Effect of exercise‐related nasopharyngeal disorders on upper airway function in racehorses

Background Exercise‐related upper respiratory tract (URT) disorders are frequently diagnosed in racehorses. Treatment recommendations are routinely based on subjective assessment of clinical evaluation and exercising endoscopy findings. Objectives To objectively investigate how palatal instability (PI), intermittent dorsal displacement of the soft palate (iDDSP), alar fold collapse (AFC), and nasopharyngeal collapse (NPC) affect upper airway function during exercise in racehorses. Study Design Observational study with case–control comparisons. Methods Inspiratory and expiratory tracheal pressures (cmH 2 O) were recorded in 91 harness racehorses demonstrating naturally occurring PI, iDDSP, AFC or NPC during high‐speed treadmill endoscopy (HSTE). Linear mixed‐effects models compared tracheal pressures recorded during active occurrence of these disorders with pressures recorded in 76 clinically normal control horses undergoing the same standardised HSTE protocol. For log‐transformed models, results were back‐transformed and expressed as ratios of geometric means. Results Inspiratory tracheal pressures were significantly lower (more negative) in horses with NPC (mean difference = −8.1 cmH 2 O; 95% CI: −12.9 to −3.4; p < 0.001) compared with controls (mean −30.0 cmH 2 O). Expiratory tracheal pressures were significantly higher (more positive) in horses with iDDSP (mean difference = +13.1 cmH 2 O; 95% CI: 11.2 to 15.1; p < 0.001), AFC (mean difference = +15.4 cmH 2 O; 95% CI: 13.2 to 17.6; p < 0.001), and NPC (mean difference = +5.8 cmH 2 O; 95% CI: 3.7 to 8.1; p < 0.001) compared with controls (mean +11.7 cmH 2 O). Main Limitations Simultaneous airflow measurements were not performed. Conclusions Naturally occurring iDDSP, AFC, and NPC significantly impair upper airway function in racehorses during exercise. Intermittent dorsal displacement of the soft palate and AFC are associated with significant expiratory upper airway obstruction, while NPC results in a combined obstruction affecting both inspiration and, to a lesser extent, expiration. Palatal instability did not result in any measurable impairment of upper airway function during exercise in racehorses.