Exhaled breath condensate hydrogen peroxide, pH and leukotriene B are associated with lower airway inflammation and airway cytology in the horse.

BACKGROUND

Exhaled breath condensate (EBC) analysis is a noninvasive method to assess the lower respiratory tract. In human subjects, EBC hydrogen peroxide (H O ), pH and leukotriene B (LTB ) are useful for detection and monitoring of inflammatory lung diseases, including asthma.

OBJECTIVES

To determine associations between EBC biomarkers and cytological and endoscopic definitions of lower airway inflammation (LAI) while controlling for sampling and environmental variables.

STUDY DESIGN

Prospective, cross-sectional study.

METHODS

Clinical, endoscopic and airway cytological findings from 47 horses were compared with EBC pH and concentrations of H O and LTB by univariate and multivariable analyses. Dichotomous (presence/absence of airway inflammation) and continuous outcome variables (differential cell counts in tracheal aspirate and bronchoalveolar lavage fluid, BALF) were evaluated and potential effects of collection and methodological factors were included.

RESULTS

EBC pH and H O concentrations were higher in horses with LAI and both were positively associated with the percentage of neutrophils in BALF (P<0.05). Mast cell percentage in BALF was negatively associated with EBC pH, and BALF eosinophil percentage was positively associated with EBC LTB (P<0.05). Ambient temperature, relative humidity and assay methodology significantly impacted some analytes.

MAIN LIMITATIONS

LAI is challenging to categorise due to a variety of clinical and cytological phenotypes. Although the study was designed to overcome this limitation, numbers of horses were small in some categories.

CONCLUSIONS

EBC pH and H O concentrations are altered by airway inflammation, suggesting a role for these biomarkers in the diagnosis and monitoring of airway disease. Environmental and methodological factors can influence these biomarkers and should be considered in the interpretation of results.