Okay, this is purely for fun, if anyone wants to give it a shot. So, if you want to play along, have fun but don't push yourself into discomfort...unless you've done this before in which case you know what you're doing anyway
I did consider why he blows precious air out of his lungs:
a) He's feeling uncomfortable, and needs to release air; it happens.
b) He can hold his breath for a lot longer, which is quite probable, since he was relaxed when he finished.