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

[Cyborg Pirate]

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

I was keeping it simple. But yes the pressure inside the balloon also increases in order to exert force outward on the ballon walls. Still in a sealed balloon ilthe partial pressures and fraction remains the same .79 and .21

 

[tursiops]

I was keeping it simple. But yes the pressure inside the balloon also increases in order to exert force outward on the ballon walls. Still in a sealed balloon ilthe partial pressures and fraction remains the same .79 and .21

You are seriously confused.
If the pressure goes up, the sum of the partial pressures must equal the total pressure, so the partial pressures must also increase. If the pressure in the balloon doubles, the N2 and O2 fractions remain the same, but the partial pressures also double.

 

[Cyborg Pirate]

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.

 

[Streydog]

I saw a show the other day on deep diving mammals. Elephant seals can dive over 5,000 ft.

 

[BRT]

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.

So inflate that balloon inside a scuba tank, put the valve on and fill the tank. The balloon inside the tank shrinks by however many BAR you put in the tank. One BAR additional and it goes to half size. 3 BAR additional and it is at 1/4 size and so on. All the nitrogen around the balloon has a partial pressure higher than .79 but the air in the balloon stays at a partial pressure of .79????? Simply not true.

 

[BRT]

Fraction and partial are interchangeable values.

Only at 1 atmosphere.

 

[mmerriman]

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.

I read this a couple of years ago that claims that whales can. Do Whales Get the Bends?

 

[w3dge]

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.

That's not how it works. That's not how any of this works.

Partial pressures aren't described as percentages - they're absolute values. It doesn't matter what depth you breathe 100% O2 at, you're still breathing 100% - whether at 6m or 600m. There is no such thing as '160% O2'. At 6m, each breath of O2 may have 160% the number of molecules as a breath at the surface, but thats a pretty clunky, and frankly inaccurate, way to express it.

Your .79/79% thing that you keep repeating is just two different ways to express the same thing - the fraction of gas. This has nothing to do with partial pressures.

Of course the partial pressures *will* increase as the balloon gets smaller. Sum of partial pressures = total pressure. Balloon gets smaller, pressure increases, partial pressure increase. A balloon filled with Air (21% O2, 79% N2) at 1ATM has a total internal pressure of 1 ATM, a volume of 1l (example). a PPO2 of 0.21ATM and a PPN2 of 0.79ATM. The very same balloon, with no gas transfer, when pressurised to 2ATM will still have 21% O2 and 79% N2. It is now has an internal pressure of 2ATM it will have a volume of 0.5l, a PPO2 of 0.42ATM and a PPN2 of 1.58ATM.

This is pretty basic stuff, I'm surprised you've managed to get it so wrong.

 

[Vicko]

That article just seams wrong to me, cant quite place it.

In freediving we roughly know what happens to the body, mammalian reflex takes over, blood shifts to the lungs and floods the alveloi so they don't collapse, unnecessary organs slow down, blood moves away from extremities and into the core.

We can still get DCS and nitrogen narcosis does happen, albeit only to elite free divers. DCS is more common in competitive spearfishing as you have divers going to 40+ meters with only 1 minute or less surface interval for multiple hours (in Greece during the preparations for the world championship 3 freedivers were diagnosed with type 1 dcs )
I also personally know 2 spearfisherman who got type 2 all tough the doctors never confirmed it, one of them is a cripple now as the first doctor he saw did not allow him to go to the chamber even tough he was paralyzed from waist down.

Air is a mixture of gas, how is it possible that an animal can choose the exact gas that dissolves in to it's tissues?

 

[tarponchik]

Air is a mixture of gas, how is it possible that an animal can choose the exact gas that dissolves in to it's tissues?

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.