Mammalian diving reflex

Submerging the face into water causes the mammalian diving reflex, which is found in all mammals, but especially in marine mammals as for example whales and seals. This reflex puts the body into energy saving modus to maximize the time that can be spent under water. The effect of this reflex is larger in cold water than in warm water, and includes three factors:

• Bradycardia, a reduction in the heart rate of up to 50% in humans.
• Peripheral vasoconstriction, the restriction of the blood flow to the extremities to increase the blood and oxygen supply to the vital organs, especially the brain.
• Blood shift, the shifting of blood to the thoracic cavity, i.e. the chest between the diaphragm and the neck to avoid the collapse of the lungs under higher pressure during deeper dives.

Thus both a conscious and an unconscious person can survive longer without oxygen under water than in a comparable situation on dry land.