Bends

Bends, in popular usage, name denoting the acute disease known medically as aeroembolism and caused by rapid decrease of the atmospheric pressure. Small bubbles or swellings under the skin characterize the disease, but its most striking symptom is excruciating pain, usually spread over many parts of the body. Temporary paralysis of some part of the body may also occur, and sometimes permanent damage or death may result. Bends is known also as caisson disease, decompression sickness, and diver's disease.

First observed in 1839, the disease soon became familiar to divers and caisson workers who had to work for long periods in compressed-air chambers. The symptoms appeared when those affected were brought back to ordinary atmospheric conditions. The only known cure was to put the victim immediately back into a pressure chamber and then slowly to lower the pressure to normal. The cause of the symptoms was not known.

During World War II airplanes were constructed that would climb within 6 minutes to more than 9000 m (about 30,000 ft), where the atmospheric pressure is less than one-third the normal. Such rapid decompression could easily cause the aviator to be stricken with bends, and so an intensive study of the disease was undertaken. Bubbles of air liberated in the blood vessels were found to block some of the small terminal vessels, cutting off the blood supply of nerve endings and giving rise to the symptoms. Of the gases in the blood, oxygen and carbon dioxide are readily reabsorbed, so that nitrogen is the chief offender. The disease can therefore be prevented or made much less severe by having the aviator breathe pure oxygen not only during flight but for some time before it. In this way the nitrogen is eliminated from the system.