How some Dolphins dive a kilometre down and don’t get the bends

[dberry]

One of the final sentences in that Scientific American article linked a few posts back really is key:
"...the lungs do not serve as a source of oxygen at depth, deep divers [cetaceans, not people] rely on enhanced oxygen stores in their blood and muscle"
They let their lungs collapse to limit the surface area available for gas exchange with that one last breath taken at the surface. This limits absorption of both N2 and O2, but they don't need the O2 from their shrunken little lungs. I'm not sure this applies equally to free divers. OTOH, SCUBA divers are constantly breathing fresh, pressurized air - we DO rely on gas exchange in the lungs for O2, and N2 absorption is an inevitable consequence. Inevitable, unless any animal has evolved semi-permeable membranes in their lungs to more selectively pass O2 and not N2. (Think how EAN32 is made, but at lower pressures.)

 

[tursiops]

Ok thanks,

I have already explained the ratio of molecular # changes and lack there of in a sealed ballon. .79 and .21 represent percentages. Therefore even the fact the pressure increases... no increase in molecules. So the percentage stays the same. If you understand decompression theory you also know that a partial pressure of O2 of 1.6 used for decompression gas at depth means that you are theoretically breathing gas that has 160% O2.... again because of the increase in molecules necessary to expand the lungs against the atmospheric pressure being applied to the body. A sealed container with no exchange of molecules in or out.. yes the pressure goes up as the volume goes down and the balloon gets smaller. All that said.... same number of molecules they never changed so the total of the pressure being exerted on the interior walls of the balloon is still represented by .79 or 79% of N2 and .21 or 21% of O2.

If there were an increase in partial pressures.... the balloon would not get smaller.

You were doing OK (except for that 160% thing...) until that last sentence.
I suggest you go back and look at the definition of partial pressure. Dalton's Law (over 200 years old) is a good place to start.

 

[tursiops]

Only at 1 atmosphere.

Another way to think about this is: 0.79 N2 at 1 atmosphere, means 0.79 x 1.0 = 0.79 atm partial pressure of N2.
At 2 atm, 0.79 x 2 = 1.58 atm partial pressure of N2.

 

[BRT]

Another way to think about this is: 0.79 N2 at 1 atmosphere, means 0.79 x 1.0 = 0.79 atm partial pressure of N2.
At 2 atm, 0.79 x 2 = 1.58 atm partial pressure of N2.

That is correct.

 

[DanielRJones]

At 100m ppn2 is going to be through the roof at 80 but there is so little of it. You are talking 1 breath full at surface so about 5l. You may get very high sat in one of the fastest compartments but that limited amount of n2 is not going far.

In a hour dive at 100m the dolphin uses 4l of n2 where we would be using over 10000l pf n2

 

[tursiops]

At 100m ppn2 is going to be through the roof at 80 but there is so little of it. You are talking 1 breath full at surface so about 5l. You may get very high sat in one of the fastest compartments but that limited amount of n2 is not going far.

In a hour dive at 100m the dolphin uses 4l of n2 where we would be using over 10000l pf n2

This is an interesting point! I'd never though of it this way. Thanks for this fresh perspective.

 

[dmaziuk]

Anyone ever heard of a free diver getting the bends?

See #19 and this: Can Freediving Cause DCS?

 

[dmaziuk]

By chemical binding. O2 can bind to hemoglobin and myoglobin, and CO2 can be converted into bicarbonate. The problem with N2 probably can be solved by sticking it to something hydrophobic, like hydrophobic transport proteins or fat tissue.

Nitrogenase, if you could get it in your system and figure out how off-gas ammonia. (Cue bad breath and fart jokes.)

 

[tarponchik]

Nitrogenase, if you could get it in your system and figure out how off-gas ammonia. (Cue bad breath and fart jokes.)

You will need some genetic engineering to achieve this.

 

[Compressor]

Actually there is some evidence that whales can get DCS. Mechanism is not known too well but there is evidence.
Link 1
Link 2
Link 3

Surprised; I was too until recently when I read these and other articles a while ago.