[Mechanical properties of the lung in paraquat-poisoned rats. Histopathologic correlates].

Paraquat intoxication in both the initial and late stages is responsible for a decrease in lung volumes and lung elasticity. In this study, we tried to separate these two stages with analysing the quasi-static pressure-volume curves (P-V) obtained both during inflation and deflation of the lungs. Three groups of rats were studied: group I: control (n = 9), group II: 11 animals studied 48 h after intraperitoneal injection of paraquat (24 mg X kg-1), group III: 6 animals studied 9 days after the administration of paraquat. Groups II and III, when compared to group I, were characterized by a significant decrease of 1) functional residual capacity (p less than 0.001), 2) the lung volume obtained for a 3 kPa distending pressure, and 3) the slope of the P-V curve during deflation (p less than 0.001). In group II, there was a clear increase in the hysteresis of the P-V loop due to an inflection of the inflation P-V limb. Such a shape is the only characteristic of the P-V curves which separates groups II and III. By contrast, the P-V curve during deflation, even when analysed with an exponential fitting, does not separate these two groups which were clearly different in their morphological aspect: alveolar edema (group II), interstitial pneumonitis (group III).