Collection of exhaled breath condensate and analysis of hydrogen peroxide as a potential marker of lower airway inflammation in cats

The objective of this study was to describe a standardised and non-invasive method for exhaled breath condensate (EBC) collection in cats and to test whether determination of hydrogen peroxide (H2O2) in EBC might be used as marker of lower airway inflammation. The technique of barometric whole body plethysmography for cats was combined with a system to condense the effluent air from the plethysmograph, allowing simultaneous EBC collection and respiratory pattern measurement. H2O2 was determined spectrophotometrically. Eighteen experimental cats were used to investigate the impact on EBC volume and EBC H2O2 of plethysmograph ventilation rate, collection duration, sample stability, within-day and day-to-day variability. After determination of a standardised EBC collection procedure, correlation analyses between EBC H2O2 and bronchoalveolar lavage (BAL) cytology of healthy and allergen-challenged Ascaris suum (AS)-sensitised cats were performed. A significant and positive correlation between EBC H2O2 and bronchoalveolar lavage (BAL) neutrophil% was found in healthy cats (P<0.001, r=0.55), whereas in AS-sensitised cats, correlation with BAL eosinophil% was significant (P<0.005, r=0.61). H2O2 was increased after an allergen challenge in AS-sensitised cats (n=6, 0.56 ± 0.12 versus 1.08 ± 0.35 μmol/L, P<0.05). This study proposes a non-invasive, well tolerated and repeatable method of EBC collection for cats and suggests that EBC H2O2 might be used as non-invasive biomarker for monitoring lower airway inflammation.