CPR found to be somewhat effective with compression's only

[Firecaptn15]

actually it really doesnt deplete that fast. except in the brain and heart which have a higher O2 demand. if the blood is circulated it moves oxygen to the brain which adds a couple of minutes. this is the reason that activation of the ems system and rapid defibrillation is so important. they have even come up with cpr adjuncts (it looks like the bottom part of a toilet plunger with a specialized handle) for rescuers (pending fda approval) which improves cpr.

as far as holding your breath you dont change the amount of O2 in your blood. hyperventilation just lowers the amt of carbon dioxide which in most people is what makes you feel the need to take a breath.