Deep: Freediving, Renegade Science, and What the Ocean Tells Us About Ourselves

by James Nestor

Scholander noticed something else: Once his volunteers were underwater, the blood in their bodies began flooding away from their limbs and toward their vital organs. He’d seen the same thing happen in deep-diving seals decades earlier; by shunting blood away from less important areas of the body, the seals were able to keep organs like the brain and heart oxygenated longer, extending the amount of time they could stay submerged. Immersion in water triggered the same mechanism in humans. This shunting is called peripheral vasoconstriction, and it explains how Bucher could dive to below one hundred feet without suffering the lung-crushing effects that Boyle’s law had predicted. At such depths, blood actually penetrated the cell walls of the organs to counteract the external pressure. When a diver descends to three hundred feet—a depth frequently reached by modern freedivers—vessels in the lungs engorge with blood, preventing them from collapse. And the deeper we dive, the stronger the peripheral vasoconstriction becomes.