DYSBARISM - THE MEDICAL PROBLEMS FROM HIGH AND LOW ATMOSPHERIC-PRESSURE

The most serious problems resulting from a change in ambient pressure are pulmonary barotrauma with air embolism and decompression sickness. The small differential pressures used in ventilators at atmospheric p ressure may tear lung tissue and, in diving, deaths have occurred from the expansion of pulmonary gas on an ascent of less than two metres. The bubbles of respired gas that enter the systemic circulation often occlude cerebral arteries and may cause infarction. In decompression s ickness, bubbles form in the tissues from supersaturation of the nitro gen or helium absorbed under pressure. Joint pain-the 'bends'-is assoc iated with gas in particular connective tissue. Serious decompression sickness results from the entry of microbubbles into the systemic vein s. Large numbers of bubbles trapped in the lung cause an acute respira tory syndrome known as 'chokes'. If the lung filter is overwhelmed, or microbubbles pass into the systemic arteries through an atrial septal defect, they may open the blood-brain barrier, affecting brain and sp inal cord function. Untreated, demyelination with relative preservatio n of axons may occur, the pathological hallmarks of multiple sclerosis . Gas bubble disease requires ur ent compression in a hyperbaric chamb er and the use of high partial pressures of oxygen.