Diffusion+of+Gases

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 * = Diffusion =
 * Diffusion is the process by which the molecule of a substance transfer through a layer or area such as the of a solution. e.g. In the lungs, gases diffuse a cross a gas - Liquid barrier which is Alveolar-capillary membran.
 * ==Fick`s Law ==
 * the rate of diffusion of a substance across unit area is proportional to the conc. gradient. of the substance.
 * e.g. Pulmonary Diffusion Capacity & CO Transfer test ( the rate of CO uptake standardized according to the tension gradient of CO.
 * ==Solubility: ==
 * the greater solubilityof the gas in the liquid, the greater will be the conc. gradient. So the diffusion of the gas across a membranof a liquidis thus proportional to its solubility in the liquid. e.g. ( CO2 VS O2 )
 * ==Graham`s Law ==
 * ( Effect of Molecular Size ): the rate of diffusion of a gas is inversely proportional to the sequare root of its molecular weight. The molecular movement of liquids is much slower & more limited than in the case of gases.
 * e.g. It is important to inject the local anesthetic close to the nerves concerned, because diffusion allows only limited penetration of the local anesthetic into the tissue.
 * ==More practical aspects of diffusion: ==
 * Diffusion of Isoflurane into & through rubber tubing system of the ventilator into the OR atomsphere.
 * Diffusion of N2O into nitrogen bubble in the tissue in Decompression sickness which will aggravate the condition.
 * Expansion of Pneumothorax by diffusion of N2O.
 * Diffusion of N2O into the cuff of ETT, so increasing the pressure on the tracheal mucosa
 * ==Summary ==
 * <span style="font-family: Arial,Helvetica,sans-serif;">Diffusion is proportional to the tension gradient and, because solubility has a pronounced effect on tension gradients, this in turn affect the rate of diffusion.
 * <span style="font-family: Arial,Helvetica,sans-serif;">Diffusion also depends on the membrane (thickness, area & constituents)
 * <span style="font-family: Arial,Helvetica,sans-serif;">Diffusion is affected by the molecular size, the larger sized molecules diffusing less rapidly than smaller ones & liquids diffusing less rapidly than gases.

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