Every single one of his tricks is just that.... a trick. You can search them on google and so fort. For example his floating card trick is done by hanging a wire on a tree or side of a building. The card tricks are just a matter of quick hands and a fake deck of cards. I'm not saying it's easy stuff, since he makes it appear real, but what I am saying is that he had years to master his trade.
I'm pretty sure there is a math to it. Like how long your lungs can provide oxygen to your body before it's completely empty.
From what I understand, not having oxygen to your brain for a few minutes can result in brain damage. So holding your breath for 17 minutes is a long time, and after so many minutes when your lungs are devoid of oxygen and your body need to release the co2 build up which would put a huge amount of stress on important body parts.
I watched him do it on Oprah. And, yes, I was watching Oprah...but that's not important right now.
This was not really a trick as much as training his body to hold air in as long as possible. Aside from bringing his heart rate way down, I'm betting he did some blood doping..but he'd never admit to that.
I read that he breathed nothing but pure Oxygen for 20 minutes before going into the tank which allows the body to last longer without breating anyway but that's perfectly withing the rule for world record attempts