diving reflex, a neural mechanism that produces an automatic change in the cardiovascular system when the face and nose are immersed in cold water. The heart rate decreases and the blood pressure remains stable or increases slightly, while blood flow to all parts of the body except the brain is reduced, thereby helping the body to conserve oxygen. The reflex occurs in humans and other mammals. It is sometimes used in the treatment of paroxysmal tachycardias. The reflex extends the duration of the viability of brain cells during apnea beyond the usual period of 5 to 10 minutes. For this reason, cardiopulmonary resuscitation should always be attempted in drowning victims regardless of their time under water.
