in man, conditions arising when there is a rapid change in the surrounding air pressure.
When there is an extremely rapid transfer from an atmosphere with higher pressure to one with lower pressure (decompression), the nitrogen dissolved in the tissues is freed, forming bubbles of gas (an average of about one liter of nitrogen is contained in human tissues). Decompression sicknesses as a rule arise at altitudes of 8,000 m or more (for example, in flight crews on long flights) and at great depths (in divers and caisson workers—caisson disease). The intensity of decompression diseases depends on the individual characteristics of the body, the degree of change, and the duration of the stay at high altitude or great depths.
Caisson disease occurs with decompression after a worker has been in a caisson or a diver has been under water. The principal disturbances arising under these conditions (elevated pressure) are caused by the absorption by the tissues of a large quantity of nitrogen. Thus, at normal atmospheric pressure, 100 ml of blood contains 1 ml (1.2 cc) of nitrogen, while at a pressure of 0.3 meganewtons per sq m (3 atmospheres) it contains 3 ml (3 cc). During decompression the nitrogen is changed from a dissolved form to a gaseous form, whereupon the formation of gas emboli is possible.
The manifestations of decompression sicknesses (muscle, joint, and substernal chest pains, itching, “high altitude cough,” autonomic, vascular, and brain disturbances or affection of the peripheral nerves) depend on the number and location of gas bubbles. The most pronounced autonomic disturbances are pallor, sweating, nausea, vomiting, dizziness, and loss of consciousness. “High altitude pains” are a result of the mechanical effect of the gas bubbles on the nerve endings, or of ischemia (local exsanguination) caused by the bubbles formed within the blood vessels. Physical exertion, chilling, and disturbance of blood circulation intensify the pains. The most effective treatment for decompression sicknesses and caisson disease is recompression in a recompression chamber—that is, the patient’s gradual transition from a high pressure atmosphere to a normal one. Decompression sicknesses can be prevented by prolonged adaptation to hypoxia, the use of certain pharmacological substances, and the inhalation of special gas mixtures. Preliminary inhalation of pure oxygen sharply decreases the appearance of decompression disturbances and the intensity of the pains.
REFERENCESIakobson, M. I. Kessonnaia bolezn’. Moscow, 1950.
Armstrong, G. Aviatsionnaia meditsina. Moscow, 1954. (Translated from English.)
N. A. AGADZHANIAN