Cardiorespiratory and metabolic responses to exercise in horses with various abnormalities of the upper respiratory tract.

The study examines how various upper respiratory tract abnormalities in racehorses, including idiopathic laryngeal hemiplegia (ILH), maxillary sinus cysts, epiglottic entrapment, vocal fold lesions, and pharyngitis, affect the horses’ cardiorespiratory and metabolic responses during exercise.

Research Methods

• A group of 13 racehorses suffering from various upper respiratory abnormalities underwent a standardized incremental exercise test. This included 9 horses with idiopathic laryngeal hemiplegia (ILH), and one each with maxillary sinus cysts, epiglottic entrapment, vocal fold lesions, and pharyngitis.
• Their results were compared to those of 20 normal racehorses. Additionally, two of the horses with ILH were tested again following surgical treatment for ILH (laryngoplasty and ventriculectomy).
• The researchers assessed several parameters during treadmill exercise on a steep incline, including heart rate, plasma lactate concentration, arterial blood gases, stride frequency, oxygen uptake (VO2), and carbon dioxide production.

Findings

• The results indicated horses with ILH showed significantly lower peak VO2 values compared to normal horses. This suggests that ILH affects the ability of the horse to take up and utilize oxygen during intense exercise.
• Horses with ILH also showed significantly higher arterial carbon dioxide tensions at lower speeds with a heart rate of 200 bpm and at 10 m/s, suggesting potential difficulties with carbon dioxide clearance from the blood.
• The horse with maxillary sinus cysts showed similarly elevated carbon dioxide tensions and abnormalities in several cardiorespiratory and metabolic indices, suggesting similar effects from this condition.
• Interestingly, horses with vocal fold lesions, aryepiglottic entrapment and pharyngitis showed arterial blood gas and cardiorespiratory indices in line with normal horses, indicating that these particular upper respiratory abnormalities may not significantly affect exercise capacity.
• Post-operative results from the two horses previously suffering from ILH showed mixed results. One showed improvements in arterial blood gases and cardiorespiratory indices while the other did not demonstrate any improvement post-surgery.

Conclusion

• The authors concluded that assessing arterial blood gases and cardiorespiratory indices during strenuous exercise can provide useful insights into exercise capacity in horses with varying upper respiratory abnormalities. This information could prove useful for making medical and training decisions for these animals.