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One of these openings (foramena) is the Foramen
Ovale existing in the septum (wall) between
the two upper chambers of the heart (the Atria).
Normally all the openings tend to close at
or shortly after birth leading eventually
to the build up of the normal circulatory
system.
In
around 17% of population, the opening between
the right and left atria remains open, a situation
known as Patent Foramen Ovale (PFO), with
minimal or no symptoms at all.
During regular diving practice, micro or silent
bubbles tend to form in the circulation, namely
in the right side of the venous system. This
includes the the right heart chambers and
the pulmonary arteries.
These
bubbles will produce no symptoms in an individual
with normal heart septa as these bubbles are
eventually filtered out at the lungs as long
as the dive profiles regarding times, depths
and rates of ascent are kept within permissible
levels.
In a person with a (PFO) condition who is
apparently normal and healthy, after a normal
dive(s), the gas bubbles, normally existing
in the right (venous) side of the circulation,
find their way to the left (arterial) side
through this opening, (Paradoxical Emboli)
resulting in the risk of Arterial Gas Embolism
(AGE) which is a serious condition.
The amount of gas that passes from the right
to the left side of the heart through that
Foramen Ovale will depend upon: the amount
and size of bubbles circulating in the right
side, the size of the foramen, and the amount
of increase in the right atrial pressure that
will push the blood carrying bubbles to the
left side.This pressure is normally increased
as a result of straining, coughing, sneezing,
and the Trendlenberg position “ feet
higher than the head”, frequently applied
by some people as first aid to DCI cases,
and most importantly Valsalva's manoever currently
practiced by divers to equalize the middle
ears.
Any
heart septal defect (including PFO), will
carry the risk of a embolism and is an absolute
contraindication to diving if discovered early
enough before causing serious damage.
Unfortunately, this defect in divers is only
discovered either accidentally, like during
a regular heart checkup or when the diver
starts to show signs and symptoms of DCI though
carrying out relatively safe dive profiles
and procedures.
The defect is revealed with the means of echocardiographic
studies with bubble contrast tests for the
heart, a rather complicated imaging procedure
and still beyond most screening recommendations.
2.
Dehydration:
Dehydration is one of the major predisposing
factors in the occurrence of DCI as dehydration
leads to an increase in blood viscosity. This
condition reduces the normal perfusion of
tissues in a way that interferes with the
effective elimination of inert gases.
During
diving, there is continuous fluid loss due
to:
1-Perspiration,
especially in hot weather.
2- Humidifying the dry gas that divers breathe
by extracting water vapour from the lungs.
3- Immersion increases urine excretion by
shifting blood from extremities to the core
of the body and giving the stretch receptors
the false feeling that the blood volume has
increased thus enhancing urine formation.
Shifting of blood happens due to closure of
the outside blood vessels (to reduce heat
loss) and abolishing the orthostatic effect
of gravity on circulation.
In
general, dehydration can happen as a result
of:
1.
Inadequate fluid intake with a moderate fluid
loss.
2.
Drinking dehydrating agents like alcohol and
strong coffee and tea.
3.
Dehydrating conditions such as diarrhea and
vomiting.
As
a rule of thumb, drinking plenty of fluids
on a diving vacation should be on top of the
list of dive briefings.
Divers should as well be advised to avoid
drinking dehydrating agents and to avoid diving
when suffering from severe diarrhea or vomiting.
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