Plethysmographic comparison of breathing pattern in heaves (recurrent airway obstruction) versus experimental bronchoconstriction or hyperpnea in horses.
Authors: Hoffman Andrew M, Oura Trisha J, Riedelberger Klaus J, Mazan Melissa R
Journal: Journal of veterinary internal medicine
Summary
# Editorial Summary Recurrent airway obstruction (heaves) in horses produces the characteristic "heave line" and visibly increased abdominal effort during breathing, yet whether this abdominal motion actually contributes meaningfully to ventilation has remained unclear. Researchers used plethysmography to measure the timing and contribution of rib cage versus abdominal movements in 15 heaves-affected horses compared with healthy controls at rest, during experimentally induced bronchoconstriction, and during naturally increased breathing rates, quantifying the phase angle (temporal lag) between compartments and each region's share of tidal volume. Heaves horses displayed severe asynchrony between rib cage and abdomen—the abdomen consistently lagged behind the rib cage, expiratory airflow patterns became chaotic rather than biphasic, and despite visible abdominal effort, the abdomen actually contributed *less* to ventilation than in controls; most strikingly, five horses exhibited "abdominal paradox" where abdominal movement was completely out of sync with airflow, causing measurable reductions in tidal volume and compensatory increases in breathing rate. Although bronchodilators improved asynchrony to some degree, the timing mismatch remained significantly worse in heaves horses even after treatment. For practitioners, this reveals that visible abdominal exertion in heaves is largely ineffective breathing—the horse is working harder with that compartment whilst it performs paradoxically, making airway management and anti-inflammatory therapy particularly important for restoring efficient ventilation patterns and reducing the respiratory muscular fatigue these horses experience.
Read the full abstract on PubMed
Practical Takeaways
- •The 'increased abdominal effort' observed clinically in heaves horses is ineffective and paradoxical—the abdomen is working out of sync with actual ventilation, so clinical impression does not reflect functional contribution to breathing
- •Heaves represents a mechanical breathing pattern disorder beyond simple airway obstruction; even after bronchodilation the rib cage/abdominal asynchrony persists, suggesting management must address both airway and respiratory mechanics
- •Assessment of respiratory effort in heaves cases should not rely on visible abdominal motion alone—plethysmographic evaluation or similar tools may be needed to understand true ventilatory contribution and treatment response
Key Findings
- •Horses with heaves exhibit severe rib cage/abdominal asynchrony with phase angle (theta) significantly increased compared to controls, with the abdomen consistently lagging behind the rib cage
- •Loss of biphasic expiratory flow pattern is unique to heaves group and represents a distinctive breathing pattern abnormality
- •Abdominal contribution to tidal volume is reduced in heaves despite clinical appearance of increased abdominal effort, with 5 horses showing abdominal paradox and significant reduction in tidal volume
- •Bronchodilation partially reduced theta in heaves (P=0.06) but theta remained significantly higher than controls, indicating mechanical dysfunction persists despite airway opening