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 In
"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.
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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.
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At
33 feet below the surface, water pressure collapses the
lungs to just half their normal volume
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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.
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| Loic
Leferme makes record-breaking dives thanks to rigorous
training and the "dive response" |
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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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