What is the diving reflex?

Your body's reaction to water that prevents you from drowning

(Image source: Pixabay)

The diving reflex is a physiological response triggered by immersion in water that evolved to protect mammals from drowning. It is strongest in aquatic mammals, but it is also present in humans, and means that the airways can be protected so an animal can survive immersed in water for a period of time.

When a mammal is holding their breath and cold water hits their face, sensitive receptors in the nasal cavity relay the information to the brain via the trigeminal nerve. This triggers an abrupt decrease in heart rate and causes the non-major blood vessels to constrict to shift blood flow towards the most important organs – the brain and the heart. Like all reflexes, it is an involuntary and automatic response. Unable to hold their breath intentionally, babies can do so instinctively due to the diving reflex.

What are the rapid responses?

1. Cold water

Facial immersion in cold water, particularly around the eyes and the forehead, are one of the main triggers of the diving reflex.

2. Breath holding

The effects of the dive reflex help conserve oxygen and prolong the amount of time we need between breaths.

3. Heart rate slows

Human heart rate slows down to between ten and 25 per cent to reduce the amount of oxygen the body needs.

4. Blood shifts

Blood shifts as blood vessels close in the outer limbs, forcing blood towards the head and torso to keep the vital organs supplied with oxygen.

 This article was originally published in How It Works issue 103

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