thumb|Diving reflex in a human [[Infant|baby]]
The diving reflex, also known as the diving response and mammalian diving reflex, is a set of physiological responses to immersion that overrides the basic homeostatic reflexes, and is found in all air-breathing vertebrates studied to date. and muskrats, and the Haenyeo divers in the South Korean province of Jeju are notable outliers.
The diving reflex is triggered specifically by chilling and wetting the nostrils and face while breath-holding, and is sustained via neural processing originating in the carotid chemoreceptors. The most noticeable effects are on the cardiovascular system, which displays peripheral vasoconstriction, slowed heart rate, redirection of blood to the vital organs to conserve oxygen, release of red blood cells stored in the spleen, and, in humans, heart rhythm irregularities.
Carotid body chemoreceptors
During sustained breath-holding while submerged, blood oxygen levels decline while carbon dioxide and acidity levels rise, As sensory organs, the carotid bodies convey the chemical status of the circulating blood to brain centers regulating neural outputs to the heart and circulation.
Circulatory responses
Plasma fluid losses due to immersion diuresis occur within a short period of immersion.
The diving reflex is closely linked to another physiological response inducing bradycardia—the trigeminocardiac reflex—which justifies its re-evaluation as a component of a broader family of trigeminal reflexes.
Examples in fiction
- Jacques Mayol in the Luc Besson film The Big Blue
- Giacinta 'Jinx' Johnson in the James Bond film Die Another Day.
- A patient in Tachycardia on ER in Season 4
- Jack Buggit in the novel The Shipping News by Annie Proulx
- In The Question #2 (March 1987), the Question recovers from drowning; his survival is attributed to the diving reflex.