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a reflex by which immersing the face or body in water, especially cold water, tends to cause bradycardia and peripheral vasoconstriction; mean aortic pressure is little affected because the reduction in cardiac output tends to balance the increased peripheral resistance that reduces peripheral blood flow. Although relatively minor in most humans, the changes can be profound in some species of diving animal, for example, ducks and seals.
A reflexive response to diving in many aquatic mammals and birds, characterized by physiological changes that decrease oxygen consumption, such as slowed heart rate and decreased blood flow to the abdominal organs and muscles, until breathing resumes. Though less pronounced, the reflex also occurs in certain nonaquatic animals, including humans, upon submersion in water.
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.
div·ing re·flex(dīv'ing rē'fleks)
A reflex by which immersing the face or body in water, especially cold water, tends to cause bradycardia and peripheral vasoconstriction; relatively minor in most humans.