Relationship between clinical signs and lung function in horses with recurrent airway obstruction (heaves) during a bronchodilator trial.
Authors: Robinson N E, Olszewski M A, Boehler D, Berney C, Hakala J, Matson C, Derksen F J
Journal: Equine veterinary journal
Summary
# Editorial Summary Robinson and colleagues investigated whether straightforward clinical assessment of respiratory effort reliably detects airway obstruction in horses with recurrent airway obstruction (heaves), using a bronchodilator challenge model. Six affected horses underwent 13 measurement periods whilst receiving graded doses of pirbuterol, yielding 468 paired observations of clinical signs (scored 1–4 for nasal flaring and abdominal effort, maximum total 8) and objective lung function measures including resistance, dynamic elastance, and pleural pressure changes. Clinical scoring proved significantly predictive of lung function changes when total scores exceeded 5, correlating well with shifts in breathing strategy, peripheral airway mechanics, and respiratory effort; however, below this threshold, horses showed substantial objective airway obstruction—evident in resistance and elastance measurements—despite minimal clinical signs. This disconnect between clinical appearance and measured pathophysiology has important implications: relying on visual assessment alone risks missing genuine airway disease in its earlier or milder stages, potentially delaying intervention when management or pharmacological support could be most effective, and underscores the value of objective lung function testing (such as transpulmonary pressure measurement or resistance assessment) as a complementary diagnostic tool in equine respiratory practice.
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Practical Takeaways
- •Clinical signs of heaves (nasal flaring, abdominal effort) underestimate disease severity in early/mild cases—horses with subtle signs may have significant airway obstruction requiring objective testing for accurate diagnosis
- •A clinical score threshold of 5 appears to represent a clinically meaningful level of obstruction; lower scores warrant further investigation with lung function testing rather than reassurance based on appearance alone
- •Implementation of accessible lung function testing in practice could improve early detection and monitoring of recurrent airway obstruction, preventing progression of subclinical disease
Key Findings
- •Clinical scoring system for nasal flaring and abdominal effort significantly correlated with objective lung function measurements across 468 assessments in 6 horses
- •Clinical scores above 5 reliably reflected changes in breathing strategy, peripheral airway obstruction, and breathing effort; scores below 5 failed to detect low-grade airway obstruction despite significant pulmonary resistance
- •Pirbuterol dose-response produced measurable changes in peak inspiratory/expiratory flow, dynamic elastance, and pleural pressure that correlated with clinical signs only at higher obstruction levels
- •Clinical examination alone misses mild to moderate airway disease, suggesting lung function testing would improve diagnostic sensitivity for recurrent airway obstruction