The Na'vi and our oxygen

[Jachyra]

I've read the survival guide, and I've never seen this answered anywhere else (I might have missed this, and if so, sorry) and maybe JC's novelization will enlightened us, but 'till then...

I was wondering if the Na'vi could actually breath our air (let's say inside hell's gate). We know they're impervious to Pandora's toxic air (for us), but what about if they have to breathe our "clean" air.

The only close call we see in the movie is when Neytiri scoops human Jake in her arms (while the module is being filled with Pandaora's "air").

How would their body react?

Just a thought...