Question about expiration

Hi all,
I haven't really thought about expiration. I just thought that if you're inhalation pressure needs to be high, its entirely okay to use EPR to give you some comfort during exhalation. But I think it was Slinky who mentioned in another post that when you use EPR, you are actually decreasing your overall pressures for the night. That sort of confused me.
We can become obstructed, I guess, in inhalation and also exhalation. Is there a way of knowing if the obstruction occurs in which of these? I'm assuming (maybe wrongly) that an obstruction in exhalation isn't quite so bad, since your O2 probably stays higher, since we have residual O2 in our exhalation. Am I making any sense?? How would it be determined if someone was having problems with exhalation obstruction?? And wouldn't exhalation obstruction be less important, since our bodies would naturally try to take in another breath, and the higher pressure for that would work? And when it would, would it over-expand the lungs, since the air from the previous breath was still in there??
Sorry if I'm asking too many crazy questions at once.

Not a crazy question at all, in fact, a good logical question. Unfortunately, my grandaughter has a band concert in 15 minutes and I've gotta get out the door but didn't want your post to get lost so just saying hi to get it bumped near the top again.