Background: Oxidative stress plays an important role in the pathogenesis of asthma. Interestingly, a low airway pH and a high concentrationof 8-isoprostane, a marker of oxidative stress, has been reported to cause infl ammatory airway diseases. However, the relationship between these 2 markers and pulmonary function has not been determined in mild asthma patients.

Methods: pH and 8-isoprostane concentration were measured in exhaled breath condensate (EBC) from patients with mild asthma (n = 44) and healthy subjects (n = 20). The relationship between acid stress (pH) and oxidative stress (8-isoprostane) was then analyzed, along with the relationships between these 2 markers and lung function.
Results: The median (interquartile range [IQR]) pH of EBC was signifi cantly lower in asthma patients than in control subjects (7.53 [7.41-7.68] vs 7.70 [7.62-7.74], P < .05), while the median (IQR) 8-isoprostane concentration of EBC was signifi cantly higher in asthma patients than control subjects (16.2 [11.7-19.1] vs 3.5 [2.6-7.9] pg/mL, P < .05). There was no correlation between pH and 8-isoprostane concentration.
Furthermore, lung function was not correlated with either pH or 8-isoprostane concentrations in EBC.

Conclusions: Acid stress and oxidative stress assessed by pH and 8-isoprostane concentration, respectively, in EBC did not show parallel changes associated with asthma and were not correlated with lung function in asthma patients. These 2 stress factors may have different roles in the pathogenesis of asthma.

Key words: Asthma. Oxidative stress. Acid stress. Exhaled breath condensate.