Mammalian Diving Response in Humans: Inconsistently Beneficial for Survival.

The mammalian diving response (DR) has evolved in all air-breathing vertebrates as a means of life preservation when immersion in water precludes normal respiration. It is highly developed in diving mammals but present in all Mammalia, including man, as well as other vertebrates. In man, the response consists of apnoea, bradycardia, peripheral and splanchnic vessel constriction with increased venous return to the heart, and increased systolic and pulse pressures. Components of this response may contribute to unexpected deaths in infants and to deaths associated with epileptic seizures. Although direct evidence is lacking, the response provides an explanation for immersion pulmonary oedema in swimmers and divers and for the occasional dissecting aneurysm and other vascular catastrophes that have been reported in scuba divers. Persistence of a vigorous dive response beyond infancy and into adulthood may be a prelude to the development of essential hypertension in later life. Although causation remains unproven, the DR provides a physiologically plausible unifying mechanism for a range of otherwise disparate adverse clinical events. Prospective clinical monitoring in at-risk populations by annual blood pressure recordings and testing of pulse response to facial wetting, together with minor changes in competitor practices, may clarify the role of the DR and guide preventive strategies.