Sadly not anymore. Although all life originated from water, we've gradually lost many of our biological ties with it. But there is still one astounding evolutionary adaptation slumbering in all of us: The mammalian diving response or dive reflex We share it with whales, dolphins, seals, penguins and the likes. While they need it to function in their everyday life, it is designed as a survival mechanism to us. However, we do not benefit from its effects merely in an emergency, but as well when diving on breath hold = freediving a.k.a. apnea.
Initial stimulus
Facial immersion in water or even just facial contact with water; the colder, the faster the reaction. The receptors in the face, especially on the forehead and around the nose, are connected to the trigeminal nerve. Said nerve transmits the information to the brain, which stimulates the vagus nerve. This results in the immediate closure of the airway as well as a number of physiological changes to optimize the body’s oxygen management towards conservation.
Additional stimuli: Breath hold, pressure increase Responses 1. Laryngospasm - only in infants up to 6 months: The vocal cords are immediately closing, thereby constricting the windpipe and thus inhibiting water from entering the lungs => prevent drowning. 2. Bradycardia - slowing of heart: The heart is one of the strongest muscles in our body and every heartbeat consumes oxygen. During breath hold our body will naturally slow down the heartbeat by 10-30% (in trained freedivers up to 50%+) to conserve oxygen and consequently extend our time under water. 3. Vasoconstriction - constriction of blood vessels: When our blood vessels constrict, blood flow to our extremities is reduced, thus increasing the concentration of oxygen-rich blood towards our vital organs (lungs, heart and brain). 4. Blood Shift - As a result of the vasoconstriction, blood is shifting from the extremities into the vital organs and chest cavity. The alveoli and capillaries in our lungs become engorged with oxygen-rich blood (= incompressible), which replaces the air space (= compressible) in our lungs. The blood acts as a cushion, preventing our lungs from collapsing when dving deeper than our residual lung volume (~35m+). Blood shift also occurs in the other organs of the body in a similar manner and with the same result. 5. Spleen Contraction - The spleen, an organ that stores red blood cells, contracts up to 20%, thereby releasing red blood cells into our circulatory system. This means that more oxygen can be stored in our blood. Furthermore, the additional blood cells allow the body to resume its normal balance faster after a prolonged breath hold. Life Hack
Calm down your nerves at any time by enabling the mammalian diving response. Simply put a cold wet towel on your face; make sure to cover the forehead and the nose. Because the dive reflex excites the vagus nerve, your heart rate drops and your body starts relaxing. To reinforce relaxation, breathe slowly and deeply in a ratio of 1:2, e.g. inhale for 10sec, exhale for 20sec, if you like you can also add a short pause (= breath hold) after the inhalation.
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