Equine veterinary journal2026; doi: 10.1002/evj.70211

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

Vermedal, H
·
Hellings, IR
·
Fretheim-Kelly, ZL
·
Fintl, C
·
Strand, E

Abstract: 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. Objective: 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. Methods: Observational study with case-control comparisons. Methods: Inspiratory and expiratory tracheal pressures (cmHO) 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 cmHO; 95% CI: -12.9 to -3.4; p < 0.001) compared with controls (mean -30.0 cmHO). Expiratory tracheal pressures were significantly higher (more positive) in horses with iDDSP (mean difference = +13.1 cmHO; 95% CI: 11.2 to 15.1; p < 0.001), AFC (mean difference = +15.4 cmHO; 95% CI: 13.2 to 17.6; p < 0.001), and NPC (mean difference = +5.8 cmHO; 95% CI: 3.7 to 8.1; p < 0.001) compared with controls (mean +11.7 cmHO). Conclusions: 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.

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Publication Date: 2026-06-24 PubMed ID: 42338322DOI: 10.1002/evj.70211Google Scholar: Lookup

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Summary

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Overview

This study objectively evaluated how specific exercise-related nasopharyngeal disorders affect upper airway function in racehorses during high-speed exercise.
It measured tracheal pressures to quantify the impact of four conditions—palatal instability, intermittent dorsal displacement of the soft palate, alar fold collapse, and nasopharyngeal collapse—on breathing performance.

Background

Upper respiratory tract (URT) disorders are common in racehorses and can limit their athletic performance by impairing airway function during exercise.
Current diagnosis and treatment decisions often rely on subjective assessments, such as clinical examination and exercising endoscopy.
The study aims to provide objective data by directly measuring airway pressures related to these disorders during exercise.

Study Design and Methods

Observational case-control study including a total of 167 harness racehorses.
Condition groups: 91 horses naturally exhibiting one of the four disorders were studied—palatal instability (PI), intermittent dorsal displacement of the soft palate (iDDSP), alar fold collapse (AFC), and nasopharyngeal collapse (NPC).
Control group: 76 clinically normal horses without airway disorders.
Procedure: High-speed treadmill endoscopy (HSTE) was performed to visualize upper airway structures during exercise.
Simultaneously, inspiratory and expiratory tracheal pressures were recorded in cmH2O to quantify airway function.
Data were analyzed using linear mixed-effects models; results were log-transformed and back-transformed to ratios of geometric means for interpretation.

Key Findings

Nasopharyngeal Collapse (NPC):
- Inspiratory tracheal pressure was significantly lower (more negative) compared to controls, indicating greater airflow resistance during inhalation.
- NPC also increased expiratory tracheal pressure compared to controls, indicating some obstruction during exhalation.
- This suggests NPC causes a combined airway obstruction affecting both inspiration and expiration, with a stronger effect on inspiration.
Intermittent Dorsal Displacement of the Soft Palate (iDDSP):
- Expiratory tracheal pressures were significantly higher (more positive), indicating obstructed airflow during expiration.
- Inspiratory pressures were not significantly different from controls.
- This points to significant expiratory upper airway obstruction caused by iDDSP.
Alar Fold Collapse (AFC):
- Also showed significantly higher expiratory tracheal pressures compared to controls.
- Indicates a marked expiratory airflow obstruction similar to iDDSP.
Palatal Instability (PI):
- Did not significantly affect inspiratory or expiratory tracheal pressures compared to control horses.
- Suggests PI does not measurably impair airway function during exercise, despite being a commonly diagnosed condition.

Interpretation

The study provides objective evidence that certain exercise-related nasopharyngeal disorders have a measurable negative impact on upper airway function during exercise in racehorses.
iDDSP and AFC predominantly obstruct airflow during expiration.
NPC causes a more global airway obstruction affecting both phases of breathing, with inspiration being more affected.
PI, despite its common recognition, does not appear to cause significant functional airflow limitation during exercise.

Limitations

Simultaneous airflow measurements (e.g., volume or flow rate) were not performed, limiting full characterization of respiratory mechanics.
The study focuses on pressure measurements only, which provide indirect evidence of obstruction.
Potential variability in measurement due to individual horse differences or exercise intensity, though statistical models accounted for some variability.

Conclusions and Clinical Implications

Objective measurement of tracheal pressures during exercise confirms that iDDSP, AFC, and NPC cause significant airway obstruction in racehorses.
These measurements could improve diagnostic accuracy for nasopharyngeal disorders and help tailor treatment decisions based on functional impairment rather than solely on visual assessment.
Palatal instability may be less clinically relevant to airway obstruction than previously thought, which could influence therapeutic strategies.
Further research including airflow and volume measurements could enrich understanding of these disorders’ impacts on equine respiratory physiology.

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APA

Vermedal H, Hellings IR, Fretheim-Kelly ZL, Fintl C, Strand E. (2026). Effect of exercise-related nasopharyngeal disorders on upper airway function in racehorses. Equine Vet J. https://doi.org/10.1002/evj.70211