when the diver ascends the gas that has dissolved in the tissues will come out of solution to form bubbles of gas in the tissues and in the blood vessels
these bubbles are then transported to the lungs where, in most cases, they are filtered out - this is the process of decompression
if the bubbles cause medical problems for the diver, then the diver is said to be suffering from decompression illness (DCI) which used to be known as caisson disease
gases that are chemically unreactive as far as the body is concerned (e.g. nitrogen, helium and neon) are sparingly soluble in blood - also oxygen, when breathed at high partial pressures, can cause problems on ascent.
there are three types of DCI recognised - "the chokes", "the staggers" and "the bends"
"the chokes" - this was seen in caisson workers - if the decompression procedure was inadequate, then the blood of the workers literally frothed - this was called "the chokes" and proved to be rapidly fatal unless rapid recompression took place
"the staggers" - in this situation the decompression was not so provocative so as to provoke "the chokes" - "the staggers" might lead to severe impairment of the nervous system or death
"the bends" - commonest form of DCI and less severe than "the chokes" or "the staggers"
research into decompression was carried out by the US Navy, leading to the publication of the US navy decompression tables in 1956
these tables indicate the maximum time that the diver may spend at a certain depth with a low risk of DCI after the ascent
these mathematical models have now been incorporated into small computers that can be worn on the wrist by divers
s allows multi-level diving to take place rather than just allowing the diver to dive to one specified depth and then to return to the surface again.
have the advantage that they can be interrogated by the diving doctor when a diver presents to a recompression chamber with the symptoms of DCI - the medical staff can ascertain the dive profiles that the diver has undertaken prior to becoming ill and enables treatment to be tailored accordingly
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