The mammalian diving reflex is a reflexinmammals which optimizes respiration to allow staying underwater for extended periods of time. It is exhibited strongly in aquatic mammals (seals,[1] otters, dolphins, etc.), but exists in a weaker version in other mammals, including humans. Diving birds, such as penguins, have a similar diving reflex. Every animal's diving reflex is triggered specifically by cold water contacting the face[2] – water that is warmer than 21 °C (70 °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.
Upon initiation of the reflex, three changes happen to the body, in this order:
Thus, both a conscious and an unconscious person can survive longer without oxygen under 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.[4][5]
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.[4] When breathing with face submerged this causes a diving reflex which increases proportionally to decreasing water temperature.[2] Activating the diving reflex with cold water can be used to treat supraventricular tachycardia.[6] However the greatest bradycardia effect is induced when the subject is holding breath with face submerged.
{{cite journal}}
: Unknown parameter |month=
ignored (help)CS1 maint: multiple names: authors list (link)
{{cite journal}}
: Unknown parameter |month=
ignored (help)
{{cite journal}}
: Cite journal requires |journal=
(help)CS1 maint: multiple names: authors list (link)
{{cite journal}}
: |access-date=
requires |url=
(help); Unknown parameter |month=
ignored (help); Unknown parameter |unused_data=
ignored (help)CS1 maint: multiple names: authors list (link)
{{cite journal}}
: Unknown parameter |month=
ignored (help)
| |
---|---|
Cranial nerve |
|
Stretch reflexes |
|
Primitive reflexes |
|
Superficial reflexes |
|
Cardiovascular |
|
Other |
|