Effect on single-breath washout and lung function of elastase-induced emphysema in rats

Lung volumes, diffusing capacity (DLCO), quasi-static pressure-volume curves (P-V), forced expiration (FE) and He-SF6 single-breath washout (SBW) were performed in Wistar rats with emphysema induced by different doses of pancreatic elastase in saline, instilled intratracheally 6 wk prior to the tests. Emphysema was quantitatively assessed by mean linear intercept (Lm) measurements on 5-microns lung sections. Lung volume, P-V curve, and FE dependence on Lm, as well as the nonsignificant dependence of DLCO on Lm, are generally similar to results reported by others. The most interesting observation concerns the SBW: N2 slopes of the alveolar plateau, compared for identical lung volumes, did not change with the degree of emphysema. By contrast, the He-SF6 slope difference did depend significantly on the degree of emphysema. Based on the diffusion front theory, the present work suggests that in rats with elastase-induced emphysema, the phase III slope modifications relate mainly to elastic and not to structural alterations.