The resistance of breathing, therefore is primarily controlled by the airway diameter. This leaves the only variable in the equation that physiologically adjusts to be the diameter of the airway. The viscosity of air does not change, and the length of the airway does not change. Looking at the math involved, it is important to make some basic assumptions. Resistance = 8(viscosity of air)(length of the tube)/(3.14)(radius of the tube)^4 However, this is more of a balance of chest wall elastic recoil, which tries to increase lung volume, and the lung’s elastic properties, which are trying to decrease lung volume.Īirway resistance is based on the physics principle of Ohm’s law where: Surface tension is reduced by type II pneumocyte cells within the lung which produce a liquid secretion composed of approximately 40% dipalmitoylphosphatidylcholine, 40 % other phospholipids, and 20 % other lipids.Ĭhest wall compliance is similarly based on elastic properties. A high surface tension tends to cause alveoli to collapse and not expand with aeration. The surface tension of the alveoli describes the ease at which the alveoli are allowed to expand. When stretched, how easily and forcefully does the tissue return to its original configuration? Elasticity is controlled by the content of elastin (stretchy fibers) and collagen (stiff structural fibers) within lung tissue. Lung compliance = 1/elastance or change in lung volume/change in lung pressureĮlastic properties are best exemplified by rubber bands.
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