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The decompression of a diver is the reduction in ambient pressure experienced during ascent from depth. It is also the process of elimination of dissolved inert gases from the diver's body, which occurs during the ascent, during pauses in the ascent known as decompression stops, and after surfacing until the gas concentrations reach equilibrium. When a diver descends in the water the hydrostatic pressure, and therefore the ambient pressure, rises. Because breathing gas is supplied at the same ambient pressure as the surrounding water, some of this gas dissolves into the diver's blood from where it is transferred by the blood to other tissues. Inert gas continues to be taken up until the gas dissolved in the diver is in a state of equilibrium with the breathing gas in the diver's lungs; at this point the diver is ''saturated''. On ascent, the ambient pressure is reduced, the inert gases dissolved in the tissues are then at a higher concentration than the equilibrium state and start to diffuse out again, possibly forming bubbles, which may lead to decompression sickness, a possibly debilitating or life-threatening condition. It is essential that divers carefully manage their decompression to avoid bubble formation and decompression sickness. A mismanaged decompression usually results from reducing the ambient pressure too quickly, allowing the dissolved inert gases such as nitrogen or helium to form bubbles in the blood and tissues in a manner similar to the fizzing of a carbonated beverage when opened. These bubbles may block arterial blood supply to tissues or cause tissue damage. If the decompression is effective, the asymptomatic venous microbubbles present after most dives are eliminated from the diver's body in the alveolar capillary beds of the lungs. If they are not given enough time, or more bubbles are created than can be eliminated safely, the bubbles grow in size and number causing the symptoms and injuries of decompression sickness.〔 Divers breathing gas at ambient pressure may need to make one or more decompression stops on ascent according to a set of decompression tables. A diver who only breathes gas at atmospheric pressure when free-diving or snorkelling will not usually need to decompress but it is possible to get decompression sickness, or taravana, from repetitive deep free-diving with short surface intervals.〔 Divers using an atmospheric diving suit do not need to decompress. The mechanisms of bubble formation and the damage bubbles cause has been the subject of medical research for a considerable time and several hypotheses have been advanced and tested. Tables and algorithms for predicting the outcome of decompression schedules for specified hyperbaric exposures have been proposed, tested and used. Although constantly refined and generally considered reliable, the actual outcome for any individual diver remain slightly unpredictable but although decompression retains some risk, this is now generally considered acceptable for dives within the well tested range of normal diving. Nevertheless, all current decompression tables advise a 'safety stop', usually of five minutes at 3 or 5 metres, even on a continuous no-decompression ascent. The immediate goal of controlled decompression is to avoid development of symptoms of bubble formation in the tissues of the diver, and the long-term goal is to avoid complications due to sub-clinical decompression injury. Decompression may be continuous or staged. A staged decompression is interrupted by decompression stops at calculated depth intervals, but the entire ascent is actually part of the decompression and the ascent rate is critical to harmless elimination of inert gas. A no-decompression dive, or more accurately, a no-stop decompression, relies on limiting the ascent rate for avoidance of excessive bubble formation. The elapsed time at surface pressure immediately after a dive is also an important part of decompression and can be thought of as the last decompression stop of a dive. It typically takes up to 24 hours for the body to return to its normal atmospheric levels of inert gas saturation after a dive.〔 When time is spent on the surface between dives this is known as the "surface interval" and is considered when calculating decompression requirements for the subsequent dive. == Decompression theory == (詳細はinert gas component of breathing gases from the gas in the lungs to the tissues of the diver and back during exposure to variations in ambient pressure. In the case of underwater diving and compressed air work, this mostly involves ambient pressures greater than the local surface pressure—but astronauts, high altitude mountaineers, and occupants of unpressurized aircraft, are exposed to ambient pressures less than standard sea level atmospheric pressure. In all cases, the symptoms of decompression occur during or within a relatively short period of hours, or occasionally days, after significant exposure to low pressure. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「decompression diving」の詳細全文を読む スポンサード リンク
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