The Mammalian Diving Reflex (MDR) is a naturally occurring reflex shown
in many mammals. The reflex makes the body reduce it’s heart rate (bradycardia),
reduce blood pressure, and shunt blood from extremities (Seedhouse 1). This has been
discovered to be displayed in many mammals such as whales, seals, penguins, and
even humans (Seedhouse 1). The biggest effect is blood shunting, which cuts blood
from far out extremities such as fingers by as much as 99% and diverts it to vital
organs such as the brain (Wolkomir 1).
The Diving Reflex is thought to have been first observed in the early 1900’s in
animals but it wasn’t believed to exist in humans until the 1950’s. There has been
many studies on the Diving Reflex in humans involving many different variables.
Swedish scientists tested the effect of water temperature and ambient air temperature
on the diving reflex (Schagatay, E, and B Holm). They found that there was an
inverse relationship between heart rate decreasing and water temperature(Schagatay,
E, and B Holm).
Another group of scientists compared the Diving Reflex of males
and females (Ruiz, Jm, Bn Uchino, and Tw Smith). Their research showed that men
generally displayed a greater decrease in heart rate then women when cold water was
applied to the face (Ruiz, Jm, Bn Uchino, and Tw Smith).
In this experiment, the heart rates of several subjects are taken during various
states such as under water, above water, breathing, and holding breath. This was done
in order to deduce if any of the subjects displayed a Diving Reflex. Four variables
were compared: sex, body mass, time, and smoking habit.