If you are hoping to increase your breath-holding record, then you’re more likely to achieve that underwater than you are on land. Humans and other mammals have evolved some important ‘dive reflexes‘ that allow us to conserve enough oxygen to survive for short periods underwater. Jump into a cold pool, and you will reflexively stop breathing, your heart rate slows down, and blood is redirected to your organs at the expense of your limbs. This is thanks to control centres in the brain stem that detect a decrease in oxygen and the sensation of water on the face. While our dive reflexes cannot compete with those of a seal, even dunking your face in a bowl of cold water is enough to experience a mild form of this reflex.
Your brain is your most expensive organ, requiring up to 20% of your total oxygen consumption. William managed 4 minutes and 9 seconds underwater, by encouraging a relaxed mental state to decrease the brain’s oxygen requirements.
But free diving to 100 metres provides the brain with more bodily challenges than oxygen deprivation alone. As William felt the pressure of the world on his shoulders as thousands of New Zealanders watched his record attempt, so did he feel the pressure of the water on his body. This change in pressure can cause ‘barotraumas’, such a rupturing of the inner ear and sinuses. At extreme depths, the pressure is so high that the concentration of gases in your body (such as nitrogen) are much higher than they normally are. This can lead ‘narcosis‘ that can impair your ability to think and coordinate your muscles – a similar feeling to alcohol intoxication. The jury is still out, but there’s even some evidence that repeated free dives can lead to early signs of brain damage.
But I think perhaps most remarkable of all, is the brain’s ability to overcome panic and fear as it descends into the darkness. Under that kind of pressure, it really is sink or swim (or sink first, then swim?) William didn’t make a new record, this time, but his brain certainly survived an epic challenge.