Mammalian Dive Reflex

In 1949, an Italian air force lieutenant named Raimondo Bucher decided to try a potentially deadly stunt off the coast of Capri, Italy. Bucher would sail out to the center of the lake, take a breath and dive 100 feet to the bottom. Scientist warned Bucher that, according to Boyle’s Law, the pressure at a hundred feet would shrink Bucher’s lungs to the point of collapse and would kill him, but it didn’t happened. In 1962 a Swedish-born researcher working for US named Per Scholander gathered a team of voulenteers, and they found MDR.

Mammalian Dive Reflex or MDR is a reflex in mammals which optimizes respiration to allow staying underwater for extended periods of time. Including human, and this MDR  help human/freediver to dive in minutes (World record is around 11 minutes, 2015).

The effect of MDR when activated is

Bradycardia – The heart slows down. This is the first response to submersion. Slowing the heart rate lessen the need for bloodstream oxygen, leaving more to be used by other organs. This is why splashing cold water on our face make us feel more refresh and calm.

Peripheral Vasoconstriction – The blood moves from the legs and arms to vital organs. When under high pressure induced by deep diving, capillaries in the extremities start closing off, stopping blood circulated to those areas. Start from fingers, hands and feets, then arms and legs; more blood for vital organs.

Splenic Contraction – The spleen releases extra red blood cells, meaning it is possible to carry more O2 in the blood.

Blood Shift – On deep dives the lungs are highly compressed and blood vessels enlarge to fill the space so that the chest not collapse with the pressure.

MDR benefits to freediving :

1.       Extended dive times

2.       Deeper relaxation

3.       Better handling of pressure of depth

4.       Oxygen conservation

MDR will active when the face is submerged, receptors that are sensitive to cold within the nasal cavity and other areas of the face relay the information to the brain and this will activate Bradycardia and Peripheral Vasoconstraction. After a while, CO2 in the body will cause Splenic Contraction to active; the the pressure will cause Blood shift to active. So totally there is 3 triggers that will activate all 4 MDR, the receptors within the nasal cavity, CO2 and water pressure.

The deeper we dive, the stronger and amphibious reflexes becomes. For more detail about the researcher Per Scholander (1962) visit here.