injuries and poisoning
Decompression Sickness
Introduction
Decompression sickness is a disorder in which nitrogen dissolved in the blood and tissues by high pressure forms bubbles as pressure decreases. Symptoms can include fatigue and pain in muscles and joints. In the more severe type, symptoms may be similar to those of stroke or can include numbness, tingling, arm or leg weakness, unsteadiness, vertigo (spinning), difficulty breathing, and chest pain. People are treated with oxygen and Recompression Therapy (high-pressure, or hyperbaric, oxygen) therapy. Limiting the depth and duration of dives and the speed of ascent can help with prevention. (See also Overview of Diving Injuries .) Air is composed mainly of nitrogen and oxygen. Because air under high pressure is compressed, each breath taken at depth contains many more molecules than a breath taken at the surface. Because oxygen is used continuously by the body, the extra oxygen molecules breathed under high pressure usually do not accumulate. However, the extra nitrogen molecules do accumulate in the blood and tissues. As outside pressure decreases during ascent from a dive or when leaving a compressed air environment, the accumulated nitrogen that cannot be exhaled immediately forms bubbles in the blood and tissues. These bubbles may expand and injure tissue, or they may block blood vessels in many organs—either directly or by triggering small blood clots. This blood vessel blockage causes pain and various other symptoms, for example, sometimes similar to those of a stroke (such as sudden weakness on one side of the body, difficulty speaking, or dizziness), or even flu-like symptoms. Nitrogen bubbles also cause inflammation, causing swelling and pain in muscles, joints, and tendons. The risk of developing decompression sickness increases with many of the following factors: Certain heart defects, such as Atrial and Ventricular Septal Defects None Cold water Dehydration Flying after diving Exertion Fatigue Increasing pressure (that is, the depth of the dive) Length of time spent in a pressurized environment Obesity Older age Rapid ascent Failure to follow appropriate decompression procedures Because excess nitrogen remains dissolved in the body tissues for at least 12 hours after each dive, repeated dives within 1 day are more likely to cause decompression sickness than a single dive. Flying within 12 to 24 hours after diving (such as at the end of a vacation) exposes people to an even lower atmospheric pressure, making decompression sickness slightly more likely. Nitrogen bubbles may form in small blood vessels or in the tissues themselves. Tissues with a high fat content, such as those in the brain and spinal cord, are particularly likely to be affected, because nitrogen dissolves very readily in fats. Type I decompression sicknesstends to be mild and affects primarily the joints, skin, and lymphatic vessels. Type II decompression sickness,which may be life threatening, often affects vital organ systems, including the brain and spinal cord, the respiratory system, and the circulatory system. 