NAUI Master Scuba Diver 116 Diving Physiology Pulmonary oxygen toxicity affects your lungs and can occur after many hours exposed to oxygen partial pressure above (approximately) 0.5 atmospheres. (Normal oxygen partial pressure in the air around you is 0.21 atmospheres.) Pulmonary oxygen toxicity is possible during saturation exposure or long term oxygen therapy. Pulmonary oxygen toxicity is also called the Lorrain Smith Effect, for Lorrain J. Smith, 19th Century scientist who first demonstrated and described the phenomenon. Central nervous system (CNS) oxygen toxicity occurs much more quickly at oxygen partial pressure above a range of about 1.4 to 2.0 atmospheres, or seven to ten times normal. CNS toxicity is also called the Paul Bert (pronounced “bear”) effect, to honor the French physiologist who first described it. Effects: Tolerance to high partial pressure of oxygen varies greatly from diver to diver and from day to day. Pulmonary oxygen toxicity primarily targets your lungs, producing chest pain and coughing. CNS toxicity targets your central nervous system nerves, which produces nausea, abnormal vision or hearing, breathing difficulty, anxiety, confusion, fatigue, incoordination, twitching of your face, lips, or hands, and convulsions. Convulsions can appear without warning and can lead to air embolism and drowning. First Aid: End your dive. Symptoms reverse when partial pressure of oxygen drops upon ascent. Get trained medical care. Bring a diver who has convulsed to the surface and administer oxygen while transferring to medical care. The convulsion itself is not dangerous, but drowning or air embolism are possibilities if a convulsing diver loses the regulator mouthpiece. Prevention: Diving to ordinary recreational diving depths while using regular compressed air does not increase the oxygen environment to toxic levels. Established depth, time, and equipment guidelines exist for technical dives using mixes with various oxygen percentages. Learn and understand the guidelines well, through course work and training, before using any oxygen enriched mixes. Wear adequate thermal protection to avoid chilling. Breathe normally, and keep your equipment in good working order to avoid increased work of breathing. Drowning and Near Drowning Near Drowning is suffocation by submersion, with at least 24 hours of survival. In contrast, drowning is death within 24 hours of suffocation by submersion. Based on dog studies, it was formerly thought that a major problem from drowning in humans was changes in your blood chemistry, depending whether you drowned in fresh or salt water. That was found not to apply to humans, who have different blood chemistry than dogs. In humans, the major problem from drowning is lack of oxygen, whether or not you inhale water. Water striking your larynx shuts it in reflex spasm (laryngospasm), which is great to keep water out of your lungs, but can cause suffocation, like choking on food. In a small percentage of drownings, it is hypothesized that laryngospasm will shut off your ability to inhale until you lose consciousness. You do not inhale water, but drown from lack of air. This is sometimes called dry drowning. But water can get past your defenses, into your lungs. It seems that most people inhale water during the drowning process, both initially and while losing consciousness. When water (or any other fluid or solid) enters your lungs, many effects occur. Cells lining your alveoli can become damaged and your lung tissue becomes inflamed and stiff. Water can wash away important surface agents covering your alveoli. These surface active agents (shortened to surfactants) reduce surface tension, and without them, the normal tensions in your lungs collapse your alveoli. Alveoli that are collapsed or filled with fluid can’t transfer oxygen to your blood. Your body cells suffocate and die. Lack of oxygen to your brain and lungs, water in your lungs, and loss of surfactant, cause a longer process of fluid accumulation (edema) in your lungs and brain. Fluid building up in your lungs can lead to pneumonia or an often fatal condition called secondary (or late) drowning (figure 4-7). Death can also occur from the effects of hypoxia even if you survive the initial incident. Effects: Labored breathing, pale, cool skin, and confusion. In severe cases there may be unconsciousness, cyanosis (blue skin), no breathing, or no pulse. Permanent brain damage is likely after only four to five minutes of hypoxia, but the time may sometimes be lon
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