Page 56 - AlertDiver_Spring2013

Q:I typically dive using enriched air nitrox
(EAN) with a mix that varies according to
planned depths. I also dive with a small
pony bottle as a redundant source of breathing
gas for emergencies. My buddy suggested that
having compressed air in the pony bottle instead
of EAN could potentially place me at risk for
decompression sickness. Is that something I need
to worry about?
A:The theoretical risk of having air in the pony
bottle is that the higher fraction of nitrogen would
increase inert-gas uptake and ultimately increase
the decompression stress. However, since ascent to the
surface should immediately follow a switch to the pony
bottle, the time spent breathing this gas would be short.
In addition, both the partial pressure of the gas being
breathed and the importance of the difference between
the gases progressively fall as depth decreases. While the
ideal choice would be to have EAN in both systems, the
practical increase in risk by having air in the bailout system
is a very small factor far outweighed by the potential
benefits of having a readily available bailout supply.
— Neal W. Pollock, Ph.D.
Q:I read on the Internet that coral can continue to
grow under my skin. Is that true?
A:No. Coral cannot live in human bodies. Corals are
marine animals and are unable to grow outside of
the marine environment. Some bacteria, parasites
and other foreign organisms evolved to live and replicate
within human tissues, but corals did not.
Although both humans and corals are members of kingdom
Animalia, their tissues and body systems are incompatible.
Histocompatibility is the property of having the same alleles
for a set of genes called the major histocompatibility complex
(MHC). The genes of the MHC exist in the tissues of most
organisms and act as antigens in the presence of incompatible
organisms. Antigens prompt the creation of antibodies by
the immune system of incompatible organisms. In humans,
the MHC is called the human
leukocyte antigen (HLA) system.
Since coral does not have an
HLA, the human immune system
treats it as a foreign substance and
attacks it.
When you are injured,
your body activates, recruits
and increases production of
leukocytes (white blood cells).
This leukocyte production
contributes to the pus that can
accumulate at wound sites and
promotes the elimination of
foreign material. If the body
is unable to eliminate foreign
material (such as coral), it
will wall off the substance
with immune cells, forming a
granuloma. If this occurs, you
may be able to feel a lump under
the skin where the granuloma
formed.
Keep an eye out for infection
(manifesting as redness, swelling,
warmth and pain) with such
injuries, but rest assured that
coral isn’t growing under your
skin. AD
— Niles Clarke, EMT, DMT
54 | SPRING 2013
RESEARCH, EDUCATION & MEDICINE // F R O M T H E M E D I C A L L I N E