While exercising, to avoid an attack or to overcome a mild attack take these two steps. Step One: thrust all of the air out of your lungs, really force it. Step Two: create an "O" shape with your lips, almost like you are about to whistle, but not that narrow, then forcibly suck air back into your lungs until you are comfortably filled with air. Repeat these steps as long as you are exercising and are worried about an attack. The breathing creates a rhythm so that you are aware of your breathing. It also causes you to mildly hyperventilate, pumping more oxygen into your bloodstream.