NAUI Master Scuba Diver 124 Diving Physiology a problem called subcutaneous emphysema. The prefix “sub” means under, and “cutaneous” means skin. Effects: Mediastinal emphysema creates substernal (under the sternum) pain, difficulty breathing, swelling, and possibility of collapse due to direct pressure on your heart and great vessels. With subcutaneous emphysema you may have voice changes, crackling under your skin, and difficulty swallowing. First Aid: Administer 100% O2 and transport to a hyperbaric treatment facility. Prevention: Breathe normally at all times when breathing compressed air. Don’t hold your breath on ascent. Ascend slowly. Don’t smoke. Avoid secondhand smoke. Get regular checkups. Pneumothorax Pneumothorax is an infrequent but serious diving malady that occurs when air gets out of your lungs and into the small, normally airless space between your lungs and chest wall. The root word “pneumo” comes from an ancient Greek word for the spirit, which the Greeks of the time believed was drawn in with each breath. Later it came to refer to air itself. “Thorax” means your chest. Normally there is almost no space between the double pleural membrane surrounding each of your lungs (explained in “Respiration”). Lung overexpansion can tear your pleural lining (as can rib cage injury from nondiving events). Air escaping into your normally airless pleural space cannot be either exhaled or reabsorbed and can partially or totally collapse your lung. On ascent, the air in your pleural space expands, further interfering with breathing and circulation. Sometimes, pneumothorax occurs without an obvious injury and is called spontaneous pneumothorax. It may occur from a weakened area in the lung that ruptures and is seen occasionally in young males who smoke. Effects: Chest pain, breathing difficulty, reduced chest movement on the affected side, leaning to the injured side, shock, and cyanosis. First Aid: Administer oxygen and transport immediately to a medical facility, not a hyperbaric chamber. Prevention: Breathe normally at all times when breathing compressed air. Don’t hold your breath on ascent. Ascend slowly. Maintain good health. Don’t smoke. Avoid secondhand smoke. Get regular checkups. Thoracic Squeeze Thoracic squeeze is rare. Thoracic squeeze is an injury of free diving, not scuba, and does not occur at ordinarily achieved depths by people free diving for fun. During free dives, you have no compressed air source to breathe that matches ambient pressure. The air in your lungs compresses with increasing depth. Your lungs cannot compress too far without being damaged. Such damage is a thoracic squeeze, far less common or dangerous than lung overexpansion. For years it was believed lung damage would result from breath-hold dives deeper than five atmospheres (40 m or 132 ft), because your lungs would be compressed below residual volume. However, compression during descent shifts blood from your extremities and abdomen into the blood vessels of your chest. Your lung volume can fall below residual volume without damage. Record breath-hold dives in excess of 130 m (425 ft) have been successfully accomplished. Effects: At some point tissue damage and hemorrhage occur. First Aid: Prompt medical attention. Prevention: Breath-hold diving during snorkeling, with lungs full of air, does not seem to pose a problem. Descending to extreme depths with less than a full breath could possibly produce a lung squeeze. A free diver (or even a scuba diver) who loses consciousness may exhale involuntarily and suffer a squeeze from an unintentional and extremely deep descent. To avoid this, breath-hold dive after full inspiration and do not lose consciousness underwater. Middle Ear Barotrauma Your middle ear is connected to your throat by your Eustachian tube, which drains and ventilates your middle ear (figure 4-13). The opening in your throat is normally closed. Muscles in your throat open it when you swallow. In diving, you use your Eustachian tube to equalize pressure in your middle ear. On descent, you open your Eustachian
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