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| == Other conditions == | == Other conditions == | ||
| ] 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 ], due to ]es, experienced by divers are ] and ]. | Other ], due to ]es, experienced by divers are ] and ]. | ||
Revision as of 12:28, 26 February 2004
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 ambient pressure without allowing the adsorbed 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 decompression stops needed to eliminate the nitrogen normally.
Air embolism and decompression sickness have very similar symptoms and treatment because they are both the result of gas bubbles in the body. In a diving context, the two are often called decompression illness.
The bends is a slang term describing a specific symptom of decompression sickness: when a bubble forms in a joint, typically the elbow, pain is experienced from that joint. The pain may be reduced by bending the joint to find a more comfortable position.
Avoiding Decompression sickness is not an exact science. Accidents can occur after relatively shallow and short dives. There are many additional risk factors, such as, age, obesity, fatigue, use of alcohol and Patent foramen ovale.
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.
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
Nitrogen is not the only breathing gas that causes Decompression Sickness. Helium causes a decompression sickness, involving helium rather than nitrogen bubbles, which occurs when gases such as heliox and trimix are breathed at depth.
If a whole dive were carried out on a Helium-rich breathing gas, the decompression stops required would be much longer than those of an air dive. Helium decompression can be accelerated by breathing Nitrox or pure oxygen, if in very shallow water, during the decompression phase of the dive.
Helium is mainly used in breathing gases to reduce nitrogen narcosis.
Sources: Diving Fizziology
Other conditions
Other diving disorders, due to breathing gases, experienced by divers are nitrogen narcosis and oxygen toxicity.