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oxygen (by about 2 percent), but that does not have
anything to do with its reactivity in the body. A
better analogy would be how wood and steel
interact with a magnet. The steel reacts, while the
wood does not.
A helium molecule, on the other hand, is one-third
the size of a nitrogen molecule. Molecule size can
make a difference in passing through some barriers,
but it is almost certainly not the only factor in uptake
and elimination or its nonnarcotic nature relative to
nitrogen. Interestingly, while helium is considered a
fast gas in terms of exchange, it can cause challenges
in decompression, resulting in the need for more
buffering of limits based on expectations of exchange
speed. You may be hearing more about decompression
related to helium in large part because of its increased
use by recreational technical divers. Broadening the
use sometimes brings out new issues not discovered in
more limited traditional use.
As I like to say, physiology does not equal math.
Physiology is much more dynamic. Seemingly logical
ideas, such as size being a critical factor, can be attractive
but do not answer the question. Asking questions,
though, and having a lifelong interest in learning are
critical in getting closer to the elusive truth.
By the way, it is not worth paying to fill your tires
with nitrogen.
— Neal W. Pollock, Ph.D.
Q:
Why does it seem like the answers I
read in
Alert Diver
or on
DAN.orgare
so conservative? You advise caution for
medical issues I would never give a second thought
to when participating in other activities such as
skiing, tennis, basketball or exercising at the gym.
It seems like your organization is afraid for anyone
but the healthiest people to dive.
A:
Many divers have medical conditions and/
or take medications and enjoy diving without
any problems. DAN’s role is to provide
information based on the available literature and
prevailing expert opinions in diving medicine, not to
decide who is allowed or prohibited from diving. We
advise divers (and potential divers) and their doctors
so they can make thoughtful and informed decisions
about diving. Sometimes DAN recommends that
divers or potential divers be evaluated by a physician
who has special training in diving medicine.
Hazards exist in the diving environment that are
not present in most other recreational activities. If
someone playing basketball gets dizzy or short of
breath, he or she can easily stop the activity and rest.
If a medical emergency arises, emergency medical
services are readily available. The underwater world,
however, is unforgiving, and problems can increase
the risk of drowning. Shortness of breath, for example,
does not always resolve with rest while underwater
because of the increased resistance involved in
breathing through a regulator. It is important to
remember that when scuba diving we are using life-
support equipment to explore an environment not
conducive to human survival.
— Scott Smith, EMT-P
Q:
I recently returned home from a two-week
liveaboard dive trip. After experiencing
some initial motion sickness while adapting
to the motion of the boat, I had a wonderful trip. At
the end of the trip, however, I felt like the dock was
rocking when we disembarked. I was queasy and
almost vomited. This feeling continued for nearly a
week before resolving. Why did this happen?
A:
While we cannot say with certainty what caused
your symptoms, you may have been suffering
from condition that’s known by various names
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