free divers use a weighted sled to descend quickly, then
inflate an airbag to shoot back to the surface
dive response also helps combat the effects of high pressure
on a diver's body. Though the water pressure compresses the
lungs, the extra blood shunted to the heart and lungs expands
the blood vessels in the chest, balancing the forces.
"A diver will be all right," says Lundgren, "as long as the
amount of pressure inside keeps in step with the pressure
do not yet know how far down the body can maintain this balancing
much blood can move in before you start bleeding into your
lungs?" Lundgren asks. "It's not unheard of for deep divers
to cough up blood when they get to the surface. I think these
divers are very close to the limit."
At the critical depth, bleeding into the lungs could
become excessive, causing permanent damage.
physiologists have yet to determine this "limit,"which
likely varies among individualsthey do know what could
happen to the unlucky diver who passes it. At the critical
depth, bleeding into the lungs could become excessive. According
to Lundgren, it's unlikely that such bleeding would result
in immediate death, but it could cause irreversible damage.
Similarly, lung edema, the leakage of clear blood plasma into
the lungs, is a serious occurrence.
can tell it has happened when a diver coughs up foam, often
tinged with blood," says Lundgren. "This is most often observed
in spear fishers, who repeatedly dive quite deeply, are really
close to their limits."
seriously, the redistribution of blood from the limbs to the
body's core puts an unhealthy load on the heart muscle. The
muscle tissue could become overly distended, resulting in
permanent damage. Or, the strain of all that extra blood could
cause the heart to beat irregularly, which can be fatal.
diver could die right there and then," says Lundgren.
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