The radiographic detection of acute pulmonary oedema. A comparison of radiographic appearances, densitometry and lung water in dogs

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Abstract
Acute pulmonary edema was induced in upright anesthetized dogs by increasing pulmonary microvascular permeability or by extracellular fluid volume overload to determine the sensitivity and specificity of the radiograph to the presence of abnormal lung water. Radiographs were taken before and after development of edema. At the end of the experiment, the inflated lungs were removed and frozen in liquid N and examined macroscopically in the frozen state. The extravascular water/dry lung weight ratio was measured gravimetrically on 7 portions of each lung. Final radiographs were examined by 2 radiologists with and without the base-line films for comparison. The change in opacity of the films was directly measured with a radiographic densitometer. When a dog''s mean extravascular water/g dry lung was increased by more than 35% it was invariably recognized, in 1 or more zones, as definite edema. Control dogs were reliably recognized as normal when base-line films were used but the distinction between normal and minor degrees of edema could not be made without the base-line films. There was a positive correlation between radiological grade and lung water, but a great deal of overlap between grades. Densitometry was not a sensitive or reliable method for diagnosing or quantifying edema. Edema was usually associated with a decrease in volume of the lower lung zones.