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meditating photoIn "No Limits," members of the French National Diving team demonstrate their remarkable breath-holding abilities. Lasting up to seven minutes between breaths, members of the team, like Loic Leferme, are able to make increasingly deeper dives. But scientists say there must be some dive limit—a depth at which the human body can no longer withstand the weight of the water. No one knows what that ultimate depth might be, but one renowned dive physiologist suspects Leferme and his contemporaries might be dangerously close to it.
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Anatomy of a Dive

The high water pressure divers experience at extreme depths can injure the heart and lungs in a number of ways—some of them lethal.


Dr. Claes Lundgren, Director of the Center for Research in Special Environments at the University of Buffalo Medical School, studies what happens to the human body during flight, space travel and diving. According to Lundgren, the high water pressure divers experience at extreme depths can injure the heart and lungs in a number of ways—some of them lethal.

lung illustration
  At 33 feet below the surface, water pressure collapses the lungs to just half their normal volume

What actually happens to the human body during a deep dive? Even at shallow depths, the water pressure can cause a squeezing sensation in our ears and sinuses. During a deep dive, this pressure can really stack up. For every 33 feet a diver descends, the weight of the water column above increases by 15 pounds per square inch. As pressure increases, the spongy tissue of the lung is compressed, leaving the free diver with only a small fraction of the air inhaled at the surface.

The Dive Response

A number of biological factors kick in to help divers like Leferme survive at 450 feet below. An ancient reflex, called the dive response, actually alters the distribution of blood in the body. Vessels in the limbs constrict, shunting blood away from muscles and towards the oxygen-needy heart and brain. The heart rate also slows, limiting the body's rate of oxygen consumption. Additionally, smooth muscles in the spleen contract, squeezing out extra oxygen-carrying red blood cells.

photo of Loic smilling
Loic Leferme makes record-breaking dives thanks to rigorous training and the "dive response"  

No one knows for sure why land-dwelling creatures display the dive response, but, according to Lundgren, it is present in all vertebrates—even triggered in fish stranded on dry land.

"It turns out to be a valuable survival tool," says Lundgren. "It's well developed in human infants. There was a movement for many years to train toddlers to swim, but it turns out you don't need to train them. It's their instinct to hold their breath, eyes open, and paddle to the surface."

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