Respiratory oscillometry testing in relation to exercise in healthy and asthmatic Thoroughbreds

Racehorses may experience exercise-induced bronchodilation or bronchoconstriction, with potential differences between healthy and asthmatic individuals.

To identify exercise-related lung function variations by oscillometry in racehorses, compare lung function between healthy and mild equine asthma (MEA) horses, assess oscillometry's potential as a predictor of racing fitness.

Prospective case-control clinical study.

Fourteen Thoroughbred racehorses (5 healthy, 9 MEA) underwent a protocol including respiratory oscillometry at rest, exercise with fitness monitoring, oscillometry at 15 and 45 min post-exercise, and bronchoalveolar lavage fluid (BALf) cytology. Oscillometry parameters (resistance [Rrs] and reactance [Xrs]) were compared within and between healthy and MEA groups at different timepoints. Associations between Rrs and Xrs at rest and 15 min post-exercise and BALf cytology and fitness indices were evaluated.

MEA horses showed higher Rrs at 15 min post-exercise (0.6 ± 0.2 cmH₂O/L/s) than healthy horses (0.3 ± 0.1 cmH₂O/L/s) (p < 0.01). In healthy horses, Rrs decreased at 15 min post-exercise compared with resting values (0.5 ± 0.1 cmH₂O/L/s) (p = 0.04). In MEA horses, oscillometry parameters did not vary with time. Post-exercise Xrs inversely correlated with total haemosiderin score (p < 0.01, r² = 0.51). Resting Rrs inversely correlated with speed at 200 bpm (p = 0.03, r² = -0.61), and Xrs with maximum heart rate (HR) during exercise (p = 0.02, r² = -0.62). Post-exercise Rrs inversely correlated with mean (p = 0.04, r² = -0.60) and maximum speed (p = 0.04, r² = -0.60), and HR variability (p < 0.01, r² = -0.74).

Small sample size, oscillometry repeatability not assessed, potential interference of upper airway obstructions, external variables influencing fitness indices.

Oscillometry identified lung function differences between healthy and MEA horses at 15 min post-exercise. Only healthy horses exhibited exercise-induced bronchodilation. Oscillometry showed potential in predicting subclinical airway obstruction.