Functional and morphologic comparison of silica- and elastase-induced airflow obstruction

We have previously shown that intratracheally instilled silica (quartz) produces both morphologic evidence of emphysema and small-airway changes, and functional evidence of airflow obstruction. To further define the nature of the airflow-associated lesions induced by silica, we compared silica-exposed rats to rats given intratracheal elastase, a standard model of emphysema. Both silica and elastase produced increases in RV and FRC along with upward shifts in the pressure-volume curves. Flows were decreased in both groups, but the changes were more severe in the silica-treated animals. Morphologically, the two treatments produced about the same degree of airspace enlargement, present in both alveoli and alveolar ducts, as well as decreased alveolar and alveolar duct surface area/unit lung volume. Elastic fiber length per unit volume was also decreased in both groups. However, small-airway walls were markedly thickened in the silica-treated compared to the elastase-treated group. We conclude that, in the parenchyma, both these agents produce morphologically similar airspace dilatation, and both induce destruction of elastic fibers. These lesions appear to correlate with abnormalities in the pressure-volume curve. Flow reductions seem to be primarily correlated with changes in small-airway wall structure.