decompression sickness, physiological disorder caused by a rapid decrease in atmospheric pressure, resulting in the release of nitrogen bubbles into the body tissues. It is also known as caisson disease, altitude sickness, and the bends. It is an occupational hazard of persons who work under greatly increased atmospheric pressure below the surface of the earth (e.g., divers and laborers who work under compressed air) when their return to normal atmospheric pressure is made too quickly. When the body is subjected to high atmospheric pressure the respiratory gases are compressed and larger amounts are dissolved in the body tissues. During ascent from depths greater than 30 ft (9.1 m), these gases escape as the external pressure decreases. Airplane pilots who go rapidly from normal atmospheric pressure to high altitudes (low atmospheric pressure) in unpressurized aircraft or in aircraft with faulty pressurizing apparatus also encounter the disorder. The decrease in air pressure releases body nitrogen in the form of gas bubbles that block the small veins and arteries and collect in the tissues, cutting off the oxygen supply and causing nausea, vomiting, dizziness, pain in the joints and abdomen, paralysis, and other neurological symptoms. In severe cases there may be shock, total collapse, and, if treatment is not prompt, death. Persons who work under increased atmospheric pressure must make the ascent to normal atmospheric pressure gradually, often through pressurized chambers, a procedure that allows the nitrogen to be released slowly from the blood and expired from the lungs. Inhalation of pure oxygen aids in clearing nitrogen from the body. Those who suffer symptoms of decompression sickness at high altitudes (commonly called aeroembolism) experience relief on returning to an atmospheric pressure normal to them; this and oxygen inhalation will usually effect recovery.

also called the bends or caisson disease

Harmful effects of rapid change from a higher- to a lower-pressure environment. Small amounts of the gases in air are dissolved in body tissues. When pilots of unpressurized aircraft go to high altitudes or when divers breathing compressed air return to the surface, external pressure on the body decreases and the gases come out of solution. Rising slowly allows the gases to enter the bloodstream and be taken to the lungs and exhaled; with a quicker ascent, the gases (mostly nitrogen) form bubbles in the tissues. In the nervous system, they can cause paralysis, convulsions, motor and sensory problems, and psychological changes; in the joints, severe pain and restricted mobility (the bends); in the respiratory system, coughing and difficulty breathing. Severe cases include shock. Recompression in a hyperbaric chamber followed by gradual decompression cannot always reverse tissue damage.

Learn more about decompression sickness with a free trial on Britannica.com.