 Objectives: Analyze the effects of airway obstruction in silicosis on the respiratory impedance and evaluated the diagnostic use of the FOT in these patients. For this, the investigators used spirometry to classify airway obstruction, which resulted in four categories: control, patients with normal exam, mild obstruction, and moderate-to-severe obstruction. Resistive data were interpreted using the zero-intercept resistance R0, the resistance at 4 Hz Rrs4 and the mean resistance Rm. The investigators also analyzed the mean reactance Xm and the dynamic compliance Crs,dyn. The total mechanical load was evaluated using the absolute value of the respiratory impedance Z4Hz. The diagnostic potential was evaluated by investigating the area under the receiver operating characteristic curve AUC. 