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WINTER 2014
RESEARCH, EDUCATION & MEDICINE
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F R O M T H E M E D I C A L L I N E
increase in risk associated with fast ascent rates. You
may be surprised to learn that 60 feet per minute
was the “fast” rate. Having said that, though, it is
important to realize that a uniformly slow rate may
be counterproductive since this can prolong inert-gas
loading in the deeper phase of the dive.
One strategy that considers relative pressure change
would be to maintain a standard ascent through
something less than the first half of the pressure
reduction (ascent), and then to progressively slow
from there to the point of performing a shallow stop
to benefit the fastest tissues (lungs, blood, then brain).
For example, the depth with one-half the pressure of
100 feet is 33 feet. It could be a reasonable strategy to
start slowing the ascent around 40 feet and ascending
progressively slower until you halt the ascent at around
15 feet. There is no magic number for the best stop
duration. One minute might be OK for a short, low-
effort dive; two to three minutes (or more) might
be reasonable if there was greater work involved.
It is important to bear in mind that safety stops by
design provide extra cushion — conservatism — in
the exposure. Missing them does not guarantee a bad
outcome. At the same time, not having a problem
following a missed stop does not mean that the stop has
no value. The safety-oriented mindset is one that has
you incorporating comfortable safety factors wherever
feasible to increase the odds of a successful outcome.
Understanding the importance of relative pressure
change is important in managing decompression
stress. Thoughtful ascent from any dive, long or short,
is inexpensive insurance. The fact that you are thinking
about the question weighs heavily in your favor.
— Neal W. Pollock, Ph.D.
Q:
I’m an avid scuba diver and spearfisher.
I’m now pregnant, and as I expected, my
doctor told me I shouldn’t scuba dive. But
I was surprised when he said I should not freedive
either. What’s the logic behind that, or is he simply
overcautious?
A:
Ethical considerations have limited both the
scope and number of studies on pregnancy
and diving (freediving and scuba diving). Most
of the literature that’s available is purely anecdotal or
consists of data collected after
delivery. In the book Women and
Pressure: Diving and Altitude
(Caroline E. Fife, M.D., and
Marguerite St. Leger Dowse, eds.,
Best Publishing, 2010), Maida Beth
Taylor, M.D., cites a retrospective
questionnaire that showed higher
rates of low birth weight, birth
defects, neonatal respiratory
difficulties and other problems
associated with scuba diving during
pregnancy. These data are limited
but sufficient to lead medical
professionals to recommend
against scuba diving while
pregnant or trying to conceive.
The data on freediving and
pregnancy are even more limited.
Most of the research on breath-
hold diving and pregnancy comes
from Ama divers in Japan and
Korea. These female divers are
revered for their diving prowess,
and the Ama tradition dates
back thousands of years. Many of
these divers continue to freedive
