What is the Mammalian Dive Reflex

What is the Mammalian Dive Reflex

Ask the average person on the street to try and hold their breath and the majority can barely hold it for no more than a few seconds without feeling as though they will pass out while experiencing an intense urge to breathe.

Yet there are many throughout the world who have developed the ability to extend their breath hold, or stay in Apnea, for extended periods of time.

Freedivers are probably best known for this ability but the common lay person would not know why.

This ability is common in Whales, Dolphins and Seals and humans can tap into this ability to a certain extent.

This is due to something called the Mammalian Dive Reflex. It is a unique set of evolutionary adaptations inherent within all mammals from a time when all life developed in the oceans. 

This reflex is triggered when a mammal’s face comes in contact with or is submerged in cool water. When this occurs, a number of fascinating physiological changes take place within the body to conserve oxygen and energy. 

Information is sent through the face and transmitted to the brain and the autonomic nervous system through the vagal nerve, resulting in the following: 

  1. A reduction of the heart rate (bradycardia).
  2. Blood flow begins to constrict in the extremities and directs it towards the vital organs, including the heart, lungs, and brain – all of which are fueled by significantly higher amounts of oxygen than other peripheral organs (peripheral Vasoconstriction).
  3. This is why the lungs (and other organs) don’t crush nor explode while freediving.  As the lungs compress with water pressure, the blood vessels around the alveoli expand with blood to compensate for the reduced volume of the lungs. This is also why freedivers train diaphragm and rib cage flexibility, because without these two factors lung barotrauma can occur, when blood can actually enter the lung cavities (blood shift).
  4. The spleen, after a few dives (with pressure), will contract and release more red blood cells, increasing its oxygen carrying capacity, which allows longer breath-holds and dives (The spleen effect). Fascinating fact, it’s been discovered that tribes in Papua New Guinea (who can dive with no equipment for over 10 minutes), have abnormally big spleens, which has been genetically modified over time through evolution)

The mammalian diving reflex is an evolutionary adaptation and is essential to being able to remain underwater for extended periods of time, it can be developed and strengthened over time to improve diving performance through experience and intentional/directed practice.