Diving physiology

Diving physiology is the set of physiological adjustments that lets air-breathing animals remain underwater, conserve oxygen, and tolerate pressure changes. These adjustments include oxygen storage, reduced heart rate, and shifts in blood flow.

Mammalian diving reflex: An autonomic response to submersion that slows the heart and constricts blood vessels in many mammals. It coordinates the rapid cardiovascular changes that conserve oxygen underwater.
Oxygen transport: The movement of oxygen from the environment to tissues through breathing, blood, and cellular uptake. Diving adaptations modify each stage of oxygen delivery and use.
Freediving: Underwater diving on a single breath, without breathing equipment. Human freedivers deliberately use breath-hold physiology while managing blackout and pressure risks.
Decompression sickness: A disorder caused by bubbles forming from dissolved inert gas during or after pressure reduction. It is a pressure-related hazard, not an oxygen-conserving dive adaptation.
Bradycardia: A slower-than-normal heart rate, which can arise from normal physiology or disease. During a dive, a reduced heart rate lowers cardiac oxygen demand.
Hemoglobin: A protein in red blood cells that binds and transports oxygen. Large blood oxygen stores depend partly on hemoglobin concentration and blood volume.
Weddell seal: An Antarctic seal capable of long, deep dives beneath sea ice. Its oxygen stores and dive patterns are among the best-studied mammalian adaptations.
Nitrogen narcosis: Impairment of judgment and coordination associated with elevated nitrogen partial pressure at depth. It arises from compressed-gas exposure rather than the normal breath-hold response.
Peripheral vasoconstriction: Narrowing of blood vessels in the limbs and other peripheral tissues. It redirects limited oxygenated blood toward organs such as the brain and heart.
Partial pressure: The pressure contributed by one gas within a mixture of gases. Changing partial pressures with depth shape gas exchange and decompression risk.

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