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

[aquacat8]

This explained it more simply for me
How do deep-diving sea creatures withstand huge pressure changes?

 

[drrich2]

Fraction and partial are interchangeable values.

Only at 1 atm/bar (surface). Think about it this way, if partial pressure & fraction were the same:

1.) Nitrogen narcosis at depth wouldn't be a thing.
2.) Nitrox wouldn't have a MOD because oxygen toxicity at depth wouldn't be a thing, either.

Richard.

 

[aquacat8]

Whales do it deeper: still don't get bent.

The question for me is not how they don't get bent, but how their organs don't get crushed, or their ribs snapped at those depths/pressures. Humans would suffer from compressive arthralgia and not be able to move. Cetacea seem to be largely immune to that.

now I’m wondering about this too...

 

[Cyborg Pirate]

1 breath of air at the surface.... is(for Scuba language) .79 (fraction) or 79% (partial pressure). .21 (fraction) or 21% O2 (partial pressure) at depth.... the same breath of air is smaller in volume but still has the exact same amount of molecules or N2 and O2 exerting pressure and same percentage. Now as metabolic processes take place (gonna keep this really simple) becomes .79 N2, .16 O2, and .05 CO2. Or 79%, 16% 5%. The partial pressure or the fraction of N2 because it is an inert gas and not matabolized or consumed bu the body remains .79. No add’l Air molecules are added or subtracted from the lungs. Only the flexible container (lungs) is changed this the smaller volume but exact same partial pressures from the said gases. So the pressure exerted outwards on the lungs is still .79 or 79% of the pressure. At depth or at the surface those values do not change. Thus interchangeable values because no added gases. If we really want to make it simple. Fill a ballon with air. So no metabolizing of O2. Same air at the surface as at depth as back at the surface. Ballon got smaller then returned to same size at surface. The fraction of N2 and of O2 stays the same, the “part” of the entire pressure value for N2 is 79% or .79 the entire ride down and up.

 

[drrich2]

the same breath of air is smaller in volume but still has the exact same amount of molecules or N2 and O2 exerting pressure and same percentage.

Okay, I think I see your point. Since the volume of gas in a free diver's lungs is reduced at the same rate the gas density increases (e.g.: at 2 atm you've got double the % N but only half the lung volume of that), the thinking is the higher density (higher partial pressure) doesn't matter, whereas with a scuba diver, he keeps filling his lungs fairly full of the higher density gas at depth.

Interesting stuff! Then the dolphin collapses part of the lung and shifts blood flow, further complicating it.

Anyone ever heard of a free diver getting the bends?

Richard.

 

[tursiops]

Fraction and partial are interchangeable values.

Only at the surface, at one atmosphere pressure.

 

[Cyborg Pirate]

Nitrogen narcosis happens because their is air exchange happening.... the same air in your tank .79 N2, .21 O2. Now.... because the tank is a fixed container it doesn’t grow or shrink with pressure exerted from the atmosphere. However your lungs do. So to fill your lungs at depth. Let’s say at 33’. It takes x2 the amount of molecules to fill the lungs as it did at the surface. So the fraction of N2 and O2 remain the same. However the molecule changes makes the partial pressure now 1.81 (.79x2) and .41 (.21 x2) so in this instance with exhaling and inhaling yes the partial pressures changed. In a breath hold from the surface..... they r interchangeable values. The narcosis happens because as you descend the increase in the inert gas causes a PH change in the body. The Ph causes a change in the cerebral spinal fluid around the brain causing headache and delirium. With frequent repeated exposure the body and brain become adapt to it and can function with it. (That’s why divers who are used to doing 30-40’ dives who drop down to lower depths and are not accustomed to it experience narcosis) fast decents in cold dark water with an increase in respiratory rate causes narcosis. Yes rapid saturation of the body with increased partial pressures of an inert gas....

 

[tursiops]

1 breath of air at the surface.... is(for Scuba language) .79 (fraction) or 79% (partial pressure). .21 (fraction) or 21% O2 (partial pressure) at depth.... the same breath of air is smaller in volume but still has the exact same amount of molecules or N2 and O2 exerting pressure and same percentage. Now as metabolic processes take place (gonna keep this really simple) becomes .79 N2, .16 O2, and .05 CO2. Or 79%, 16% 5%. The partial pressure or the fraction of N2 because it is an inert gas and not matabolized or consumed bu the body remains .79. No add’l Air molecules are added or subtracted from the lungs. Only the flexible container (lungs) is changed this the smaller volume but exact same partial pressures from the said gases. So the pressure exerted outwards on the lungs is still .79 or 79% of the pressure. At depth or at the surface those values do not change. Thus interchangeable values because no added gases. If we really want to make it simple. Fill a ballon with air. So no metabolizing of O2. Same air at the surface as at depth as back at the surface. Ballon got smaller then returned to same size at surface. The fraction of N2 and of O2 stays the same, the “part” of the entire pressure value for N2 is 79% or .79 the entire ride down and up.

What you are missing is that the pressure in your balloon has increased as you take it deeper.

 

[Nick Steele]

Yea I am confused, if your not taking in new nitrogen under the surface how could you get the bends?

Take a look at the pearl divers of the Polynesian islands. They routinely get a sickness named Taravana which is believed to be DCS. Granted this is from repetitive dive to 100-140’ with short SI but it does happen.


OTOH I wouldn’t be surprised if they made very limited deep dives in a row. I never thought of the bends in reguards to marine animals but it is a very interesting topic like how they combat the pressure on their bodies.

 

[Cyborg Pirate]

This is also why when a diver is “Narced” going up a few feet before continuing the descent eases the narcosis. Reducing the pressure gradient, slowing the respiratory rate and giving the brain and body a moment to self regulate usually will allow a diver to continue to descend after narcosis has set in.