Arterial Venous rupture. The best technique is to maintain normal lung volume during your ascent by breathing normally. As long as you breathe normally during ascent, there is little danger of suffering a long overexpansion injury. It is essential that you always breathe whenever you are under water on scuba. During your course, you will learn a variety of techniques for dealing with out-of-air emergencies. Knowing how to deal with an out-of-air emergency will help avoid a lung overexpansion injury. Note Divers who smoke have a higher risk of suffering a lung overexpansion injury due to lung damage from smoking. There are three general types of lung overexpansion injuries: air embolism, pneumothorax, and tissue emphysema. Air Embolism The most serious result of a lung overexpansion injury is an air embolism or arterial gas embolism Chapter 4- Diving Science (AGE). The word embolism means plug and an air embolism refers to a plug of air in the bloodstream (figure 4-28). The greatest danger in this situation is that a plug of air will block the flow of blood to the brain. An air embolism can cause unconsciousness, paralysis, permanent brain damage, and even death. It is one of the most serious of all diving accidents. Pneumothorax If a lung ruptures, and the escaping air gets into the pleural lining surrounding the lungs, the escaped air can cause a condition known as a pneumothorax, which is a collapsed lung. This is not fatal by itself, but it is painful, can lead to serious complications, and requires immediate medical attention. Tissue Emphysema If air from a ruptured lung escapes into the chest cavity below the breastbone, it causes a condition known as a mediastinal emphysema (air in the middle tissues). In this case, the air is around the heart, and expansion of the air will cause pressure on the heart and the large blood vessels leading into and out of the heart. Diving Science 113 Circulation of Air Sac Airway Air Sacs (Alveoli) FIGURE 4-27. THE INSIDE OF YOUR LUNGS RESEMBLE STALKS OF BROCCOLI. Bubbles block circulation (Air embolism) Ruptured air sacs (Breath held while ascending) FIGURE 4-28. IF A LUNG RUPTURES AND INTRODUCES AIR INTO THE BLOODSTREAM, IT CAN CAUSE A BLOCKAGE CALLED AN AIR EMBOLISM.
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