The critical bit for many interesting practical applications is this:

    A significant problem, however, arises from the high 
    viscosity of the liquid and the corresponding reduction 
    in its ability to remove CO2.[3][20] All uses of liquid 
    breathing for diving must involve total liquid 
    ventilation (see above). Total liquid ventilation, 
    however, has difficulty moving enough liquid to carry 
    away CO2, because no matter how great the total pressure 
    is, the amount of partial CO2 gas pressure available to 
    dissolve CO2 into the breathing liquid can never be much 
    more than the pressure at which CO2 exists in the blood 
    (about 40 mm of mercury (Torr)).[20]

This has been a known issue since the 50's and shows no sign of going away. The paragraph is a bit muddled--it's the diffusion coefficient, not the viscosity, that is relevant--but the inability of oxygenated liquids to carry away CO2 has so far been the major impediment to doing any of the really cool things this technology has promised for so long.

What I instantly thought of was `The Abyss`. It was referenced towards the end and it appears the rat -and not the actor- was submerged in this fluid. Very cool! http://www.nytimes.com/1989/08/06/movies/film-the-abyss-a-fo...

For me it reminds me of the LCL in anime series Evangelion. I have seen it pop up a few times in modern sci-fi.

Same. NGE is actually referenced in the "Fiction" section of the wiki entry, along with others.

I seem to remember this being in the book "The Sphere", though I might be wrong. I actually always thought that it was something rarely-used-but-possible.

The overlap between close-to-current sci-fi and real life in my brain is occasionally saddening/shameful.

Interstellar seemed to suggest use of a similar method when the astronauts were in hibernation.

Although I am wearing a scifi hat, not reality, assuming they don't need to breathe in hibernation, the full fluid immersion is probably a good way to regulate internal body temperature.

This is why I posted the link. I never realized the liquid was real and that the scene was shot using it. After watching the scene I thought, did they drown that rat? Effects were good, but not that good!

How would you return to breathing normal air after having your lungs flooded with this liquid?

Someone slaps your butt and you start breathing and crying.

From memory when they do it with babies they just let it evaporate out.

In babies, I would guess that some of the amniotic fluid is also absorbed into the blood stream. Both that and evaporation seem much less likely to work with perfluorocarbons.

Forgive me for being a bit too simple on this subject - wouldn't having a liquid in your lungs, throat and mouth really make it difficult or impossible to talk?

Not sure using it for diving or space travel is a great plan if that's the case. Sure you could have a text or flashing lights method of talking but there's no communication method faster than yelling "HELP!" into your radio that I can think of

Divers don't talk that much, actually.

See, there is an air intake in your mouth - and trying to talk under water does not exactly result in the noises you expect when you're talking into air.

The sign used by divers to alert others is banging your knife against the air tank. There are actual hand signs for 'I'm in trouble' or 'I'm out of air'.

Fair enough, like I say I'm not familiar with the subject but curious. I was more picturing the masks that look a bit like gas masks that have radios in them. My extent of diving knowledge is limited to movies and Mythbusters, I'll admit.

Thanks for that information :)

Sign language is the answer.

While I find this kind of stuff interesting, I still don't see why it is being posted here.

People like you finding it interesting is literally the definition of what should be posted on HN.

That said, I would love it if the OP game some additional context on why they submitted it - is this a response to something? Was there a new advance here? Just something cool they saw?

I wish here was a good way to include context with a bare link. In this case, I just learned the rat in The Abyss was actually submerged in breathing fluid, a substance I thought was fictitious. This blew my mind, so I shared.