Measurement of pulmonary edema in intact dogs by transthoracic gamma-ray attenuation

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Abstract
The attenuation of the 122 keV gamma ray of cobalt-57 was evaluated across the thorax of anesthetized dogs as a method for following the time course of lung water changes in acute pulmonary edema induced by increased microvascular permeability or increased microvascular hydrostatic pressure. The .gamma.-rays traversed the thorax centered on the 7th rib laterally where the lung mass in the beam path was greatest. Calibration measurements in isolated lung lobes demonstrated the high sensitivity and inherent accuracy of the method over a wide range of lung water contents. In control dogs, reproducibility averaged .+-. 3%. Increased permeability edema led to large, rapid increases in the transthoracic .gamma.-ray attenuation (TGA); increased pressure caused an immediate, modest increase in TGA (vascular congestion) followed by a slow further increase over 2 h. There was a fairly good correlation between the increase in extravascular lung water and the lung water and the change in TGA. The method is simple, safe and nonivasive and appears to be useful for following the time course of lung water accumulation in generalized lung edema in anesthetized animals.

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