From humans to the primitive, egg-laying platypus, all mammals are born with something called a diving reflex, also known as the mammalian diving reflex or diving response. It’s a clever physiological mechanism enabling our body to manage and tolerate lower levels of oxygen when underwater.
We’re all born with a number of primitive reflexes, primitive reflexes are reflexes that originate in the central nervous system and are lost as we grow. They are exhibited in normal babies and are apparent when stimulated in particular ways. We have covered many primitive reflexes in past weeks:
Palmar grasp reflex in week 24 – here we looked at the “hanging Babies from a stick” experiments!
Parachute reflex in week 37 – when we found out why babies exhibit a skydiving-like posture in certain circumstances.
Babkin Reflex in week 46 – here we uncovered how to turn your child into a human Pez dispenser!
Swimming reflex in week 64 – we discovered that babies will “swim” from birth!
Asymmetrical tonic neck reflex in week 72 – we got wind of your baby’s ninja skills!
This week we’re not looking at a primitive reflex, meaning that it won’t disappear as we age. In contrast, the diving reflex stays with us throughout our lives, but similar to primitive reflexes, it is more strongly exhibited in babies, especially between birth and 6 months old. Its effects lessen and change as we age, but it stays with us and is used to the advantage of free divers.
To find your inner dolphin, just hold your breath underwater and let your dive reflex take care of the rest. Holding your breath underwater has the nice sounding term – wet apnoea, apnoea simply means not breathing. Holding your breath on dry land will, as studies have shown, not trigger the same physiological response that makes the dive reflex so interesting.
There are two key things that happen when your dive reflex kicks in – Bradycardia and peripheral vasoconstriction; both of these enable our body to manage and tolerate lower levels of oxygen.
Bradycardia – a slow heart rate. Typically a human heart rate slows down by 10-30% and when trained, this can rise to more than 50%. This response is triggered when your face comes into contact with water, the colder the water the quicker and greater the response.
Peripheral vasoconstriction – The constriction of the blood vessels in your extremities. Following immersion in water, blood flow is reduced in limbs and skin to allow the body to focus its oxygen to the most vital oxygen sensitive organs, the heart and brain.
Babies, until the age of 6-months-old, have an extra ability stacked onto their dive reflex. They have a physiological difference in the way their windpipe, by the vocal chords, works. If we were to take in water, whilst underwater, it would enter our lungs. However, if you were less than 6-months-old, the spontaneous closing of this part of the airway ensures no water can enter the lungs and instead, it would go straight into your stomach.