Mechanics of edematous lungs.
Using the parenchymal marker technique, we measured pressure (P)-volume (P-V) curves of regions with volumes of approximately 1 cm3 in the dependent caudal lobes of oleic acid-injured dog lungs, during a very slow inflation from P = 0 to P = 30 cmH2O. The regional P-V curves are strongly sigmoidal. Regional volume, as a fraction of volume at total lung capacity, remains constant at 0.4-0.5 for airway P values from 0 to approximately 20 cmH2O and then increases rapidly, but continuously, to 1 at P = approximately 25 cmH2O. A model of parenchymal mechanics was modified to include the effects of elevated surface tension and fluid in the alveolar spaces. P-V curves calculated from the model are similar to the measured P-V curves. At lower lung volumes, P increases rapidly with lung volume as the air-fluid interface penetrates the mouth of the alveolus. At a value of P = approximately 20 cmH2O, the air-fluid interface is inside the alveolus and the lung is compliant, like an air-filled lung with constant surface tension. We conclude that the properties of the P-V curve of edematous lungs, particularly the knee in the P-V curve, are the result of the mechanics of parenchyma with constant surface tension and partially fluid-filled alveoli, not the result of abrupt opening of airways or atelectatic parenchyma.
Wilson
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Department of Aerospace Engineering and Mechanics, University of Minnesota, Minneapolis 55455, Minnesota, USA. wilson@aem.umn.edu
Anafi
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Hubmayr
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D000399:Air Pressure; D000465:Algorithms; D000818:Animals; D004285:Dogs; D008168:Lung / Q000503:physiopathology*; D008176:Lung Volume Measurements; D008954:Models, Biological; D011650:Pulmonary Alveoli / Q000502:physiology; D011654:Pulmonary Edema / Q000503:physiopathology*; D012121:Respiration, Artificial; D015656:Respiratory Mechanics / Q000502:physiology*; D013500:Surface Tension