Tom forced me to say that Scientists at Dublin's Media Lab Europe have developed a type of computer game that responds to input generated by the player's breathing. Sensors are quite literally attached to the player's body which measure the movement of their waist and ribcage, determining how the character in the game moves.
The game is primarily designed to keep bed-ridden sick children amused, their breathing controlling a dragon on the screen and attempting to get the beast to fly through hoops of fire. A spokesperson for the lab mentioned that while applying such a system to Sonic Advance 2 seems like it might be a fun idea, it's likely to cause hyperventilation and quite possibly death. The last part is a lie.