Objective: To evaluate the levels of hydrogen peroxide (H(2)O(2)) 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] FEV(1), 88 +/- 5% predicted) were studied as a control group.
Methods: H(2)O(2) and 8-isoprostane levels were measured in EBC, and the values were correlated with variables expressing COPD severity (ie, FEV(1) 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 H(2)O(2) was significantly elevated in COPD patients compared to control subjects (mean, 0.66 micromol/L [95% confidence interval (CI), 0.54 to 0.68 micro mol/L) vs 0.31 micro mol/L [95% CI, 0.26 to 0.35 micromol/L], respectively; p < 0.0001). The difference was primarily due to the elevation of H(2)O(2) in patients with severe and moderate COPD, whose expired breath H(2)O(2) levels were significantly higher than those of patients with mild disease (mean, 0.96 micromol/L [95% CI, 0.79 to 1.13 micromol/L], 0.68 micromol/L [95% CI, 0.55 to 0.81 micromol/L], and 0.33 micromol/L [95% CI, 0.24 to 0.43 micromol/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 H(2)O(2) has a better repeatability and stability than 8-isoprostane. Furthermore, we observed significant correlations of H(2)O(2) with FEV(1), 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 H(2)O(2) and 8-isoprostane are elevated in the EBC of patients with COPD, but that H(2)O(2) seems to be a more repeatable and a more sensitive index of the inflammatory process and the severity of the disease.