Mammalian diving reflex

The mammalian diving reflex is a set of physiological responses to facial immersion and breath-holding, including slowed heart rate and reduced blood flow to some tissues.

Trigeminal nerve: The fifth cranial nerve, which carries facial sensation and controls muscles used for chewing. Cold water on facial skin activates sensory pathways that help initiate the reflex.
Facial immersion: Submersion of the face in water, exposing facial sensory regions to water and temperature. Water on the face is a major trigger, especially when it is cold.
Freediving: Underwater diving while holding one's breath, without breathing equipment. Freedivers rely on some reflex effects, though they cannot eliminate the risks of breath-holding.
Mammalian diving adaptations: Anatomical and physiological traits that help aquatic and semi-aquatic mammals dive and forage underwater. The reflex is one response within a broader suite of adaptations in diving mammals.
Bradycardia: A heart rate slower than the normal range for a person's age and condition. The reflex slows the heart, reducing cardiac oxygen demand.
Chemoreceptor: A sensory cell or organ that detects chemical changes such as carbon dioxide or oxygen levels. Chemoreceptors help regulate breathing as oxygen falls and carbon dioxide rises during apnea.
Cold-water immersion: Submersion or exposure of the body to water cold enough to cause substantial heat loss. Cold facial immersion can intensify the reflex while whole-body cold shock creates additional hazards.
Aquatic mammal: A mammal that lives in water for all or much of its life. Specialized aquatic mammals show stronger and more sustained diving physiology than humans.
Peripheral vasoconstriction: Narrowing of blood vessels in the limbs and other peripheral tissues. The reflex restricts peripheral circulation to preserve oxygen for vital organs.
Oxygen delivery: The transport of oxygen from the lungs through blood to tissues. The reflex alters circulation to prioritize oxygen supply during submersion.

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