Breathing is central for us in sitting and meditation because we get more oxygen when we think about it. 

I recall a music teacher saying that it was important to breath diaphramatically when singing or playing a musical instrument because this fill the lungs with about 1/3 more air than when we breathe with just the chest muscles.  Ergo 1/3 more oxygen.

He elaborated that breathing diaphramatically is the natural way, as is done by all babies, and that as we grow older and take on the tensions associated with daily living we tend to breathe higher in the chest. 

High breathing, as I call it, is stress related.  Low breathing returns us to relaxation, and our natural state. 

It feels good to relax.  It feels good to just let go of all of the tension that has built up in us by focusing on diaphramatic breathing, feeling the air fill our lungs, and letting it out slowly, slowly, slowly, relaxing more and more, with every breath.

Once upon a time I asked Chontri "What happened to you if I kill myself?"

and he said "You won't do anything like that"

how funny