The ability of a gas to stay in solution is greater when its partial pressure is higher and when it has higher solubility in water. For example: more CO2 is dissolved in blood plasma because the solubility of CO2 is 24x greater than the solubility of O2. The air we breathe contains ~ 79% N2 and this gas has little or no effect on body functions and very little dissolves in blood plasma because of its low solubility at sea level. As total air pressure increases, all the partial pressures of the individual gases increase. For example: When a scuba diver breaths air under high pressure the N2 in the mixture can have serious side effects. Since the partial pressure of N2 is higher in mixture of compressed air then air at sea level, a considerable amount of N2 dissolves in blood plasma and interstitial fluid. This produces “giddiness”, and other symptoms of alcohol intoxication. This condition is called Nitrogen Narcosis. If the diver comes to the surface slowly, most of the N2 can be exhaled. However, if the ascent is too rapidly (pressure drops), N2 comes out of solution too quickly and forms gas bubbles in the tissues resulting in Decompression Sickness.
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