Oscillometric assessment of bronchodilator response in horses with severe asthma during remission

Abstract Background During clinical remission of severe equine asthma (SEA), affected animals can be challenging to distinguish from healthy horses. In humans, the degree of bronchodilation achieved with a β 2 ‐adrenergic bronchodilator is helpful in differentiating asthmatics from healthy subjects. Objective To determine whether the response to an inhaled bronchodilator improves the sensitivity of oscillometry in detecting subclinical airway obstruction in horses with asthma. Study Design In vivo experiments. Methods Nine control university‐owned horses and 10 SEA horses in remission from a research herd were studied in the main sub‐study. Oscillometry was performed at baseline, 8, and 30 min after the inhalation of a β 2 ‐adrenergic bronchodilator. Whole‐breath and within‐breath resistance (R) and reactance from 3 to 7 Hz were compared. Data were analysed with two‐way ANOVAs. Results At baseline, the inspiratory reactance at 3 Hz was significantly higher in the healthy control group (0.014 ± 0.007 kPa/L/s) compared to the asthma remission group (0.003 ± 0.01 kPa/L/s, p = 0.01). The R3/R7 ratio, a variable representing the frequency‐dependence of airway obstruction, was improved at 30 min in both groups (from 0.77 ± 0.08 to 0.68 ± 0.06 kPa/L/s in the control group [ p = 0.003] and from 0.76 ± 0.09 to 0.69 ± 0.10 kPa/L/s in the SEA group [ p = 0.01]). Similarly, the bronchodilator produced comparable improvements in pulmonary reactance in both groups. Main Limitations The small number of horses. Conclusion Only within‐breath analysis with oscillometry distinguished horses with SEA in remission from control horses. Salbutamol administration did not improve this discrimination, as the magnitude of bronchodilation was similar in both groups.