This condition is obviously dangerous, painful, and also requires immediate medical attention. A subcutaneous emphysema occurs when air from a ruptured lung collects under the skin, usually of the neck. This condition can cause swelling in the neck, a crackling sound when the skin is probed, voice changes, and difficulty in swallowing. It also requires immediate medical attention. Hyperbaric Treatment If you do suffer an arterial gas embolism, you will need to be treated in a recompression chamber or hyperbaric chamber as soon as possible. The chamber is pressurized to reduce bubble size and restore blood circulation. Then, the pressure in the chamber is released slowly, allowing the gas to move from your bloodstream and out of your body with each of your exhalations. If you have any signs or symptoms of an air embolism, you must seek medical attention at an operational chamber immediately. You should never go back under water to try to relieve the symptoms. Breathing and Circulation Transporting oxygen through your body is a vital function of the circulatory system, and proper gas exchange in the lungs is critical. Each breath begins when your diaphragm moves and your chest muscles pull your ribs out. These motions expand your chest and draw air into your lungs. Breathing in causes the alveoli to fill with fresh air. Oxygen is absorbed through the walls of the alveoli and then through the walls of your capillaries into your bloodstream. This oxygen-rich blood is pumped by the heart through your arteries to your tissues. Your body metabolizes (uses) the oxygen and converts it to carbon dioxide and other waste products. Your circulatory system moves the carbon dioxide through your veins and back to your lungs, where it passes through the walls of the alveoli and out into the air when you exhale. Then the cycle starts again (figure 4-29). At rest, most people exchange a few pints of air with each breath. When you are active, your breathing rate increases. This is your body’s response to the increased production of CO2 created by activity. The harder you exercise, the more air you breathe. Because the cylinders you use for diving hold only a finite amount of air, you can see how exertion uses up your air supply faster than when you are relaxed. How Carbon Dioxide Controls Your Breathing Actually, your breathing rate is not controlled by the amount of oxygen, but by the amount of carbon dioxide, in your bloodstream. Based on input from chemical receptors in parts of your body, your brain senses the carbon dioxide level in your blood and then increases or decreases the muscular activity that controls breathing. The more carbon dioxide you have in your blood, the more you want to breathe. How to Breathe Under Water Because pressure and density are different under water than on land, you must modify your breathing to accommodate these differences. Generally, for maximum efficiency, your breathing should be slightly slower than normal and deeper than you usually breathe (figure 4-30). NAUI Scuba Diver 114 Diving Science Gas exchange in lungs Circulation in body tissues Arterial blood from tissues FIGURE 4-29. YOUR BLOODSTREAM CIRCULATES OXYGEN TO YOUR TISSUES AND REMOVES CARBON DIOXIDE.
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