NAUI Master Scuba Diver 114 Diving Physiology the situation. Ascend normally to the surface, if necessary, to be sure you do not have ill effects while under water. Prevention: Don’t hyperventilate. If you find you hyperventilate frequently without meaning to, see your physician for screenings for the various problems behind it, such as anxiety or pulmonary and cardiac disease. Don’t hyperventilate deliberately before free diving. Inhale and exhale normally only a few times before free diving. Dive with a buddy system and emergency plan. Overexertion Overexertion is more than just a respiratory problem, of course. The major factor in overexertion is being out of shape for the task. Other factors include using a poorly maintained or designed regulator, wasted effort by using inefficient kicking mechanics, and becoming too cold or overheated. Effects: Labored breathing, and sometimes anxiety, lead to a deteriorating spiral of cause and effect under water. If you are struggling, you may need air at a higher rate than some regulators can provide, producing air hunger and possibility of panic. First Aid: Stop activity, rest, and allow your breathing to gradually return to normal. In a current where you cannot stop, find something to hang on to until you catch your breath. Prevention: Get in shape. Swim with fins regularly. Plan your dive and precheck conditions, currents, and the weather. Start your dive upcurrent so you can ride back when you are tired. Pace your efforts to avoid overexertion. Hang a trail line from the boat to grab if you overshoot the boat in strong current. Have your main and secondary regulators serviced regularly according to manufacturer’s specifications. Carbon Monoxide Toxicity Carbon monoxide (CO) is a poisonous gas. CO is directly toxic to your body, and stops your blood from carrying oxygen and carbon dioxide. It used to be popular to describe carbon monoxide toxicity as simply a matter of CO combining with your hemoglobin (making carboxyhemoglobin), preventing your hemoglobin from carrying oxygen. The situation is far more serious. CO enters your tissues and stops vital functions inside your cells. Because of that, the conjecture that increased pressure of oxygen at depth would offset carbon monoxide toxicity is not valid. Your cells are killed by more than hypoxia. Partial pressure of CO increases with depth, providing more molecules of CO with each breath from a contaminated tank. Since your number of hemoglobin molecules does not change, effects of CO increase with depth. Concerning the conjecture that increased pressure of oxygen at depth would keep the binding ratio of hemoglobin to oxygen the same as at lesser pressure negating those effects, your hemoglobin binds CO 200 to 300 times more readily than O2. CO and O2 compete for binding sites on your hemoglobin, but it is a mismatched competition. Your hemoglobin also holds on to carbon monoxide tightly - too tightly in fact. It is difficult and time consuming to get the carbon monoxide back out of you. CO has time to work its serious harm. CO leaves your body in half-time fashion, just like nitrogen. At sea level breathing regular air, it takes about five and a half hours before half the CO leaves your body, and another five and a half Normal Oxygen Level Level of Gases Time Blackout Oxygen Carbon Dioxide Normal Level Limited Hyperventalation Excessive Hyperventalation FIGURE 4-6. HYPERVENTILATION AND SHALLOW WATER BLACKOUT
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