Exhaled breath condensate pH and H2O2 for the assessment of lower airways inflammation

Aims: Measurement of Exhaled Breath Condensate (EBC) pH and H2O2 concentrations is useful for daily monitoring of human patients with asthma and COPD. In the horse correlation between EBC H2O2 and bronchoalveolar neutrophilia has been reported, however EBC pH has not been evaluated in the horse. The aim of this study was to further on validate the application of EBC analysis for studies on equine RAO. Methods: EBC was obtained by making each horse breathe for 10 min into a facemask connected by rubber tubing to an inert plastic condensation chamber maintained at <-80ºC. The EBC samples were analysed for pH and H2O2 content within 1h of collection. H2O2 was measured with a spectrophotometric assay. Horses were allocated to one of 3 groups: healthy horses kept >10h/day on pasture (n=4), healthy stabled horses (n=17) and horses with confirmed RAO (n=5). Intra- and inter-day variability was assessed by sampling five horses kept in the same stabled environment on three occasions for three consecutive days. One-way ANOVA was used to detect significant differences (p<0.05) between groups and to evaluate any significant intra- and inter-day variation. Results: All the horses tolerated sample collection. No significant differences between horses of the three groups for either pH or H2O2 measurements were found. Significant intra- and inter-day variations were detected for each of the five horses studied. Both the intra- and inter-day variations were greater than the difference between horses with RAO and controls. Conclusion and practical significance: In contrast with previous literature, from the results of this study it appears that measurement of EBC pH and H2O2 have limited applications in differentiating animals with disease from healthy controls due to wide intra- and inter-day variability. Acknowledgments: The Horse Trust for funding this project. Cathy Wyse, David Rendle and Julie Oswald for their assistance.