Lung function and airway cytologic profiles in horses with recurrent airway obstruction maintained in low-dust environments.
Authors: Miskovic M, Couëtil L L, Thompson C A
Journal: Journal of veterinary internal medicine
Summary
# Lung Function and Airway Cytology in Environmentally Managed RAO Horses Environmental management alone—without ongoing pharmacological treatment—fails to fully resolve the pathophysiology of recurrent airway obstruction (RAO), despite being a cornerstone recommendation in equine respiratory medicine. Miskovic and colleagues examined 24 horses diagnosed with RAO and maintained in low-dust conditions for 1 to 6 years alongside age-matched controls, utilising clinical scoring, comprehensive pulmonary function testing (including forced expiratory manoeuvres), and bronchoalveolar lavage cytology to characterise their airway status. Whilst standard lung function parameters showed no difference between RAO and healthy horses at any timepoint, forced expiratory flow rates between 75–95% of vital capacity remained significantly depressed in RAO horses (P < 0.02), indicating persistent small-airway obstruction independent of disease duration. Notably, cytological examination of lavage fluid revealed no elevation in total cell counts or neutrophil percentages in RAO horses compared to controls, suggesting the mechanical obstruction had become dissociated from active inflammation. These findings imply that once airway remodelling has occurred in RAO, environmental modification alone cannot reverse structural changes, and practitioners should temper expectations about the reversibility of lung function deficits even in optimally managed cases; conversely, the absence of cytologic inflammation provides reassurance that low-dust environments do suppress the inflammatory cascade, potentially preventing further deterioration.
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Practical Takeaways
- •Low-dust environmental management alone is insufficient to resolve airway obstruction in RAO horses; persistent peripheral airway damage likely reflects irreversible structural remodeling requiring ongoing medical intervention
- •Standard lung function tests may underestimate RAO severity—forced expiratory maneuvers are more sensitive for detecting persistent peripheral airway obstruction in apparently stable horses
- •Absence of elevated airway neutrophils on BAL fluid analysis does not indicate resolution of RAO pathology; clinical monitoring and advanced lung function testing remain necessary despite normal cytology
Key Findings
- •RAO horses maintained in low-dust environments showed persistent peripheral airway obstruction (reduced forced expiratory flow at 75-95% vital capacity) at all time points compared to healthy controls (P < 0.02)
- •Clinical scores were significantly higher in RAO horses at 2-3 years post-diagnosis (P = 0.018) but standard lung function parameters showed no differences between groups
- •BALF cytologic evaluation revealed no differences in total nucleated cell counts or differential cell counts between RAO and non-RAO horses at any time point despite persistent obstruction
- •Peripheral airway obstruction in RAO horses appears irreversible and persists without associated cytologic airway inflammation evidence