What is the Mammalian Diving Reflex?

The mammalian diving reflex is a phenomenon that occurs in mammals when they are submerged in cool water below 21 degrees centigrade (or 70 degrees fahrenheit), in which the body’s natural cardiovascular responses are altered to maintain cerebral and cardiac blood flow. It has been hypothesized that the mammalian diving reflex has been used by mammals over centuries of evolution to enable them to reach greater depths in streams and oceans, while hunting and gathering food.

Mammalian Diving Reflex

When the face of a mammal (this includes humans) is submerged in cold water and the process of normal breathing is ceased, the following physiological responses occur in order to improve cerebral perfusion and cardiac blood flow:

1.  The larynx spasms.

2. The heart rate slows to conserve energy.

3. Blood vessels constrict in order to shunt blood through to the vital organs of the body (heart and brain).

Through the mammalian diving reflex the colder the water temperature the more oxygen is shunted (diverted) towards the heart and brain.

Mammalian Diving Reflex In Children

In children the mammalian diving reflex is more significant due to the following reasons:

1. They have a much smaller body surface area and will become hypothermic much faster.

2. Their metabolic needs are often higher than an adult.

For paramedics, the concept of the mammalian diving reflex becomes important when attempting to resuscitate a patient who has had a near drowing event. Persons who ordinarily would have been pronounced dead on the paramedic’s immediate arrival otherwise, may actually have a good chance of resuscitation due to the mammalian diving reflex.

Mammalian Diving Reflex and Medicine

The principles of the mammalian diving reflex has been used in medicine in the treatment of multiple injuries and illnesses including the following:

1. The rapid infusion of cold hartmans solutions (RICH) trial in which patients in cardiac arrests were infused with high doses of cold hartmans to reduce the patients core body temperature. Although, strictly speaking, this is not triggering the mammalian diving reflex, the principles of its benefits, are based on the mammalian diving reflex.

2. To this day, one treatment available for neonates who have a run of SVT (which is a pre-terminal event in neonates) are dipped head first in a cold bucket of water in order to artificially stimulate the mammalian diving reflex and therefore reduce the heartrate. The mammalian diving reflex is known to reduce the heart rate by 25%.