Human Gills - Take Oxygen from Water

[Fluidic Kimbo]

Humans are warm-blooded. Warm-blooded animals need a lot more oxygen than cold-blooded animals. 99% of fish cold-blooded.

A human scubadiver needs 1.5 liters of oxygen per minute while swimming, or 0.64 liters per minute while resting.

If we were to develop a human gills device, at least 192 litres of sea water per minute would have to pass through the artifical gills system, and so we'd need some sort of pump or vacuum with a decent amount of power.

So an artifical gills device for humans would be as heavy as a fuel source (or battery), as well as a pump, and if it's sucking water in strongly (192 litres/minute) then you'd be creating a current in the water.

It's more convenient just to go scubadiving with a tank of oxygen. Although it would have been really cool if we could have made human gills.

[SampsonandDelilah]

I feel like you should watch Amazon’s “The Boys”.

In particular the character “The Deep”...might be right up your alley Kimbo

[Octaneforce]

They got some human gills mouthpeice in starwars when they meet jarjar binks. I remember seeing it as a kid and saying man that would be cool to have. Obviously fictional tho

[Beetlegeuse]

There isn't enough (breathable) oxygen in water (as a rule) to support the respiration of ̶a̶n̶y̶ most warm-bodied ̶c̶r̶e̶a̶t̶u̶r̶e̶ creatures.

Fish don't respire the oxygen from the water molecules (H₂O) themselves. Nor could they because separating that oxygen atom from the two hydrogens would require a process (thermogenic or otherwise) energetic enough to break the molecule's covalent bond. IOW, the aqueous oxygen is not bio-available. Instead their gills filter out the molecules of oxygen (O₂) that are dissolved within the water. And the amount of dissolved oxygen in water is well less than the oxygen in an equivalent volume of air, and can be as little as 1/20th as much. Which explains why so few species of fish are warm-blooded. Because cold-blooded animals have a slower metabolism that requires less oxygen.




And to make matters worse for humans who aspire to have gills, in a seeming fizziks incongruity, there's more dissolved oxygen in cold water than in warm. Ordinarily you can dissolve more of anything in warm water because it's more energetic. But the oxygen molecule is an odd duck because it's so volatile. It boils off readily from warm water, reducing DO levels, but tends to remain in solution better in cold water. Which explains the significantly higher density of marine life in the arctic and the antarctic than at the equator. And why so many great whales spend their feeding season in the coldest waters on earth, but return to warmer waters for spawning. So even if you wanted to risk it, instead of going to Bermuda, where the water can be mid-80s°F on your gill-diving holiday, your gills would be more efficient if you went to Tierra del Fuego, where the water rarely gets above 40°F.

So thanks very much but I think I'll stick with scuba tanks and holidays to Bali.

[Fluidic Kimbo]

First I would have to reduce my resting metabolic rate to that of Rosanne:



So let's say I get my O₂ need down to about 350cc per minute. (Of course that 350cc is a volume at standard temperature and pressure).

Looking at your graph above, 20 degree Celsius sea water can hold about 7.5 mg/litre of dissolved O₂.

1 mole of O₂ weighs 32 grams (each oxygen atom has an atomic mass of 16).

7.5mg of O₂ = 0.000234 moles of O₂

So each litre of sea water has 0.000234 moles of O₂ dissolved in it. Using the 'ideal gas formula' we can get the volume as follows:

101 kPa = (volume)(0.000234)(Avogadro's constant)(20 degrees celsius)

This figure comes out at 5.647cc. So each litre of sea water contains 5.657cc of O₂.

So at my Rosanne metabolic rate of 350cc of O₂ per minute, I would need to process 62 litres of sea water per minute. That's quite a lot, which means the gills would have to be either very big, or very powerful for their size.

Perhaps the gills could run down my neck, down my trunk, down my leg, and maybe have a honeycomb structure for maximal surface area (although I'm not certain yet how that would work).

I have never been scubadiving yet but I want to give it a try. Also I want to go down in a submarine. Lots of people are obsessed with outer space, but there's still so much more to see right here on Earth.

[Fluidic Kimbo]

If we can find a safe, easy and efficient way to split the water molecule, something like:

2H₂O → 2H₂ + O₂

Then we could breathe 80% of the O₂ and then possibly use the hydrogen along with the 20% remaining oxygen as a fuel source to power the motor sucking in the water (I think a PEM cell uses oxygen and hydrogen as fuel).

Even better if we can then take the carbon dioxide we exhale, remove the carbon atom and breathe in the oxygen again.