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Revision as of 20:56, 9 February 2004 by Mark.murphy (talk | contribs)(diff) ← Previous revision | Latest revision (diff) | Newer revision → (diff)Decompression sickness, DCS or the bends is caused by breathing nitrogen at high pressure so that it is adsorbed into the tissues of the body in high concentrations and then reducing the pressure without allowing the adorbed gas time to safely leave the body through the lungs. It typically happens to SCUBA divers who do long, deep dives without slowly ascending and making the necessary decompression stops.
Cause
When air under high pressure is breathed for any length of time, nitrogen dissolves in the body fluids in higher than usual concentration (Henry's Law). Moving the body to a lower pressure causes the gas to come back out of solution, and form bubbles in the blood. The physiologist J.S. Haldane studied this problem in the early 20th century, eventually devising the method of staged, gradual decompression, whereby the pressure on the diver is released slowly enough that the nitrogen comes gradually out of solution without forming bubbles. Repeated cases of decompression sickness can lead to brittle bones. Severe cases can lead to death because large bubbles can impede the flow of oxygen-rich blood to the brain and other vital organs.
Treatment
The is only one final treatment of decompression sickness: recompression in a hyperbaric chamber.
A useful first aid treatment is to breath high concentrations of oxygen: either pure oxygen or a rich nitrox.
Avoiding decompression sickness
Decompression tables and dive computers have been developed that help the diver choose the depth and duration of decompression stops for a particular dive profile at depth.
History
An alternative name is caisson disease; this name comes from the 19th century, when large engineering excavations (bridges, tunnels) required the work to be done in "caissons" under pressure to keep water from flooding the excavations. This was a major factor for laborers working on the Brooklyn Bridge, and incapacitated the project leader Washington Roebling.
Helium
Because helium has a far lower solubility in water, nitrogen decompression sickness can be avoided by using other breathing gases such as heliox and trimix instead of air. Unfortunateley there is a Helium decompression sickness, which takes longer exposure to helium before it becomes a problem. Helium is mainly used in breathing gases to reduce nitrogen narcosis.
Other conditons
Air embolism and decompression sickness have very similar symptoms because they are both the result of gas bubbles in the body. In a diving context, the two are often called decompression illness or DCI.
Other diving disorders, due to breathing gases, experienced by divers are nitrogen narcosis and oxygen toxicity.