This paper reviews the contributions of hypothermia and the
mammalian diving reflex (MDR) to human survival of cold-water
immersion incidents. It also examines the relationship between
the victim’s age and MDR and considers the protective role
played by hypothermia. Hypothermia is the result of a reduced
metabolic rate and lowered oxygen consumption by body tissues.
Although hypothermia may produce fatal cardiac arrhythmias such
as ventricular fibrillation, it is also associated with bradycardia
and peripheral vasoconstriction, both of which enhance oxygen
supply to the heart and brain. The MDR also causes bradycardia
and reduced peripheral blood flow as well as laryngospasm, which
protects victims against rapid inhalation of water. Studies of
drowning and near drowning of children and adults suggest that
victim survival depends on the presence of both hypothermia
and the MDR, as neither alone can provide adequate cerebral
protection during long periods of hypoxia. Future research is
suggested to improve patient care.