Measurement of respiratory function by impulse oscillometry in horses.
Authors: van Erck E, Votion D, Art T, Lekeux P
Journal: Equine veterinary journal
Summary
# Impulse Oscillometry as a Clinical Tool for Equine Respiratory Assessment Conventional pulmonary function testing in horses has limited clinical utility owing to technical constraints and poor sensitivity, creating a clear need for alternative diagnostic approaches. Van Erck and colleagues evaluated impulse oscillometry (IOS)—a forced oscillation technique measuring respiratory resistance and reactance across frequencies of 5–35 Hz during spontaneous breathing—in 38 healthy horses and 6 with heaves, establishing reference values and assessing repeatability across different biometric parameters. Critical technical prerequisites emerged: the facemask required excellent airtightness with minimal dead space, and standardised head positioning was essential to prevent upper airway geometry changes from confounding results; importantly, horse size had negligible influence on IOS parameters within standard breeds, enhancing clinical applicability. Horses in heaves crisis demonstrated distinctive diagnostic signatures—specifically, resistance increases greater than 0.10 kPa/l/sec at 5 Hz (R5Hz), with R5Hz values exceeding those at 10 Hz, combined with negative reactance values between 5–20 Hz—and measurements proved reliably repeatable in both health and disease. IOS offers equine practitioners a rapid, minimally invasive method suitable for both clinic and field use, with particular promise for detecting lower airway obstruction and monitoring respiratory disease progression without the constraints imposed by traditional pulmonary function testing.
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Practical Takeaways
- •IOS is a quick, minimally invasive alternative to traditional pulmonary function testing that can be used in clinical and field settings for respiratory assessment
- •Proper technique including airtight facemask fit and standardized head positioning is essential for reliable and repeatable measurements
- •Specific IOS threshold values (R5Hz >0.10 kPa/l/sec, R5Hz>R10Hz, negative Xrs 5-20 Hz) can help identify horses in heaves crisis
Key Findings
- •IOS measurements of respiratory resistance (Rrs) and reactance (Xrs) are repeatable in both healthy and diseased horses
- •An increase in R5Hz >0.10 kPa/l/sec combined with R5Hz>R10Hz and negative Xrs values between 5-20 Hz is indicative of heaves crisis
- •Standardization of head position is necessary to avoid variations in Rrs due to upper airway geometry changes
- •Horse size had negligible influence on IOS parameters in standard-type breeds