Nitrogen, Dissolved blood

Divers now breathe a mixture of oxygen and helium instead of the oxygen-nitrogen mixture of ordinary air. Nitrogen dissolves in a diver s blood and causes the "bends helium will not dissolve to such an extent. 

Sample preparation 1 mL Whole blood + 1 mL 50 mM pH 6.6 KH2PO4, vortex, add 6 mL diethyl ether, shake at 150 20 oscillations/min on a reciprocating shaker for 15 min, centrifuge at 1500 g for 10 min. Remove the organic layer and evaporate it to dryness at 37° under a stream of nitrogen. Dissolve residue in 200 xL mobile phase, centrifuge at 1000 g for 3 min, inject a 40 p,L aliquot of the supernatant. 

For example, when a diver at a depth of IS m or so breathes in conqnessed air from a supply tank, more than normal nitrogen dissolves in the blood and other body fluids due to the higher pressure at that depth. When the diver ascends quickly, the partial pressure decreases and the excess dissolved nitrogen escapes forming bubbles in the bloodstream. These bubbles restrict blood flow and cause death. This condition is known as " bends , A mixture of helium-oxygen is used in conqnessed gas tanks in recent times, instead of air (oxygen-nitrogen. mixture) as the solubility of helium is very low in blood. 

The Determination of Dissolved Nitrogen in Blood by Gas Phase Chromatography Biomedicine 26(2) 122-130 (1977) CA 87 49563w... 

Gas Chromatographic Determination of Small Volumes of Nitrogen Dissolved in Blood... 

Another consequence of the effect of pressure on gas solubility is the painful, sometimes fatal, affliction known as the bends. This occurs when a person goes rapidly from deep water (high pressure) to the surface (lower pressure), where gases are less soluble. The rapid decompression causes air, dissolved in blood and other body fluids, to bubble out of solution. These bubbles impair blood circulation and affect nerve impulses. To minimize these effects, deep-sea divers and aquanauts breathe a helium-oxygen mixture rather than compressed air (nitrogen-oxygen). Helium is only about one-third as soluble as nitrogen, and hence much less gas comes out of solution on decompression. 

The volume of blood in the body of a certain deep-sea diver is about 6.00 L. Blood cells make up about 55% of the blood volume, and the remaining 45% is the aqueous solution called plasma. What is the maximum volume of nitrogen measured at 1.00 atm and 37°C that could dissolve in the diver s blood plasma at a depth of 93 m, where the pressure is... 

Scuba divers experience similar pressure changes. The amount of air dissolved in the blood increases significantly as the diver descends. If a diver returns to the surface too quickly, nitrogen gas dissolved in the blood forms bubbles in the same way as the CO2 in a freshly opened carbonated drink. These bubbles interfere with the transmission of nerve impulses and restrict the flow of blood. The effect is extremely painful and can cause paralysis or death. The bubbles tend to collect in the joints, where they cause severe contractions. This is the source of the name of this dangerous condition—the bends . 

Divers avoid the bends by returning to the surface slowly, taking short decompression stops at intermediate depths to allow excess gas to escape from their blood without forming bubbles. Another way divers reduce the risk of the bends is by using helium-oxygen gas mixtures instead of compressed air. Helium is only half as soluble in water as nitrogen is, so less gas dissolves in blood. 

Deep-sea divers breathe compressed air. Nitrogen is not very soluble in blood at normal pressures but at great depths, when the divers bodies are exposed to very high pressures, the nitrogen becomes more soluble. The dissolved nitrogen comes out of solution rapidly when the divers return to the surface, and numerous small bubbles form in the bloodstream. These bubbles can burst the capillaries—the narrow vessels that distribute the blood—or block them and starve the tissues of oxygen... 

A helium-oxygen mixture is used in diving gas instead of compressed air (nitrogen-oxygen). If air were used, nitrogen would dissolve in the diver s blood at the high underwater pressures and would be released as painful bubbles when the diver returned to the surface. 

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