THE MAMMALIAN DIVE REFLEX

The mammalian dive reflex is something that all mammals share, and it serves to protect the host’s organs from damage caused by lack of oxygen.

The reflex is triggered when the sensory receptors, especially in the face and head, come into contact with water.

The reflex causes various systems to come into effects. First the heart rate slows to preserve blood oxygen levels. For the average person this can results in and increase of 10 to 30% and up to 50% for trained individuals.

The other survival reflex is to constrict the blood vessels which results in reduced blood supply to the outer extremities thus reserving oxygen for the vital organs.

The dive reflex is only triggered by water and forced breath-holding without water (dry) results in less overall time than a wet breath hold.

An interesting thing also happens during deep dives. A process called “blood shift” allows plasma/water to pass freely throughout the thoracic cavity so its pressure remains stable and the lungs aren’t crushed.

Another cool thing that happens is when under pressure, the spleen releases an emergency supply of blood which further increases blood oxygen supply.

It’s interesting to note that for adults, to trigger the dive reflex breath holding must be present. Infants however don’t need to hold their breath to trigger the response. This lasts in general for up to 12 months in most infants.