Pulmonary mechanics during induced pulmonary edema in anesthetized dogs

¹ Department of Physiology, Harvard School of Public Health, Department of Pediatrics and Pathology, Harvard Medical School, and the Children's Medical Center, Boston, Massachusetts

In order to study the mechanisms underlying the changes in the mechanical properties of the lungs during pulmonary edema, pulmonary vascular congestion was produced in spontaneously breathing, anesthetized dogs by partial aortic obstruction and intravenous infusion. Brief periods of congestion were associated with small changes in the lung compliance compared with the progressive and striking compliance reduction (–78%) noted with more prolonged congestion. Lung volume at end-expiration showed little change if edema fluid and trapped gas as well as the ventilated gas volume were taken into account. When edematous lungs were forcibly inflated beyond the tidal range, it was found that the overall compliance at a distending pressure of 30 cm H₂O was not much less (–6%) than that of normal lungs. Furthermore, edematous lungs manifested marked ‘static’ hysteresis during such maneuvers. These findings suggested that surface phenomena were responsible for the mechanical behavior of edematous lungs rather than vascular congestion, per se, or intrinsic tissue changes. This was borne out by experiments on excised lungs which showed that the elastic properties of edematous lungs were not significantly different from normal lungs when surface forces were minimized.

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