DEVELOPMENT OF EARLY DETECTION OF ADULT RESPIRATORY DISTRESS SYNDROME

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In adult respiratory distress syndrome (ARDS), the decrease in activity of surfaceactive material (surfactant), which increases the alveolar surface tension and decrease the alveolar surface-to-volume (S/V) ratio, is observed in the early stage. In our previous study, we developed the light scattering stereology which measures the optical mean free path, lambda(equivalent to an inverse of the S/V ratio). In the present study, we aimed to develop a detection method of permeability pulmonary edema in ARDS,using the light-scattering stereology.In mechanically ventilated dogs with open chest, we modified the light-scattering stereology, and were able to measure lambda continuously. The S/V ratio was smaller in inspiration than in expiration, suggesting a greater surface tension in inspiration. In ventilated lungs, the surface tension became less than the tissue force of the septa as the ventilatory frequency increases.To examine the effect of surfactant on the S/V ratio, we washed the lung with saline. After saline lavage, the S/V ratio decreased, suggesting that the alveolar surface tension increases by lavage of surfactant. In ARDS model of oleic acid (OA) -induced pulmonary edema, the S/V ratio decreased but the saline-filled pressure-volume curve did not differ between control and OA-induced edema. It is likely that the activity of surfactant may decrease by exudation of plasma, resulting in an increase in alveolar surface tension. In dogs injected by lipopolysaccharide (LPS), the S/V ratio decreased before hypoxemia and the decrease in lung compliance occurred. Thus, light-scattering stereology is able to measure the S/V in live animals and detect the change in surface tension. We concluded that pulmonany edema may be detected in early phase by using the light-scattering stereology.