[clort]

Yes the lungs are collapsed completely. A seal, as I understand it, has extremely haemoglobin rich blood and stores all its oxygen there for the dive.

[madhadron]

For diving mammals, most of the oxygen is carried in the muscles by myoglobin. It turns out that the myoglobin density in muscles is very precisely related with the diving ability of the mammal, and the the density is also very precisely correlated with the surface charge (and thus the exact sequence) of the myoglobin protein. There's an amazing paper about this that then uses myoglobin sequence to infer the diving abilities of extinct mammals.[1]

I'm not in general willing to be a guinea pig for genetic manipulation, but toothed whale myoglobin and being able to dive with empty lungs for half an hour or 45 minutes? Sign me up.

[1]: Mirceta, S., Signore, A. V., Burns, J. M., Cossins, A. R., Campbell, K. L., & Berenbrink, M. (2013). Evolution of mammalian diving capacity traced by myoglobin net surface charge. Science, 340(6138), 1234192–1234192. http://doi.org/10.1126/science.1234192

[notduncansmith]

I read that some seals can also force air into respiratory cavities in their skull, which keeps them from suffering decompression sickness.

[clort]

I am not sure how deep they would be able to go with this technique but it might be helpful in shallow water. I mean, to equalise at 20m they would need to generate 2bar (~30psi) of pressure. That is quite a lot! For reference, humans can normally push about 0.1bar (1-2psi) by blowing.. and their sinuses would need to withstand that pressure at the surface, before they dive.

Also, this has nothing to do with decompression sickness (aka 'the bends'). That is to do with dissolved gases in the blood which turn into bubbles when the pressure is lowered.

[notduncansmith]

Idk, I was just referring to Wikipedia where it says:

> Air is forced from the lungs during a dive and into the upper respiratory passages, where gases cannot easily be absorbed into the bloodstream. This helps protect the seal from the bends.

https://en.m.wikipedia.org/wiki/Earless_seal

[zaarn]

>Also, this has nothing to do with decompression sickness (aka 'the bends'). That is to do with dissolved gases in the blood which turn into bubbles when the pressure is lowered.

Dissolved gases dropping out of solution and forming bubbles is literally decompression sickness.

[clort]

Yes, I'm pretty sure that is exactly what I wrote?

[zaarn]

Dissolved bubbles in blood has everything to do with the bends.

[clort]

You have twice restated exactly what I have written, thank you.

and for clarity: 'forcing air into respiratory cavities in the skull' would not prevent the bends.

[glofish]

this is a good point, there is a lot more to diving really deep than storing a sufficient amount of oxygen. Basic physiological processes work differently at high pressures.

[glofish]

ah, fascinating! now it makes sense, it stores the air somewhere else!