Dynamic upper airway changes and arterial blood gas parameters during treadmill exercise

Area of Science:

• Equine respiratory physiology
• Exercise-induced respiratory disease in horses

Background:

• Dynamic upper airway abnormalities are a concern in equine athletes.
• Understanding the link between upper airway dysfunction and gas exchange is crucial for performance.

Purpose of the Study:

• To investigate the relationship between dynamic upper airway abnormalities and arterial blood gas tensions during high-speed exercise in horses.
• To identify specific upper airway abnormalities associated with impaired gas exchange.

Main Methods:

• High-speed treadmill exercise testing with simultaneous upper airway videoendoscopy and arterial blood gas analysis.
• Inclusion of control Thoroughbreds for normative blood gas values.
• Echocardiography and tracheal washes were performed post-exercise.

Main Results:

• 45% of horses exhibited upper respiratory tract (URT) abnormalities, with 45% of these showing significantly lower exercising PaO2 and 35% showing elevated PaCO2.
• Pharyngeal collapse (PC) was strongly associated with abnormal blood gases, especially when it was the sole identified disorder.
• Horses without URT disease, particularly Standardbreds, also demonstrated a high incidence of abnormal blood gases, suggesting other factors may be involved.

Conclusions:

• Dynamic upper airway dysfunction, including pharyngeal collapse, can significantly impair gas exchange during strenuous exercise in horses.
• While multiple URT abnormalities increase the likelihood of gas exchange issues, PC is a key contributor.
• Standardbreds without apparent URT disease showed a higher prevalence of abnormal blood gases, indicating a need for further investigation into non-URT related causes of exercise intolerance.