Effects of lung injury on pulmonary surfactant aggregate conversion in vivo and in vitro.

Within the alveolar space pulmonary surfactant is converted from the surface active large aggregates (LA) to the inactive small aggregates (SA). This conversion is affected by a change in surface area, lung injury, breathing pattern, and protease activity. This study examined the effect of N-nitroso-N-methylurethane-induced acute lung injury on aggregate conversion in mechanically ventilated and spontaneously breathing rabbits. Both the in vitro surface area cycling techniques and the in vivo technique of intratracheally injecting radiolabeled LA were used for analyzing aggregate conversion. Mechanical ventilation of injured lungs resulted in increased aggregate conversion and increased surfactant aggregate ratios compared with controls. Spontaneously breathing injured animals had aggregate conversion and aggregate ratios that were not significantly different from controls. In vitro aggregate conversion was slower for LA obtained from injured animals compared with normal animals. We conclude that the mechanical stress of mechanical ventilation results in increased aggregate conversion and aggregate ratios. Furthermore, in vitro conversion of isolated LA does not necessarily reflect the conversion of aggregates within the alveoli.

Timing of exogenous surfactant administration in a rabbit model of acute lung injury.

The purpose of this study was to evaluate early vs. late administration of exogenous surfactant in an adult rabbit model of acute lung injury. Lung injury was induced by repetitive whole lung saline lavage and subsequent mechanical ventilation. Bovine lipid extract surfactant was instilled either 1 (Early) or 4 h (Late) after the last lavage. Animals were monitored for 7 h after the last lavage. Although arterial PO2 values increased significantly immediately after treatment in both the Early and Late groups, this improvement was not sustained in the Late group. There was also a higher incidence of pneumothoraxes in the Late group vs. both the Early group and a nontreated control group. The ratio of poorly functioning small surfactant aggregates to superior functioning large aggregates was higher in the Late group compared with the Early group. Morphological analysis revealed that early surfactant treatment prevented the progression of lung injury over time. We conclude that administration of exogenous surfactant at an early time point in lung injury resulted in superior responses compared with later treatments.

Alveolar surfactant aggregate conversion in ventilated normal and injured rabbits.

Alveolar surfactant can be separated into two subtypes; large aggregates and small aggregates. Large aggregates represent the surface active form of surfactant and are the metabolic precursors of small aggregates. Previous studies examined the mechanism by which large aggregates are converted into small aggregates in vitro. We used intratracheal injection of radiolabeled large aggregates in rabbits to probe the aggregate conversion in vivo. After this injection, animals were mechanically ventilated for 60 min. After the animals were killed, the lungs were lavaged, and the percentage of radiolabel present in the small aggregate fraction was determined. Our results showed that ventilation resulted in aggregate conversion and that increases in tidal volume, but not in respiratory rate, correlated with increased conversion. Aggregate conversion in rabbits with acute lung injury correlated significantly with severity of injury. We conclude that a change in surface area (i.e., respiration) is necessary for aggregate conversion in vivo and that the ventilation strategy can affect this conversion. Furthermore, increased aggregate conversion in injured lungs might contribute to increased small-to-large aggregate ratios in these lungs compared with normal lungs.

[Recurrent water intoxication during successive episodes of acute bronchitis: Schwartz-Bartter syndrome? (author's transl)]. / Intoxication par l'eau récidivante lors d'épisodes de bronchite aigue: syndrome de Schwartz-Bartter?

Mental confusion with hyponatremia and oliguria was recorded during each of three successive episodes of acute bronchitis. Antibiotics proved sufficient therapy and led to recovery. Thus, as in pneumonia, inappropriate secretion of antidiuretic hormone (ADH) may be seen in acute bronchitis.