December 2013

Diving reflex

Important facts about near drowning

Diving reflex

The diving reflex can protect humans in cold-water immersions, but rescuers may be tricked into believing the victims are beyond recovery.

Most people recovered in cold water near-drowning cases show the typical symptoms of death:

  • Cyanotic (blue) skin
  • No detectable breathing
  • No apparent pulse or heartbeat
  • Pupils fully dilated (open)

These symptoms didn’t always mean the victim was dead. Instead, they were the body’s way of increasing its chances of survival through what scientists call the mammalian diving reflex.

The diving reflex is most evident in marine mammals such as whales, seals or porpoises. During the diving reflex, the body diverts blood to circulate it (at only 6 to 8 beats per minute in some cases) between the heart, brain and lungs.

Marine mammals have developed this ability to the point where they can remain under water for extended periods of time (more than 30 minutes in some species) without brain or body damage.

In humans, the diving reflex is not as pronounced as in marine mammals. The factors enhancing the diving reflex in humans include

  • Water temperature Colder water creates a more profound response that may be more protective to the brain.
  • Age Younger victims have a more active reflex.
  • Facial immersion Cold-water stimulation of the face triggers the pathways necessary for these responses.

Although the diving reflex can protect humans in cold-water immersions, it may confuse rescuers into thinking that a victim is dead.

Using CPR in accordance with your training, start resuscitative efforts for these victims immediately. Numerous children have been brought up from freezing water after 30 minutes and successfully resuscitated.



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