Is it possible to fill human lungs with some liquid and viscouse substance which would allow only oxigen pass through it (easily), not any other atoms or molecules? I've read such experoments been conducted on mice who were capable to breath underwater with lungs filled with perfluorocarbone liquid. But what I'm looking for is to breath fresh air, not underwater.

If lungs are filled with liquid, how will a 'breath of fresh air' also enter the lungs?

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

Wow that's like in the movie The Abyss.

1 hour ago, Kylo RenSkins said:

Wow that's like in the movie The Abyss.

Yes, I meant to mention that but then forgot!

That helps in the case where pressures are also a problem ( as in The Abyss ).

Otherwise, what's wrong with a supplied air respirator, or SCBA.
It keeps everything other than 'fresh' air out, and, since it's external, it can be removed without coughing up a gallon or more of liquid.
 

According to this article Liquid Breathing may be one step closer to reality.

https://www.google.com/amp/s/phys.org/news/2017-03-liquid-closer.amp