Monday 23 March 2009
Decompression disease is encountered in deep-sea divers and underwater workers who spend long periods in caissons or tunnels, under increased atmospheric pressure. The injury, encountered with too rapid decompression, is a function of Henry’s law, which in essence states that the solubility of a gas in a liquid (e.g., blood) is proportional to the partial pressure of that gas in the environment.
As the underwater depth and consequent atmospheric pressure increase, increasing amounts of oxygen and accompanying gases (nitrogen or helium) dissolve in the blood and tissue fluids. Once ascent begins (decompression), the dissolved gases come out of solution and form minute bubbles in the bloodstream and tissues.
Coalescence of these bubbles produces even larger masses capable of becoming significant emboli in the bloodstream. The oxygen bubbles are soluble in blood and tissues and so redissolve. The nitrogen and helium dissolve only slowly.
Periarticular bubbles produce the bends. Bubbles formed within the lung or gaseous emboli give rise to respiratory difficulties, with severe substernal pain referred to as the chokes. Various central nervous system manifestations may appear, ranging from headache and visual disturbances to behavioral disorientation. Involvement of the inner ear may produce vertigo and the staggers.
All these manifestations may appear within hours of the too rapid ascent, but skeletal manifestations-caisson disease of bone-may sometimes appear days later. These take the form of foci of aseptic necrosis, typically of femoral and humeral heads, and medullary foci, particularly in the lower femur and upper tibia, attributed to embolic occlusion of the vascular supply.