Basic Gas Physics |
Causes of DCI
|
Symptoms of DCI
The two Gas Laws relevant in this context will be familiar to all divers;
Henry's law indicates that the higher the partial pressure of a gas in the blood,
the more of it there will be dissolved in tissues. The amount of nitrogen dissolved
in body tissues is therefore related to time at depth - the 'gas load'.
Boyle's Law means that for a bubble of gas the volume will increase as the pressure
on it decreases.
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Causes of Decompression Illness (DCI)
Bubbles can form in the circulation in a number of ways, including simple misfortune;
It is likely that all divers form bubbles to an extent, but normally the lungs
are able to filter these out so that they do not cause any problems.
An excessive gas load, omitted decompression or rapid ascent may generate more
bubbles than can be filtered so that they pass onto the arterial side of the
circulation and then lodge in vital organs.
Bubbles can also form in the absence of significant gas load by minor degrees
of lung trauma allowing a direct leak into the arterial circulation - the arterial
gas embolism. This is usually a consequence of rapid ascent, and can occur from
as shallow as three metres.
Breath holding on ascent is not always necessary to give rise to this form of
DCI. Technical divers may be prone to in-water DCI due to gas switching and
consequent alteration in gas diffusion.
It is important to remember that diving within tables is not a cast-iron
guarantee of safety.
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Symptoms of decompression illness
Any unusual symptoms starting within 24 hours of a dive should ideally be discussed
with a diving medical specialist or hyperbaric unit.
There is no such thing as a minor bend. Bubbles do not occur singly. Even apparently
mild symptoms may lead on to more serious manifestations if ignored.
JOINT
Limb pain may begin in a joint or anywhere along a limb. It may begin
during decompression or up to 24 hours later. Late complications include a form
of accelerated arthritis called dysbaric necrosis. Pain in the trunk itself
occurring soon after surfacing is particularly worrying - this may indicate
the onset of a severe form of nervous system involvement.
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NERVOUS SYSTEM
Problems in this area can range from seemingly trivial to the catastrophic.
Again, the importance of early recompression is paramount. Symptoms may range
from;
Muscular problems with:
Walking
Grip
Urination
Sensory problems with:
Numbness
Pins and needles
Constitutional symptoms with:
Fatigue
Poor concentration *
Short-term memory loss
Visual disturbances
Confusion
Headache
* Important, but often overlooked
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LUNG
Although rare, the "chokes" is a serious form of DCI. The lungs become
overloaded by bubbles which interfere with their function. The diver usually
presents soon after surfacing with shortness of breath, cough and possibly chest
pain.
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BALANCE
Often initially mistaken for seasickness by divers and doctors
alike, a special form of DCI may affect the balance organ. Symptoms include
vertigo (a sense of spinning), tinnitus (ringing in the ears), nausea and vomiting.
Since similar symptoms can also occur with barotraumas it is important to get
them checked out by a diving medical specialist as soon as possible.
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SKIN
Skin
rashes caused by DCI need to be distinguished from suit squeeze. Although not
dangerous in itself, skin bends show the presence of bubbles elsewhere in the
circulation that may not yet have caused symptoms.
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