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Work done on Breathing (Cont/…) |
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Elastance |
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The tension generated when an elastic tissue is placed under stress is directly related to the stiffness of the tissue and the length by which the tissue is stretched. In other words, the stiffer the tissue, the more force is required to stretch it while the more the tissue is stretched (the larger the volume) the higher is the tension generated. The work required to expand the lungs against its elastic forces is called compliance work. |
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Frictional Resistance |
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Frictional resistance within the lungs is a result of the viscosity of the lung and chest wall structures, called tissue resistance and the resistance due to the sir movement, called airway resistance. |
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Inertia |
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The inertia encountered in the lungs is due to the inertia of the lung and chest wall and air movement. During quiet breathing, the lung and chest wall are accelerated by a very small amount, and thus even though their combined mass is considerable, their overall inertia is small (Force=mass x acceleration). In the case of air flow, the acceleration is large but the mass is low, so even in the case of air, the overall inertia is small. In actual fact the work done against the inertia is less than 5% of total work done during quiet inspiration. On the contrary, this work can be considerable during forceful breathing, as the acceleration can be considerable. |
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