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Health Matters
Dr Anke Fabian looks at the risks of dehydration
this summer and offers her advice on what divers
can do to stay wet.
summer is the best time to go diving in the egyptian red sea and Children divers are more susceptible to dehydration than adults
resorts attracts millions of scuba tourists over this period from June because they have smaller body weights and higher turnover of water
through to september. ironically, even while surrounded by a whole and electrolytes. the elderly and those with illnesses are also at higher
ocean, a diver is always at risk of running out of water. Dehydration risk.
cases are naturally at their highest at this time.
Causes of dehydration:
Dehydration (hypohydration) is
• summer in egypt means high air
defined as excessive loss of body
temperatures, warm water, sun-exposure.
water. it can be caused by losing too
this intensifies perspiration and sweating
much fluid, not drinking enough
topside and underwater, especially while
liquids, or both. not having enough
handling heavy equipment in a full wetsuit
fluid in the system can cause major
or direct sun exposure.
problems, as water is crucial for
the functioning of our biophysical
• Fluid loss through breathing compressed
systems and biochemical processes.
Children divers are more susceptible to
air from a scuba cylinder is also a major
in physiological terms, it entails a
dehydration than adults because they have
factor. a scuba diver loses the most fluids
this way. moisture tends to flow from wet
relative deficiency of water molecules smaller body weights and higher turnover of
to dry areas. as the cylinder contain air
in relation to other dissolved water and electrolytes.
(or other gas mixes), which is drier than at
solutes (blood cells). the viscosity
the surface, our exhaled air underwater
is increased - the blood is literally
contains a lot of moisture.
getting ‘thicker’. this is detrimental to the haemodynamic flow
characteristics of the blood circulation.
• Diuresis means an increased production of urine by the kidneys.
every diver has probably experienced the effect of water pressure on
in the blood cell count, we would see an increased “hematocrit (the
the functioning (or over-functioning) of the kidneys causing the urge
volume of red blood cells in the blood). some definitions even require
to urinate underwater. the so called ‘immersion diuresis’ is caused
a rise in blood sodium concentration (normal range 15-147 mmol/l),
by immersion of the body in water and mainly triggered by lower
but in reality a loss of body water usually accompanies a loss of solutes
temperature and by pressure. it is independent of the depth. Both
as well.
factors cause a centralisation of the main blood circulation from the
periphery of the limps to the core, in differently mechanisms. this
Hypovolemia is specifically a decrease in the volume of blood plasma.
means the body detects a rise in blood pressure and inhibits the
Furthermore, hypovolemia defines water deficiency only in terms
release of a certain hormone (vasopressin), causing an increase in the
of volume rather than specifically water. the hematocrit would be
production of urine.
normal. nevertheless, the conditions usually appear simultaneously.
issue 2 august / september 2009
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