Assessment of a methodology for determination of H[2]O[2] concentration and pH in exhaled breath condensate in horses with and without lower airway inflammation
Measurement of hydrogen peroxide (H2O2) concentration and pH in exhaled breath condensate (EBC) is useful for detection and monitoring of diseases of the lower respiratory tract in humans, including asthma and chronic obstructive pulmonary disease. In contrast, limited information on the use of these parameters for the investigation of lower airway inflammation (LAI) is available for horses. Aims of the current study were to develop a device to collect EBC from non-sedated horses, assess inter-day and intra-day variability of EBC H2O2 concentration and pH and determine if there was an association between these parameters and the presence and severity of LAI. The methodology used for collection of EBC was adapted from that used in a previous study (Wyse et al. 2005) and was evaluated for its repeatability. Hydrogen peroxide was measured using previously reported analytic methods (Wyse et al. 2005). During studies for the determination of a methodology for measurement of pH in EBC, samples of EBC were divided into 3 aliquots. One aliquot was left non-deaerated, one aliquot was deaerated with argon and one aliquot underwent standardisation with CO2. The pH of each aliquot was measured using a bench pH meter. The most repeatable measurement of EBC pH was obtained from plain samples (i.e. non-dearated). Intra-day and inter-day variability of H2O2 concentration and pH were assessed by collecting and analysing EBC three times a day for 3 consecutive days. For H2O2 the variability in concentrations was large (60-103%), while the pH of EBC had little variability (3-7%). No significant difference in the intra-day or inter-day H2O2 concentrations or pH measurements were found in control or LAI horses, except for inter-day H2O2 concentration in horses with LAI (p=0.019). There was no significant difference in EBC H2O2 concentration between control horses (Mean +/- SD) and horses with LAI (mean +/- SD). There was no significant difference in EBC pH between control horses (Mean +/- SD) and horses with LAI (mean +/- SD), however a trend for a reduced pH in horses with LAI was observed (p= 0.079). The results of this study suggest that EBC H2O2 concentration is not suitable for detecting mild LAI or monitoring horses with LAI due to the high variability. The pH of EBC is more stable overtime and the measurements are more repeatable than H2O2 concentration and further studies are required to improve the stability of its measurement and to assess its sensitivity in a population of horses with more severe LAI against healthy controls. Further studies are also required to determine whether determination of H2O2 concentration in EBC is useful for detection of marked LAI in horses
