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Use Less Air
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You
think your air consumption is low? Maybe, but
compared to the experts at the game, the whales,
porpoises and seals who make their livings where
air is scarce, you are a disgrace. You blow off
that precious resource like a teenager with a
sudden inheritance.
Consider the documented record for the longest
dive on a single lungful of air: one hour, 52
minutes, set on Aug. 25, 1969, by a sperm whale.
If that whale's lungs were average, they were
about half the size of yours in proportion to
its body. As if you had only one lung. How long
do you think you could stretch one lung of air?
A minute?
OK, not a fair comparison. After millions of
years of practice holding their breath, whales
should be better at it than you and I. Among its
natural advantages, a whale has lungs able to
exchange 80 to 90 percent of their volume with
each breath while humans exchange only 10 to 15
percent. Having more myoglobin, whales are able
to store three to 10 times as much oxygen in
their muscles as humans can. With bigger red
blood cells, and twice as many of them per
liter, their blood can store much more oxygen,
too. Their mammalian diving reflex is more
pronounced, so they are better able to shut down
parts of their body that would otherwise waste
oxygen. By contrast, we humans are like cars
designed for a world of free gasoline.
Though whales have a long head start, you can
take a few baby steps down their evolutionary
road and use your limited air supply more
efficiently. Not only will a tank last longer,
you'll feel less tired and more relaxed at the
end of a dive. To begin with, you can extract
more value from each breath by taking deeper
breaths when you inhale and forcing out more
carbon dioxide when you exhale. You'll never
reach the whale's ability to replace 80 to 90
percent of its lung volume with each breath, but
you can do a lot better than you are now.
Breathe Deeply
It's
probably not obvious why taking deep breaths
should make your limited air supply last longer.
Whales take their deep breaths directly from the
atmosphere, after all. If 80 cubic feet is all
you have to draw on, won't it last longer if you
just sip at it? My bank balance certainly seems
to.
Some divers try to save air by deliberately
taking short, shallow breaths, breathing from
the top half of their lungs. But they end up
wasting air, not saving it. The reason is that
they're retaining and building up carbon
dioxide, and it's too much carbon dioxide, not
too little oxygen, that triggers the urge to
take the next breath.
"When you're breathing at a higher lung volume
and taking a fairly shallow breath, you retain
more carbon dioxide, which gives you more of a
ventilatory drive," says Dr. Richard Vann, vice
president for research at Divers Alert Network.
"You'd be better off ventilating a higher tidal
volume and exhaling closer to your residual
volume. In other words, blow out the carbon
dioxide."
Short, shallow breaths leave more than 85 to 90
percent of your lungs filled with carbon
dioxide-rich "dead air." All that carbon dioxide
itches to get out, so you're forced to take
another breath before you actually need the
oxygen. You draw air you don't need from your
tank, cycle it through the top half of your
respiratory system just to pick up the carbon
dioxide most urgent to escape, and dump it into
the ocean.
Don't believe it? I wasn't sure I did either, so
I tried an experiment. I measured my surface air
consumption using a digital pressure gauge and a
stopwatch. I tried it first breathing as slowly
and deeply as I could, and then taking short
breaths on half-full lungs. Both times, I tried
not to take another breath until I felt the urge
to do so, as if I were trying to conserve air.
The result? When breathing slowly and deeply, 50
psi lasted 30 percent longer. Short, shallow
breathing burned through the air faster.
Admittedly, this was a "shade-tree" experiment
that might not pass muster with the National
Science Foundation, so take it for what you
think it's worth. It suggests to me that short,
shallow breaths don't save air and that you can
almost certainly stretch that 80 cubic feet by
inhaling deeply, by holding that air in your
lungs for a moment or two for maximum gas
exchange (use your diaphragm instead of closing
your throat), and then exhaling as completely as
you can so you expel as much carbon dioxide as
possible.
Your carbon dioxide level can rise before you
know it. Maybe because you're kicking hard. Or
maybe you're just breathing hard. One of the
dangerous aspects of short, shallow breathing is
that it's a vicious circle. The shallower and
faster you breathe, the more carbon dioxide you
generate just sucking on the reg. So you suck
harder. "Basically, it's suffocation," says
Vann. "It's a scary experience. You're
hyperventilating, but you're always ventilating
your upper airways and not exchanging gas." It
takes constant attention to keep your breathing
slow and deep because it's not natural under
stress. If your pattern of breathing changes,
try to slow down and calm down.
Two warnings, however. There's such a thing as
too little carbon dioxide, too, so don't
exaggerate the slow, deep breaths to the point
of hyperventilation, which can lead to blackout
because you suppressed too far the urge to
breathe. And slow, deep inhales followed by
slow, complete exhales may cause you to rise and
fall a few feet in the water column. When
pinpoint depth control is important--when you're
hovering over fragile coral for a photo, for
example--you'll have to take shorter, quicker
breaths not to disturb your buoyancy.
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