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NAUI Scuba Diver 116 Diving Science exertion. You must learn to breathe slowly and deeply whenever you use scuba gear. What Happens When You Inhale Water Any time you are in the water, whether you are free diving, on scuba, or swimming, the possibility exists that you will get a mouthful of water when you least expect it. This commonly happens to swimmers, and sometimes happens to divers. Even a few drops of water can cause you to cough or choke. Keep your regulator in your mouth and choke or cough right through the mouthpiece. You can also sneeze through your regulator. You can almost eliminate choking as a problem if you always inhale cautiously when taking your first breath after clearing your regulator or snorkel. If you do inhale a little water, cough and swallow repeatedly. Do not ascend when coughing or choking. Coughing and choking or your response to it can close your airway and ascending could cause a lung overexpansion injury. Verify What You Have Learned Review the following questions about your lungs and breathing: 24. Lung expansion injuries are caused by ________________________ or _________________________. 25. Lung volume should be kept as ____________________ as possible during your ascent from a dive. 26. The stimulus to breathe is the amount of __________________ in your blood. 27. When you are breathing on scuba, you should breathe ___________________ and __________________________. 28. If you should choke, cough, or sneeze while diving, you should __________________________. INDIRECT EFFECTS OF PRESSURE The primary effects of pressure are physical changes that are easy to see and experience. Other, more subtle, effects from pressure are just as important to your safety under water. These indirect effects of pressure impact divers by means of the gases in the air we breathe while diving. Ingassing and Offgassing When you breathe in and out, the air you breathe is 78% nitrogen. Nitrogen is a metabolically inert gas, which means that your body does not use it. However, nitrogen is absorbed and dissolved in your bloodstream and tissues. The pressure of nitrogen is balanced between the air and your body. This state is called equilibrium. Under increased pressure, the air you breathe is denser and the partial pressure of nitrogen you inhale with each breath is increased. Therefore, the pressure of nitrogen in the air you are breathing is greater than the pressure of nitrogen in your body. Your body ingasses nitrogen until the partial pressure of nitrogen in the air you breathe is equal to the pressure of nitrogen in your body. When you ascend, the pressure decreases, and the partial pressure of nitrogen decreases. Now the pressure of nitrogen in your body is greater than the partial pressure of nitrogen in the air you are breathing. To compensate, your body offgasses nitrogen until the nitrogen is balanced between the air and your body. Decompression Sickness A problem called decompression sickness (DCS) can occur if you absorb a great deal of nitrogen and then ascend too quickly. It takes time for nitrogen to enter your body and it takes time for the nitrogen to leave your body. When you ascend your body begins to eliminate nitrogen. If too much is still present after you surface, the excess nitrogen forms bubbles in your body (figure 4-31). There are different types of DCS. Each type has its own symptoms. When bubbles form in your blood, they can create microscopic clots that impair your circulation. When


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