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The “impossible” science of free diving

posted by Jason Kottke   Mar 26, 2015

This article on the science of free diving is fascinating. Boyle’s Law predicted that the human body couldn’t survive depths past 100 feet — after which, the lungs would rupture — but millions of years of evolution has equipped the human body with all sorts of tricks to survive at depths of over 900 feet.

Lundgren, among others, demonstrated how these phenomena might counteract Boyle’s law. He recruited volunteer firemen from a fire brigade in the Swedish city of Malmo, submerged them up to the neck in water, and used a heart catheter to measure the increase in blood circulation in the chest. Lundgren discovered the body was able to counteract the increased outside water pressure by reinforcing vessels in the walls of the lungs with more blood, in much the same way we increase tire pressure by adding more volume of oxygen to the inside of a tire.

Boyle’s Law had not been overturned. Scientists simply hadn’t taken into account the effect this counterforce could exert to allow survival underwater. “A lot of blood, much more than was usually thought, can be transferred from the blood circulation out in the tissues into the blood vessels of the lung,” Lundgren said, placing that amount at about half a gallon. The extra, densely packed blood can act as a bulwark, exerting a counterforce against the increased pressure pushing inward by the water.