Impulse oscillometry parameters and diffusing capacity of the lung in patients with pulmonary tuberculosis: is there an inter-relationship?

Assessment of pulmonary gas exchange is essential in patients with respiratory diseases. However, the diffusing capacity of the lung cannot be assessed in some patients due to their physical condition or cognitive limitations. Impulse oscillometry requires minimum patient cooperation, is easy for patients, and allows for quick, reproducible measurements. The aim of the study was to determine the relationship between impulse oscillometry parameters and diffusing capacity of the lung in patients with pulmonary tuberculosis. Methods. This was a retrospective observational study in adult patients with a confirmed diagnosis of pulmonary tuberculosis. We evaluated their spirometry, body plethysmography, Carbon Monoxide Diffusing Capacity (DLCO), and impulse oscillometry measurements. The study did not include patients with smoking experience of more than 10 pack-years, nonspecific respiratory diseases, chest surgery, and extrapulmonary causes of chest mobility restriction. The Kruskal – Wallis criterion, the χ2 criterion, Spearman rank correlation, and ROC analysis were used. Results. A moderate relationship was revealed between DLCO and IOS parameters: with frequency dependence of resistance (Rrs5–20), resonant frequency (Fres), deviation of reactance at 5 Hz from the predicted value (∆Xrs5), and reactance at 5 Hz (Xrs5) (–0.32; –0.33; –0.34; 0.32, respectively, p < 0.05). The reactance area (AX) showed a considerable relationship with DLCO and alveolar volume (VA) (–0.51; –0.57, respectively, p < 0.05) and a moderate relationship with the poorly Poorly Communication Fraction (PCF) 0,31 ( p < 0,05). The ROC analysis showed that if DLCO was less than 75%, the cut-off level of AX was 0.30 kPa/l (AUC = 0,746), and if DLCO was less than 50%, the cut-off level of AX was 0.41 kPa/l (AUC = 0,840). Conclusion. The diffusing capacity of the lung in patients with pulmonary tuberculosis correlates with the changes in total respiratory resistance and its components.