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Chapter 13 — 4
Bubbles can form in any tissue in the body including blood. The pressure in each bubble will
be the same as the environmental pressure (if it was not, the bubble would expand or contract
until it was) and the bubble size is governed by Boyle's Law as the pressure changes.
At the onset of DCS, the pressure of N
2
in the tissues is supersaturated (greater than the
environmental pressure) so there is an immediate diffusion (pressure) gradient of N
2
which
then diffuses into any bubbles (or nuclei) present, causing them to expand.
A bubble of DCS contains mainly N
2
if the diver has been breathing air, but the other gases
present in the tissues, such as carbon dioxide (CO
2)
, oxygen (O
2
) and water vapour, also
diffuse into it.
Once a bubble has formed its behaviour depends on several factors. Any increase in pressure
such as diving or recompression will reduce its size while any decrease in pressure such as
ascent in the water, over mountains or in aircraft, will expand it. The bubble will continue to
grow in any tissue until the
N
2
excess in that tissue has been eliminated. Once this has
occurred (which may take hours or days) the bubble will begin to decrease in size but it may
take hours, days or weeks to disappear. In the meantime the bubble can damage the tissues
around it.
Fig. 13.1
There is good evidence that bubbles frequently form in tissues and blood of recreational
divers after routine no-decompression dives, even when the tables have been faithfully
followed. These bubbles do not usually cause symptoms but certainly cause doubt about the
validity of both the decompression tables and dive computer algorithms.
Tissue damage by a bubble results from several factors. Bubbles in the blood obstruct blood
vessels in vital organs such as the brain, while bubbles forming in the tissues may press on
blood vessels and capillaries, obstructing their blood flow. Bubbles in the blood can also
stimulate the clotting process causing the blood to clot in the blood vessels, obstructing blood
flow to vital organs, and reducing the ability of the remainder of the blood to clot adequately.
Many other biochemical and physiological changes with ill-defined sequelae occur in the
tissues and blood vessels during both decompression and DCS. In the brain, spinal cord and
other tissues, bubble pressure in or on nerves may interfere with nervous system functioning.