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Equine veterinary journal2025; doi: 10.1111/evj.14557

Inspiratory and expiratory tracheal pressures during high-intensity exercise in harness racehorses.

Abstract: Exercise-related upper respiratory tract (URT) disorders are common in racehorses. Objective assessment of URT mechanics is essential to quantify degrees of obstruction caused by URT disorders identified upon dynamic endoscopy. Objective: To establish reference values for inspiratory and expiratory tracheal pressures (cmHO) during high-speed treadmill endoscopy in harness racehorses with clinically normal URTs. Methods: Prospective observational study. Methods: Tracheal pressures were measured in harness racehorses (Standardbreds and Norwegian-Swedish coldblooded trotters) in which no URT abnormalities were detected. Peak inspiratory and expiratory tracheal pressures were determined for each minute (phase) of a standardised treadmill test, which alternated between trotting with free head carriage (phases 1, 3, 5 and 7) and with poll flexion (phases 2, 4 and 6). Linear mixed-effects models assessed changes in tracheal pressures across the exercise test, and effects of breed, racing experience, respiratory rate and head-neck position (free vs. poll flexion). Results: Seventy-six horses were included. Mean (SD) peak inspiratory tracheal pressures ranged from -21.8 (5.0) cmHO in phase 1 to -34.9 (5.3) and -34.3 (5.7) cmHO in phases 6 and 7. Inspiratory pressures became significantly more negative across phases (p < 0.001) and were -3.5 cmHO (95% CI: -4.0 to -3.0, p < 0.001) lower during poll flexion versus free head carriage. Expiratory tracheal pressures remained stable across exercise phases (11.5 [2.8] to 12.5 [2.6] cmHO) with no significant changes. There were no significant differences between the two breeds. Respiratory rate ranged from 79.8 (12.6) to 90.8 (15.0) breaths/min and remained stable between 89.6 and 90.8 breaths/min through phases 3-7. Conclusions: Simultaneous airflow measurements were not performed. Conclusions: Inspiratory pressures became more negative with exercise progression and were significantly lower during poll flexion versus free head carriage. Reference values for tracheal pressures from clinically normal horses provide an objective tool for evaluating URT function during exercise. Background: Les problématiques de voies respiratoires supérieures (URT) associées à l'exercice sont communes chez les chevaux de course. L'évaluation objective de la mécanique des voies respiratoires supérieures est essentielle afin de quantifier les degrés d'obstruction causés par ces problématiques, identifiées en endoscopie dynamique/embarquée. Objective: Établir des valeurs de référence pour les pressions trachéales (cmH20) inspiratoires et expiratoires durant l'endoscopie au tapis roulant à haute vitesse, chez les chevaux de course attelés avec voies respiratoires supérieures cliniquement normales. TYPE D'ÉTUDE: Étude prospective observationnelle. MÉTHODES: Les pressions trachéales sont mesurées chez les chevaux des course attelés (trotteurs Standardbreds et coldbloods Norvégien‐Suédois) sans anomalie des voies respiratoires supérieures détectées. Les pressions trachéales inspiratoires et expiratoires maximales ont été déterminées à chaque minute (phase) d'un test de tapis roulant standardisé, qui alternait entre du trot avec le port de tête libre (phases 1, 3, 5 et 7) et avec la nuque fléchie (phases 2, 4, 6). Des modèles linéaires à effets mixtes évaluent des changements de pressions trachéales durant le test d'exercice et les effets de race, expérience en course, fréquence respiratoire et position de la tête et du cou (libre vs fléchi). RÉSULTATS: Soixante‐seize chevaux ont été inclus. La moyenne (SD) des pressions trachéales inspiratoires maximales s'étendait de −21.8 (5.0) mcH20 en phase 1 à −34.9 (5.3) et −34.3 (5.7) cmH20 en phases 6 et 7. Les pressions inspiratoires sont devenues significativement plus négatives au travers des phases (p < 0.001) et étaient −3.5 cmH20 (95% CI: −4.0 to −3.0, p < 0.001) inférieures durant la flexion de la nuque par rapport au positionnement de la tête. Les pressions trachéales expiratoires sont demeurées stable au travers des phases (11.5 [2.8] to 12.5 [2.6] cmH2O) sans changement significatif. Il n'y avait pas de différence significative entre les 2 races de chevaux. La fréquence respiratoire s'étendait de 79.8 (12.6) à 90.8 (15.0) respirations/minute et est demeurée stable entre 89.6–90.8 respirations/minutes au travers des phases 3 à 7. Unassigned: Aucune mesure de débit d'air enregistrée simultanément. Conclusions: Les pressions inspiratoires sont devenues plus négatives lors de la progression de l'exercice et étaient significativement diminuées durant la flexion de la nuque par rapport à un positionnement de tête libre. Les valeurs de référence pour les pressions trachéales provenant de chevaux cliniquement normaux constituent un outil objectif pour évaluer la fonction des voies respiratoires supérieures durant l'exercice.
© 2025 The Author(s). Equine Veterinary Journal published by John Wiley & Sons Ltd on behalf of EVJ Ltd.
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Publication Date: 2025-07-21 PubMed ID: 40686083DOI: 10.1111/evj.14557Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

This study aimed to establish tracheal pressure reference values during high-speed exercise for racehorses without upper respiratory tract (URT) disorders. The findings revealed that inspiratory pressures became increasingly negative as exercise intensity increased and were significantly lower when horses had their necks flexed compared to a free head carriage. Expiratory pressures remained unaltered, and there were no significant differences between breeds.

Objective of the Study

  • The primary aim of the study was to derive reference values for inspiratory and expiratory tracheal pressures in harness racehorses during high-intensity exercise. These values could serve as a benchmark for identifying degrees of obstruction caused by URT disorders in horses during dynamic endoscopy.

Study Methods

  • The researchers used a prospective observational study design, where tracheal pressures were measured during a standardized treadmill test in two breeds of harness racehorses without any URT abnormalities.
  • Peak inspiratory and expiratory tracheal pressures were measured for each minute of the exercise session which alternated between free head carriage and poll flexion.
  • A linear mixed-effects model was used to evaluate changes in tracheal pressures across the exercise test, considering factors such as breed, racing experience, respiratory rate, and head-neck position.

Results of the Study

  • A total of seventy-six horses were included in this study, and the results showed that inspiratory pressures increasingly turned negative with the progression of the exercise, and were more pronounced during poll flexion as compared to a free head carriage position.
  • The expiratory pressures, on the other hand, remained consistent across all exercise phases with no significant changes.
  • There were no distinctions observed between the two horse breeds. The respiratory rate remained relatively stable through the majority of the phases ranging between 89.6 and 90.8 breaths per minute.

Conclusions of the Study

  • The research concluded that inspiratory pressures become more negative as the exercise intensity increases and were notably lower during poll flexion when compared to free head carriage.
  • However, it should be noted that simultaneous airflow measurements were not performed which could affect the absolute understanding of URT function during exercise.
  • Despite this, the derived reference values for tracheal pressures in clinically normal horses offer a solid tool for assessing URT function in horses during vigorous exercise.

Cite This Article

APA
Vermedal H, Hellings IR, Fretheim-Kelly ZL, Fintl C, Olsen HMB, Strand E. (2025). Inspiratory and expiratory tracheal pressures during high-intensity exercise in harness racehorses. Equine Vet J. https://doi.org/10.1111/evj.14557

Publication

Equine veterinary journal
ISSN: 2042-3306
NlmUniqueID: 0173320
Country: United States
Language: English

Researcher Affiliations

Vermedal, Hanna
  • Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Oslo, Norway.
Hellings, Ingunn Risnes
  • Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Oslo, Norway.
Fretheim-Kelly, Zoe Louise
  • Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Oslo, Norway.
Fintl, Constanze
  • Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Oslo, Norway.
Olsen, Hanna Margrethe Berg
  • Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Oslo, Norway.
Strand, Eric
  • Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Oslo, Norway.

Grant Funding

  • 311955 / Norwegian Research Council
  • H-19-47-472 / Swedish-Norwegian Foundation for Equine Research

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