The diving reflex is initiated when the face, particularly the forehead and nose, comes into contact with cold water. This triggers a series of coordinated responses, including a slowdown of the heart rate (bradycardia), constriction of blood vessels in the extremities (peripheral vasoconstriction), and a shift in blood flow to vital organs (blood shunting). These responses help to conserve oxygen and prioritize its delivery to essential organs such as the heart and brain.
The evolutionary significance of the diving reflex lies in its role in enabling mammals, including humans, to survive in aquatic environments. By slowing the heart rate and reducing blood flow to non-essential muscles, the body can extend the time an individual can remain submerged without breathing. This reflex is particularly pronounced in aquatic mammals like seals and dolphins, but it is also present in humans, albeit to a lesser extent.
To test the diving reflex, an individual can immerse their face in cold water or apply a cold, wet cloth to the face. The expected responses include a noticeable reduction in heart rate and a feeling of cold-induced peripheral vasoconstriction, where the extremities may feel cooler due to reduced blood flow.
In infants, the diving reflex is especially pronounced. Newborns can instinctively hold their breath and exhibit a more pronounced bradycardia when their face is submerged in water. This response is part of the suite of primitive reflexes that help infants adapt to their environment and is thought to be a survival mechanism inherited from our evolutionary past.
As individuals age, the diving reflex remains present but tends to be less pronounced compared to infants. Nevertheless, it continues to play a role in activities such as swimming and free diving, where conserving oxygen is beneficial.