Inclined running increases pulmonary haemorrhage in the Thoroughbred horse.
Authors: Kindig C A, Ramsel C, McDonough P, Poole D C, Erickson H H
Journal: Equine veterinary journal
Summary
# Editorial Summary: Inclined Running and Exercise-Induced Pulmonary Haemorrhage Exercise-induced pulmonary haemorrhage (EIPH) in racehorses results from both high blood pressure within the lungs and mechanical stress from breathing dynamics, yet the relative contribution of each mechanism remains unclear. Kindig and colleagues investigated this question by exercising six Thoroughbreds to fatigue on both level and 10% inclined treadmills, measuring pulmonary arterial pressure, ventilatory patterns, and EIPH severity via bronchoalveolar lavage fluid analysis. Inclined running produced a characteristic ventilatory shift—lower breathing frequency (122.6 versus 127.8 breaths/minute) but greater tidal volumes (13.1 versus 11.5 L)—whilst simultaneously reducing peak pulmonary arterial pressure by approximately 9 mmHg compared to level running. Despite this reduction in intravascular pressure, EIPH severity increased significantly during inclined exercise (49.6 versus 37.0 × 10⁶ red blood cells/ml), suggesting that mechanical stress from larger pressure swings in the pleural space and lungs matters substantially. For practitioners managing EIPH-prone horses, this finding underscores that workload intensity alone cannot predict bleeding risk; the *mechanics* of breathing—shaped by exercise gradient, stride frequency and lung mechanics—equally influence capillary failure and warrant consideration when designing training programmes and managing upper airway conditions that alter respiratory patterns.
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Practical Takeaways
- •Inclined training/racing increases pulmonary bleeding risk in Thoroughbreds even when peak arterial pressures are lower, suggesting track gradient is an underappreciated risk factor for EIPH
- •The increased tidal volumes and breathing pattern changes with inclined work may be as important as peak pulmonary pressure in triggering capillary failure
- •Training program design should consider that hill work may require modified intensity or additional recovery time to minimize EIPH severity
Key Findings
- •Inclined (10%) treadmill running increased EIPH severity (49.6 vs 37.0 × 10⁶ RBC/ml BAL fluid) despite reduced peak pulmonary arterial pressure (96 vs 105 mmHg)
- •Inclined running reduced breathing frequency (122.6 vs 127.8 breaths/min) while increasing tidal volume (13.1 vs 11.5 L)
- •Time to fatigue and end-exercise lactate levels were similar between level and inclined running conditions
- •Extravascular factors (intrapleural pressure changes from altered ventilatory patterns) appear to play an important role in EIPH aetiology independent of intravascular pressure