Why couldn’t we just use a bag and reuse the air we breathe when underwater

Question

I’ve always wondered this since I was a child, and I see people use bags to rebreathe the air they have in their lungs for panic attacks, which only increases my curiosity.

In: Biology

Answer 1

We can, and we do (albeit not using something as simple as a bag):

[https://en.wikipedia.org/wiki/Rebreather](https://en.wikipedia.org/wiki/Rebreather)