Experimental radiation pneumonitis: changes in physiology of the alveolar surface.

Mice received 2400 rads in two fractions to the thorax; 4 months later at a time when deaths began, mechanical and biochemical properties of the lungs were studied and compared to those of littermate controls. The principal mechanical change was a large increase in the elastance of the alveolar surface element and abnormal surface tension properties of the AF. Alveolar fluid phospholipid content and saturation were only minimally change; however the alveolar fluid contained a large excess of protein, possibly of circulatory origin. The latter may explain the fall in compliance of the alveolar surface and hence of the lung in radiation pneumonitis. A small increase in elastance of the lung tissue element was also found; this correlated with a decrease in lung volume and a small increase in lung hydroxyproline content. These changes may signify the early development of radiation fibrosis. Other features of this model are the frequent occurrence of pleural effusions and the presence of increased numbers of alveolar macrophages in the alveolar lavage.