity, but assuming you overcome chemical problems, there will be a limit to your diaphragm and intercostal muscles capacity to create a low pressure for inhaling and high pressure for exhaling.
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    Quote Originally Posted by gdpvk View Post
    i understand the biochemistry problems nitrogen narcosis and oxygen toxicity, but assuming you overcome chemical problems, there will be a limit to your diaphragm and intercostal muscles capacity to create a low pressure for inhaling and high pressure for exhaling.
    Wrong.

    You evidently still fail to understand the physics of the situation. As I have explained already, the pressure on both sides of your diaphragm, intercostal muscles, ribcage and every other conceivable interface or structure in the body is equal. Equal.

    What would put a strain on these structures is a pressure difference.

    No pressure difference, no effect.

    Your breathing muscles create a very small -ve pressure difference to allow you to inhale and a very small pressure difference to cause you to exhale. All the muscles and other structures have to do is create exactly the same pressure difference that they do on the surface. It does not matter at all whether the ambient pressure is 1 bar or 50bar from that point of view. The ambient pressure has no effect on the pressure difference.

    What you may not have thought through is that the human body is, apart from the air cavity in the lungs (and a bit of gas in the digestive tract), entirely solid and liquid in nature. It is thus hydraulically incompressible, in other words jacking up the pressure does not alter any of the dimensions and imposes no stresses, - so long as the air cavity is pressurised to the ambient pressure.
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    you are assuming a neutral position, but your body has create lower pressure in order to inhale and higher pressure to exhale, which will get harder as the air pressure in your lungs increases
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    but your point is creating minor pressure difference even at high pressure should not be a problem which i dont think can apply for everyone, you will probably need to undergo lots of exercise and train your body to be able to breathe in that pressure.
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    Quote Originally Posted by gdpvk View Post
    you are assuming a neutral position, but your body has create lower pressure in order to inhale and higher pressure to exhale, which will get harder as the air pressure in your lungs increases
    Why? If you create a -ve pressure difference of 0.1bar to inhale and ditto for exhaling, why would the effort to achieve this differ according to whether the ambient pressure is 1bar or 10bar.
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  18. #17  
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    Quote Originally Posted by gdpvk View Post
    but your point is creating minor pressure difference even at high pressure should not be a problem which i dont think can apply for everyone, you will probably need to undergo lots of exercise and train your body to be able to breathe in that pressure.
    You're still not getting it. The ambient pressure makes no difference. It is the same on both side of the muscles in question and so the pressure exerted on one side is balanced by the pressure on the other, cancelling the forces out completely.
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  19. #18  
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    Quote Originally Posted by gdpvk View Post
    you are assuming a neutral position, but your body has create lower pressure in order to inhale and higher pressure to exhale, which will get harder as the air pressure in your lungs increases
    Except that it IS a "neutral position" - just like you are breathing now.
    Internal air is at ambient pressure so all you have to do is get your diaphragm to move slightly to expand or contact your lungs.

    but your point is creating minor pressure difference even at high pressure should not be a problem which i dont think can apply for everyone, you will probably need to undergo lots of exercise and train your body to be able to breathe in that pressure.
    Complete and utter nonsense. The "high pressure" is internal AND external - i.e. they're equal so ANY contraction/ expansion of the lungs creates the requisite pressure differential for breathing.
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    Quote Originally Posted by gdpvk View Post
    i understand the biochemistry problems nitrogen narcosis and oxygen toxicity, but assuming you overcome chemical problems, there will be a limit to your diaphragm and intercostal muscles capacity to create a low pressure for inhaling and high pressure for exhaling.
    No. Your lungs and muscles don't know the difference. They are working to move air through your lungs, and the work that they do is proportional to the difference between the pressure of the air in your lungs and the water outside.

    Do this experiment:

    1) Get a long tube, put one end in the air, then go to the bottom of s 6 foot deep pool and try to breathe through it. It will be very hard, because you are trying to pull 15psi air into an 18psi environment.

    2) Get a SCUBA rig. Sit at the surface and breathe through the regulator. Now go to the bottom and breathe through the regulator. There will be no difference, because you are pulling 18psi air into an 18psi environment. Your muscles have no extra work to do.
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    ok i understand what you are saying, still i wonder how much workload can human diaphragm handle
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  22. #21  
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    Quote Originally Posted by gdpvk View Post
    ok i understand what you are saying, still i wonder how much workload can human diaphragm handle
    For that I would consult a sports physio dealing with weightlifters (for maximum force) or rowers (for sustained extreme exertion), I think.
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