 When not breathing for long and dangerous periods of time in cold water, a person's body undergoes great temporary changes to try to prevent death.It achieves this through the activation of the mammalian diving reflex, which has 3 main properties.Other than Bradycardia and Peripheral vasoconstriction, there is a blood shift which occurs only during very deep dives that affects the thoracic cavity (a chamber of the body protected by the thoracic wall.)