PRESSURE - in it. As the pressure in the jar is gradually...

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PRESSURE-VOLUME RELATIONSHIPS: In the pulmonary physiology absolute pressure means atmospheric pressure (760 mm Hg at sea levels). The pressures and the pressure differences of the respiratory system are expressed as relative pressures to the atmospheric pressure. When it is said that alveolar pressure is zero, it means that alveolar pressure = atmospheric pressure. If one excises animal lung and places it in a jar, one could measure the changes in volume with a spirometer through a cannula attached to the trachea. When the pressure inside the jar below atmospheric pressure, the lung expands and the change in its volume is measured and the pressurevolume curve is plotted. When there is no pressure distending the lung there is a small volume of gas
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Unformatted text preview: in it. As the pressure in the jar is gradually reduced, the volume of the lungs increases. This is initially a rapid event but after a certain pressure the changes become less evident. It means that the lung is stiffer when it is expanded and thereby, the pressure-volume curves during inflation and deflation are different = hysteresis . Another important point is the volume at a given pressure during deflation is always larger than during inflation. Even when the pressure outside the lung is increased above the atmospheric pressure, very little further air is lost and the air is trapped in the alveoli. The volume of the air trapped in the lung is increased with age and in some respiratory diseases...
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This note was uploaded on 11/08/2011 for the course BIOLOGY BSC1086L taught by Professor Leostouder during the Fall '10 term at Broward College.

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