NAUI Master Scuba Diver 122 Diving Physiology Pulmonary Overinflation Rupture of the Alevolar Lining Pulmonary Interstitial Emphysema Arterial Gas Embolism This section covers barotrauma of your lungs, middle ear spaces, sinuses, air spaces behind dental fillings, and gastrointestinal tract. Lung Barotrauma Most forms of lung barotrauma occur when something blocks air from leaving your lungs on ascent through existing air passages (figure 4-12). The air will make its own holes. Another (rare) form of lung barotrauma, thoracic squeeze, is not due to ruptured alveoli, but rather too much compression at extreme depth during free diving without scuba. Lung overpressurization can result from a pressure change as small as slightly over one meter, or about four feet. In lung overexpansion barotrauma, expanding air that you do not exhale expands your lungs, specifically your alveoli. If expansion continues, your alveoli can rupture, letting air out. What happens next depends where the air goes - air embolism, diving emphysema, or pneumothorax (figure 4-11). The most common way to get a lung overpressure injury is if you hold your breath during an ascent after breathing compressed air. Less commonly, lung overpressurization can occur during ascent even if you are exhaling, but have lung ailments or deformities that block some of your airways. Another theorized possibility is that forced, continuous exhalation can collapse your small airways. Air in your alveoli beyond the collapsed airways expands as pressure decreases on ascent, and can lead to ruptures. Air Embolism Bubbles of air escaping damaged alveoli can flow into your arterial circulation. They travel around until they get stuck. Stuck bubbles can block blood flow in arteries in your heart, brain, and other important places, blocking their oxygen supply. Your body starts cascades of chemical and cellular defenses to try to cope with these strange invaders. Blockade of your arterial bloodstream by gas bubbles (emboli) is called arterial gas embolism (AGE), or air embolism. Effects: Effects are dramatic and usually occur within seconds of surfacing. Specifics are determined by the location of the blockage. Blocked circulation to your heart produces symptoms similar to heart attack. Blocked blood flow to your brain produces symptoms like a stroke: dizziness, incoordination, paralysis, convulsions, changes in mental and emotional functioning, unconsciousness, even death. Other organs may be affected, including your liver, spleen, or kidneys. Unconsciousness with no warning may occur in many cases. FIGURE 4-11. LUNG OVERPRESSURE CONSEQUENCES. Pneumothorax (Tension Pneumothorax) Mediastinal Emphysema Subcutaneous Emphysema
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