Mammalian diving reflex
Encyclopedia
The mammalian diving reflex is a reflex
in mammal
s which optimizes respiration
to allow staying underwater for extended periods of time. It is exhibited strongly in aquatic mammal
s (seal
s, otter
s, dolphin
s, etc.), but exists in a weaker version in other mammals, including human
s. Diving bird
s, such as penguin
s, have a similar diving reflex. Every animal's diving reflex is triggered specifically by cold water contacting the face – water that is warmer than 21 °C (69.8 °F) does not cause the reflex, and neither does submersion of body parts other than the face. Also, the reflex is always exhibited more dramatically, and thus can grant longer survival, in young individuals.
Thus, both a conscious and an unconscious person can survive longer without oxygen
under cold water than in a comparable situation on dry land. Children tend to survive longer than adults when deprived of oxygen underwater. The exact mechanism for this effect has been debated and may be a result of brain cooling similar to the protective effects seen in patients treated with deep hypothermia
.
When the face is submerged, receptors that are sensitive to cold within the nasal cavity and other areas of the face supplied by cranial nerve V (trigeminal) relay the information to the brain and then innervate cranial nerve X, which is part of the autonomic nervous system. This causes bradycardia and peripheral vasoconstriction. Blood is removed from the limbs and all organs but the heart and the brain, creating a heart-brain circuit and allowing the mammal to conserve oxygen.
In humans, the mammalian diving reflex is not induced when limbs are introduced to cold water. Mild bradycardia is caused by subjects holding their breath without submerging the face within water. When breathing with face submerged this causes a diving reflex which increases proportionally to decreasing water temperature. Activating the diving reflex with cold water can be used to treat supraventricular tachycardia
. However the greatest bradycardia effect is induced when the subject is holding breath with face submerged.
Reflex
A reflex action, also known as a reflex, is an involuntary and nearly instantaneous movement in response to a stimulus. A true reflex is a behavior which is mediated via the reflex arc; this does not apply to casual uses of the term 'reflex'.-See also:...
in mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s which optimizes respiration
Respiration (physiology)
'In physiology, respiration is defined as the transport of oxygen from the outside air to the cells within tissues, and the transport of carbon dioxide in the opposite direction...
to allow staying underwater for extended periods of time. It is exhibited strongly in aquatic mammal
Aquatic mammal
Aquatic and semi-aquatic mammals are a diverse group of mammals that dwell partly or entirely in bodies of water. They include the various marine mammals who dwell in oceans, as well as various freshwater species, such as the Platypus and the European Otter.-Groups:* Order Sirenia: Sirenians**...
s (seal
Pinniped
Pinnipeds or fin-footed mammals are a widely distributed and diverse group of semiaquatic marine mammals comprising the families Odobenidae , Otariidae , and Phocidae .-Overview: Pinnipeds are typically sleek-bodied and barrel-shaped...
s, otter
Otter
The Otters are twelve species of semi-aquatic mammals which feed on fish and shellfish, and also other invertebrates, amphibians, birds and small mammals....
s, dolphin
Dolphin
Dolphins are marine mammals that are closely related to whales and porpoises. There are almost forty species of dolphin in 17 genera. They vary in size from and , up to and . They are found worldwide, mostly in the shallower seas of the continental shelves, and are carnivores, mostly eating...
s, etc.), but exists in a weaker version in other mammals, including human
Human
Humans are the only living species in the Homo genus...
s. Diving bird
Diving bird
Diving birds are birds which plunge into water to catchfish or other food. They may enter the water from flight, as does the brown pelican , or they may dive from the surface of the water...
s, such as penguin
Penguin
Penguins are a group of aquatic, flightless birds living almost exclusively in the southern hemisphere, especially in Antarctica. Highly adapted for life in the water, penguins have countershaded dark and white plumage, and their wings have become flippers...
s, have a similar diving reflex. Every animal's diving reflex is triggered specifically by cold water contacting the face – water that is warmer than 21 °C (69.8 °F) does not cause the reflex, and neither does submersion of body parts other than the face. Also, the reflex is always exhibited more dramatically, and thus can grant longer survival, in young individuals.
Effect
Upon initiation of the reflex, three changes happen to the body, in this order:- BradycardiaBradycardiaBradycardia , in the context of adult medicine, is the resting heart rate of under 60 beats per minute, though it is seldom symptomatic until the rate drops below 50 beat/min. It may cause cardiac arrest in some patients, because those with bradycardia may not be pumping enough oxygen to their heart...
is the first response to submersion. Immediately upon facial contact with cold water, the human heart rateHeart rateHeart rate is the number of heartbeats per unit of time, typically expressed as beats per minute . Heart rate can vary as the body's need to absorb oxygen and excrete carbon dioxide changes, such as during exercise or sleep....
slows down ten to twenty-five percent. Seals experience changes that are even more dramatic, going from about 125 beats per minute to as low as 10 on an extended dive. Slowing the heart rate lessens the need for bloodstream oxygen, leaving more to be used by other organs. - Next, peripheral vasoconstriction sets in. When under high pressure induced by deep diving, capillaries in the extremities start closing off, stopping blood circulation to those areas. Note that vasoconstriction usually applies to arterioleArterioleAn arteriole is a small diameter blood vessel in the microcirculation that extends and branches out from an artery and leads to capillaries.Arterioles have muscular walls and are the primary site of vascular resistance...
s, but in this case is completely an effect of the capillaries. Toes and fingers close off first, then hands and feet, and ultimately arms and legs stop allowing blood circulation, leaving more blood for use by the heart and brain. Human musculature accounts for only 12% of the body's total oxygen storage, and the body's muscles tend to suffer crampCrampCramps are unpleasant, often painful sensations caused by muscle contraction or over shortening. Common causes of skeletal muscle cramps include muscle fatigue, low sodium, and low potassium...
ing during this phase. Aquatic mammals have as much as 25 to 30% of their oxygen storage in muscle, and thus they can keep working long after capillary blood supply is stopped. - Finally is the blood shiftBlood shiftBlood shift has at least two separate meanings:*In medicine, it is synonymous with left shift.*In biology, it may refer to a phenomenon seen when mammals submerge in water. It is part of the mammalian diving reflex. Blood vessels in the extremities contract, leaving a higher percentage of the...
that occurs only during very deep dives. When this happens, organ and circulatory walls allow plasmaBlood plasmaBlood plasma is the straw-colored liquid component of blood in which the blood cells in whole blood are normally suspended. It makes up about 55% of the total blood volume. It is the intravascular fluid part of extracellular fluid...
/water to pass freely throughout the thoracic cavityThoracic cavityThe thoracic cavity is the chamber of the human body that is protected by the thoracic wall ....
, so its pressure stays constant and the organs aren't crushed. In this stage, the lungs' alveoli fill up with blood plasma, which is reabsorbed when the animal leaves the pressurized environment. This stage of the diving reflex has been observed in humans (such as world champion freediver Martin Štěpánek) during extremely deep (over 90 metres or 300 ft) freedives.
Thus, both a conscious and an unconscious person can survive longer without oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
under cold water than in a comparable situation on dry land. Children tend to survive longer than adults when deprived of oxygen underwater. The exact mechanism for this effect has been debated and may be a result of brain cooling similar to the protective effects seen in patients treated with deep hypothermia
Hypothermia
Hypothermia is a condition in which core temperature drops below the required temperature for normal metabolism and body functions which is defined as . Body temperature is usually maintained near a constant level of through biologic homeostasis or thermoregulation...
.
When the face is submerged, receptors that are sensitive to cold within the nasal cavity and other areas of the face supplied by cranial nerve V (trigeminal) relay the information to the brain and then innervate cranial nerve X, which is part of the autonomic nervous system. This causes bradycardia and peripheral vasoconstriction. Blood is removed from the limbs and all organs but the heart and the brain, creating a heart-brain circuit and allowing the mammal to conserve oxygen.
In humans, the mammalian diving reflex is not induced when limbs are introduced to cold water. Mild bradycardia is caused by subjects holding their breath without submerging the face within water. When breathing with face submerged this causes a diving reflex which increases proportionally to decreasing water temperature. Activating the diving reflex with cold water can be used to treat supraventricular tachycardia
Supraventricular tachycardia
Supraventricular tachycardia is a general term that refers to any rapid heart rhythm originating above the ventricular tissue. Supraventricular tachycardias can be contrasted to the potentially more dangerous ventricular tachycardias - rapid rhythms that originate within the ventricular...
. However the greatest bradycardia effect is induced when the subject is holding breath with face submerged.
Examples in fiction
- Virgil "Bud" Brigman in the James CameronJames CameronJames Francis Cameron is a Canadian-American film director, film producer, screenwriter, editor, environmentalist and inventor...
film The AbyssThe AbyssThe Abyss is a 1989 science fiction film written and directed by James Cameron. It stars Ed Harris, Mary Elizabeth Mastrantonio, and Michael Biehn. The original musical score was composed by Alan Silvestri...
. - Giacinta 'Jinx' Johnson in the James BondJames Bond (film series)The James Bond film series is a British series of motion pictures based on the fictional character of MI6 agent James Bond , who originally appeared in a series of books by Ian Fleming. Earlier films were based on Fleming's novels and short stories, followed later by films with original storylines...
film Die Another DayDie Another DayDie Another Day is the 20th spy film in the James Bond series, and the fourth and last film to star Pierce Brosnan as the fictional MI6 agent James Bond; it is also the last Bond film of the original timeline with the series being rebooted with Casino Royale...
. - A patient in TachycardiaTachycardiaTachycardia comes from the Greek words tachys and kardia . Tachycardia typically refers to a heart rate that exceeds the normal range for a resting heart rate...
on ERER (TV series)ER is an American medical drama television series created by novelist Michael Crichton that aired on NBC from September 19, 1994 to April 2, 2009. It was produced by Constant c Productions and Amblin Entertainment, in association with Warner Bros. Television...
in Season 4ER (season 4)The fourth season of the American fictional drama television series ER first aired on September 25, 1997 and concluded on May 14, 1998. The fourth season consists of 22 episodes.- Plot :...