Mammalian diving reflex The mammalian diving reflex is a reflex
in mammals which optimizes respiration to allow staying
underwater for extended periods of time. It is exhibited
strongly in aquatic mammals (seals, 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 – 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 a body, in this order: - Bradycardia is the
first response to submersion. Immediately upon facial contact
with cold water, the human heart rate slows down ten to twenty-
five percent. Seals experience changes that are even more
dramatic, going from about 125 beats per