Chapter 4- Diving Physiology Diving Physiology 115 hours for the next 25% to leave, and so on. By breathing 100% oxygen at the surface, the half-time drops to just under one and a half hours. At 3 ATAs pressure in a hyperbaric chamber, the half-time is about 23 minutes. Contamination of your tank air with CO can come from fumes drawn into the air intake of the compressor. These fumes can come from traffic exhaust or from partial combustion of lubricating oil within a compressor not properly operated or maintained. Smoking cigarettes creates carboxyhemoglobin in your blood. The exhaled breath of a smoker can contain more carbon monoxide than the US Navy allows in its compressed air. Effects: Headache, dizziness, nausea, weakness, confusion, greatly reduced exercise tolerance, clumsiness, and bad judgment. You may lose consciousness and stop breathing without warning. Because CO combined with hemoglobin is red, a person suffering CO toxicity is often said to exhibit unnatural redness of lips or nail beds. Redness occurs sometimes, but not always, and would not be well seen underwater where you can’t see much of the color red. A percentage of people who inhale enough CO to become unconscious go on to develop brain or other neurologic damage, even if hyperbaric treatment revives them. First Aid: End the dive. Administer oxygen on the way to a hyperbaric treatment hospital for immediate care. Hyperbaric oxygen greatly reduces the half-life of carbon monoxide, as described above, and directly blocks a destructive process of carbon monoxide, called lipid peroxidation, inside your cells. Prevention: Don’t smoke or inhale secondhand smoke. CO is colorless and odorless. You have no way of knowing if your air is contaminated until you test it. Get your air fills from filling stations that regularly test the air and maintain purity standards. Grade E standards, for example, allow no more than 10 parts per million (10 ppm). Most industry standards call for testing every three months. Several agencies set standards for breathing air, including the Compressed Gas Association (CGA), the National Fire Protection Association (NFPA), and the United States Navy. The Occupational Safety and Health Act (OSHA) regulates commercial dive operations but not recreational operations. Diving industry standards call for air suppliers to adhere to one of the major standards. Small, relatively inexpensive personal CO detectors are available so you can test your own tank air before use. An industry-wide project called AIR AWARE educates recreational divers and filling suppliers about understanding and maintaining air quality standards. You spent a lot of time and money for your diving equipment and education. Be sure to attend to a very important piece of equipment - the air you breathe. Oxygen Toxicity Although it may sound strange, oxygen is toxic to every living thing on the planet. It is a matter of how much oxygen is present for how long before it is a problem. Originally, oxygen was a toxic byproduct of life on the primordial Earth. When enough oxygen accumulated in the early atmosphere, other life forms evolved that could use oxygen. Some organisms still cannot live with any oxygen at all. They are anaerobes. Some anaerobes cause problems to humans, such as gangrene and botulism. Hyperbaric oxygen is one of the treatments for the problems they cause. Other organisms can live in an oxygen atmosphere, and would die without it. Over the eons, they developed defenses against the toxic effects of oxygen. As a human, you have three main defenses. When oxygen tensions increase with increased pressure at depth, your blood vessels constrict to decrease oxygen delivery. Your hemoglobin releases less oxygen to your cells. You also have an entire antioxidant brigade against the oxidizing effects of oxygen free radicals formed at high pressures. Oxygen free radicals are small molecules that form in your body all the time. More form in many situations including exposure to smoke or high oxygen environments. Too much oxygen for too long creates too many damaging free radicals. Although much is still unknown about the mechanisms, it is generally accepted that when these oxygen free radicals overwhelm your system, oxygen toxicity occurs. Oxygen toxicity affects your entire body, but primarily targets your lungs or nervous system depending on the dose.
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