Influence of breathing pattern and lung inflation on impulse oscillometry measurements in horses.
Authors: Van Erck E, Votion D, Kirschvink N, Genicot B, Lindsey J, Art T, Lekeux P
Journal: Veterinary journal (London, England : 1997)
Summary
# Editorial Summary: Breathing Pattern Effects on Impulse Oscillometry in Horses Impulse oscillometry (IOS) is increasingly used to assess equine respiratory mechanics non-invasively, but whether breathing parameters affect measurements has remained unclear. Researchers performed controlled in vitro testing on isolated equine lungs whilst manipulating inflation levels and ventilation patterns, followed by in vivo studies in five healthy horses where breathing was altered via lobeline hydrochloride injection, with measurements compared against a current reference technique. Respiratory rate and tidal volume had negligible influence on IOS parameters across a wide physiological range (7–42 breaths/min and 0.4–25 L respectively), though lung inflation did produce minor effects on resistance at 5 Hz. The critical finding emerged from in vivo data: maximal pleural pressure changes and peak airflow velocities—rather than breathing frequency alone—were the primary drivers of resistance and reactance variability, with hyperpnoeic breathing (fourfold increase in pleural pressure swings) significantly increasing respiratory system resistance at 5 and 10 Hz and decreasing reactance across all frequencies. For practitioners, this means IOS readings remain reliable when horses simply breathe faster at rest, but results will legitimately reflect genuine mechanical changes during forced or laboured breathing, making the technique valuable for detecting altered respiratory mechanics rather than being confounded by tachypnoea alone.
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Practical Takeaways
- •IOS measurements in horses are stable across normal variations in respiratory rate and breathing depth, allowing valid comparisons without strict breathing control protocols
- •Changes in IOS parameters reflect actual alterations in respiratory mechanics from hyperpnoea rather than artefactual effects from breathing pattern variations
- •Clinicians can use IOS to detect pathological changes in respiratory mechanics even when horses show variable breathing patterns during testing
Key Findings
- •Respiratory rate (7-42 breaths/min) and tidal volume (0.4-25 L) had minor or no influence on impulse oscillometry parameters
- •Lung inflation effects on resistance at 5 Hz were limited within physiological ranges
- •Maximal pleural pressure changes and peak flows were the main determinants of respiratory system resistance and reactance variability
- •Hyperpnoeic breathing caused fourfold increase in pleural pressure and significant increases in resistance at 5-10 Hz with decreases in reactance at all frequencies