CAISSON DISEASE, or COMPRESSED AIR DISEASE, a disorder occurring among workers in compressed air, who are submitted to a pressure of two or three atmospheres, as in bridge-caissons. The symptoms of the dis ease do not appear while the workman is under compression but come on after decompression when some minutes or even hours have elapsed. The symptoms were at first thought to be due to mechanical pressure which by producing changes in the distribution of the blood caused congestion or blood stases when pressure was removed. This, however, is contrary to the adaptability of body fluids to pressure and does not agree with experimental evidence. The gas emboli theory is now generally accepted. According to this theory blood in compressed air absorbs an increased amount of oxygen and nitrogen which under compression is distributed to the fluids of the various parts of the body. If now rapid decompression takes place bub bles of gas form in the blood more rapidly than the gas can be cast off by the lungs and numerous capillary emboli result. These then cause pain in local regions, either by direct or mechanical force, or by cutting off the local blood supply. There may be more or less gen eral pain involving two or three or all of the extremities and sometimes severe abdominal pain with prostration, which in some cases re sult in unconsciousness, collapse and death.
These symptoms are due to the presence of cord or brain lesions, the result of the gas em boli in the blood supply to the central nervous system. Vertigo with deafness and occasional labyrinthine hemorrhage are sometimes pres ent and probably point to embolism in the laby rinth. Dyspncea and sense of constriction in the chest are also sometimes_present but are not fatal. The most successful treatment is that of recompression with gradual decompres sion carried on in a medical air-lock. This is now required by law in some countries. Pro phylactic measures are carried out by careful examination of the workman and elimination of those unfitted for work in compressed air. Predisposing factors are youth or too ad vanced age, alcoholism, organic disease and fat ness. New men should be given a short shift and workmen should be carefully supervised. Fatigue is also a factor. Certain countries and states already have laws regulating shifts and providing for gradual decompression, gauged according to the pressure undergone, which are the chief preventive measures.