Objective: To evaluate the levels of hydrogen peroxide (H2O2) and 8-isoprostane in the expired breath condensate (EBC) of patients with COPD, and to assess the relationship between the above markers of oxidative stress and parameters expressing inflammatory process and disease severity.
Setting: Inpatient respiratory unit and outpatient clinic in tertiary care hospital.
Design: Cross-sectional study.
Patients: Thirty stable COPD patients (all smokers) with disease severity ranging from mild to severe. Ten subjects who were smokers with stage 0 disease (ie, at risk for COPD; mean [± SD] FEV1, 88 ± 5% predicted) were studied as a control group.
Methods: H2O2 and 8-isoprostane levels were measured in EBC, and the values were correlated with variables expressing COPD severity (ie, FEV1 percent predicted, dyspnea severity score (ie, Medical Research Council scale) and airway inflammation (ie, differential cell counts from induced sputum).
Results: The mean concentration of H2O2 was significantly elevated in COPD patients compared to control subjects (mean, 0.66 μmol/L [95% confidence interval (CI), 0.54 to 0.68 μmol/L) vs 0.31 μmol/L [95% CI, 0.26 to 0.35 μmol/L], respectively; p < 0.0001). The difference was primarily due to the elevation of H2O2 in patients with severe and moderate COPD, whose expired breath H2O2 levels were significantly higher than those of patients with mild disease (mean, 0.96 μmol/L [95% CI, 0.79 to 1.13 μmol/L], 0.68 μmol/L [95% CI, 0.55 to 0.81 μmol/L], and 0.33 μmol/L [95% CI, 0.24 to 0.43 μmol/L], respectively, p < 0.0001). The mean concentration of 8-isoprostane was significantly elevated in patients with COPD compared to that of the control group (47 pg/mL [95% CI, 41 to 53 pg/mL] vs 29 pg/mL [95% CI, 25 to 33 pg/mL], respectively; p < 0.0001) but did not differ significantly among the different stages of the disease (p = 0.43). Repeatability and stability data within measurements showed that H2O2 has a better repeatability and stability than 8-isoprostane. Furthermore, we observed significant correlations of H2O2 with FEV1, neutrophil count, and dyspnea score. Those correlations existed only in patients with moderate and severe disease. No correlations were found between levels of 8-isoprostane and the above parameters.
Conclusions: We conclude that levels of H2O2 and 8-isoprostane are elevated in the EBC of patients with COPD, but that H2O2 seems to be a more repeatable and a more sensitive index of the inflammatory process and the severity of the disease.