Decompression Sickness - Causes

Air is primarily a mixture of two gases, oxygen and nitrogen. The oxygen we breathe in is used by cells in our bodies to metabolize (burn up) food. The nitrogen has no function in our bodies. Most of it is expelled from the body when we breathe out. Some of it is absorbed into our body tissues and our bloodstream.

As a person goes underwater, pressure increases on his or her body. The deeper one goes, the greater the pressure. This increased pressure forces more and more air into the body. All gases become more soluble (dissolve better) as pressure increases. Increased pressure causes no problem with oxygen, which is used up by the body. But it can cause problems with nitrogen. Deep under water, where the pressure is high, much more nitrogen dissolves in blood than it does at the surface.

Decompression sickness occurs when a person returns to the surface after being deep under water. When that happens, pressure on the person's body decreases. Nitrogen begins to come back out of the blood. If the person comes to the surface slowly, there is no problem. The nitrogen gas can escape from the blood slowly and be exhaled.

If the person comes up too quickly, however, a problem can develop. Nitrogen begins to form tiny bubbles as it escapes from the blood. The bubbles cannot be exhaled through the lungs. Instead, they can block blood vessels, push on nerves, and cause other disturbances in the body.

The amount of risk for DCS depends on the depth to which a person has gone under water. The deeper the dive, the greater the risk. To avoid decompression problems, divers may need to stop one or more times on their way back to the surface. Charts developed by the U.S. Navy and other groups list the number of stops and the time to be spent at each stop. When these directions are followed, nitrogen has time to escape from the bloodstream normally. Bubbles do not form, and DCS does not occur.

A number of factors can increase the risk of DCS for divers. For example, people who are overweight or who have recently had alcohol to drink are at greater risk for DCS. Also, people planning to fly or travel to high-altitude locations after diving are at increased risk for DCS because they experience further decompression at higher altitudes. Experts recommend that individuals wait between twelve to twenty-four hours after a dive before flying or traveling to high altitudes.