Oscillation mechanics of the respiratory system in never-smoking patients with silicosis: pathophysiological study and evaluation of diagnostic accuracy

Paula Morisco de Sá, Agnaldo José Lopes, José Manoel Jansen, Pedro Lopes de Melo, Paula Morisco de Sá, Agnaldo José Lopes, José Manoel Jansen, Pedro Lopes de Melo

Abstract

Objectives: Silicosis is a chronic and incurable occupational disease that can progress even after the cessation of exposure. Recent studies suggest that the forced oscillation technique may help to clarify the changes in lung mechanics resulting from silicosis as well as the detection of these changes. We investigated the effects of airway obstruction in silicosis on respiratory impedance and evaluated the diagnostic efficacy of the forced oscillation technique in these patients.

Methods: Spirometry was used to classify the airway obstruction, which resulted in four subject categories: controls (n=21), patients with a normal exam (n=12), patients with mild obstruction (n=22), and patients with moderate-to-severe obstruction (n=12). Resistive data were interpreted using the zero-intercept resistance (R0), the resistance at 4 Hz (Rrs4), and the mean resistance. We also analyzed the mean reactance (Xm) and the dynamic compliance. 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. ClinicalTrials.gov: NCT01725971.

Results: We observed significant (p<0.0002) increases in R0, Rrs4, Rm, and Z4Hz and significant reductions in Crs,dyn (p<0.0002) and Xm (p<0.0001). R0, Rrs4, Rm, and Z4Hz performed adequately in the diagnosis of mild obstruction (area under the curve>0.80) and highly accurately in the detection of moderate-to-severe obstruction (area under the curve>0.90).

Conclusions: The forced oscillation technique may contribute to the study of the pathophysiology of silicosis and may improve the treatment offered to these patients, thus representing an alternative and/or complementary tool for evaluating respiratory mechanics.

Conflict of interest statement

No potential conflict of interest was reported.

Figures

Figure 1
Figure 1
Mean course of Rrs (A) and Xrs (B) as a function of frequency in the normal subjects and in the patients with silicosis. CG: control group; NE: normal upon spirometric examination; MO: mild obstruction; MSO: moderate-to-severe obstruction.
Figure 2
Figure 2
Resistive parameters at 4 Hz (Rrs4; A), total resistance (R0; B), mean resistance (Rm; C), and resistance slope (S; D) in the normal subjects and in the patients with silicosis. The bottom and top of the box plot represent the 25th and 75th percentile values, respectively, while the circle represents the mean value, and the bar across the box represents the 50th percentile value. The whiskers outside the box represent the 10th to 90th percentile values.
Figure 3
Figure 3
Comparative analysis of the reactive parameters in the normal subjects and in the patients with silicosis. Mean values (Xm; A), dynamic compliance of the respiratory system (Cdyn,rs; B), resonant frequency (fr; C), and impedance modulus at 4 Hz (Z4Hz; D).

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