Within-Breath Oscillatory Mechanics in Horses Affected by Severe Equine Asthma in Exacerbation and in Remission of the Disease

SIMPLE SUMMARY: Equine asthma shares similarities with human asthma. The aim of the study was to evaluate whether within breath analysis improved the sensitivity of oscillometry at detecting subclinical airway obstruction in horses with asthma in remission of clinical signs. From this study, we can conclude that the within-breath oscillometry is sensitive in discriminating horses with severe asthma in clinical remission of the disease from control horses. Additionally, oscillometry allowed to identify the increase in expiratory reactance similar to that due to expiratory flow limitation observed in human asthmatic patients with airway obstruction. ABSTRACT: Oscillometry is a technique that measures the resistance (R) and the reactance (X) of the respiratory system. In humans, analysis of inspiratory and expiratory R and X allows to identify the presence of tidal expiratory flow limitation (EFLt). The aim of this study was to describe inspiratory and expiratory R and X measured by impulse oscillometry system (IOS) in horses with severe asthma (SEA) when in clinical remission (n = 7) or in exacerbation (n = 7) of the condition. Seven healthy, age-matched control horses were also studied. Data at 3, 5, and 7 Hz with coherence > 0.85 at 3 Hz and >0.9 at 5 and 7 Hz were considered. The mean, inspiratory and expiratory R and X and the difference between inspiratory and expiratory X (ΔX) were calculated at each frequency. The data from the three groups were statistically compared. Results indicated that in horses during exacerbation of severe asthma, X during expiratory phase is more negative than during inspiration, such as in humans in presence of EFLt. The evaluation of X during inspiration is promising in discriminating between horses with SEA in remission and control horses.