Shift, the shifting of blood to the thoracic cavity, the region of the chest between the diaphragm and the neck, to avoid the collapse of the lungs under higher pressure during deeper dives. Archived from the original (PDF) on Retrieved b "Drowning". DiMaio, Dominick; DiMaio, Vincent.M. The level of carbon dioxide in the blood after hyperventilation may then be insufficient to trigger the breathing reflex later in the dive and a blackout may occur without warning and before the diver feels any urgent need to breathe. 15 People have drowned in as little as 30 mm of water lying face down. The Alliance for Safe Children. "WHO Disease and injury country estimates".