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: Breathing Mechanics in Equine Heaves Recurrent airway obstruction (heaves) in horses is clinically characterised by visible abdominal effort during breathing, yet whether this abdominal contribution actually improves ventilation has remained unclear. Using plethysmography to measure rib cage and abdominal motion simultaneously, researchers compared 15 horses with naturally occurring heaves against healthy controls at rest, during experimentally induced hyperpnoea and bronchoconstriction, quantifying the phase relationship (asynchrony) between compartments and their relative contributions to tidal volume. The heaves group exhibited severe rib cage/abdominal asynchrony with markedly increased phase angles, loss of normal biphasic expiratory flow patterns, and critically, a *reduced* abdominal contribution to ventilation—contrary to the appearance of exaggerated abdominal effort; a subset of five horses displayed "abdominal paradox," where abdominal motion completely opposed airflow despite observable muscular effort, resulting in significantly lower tidal volumes and compensatory tachypnoea. Although bronchodilation partially improved these metrics, the asynchrony persisted substantially above control levels, suggesting that the mechanical dysfunction in heaves involves both reversible airway obstruction and irreversible breathing pattern abnormality. For practitioners, this finding reframes what we observe clinically: the dramatic abdominal breathing in heaves represents inefficient, dyscoordinated effort rather than beneficial ventilatory compensation, with important implications for understanding disease severity, prognosis, and the limitations of airway-directed therapy alone in managing these cases.
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Practical Takeaways
- •The visible 'abdominal effort' in heaves horses does not translate to effective ventilatory contribution—the rib cage is doing most of the work despite appearing less active
- •Some heaves horses develop abdominal paradox where abdominal muscles work against airflow; recognition of this pattern may help identify more severe cases
- •Airway obstruction alone doesn't fully explain breathing mechanics in heaves; neuromuscular coordination of breathing compartments is fundamentally altered and incompletely reversed by bronchodilation
Key Findings
- •Heaves is characterized by severe rib cage/abdominal asynchrony with phase angle significantly increased compared to controls
- •Abdominal contribution to ventilation is reduced in heaves despite visible increased abdominal effort
- •A subgroup of heaves horses (n=5) showed abdominal paradox with significantly reduced tidal volume and increased respiratory rate
- •Bronchodilation reduced asynchrony but phase angle remained significantly higher in heaves horses compared to controls