Decompression Sickness

DECOMPRESSION SICKNESS, a term used to designate diseases that are dependent on a decrease in ambient pressure. The animal organism usually withstands very significant atmospheric pressure (about 760 mm of mercury) due to the fact that this pressure is balanced by the osmotic pressure inherent in cells and tissues, as well as by the pressure of gases located in body cavities. The effect of a local decrease in external pressure can be observed when using dry cupping glasses. The skin is sucked in by the cup, cutaneous vessels dilate, and hyperemia occurs, accompanied by limited hemorrhage into the skin per diapedesin. With the rapid release of ascites through a puncture of the abdominal wall with a trocar, the decrease in pressure affects mainly the labile vessels, primarily the veins of the abdominal cavity. Their rapid expansion can cause collapse due to the depletion of blood in functionally important organs. With a general decrease in external pressure, phenomena occur that are caused by a disturbance of osmotic equilibrium and the stretching of the walls of cavities. With slow rarefaction of the atmosphere, these phenomena are not sharp: a person can tolerate atmospheric rarefaction down to 192 mm Hg, corresponding to an altitude of 11,650 m, provided that a mixture of O₂ and CO₂ is inhaled in certain quantitative ratios. Without observing this condition, when ascending above 4,000 m, symptoms of mountain sickness (see) occur, the origin of which depends both on the decrease in barometric pressure and, mainly, on the decrease in the partial pressure of oxygen and the resulting insufficient saturation of blood hemoglobin with oxygen. Likewise, the complex symptom complex characteristic of aviators' disease (see Aviation hygiene) largely depends on the relatively rapid decrease in atmospheric pressure and the corresponding decrease in the partial pressure of oxygen. Disorders of cardiac activity are caused by fluctuations in intravascular pressure. Respiratory disorders are apparently dependent on the disturbance of blood gas absorption. Increased frequency and depth of breathing, and increased heart rate to some extent contribute to the improvement of gas exchange. Decompression sickness can be caused by sudden fluctuations in atmospheric pressure during explosions, for example, of grenades. Rapid and significant decreases in previously increased pressure are particularly sharp in their effects. In divers, who are subjected to very significant pressure from the water column, decompression sickness can be observed upon rapid ascent to the water surface (see Diving operations). Likewise, decompression sickness can be observed during caisson work. Upon rapid exit from a caisson, where the pressure sometimes reaches almost 4 atmospheres, sharp phenomena of caisson disease occur (pain in the abdomen and joints, hemorrhages into the skin and lungs, bleeding from the nose and ears). A particular danger is the release in a free state of blood gases that had previously dissolved under higher pressure in greater quantities. Oxygen and carbon dioxide are partially bound chemically, but nitrogen remains in the blood in the form of bubbles and can cause gas embolism, sometimes with a lethal outcome (see Blood gases, Pressure). Gas embolism of the capillaries of nerve tissue, which absorbs significant amounts of nitrogen under increased pressure, causes multiple focal lesions, predominantly of the spinal cord, and causes serious disorders (decompression myelitis, see). For the prevention and treatment of caisson disease, see Caisson operations.