Holly shit…
What the hell are we discussing....
AIR!?
Well but since I've nothing to do I'm going to join in:
Oda made no mistake.
Coup the Burst and Gao Cannon, are massive attacks, and they could even be used in reality in a much reduced scale, by using the Coke to drastically reduce the pressure in one place, sucking a lot of air into a chamber, Then when the coke was all wasted, the "door" of the chamber would be closed, and another door connected to the "Scape pipe", the huge amount of pressure would be released and the boat would fly (not in shounen proportions, of course), kind of the same of a vacuum cleaner, I guess it would be possible for it to work with coke...
Now if the air is limited, the Coke would suck in all the air (that is in the bubble) and send it to the water. The bubble would shrink, and the Straw Hats would choke. This problem would be solved by connecting the chamber to the outside of the bubble, but maybe thats not easy to do, and would ruin the amazing plot device that is keeping them from rushing to F.I.!
I think everyone can understand that much.
Now Luffy is in a one man bubble.
Normally it would require lots of air to insuflate Luffy's arm... much more than it would take to fill that same space in the atmosphere, but this is a shounen, and its pretty much a given that a long breath its all that is needed...
Now that bubble has enough air for that... but even if it hadn't it would only shrink and directly touch Luffy's skin during the time he is doing the attack. He would hold his breath. And when its over he would release the air into the bubble.... simple. And as the air wasn't used for respiration it wouldn't be wasted and would have enough O2.
I know its stupid to put science into a Shounen manga, and that I prolly have killed some Kitty girls, but in this case Oda wasn't incoherent at all, and I was bored.
So I decided to be a good boy and enlighten your minds (jokin').