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Artificial gills for humans?

Discussion in 'Science & Technology' started by Zkribbler, Aug 15, 2018.

  1. Zkribbler

    Zkribbler Warlord

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    An artificial gill for a human? I think not?

    "this will require a gill with a surface of 32 square meters (344 square feet)."

    Aye, there's the rub. IMHO, this will be more applicable as the skin of a mini-sub than as a "gill" for a Free-swimming human.
     
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  2. tjs282

    tjs282 Unabashed immigrant

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    Nanoscale engineering might eventually allow this: after all, the alveolar microstructure of human lungs already provides a surface area of ~70 sq.m for gas exchange. A single alveolus has a diameter of ~200 µm (0.2 mm), i.e. a spherical surface of ~1.26×105 sq.µm (0.13 sq.mm). Not sure what resolution the average 3D printer can currently achieve, but I suspect not this small...

    That said, I believe you're right: the device can't possibly work as advertised.

    Spoiler Condensed lecture/info-dump about why it can't work. :
    Scuba cylinders only 'work' as a gas supply (whether air, nitrox, trimix or heliox) because their contents are at a much higher pressure (200-300 bar, 3000-4500 psi) than the ambient pressure underwater (practical depth limits of 'recreational' trimix-scuba are around 200 m, 21 bar/ata); the scuba regulator steps this very high tank-pressure down to ambient, allowing relatively effortless inhalation at all depths, and providing sufficient gas to allow the diver to fill his lungs comfortably (to their normal surface volume). While closed-circuit rebreathers are much more gas-efficient than open-circuit scuba, they also require a high-pressure 'diluent' cylinder to maintain a constant volume within the breathing-loop as the diver descends.

    Dissolved gas is generally measured in mg/L, and, barring stratification, dissolved O2/N2 levels are generally fairly constant through the [marine] water column. Since increasing water pressure would not (AFAIK) translate to a similarly increased dissolved gas pressure in the water nor, by extension, increased pressure/volume in the gill. So it's not enough for this gill just to be able to extract O2 from/release CO2 into the water, it would also have to have some mechanism to equalise its gas-delivery pressure/volume to ambient. Otherwise, it's difficult to see how it could possibly provide comfortable inhalation even at as little as 5 m depth (where pressure is 'only' 50% greater than surface pressure, hence requiring 'only' 50% more gas to fill any given volume).

    Then there's the question of how the gill is actually supposed to work in purely mechanical terms. I don't believe the user would be able to simply breathe in and out of the gill like it was some glorified paper bag, because of the massive amount of 'dead space' that would include: he would swiftly pass out from hypoxia. So the gill-harness would have to loop the airflow through 1-way valves like a rebreather does, allowing the user to draw in fresh gas from one side, and exhale stale gas into the other (with the gas-exchange to the water taking place as the gas flows back round to the 'inhalation' side).

    And finally no-one can breathe 100% O2 at any great depth, anyway, because it becomes toxic at high (partial) pressure. For decompression on 100% O2, most tech-dive training agencies mandate a maximum depth of 6 m, pO2 = 1.6 ata; any deeper than that and you're risking epileptic-like convulsions without warning. (Combat-divers using O2 rebreathers and full-face masks might go as 'deep' as 10 m, pO2 = 2.0 ata, but if they convulse, they're less likely to drown).

    I suppose the gill-material could theoretically be used to replace the O2 cylinder, CO2 scrubber, and counterlung of a fully-closed-type rebreather, but like a rebreather, such a setup would still also need a diluent cylinder to allow the user to breathe comfortably and safely below the surface, and likely also electronics to monitor the pO2.
     
    Last edited: Aug 15, 2018
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  3. Zkribbler

    Zkribbler Warlord

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    This is why I love this site. I would never thought of this in a million years. Bravo. :clap: :thanx:
     
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  4. Timsup2nothin

    Timsup2nothin Another drone in the hive mind

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    The willingness of the subject is an issue, but the future for this is a direct water to blood gill membrane. There is too much inefficiency in transferring O2 from the water into a breathable atmosphere and then breathing it. But if you were willing to (temporarily?) idle your lungs so you couldn't suck them full of water and shunt the pulmonary vein through a gas transfer gill to directly oxygenate the blood you could conceivably use a much smaller surface area.
     
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  5. Zkribbler

    Zkribbler Warlord

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    You first :scared:
     
  6. Timsup2nothin

    Timsup2nothin Another drone in the hive mind

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    If it's reversible I'd probably be game. If it's permanent...maybe.
     
  7. Smellincoffee

    Smellincoffee Trekkie At Large

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    They can create the physical organ, but how are they going to get the brain to manage it?
     
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  8. HoloDoc

    HoloDoc Chieftain

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    Indeed. Experiments with rats and mice in liquid environments, like what is done to the divers in The Abyss, had them all dying of stress-induced heart attacks after a short time. I imagine that even if some sort of cybernetic hookup is developed allowing mental control of this device - and I think liquid-breathing research is further along and more likely to succeed, myself - the brain's survival instinct regarding liquid will be a much bigger issue.
     

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