decompression

Last reviewed 01/2018

• 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

Reference:

• 1) Edge CJ. Recreational diving medicine.Current Anaesthesia Critical Care 2008; 19 (4): 235-246.