Interesting article from Scientific American-
It's logical to think that the brain's need for oxygen is what limits how long people can hold their breath. Logical, but not the whole story
Investigating what limits our control over breath holding has been difficult, but decades of research suggest that the diaphragm, which contracts to inflate the lungs, plays a key role.
The best hypothesis is that the diaphragm sends signals to the brain about how long it has been contracted and how it is biochemically reacting to depleted levels of oxygen or rising levels of carbon dioxide. Initially those signals cause mere discomfort, but eventually the brain finds them intolerable and forces breathing to start again..... more