Not sure how it's supposed to be used exactly, but it's being fed into your life support system to boost it. If any body part would be directly impacted by a change in that system, lungs would be an obvious candidate.

Maybe using it changes the composition of whatever the life support system makes you breathe, or yeah, maybe it's a liquid sent directly into your lungs like that stuff they use in The Abyss.

Of which the rat experiment part was a real thing apparently. They just had to use shots from 5 different fluid-breathing rats because the poor fuckers were so panicked they shat themselves constantly in terror.