Relationship of pulmonary arterial pressure to pulmonary haemorrhage in exercising horses.
Authors: Langsetmo I, Meyer M R, Erickson H H
Journal: Equine veterinary journal
Summary
# Editorial Summary: Exercise-Induced Pulmonary Haemorrhage and Pressure Thresholds Exercise-induced pulmonary haemorrhage (EIPH) develops when pulmonary capillaries fail under excessive transmural pressure during intense work, but the specific pressure at which this capillary stress failure occurs in horses has remained unclear. Langsetmo and colleagues measured pulmonary arterial and oesophageal pressures in five geldings exercised at four different speeds (9–15 m/s) over multiple sessions, calculating transmural pressure by electronic subtraction and quantifying red blood cells in bronchoalveolar lavage fluid collected within an hour of exercise. Haemorrhage became significantly apparent only at the highest speed (15 m/s), with analysis revealing a critical threshold of approximately 95 mmHg transmural pulmonary arterial pressure, above which capillary rupture and red cell lysis consistently occurred. This work establishes that high-speed sprint exercise frequently exceeds the pressure tolerance of the equine pulmonary circulation, with immediate practical implications for racing operations: monitoring exercise intensity and recognising that even elite performers regularly sustain subclinical or clinical pulmonary bleeding during competition-level speeds. Understanding this physiological ceiling may inform decisions around training protocols, racing schedules, and interventions aimed at reducing cumulative airway damage in athletic horses.
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Practical Takeaways
- •Horses exercised at very high speeds (15 m/s) are at significantly higher risk of EIPH than those at moderate speeds; monitor for clinical signs and consider exercise intensity management
- •A physiological pressure threshold for pulmonary haemorrhage exists; this knowledge can help inform training programmes to avoid excessive capillary stress
- •Bronchoalveolar lavage within 1 hour post-exercise is a useful diagnostic tool for detecting subclinical EIPH in performance horses
Key Findings
- •Haemorrhage occurs at a transmural pulmonary arterial pressure threshold of approximately 95 mmHg in exercising horses
- •Red cell counts in bronchoalveolar lavage fluid were significantly elevated only after high-speed runs at 15 m/s, not at lower speeds (9, 11, 13 m/s)
- •Red cell lysis was apparent at transmural pulmonary arterial pressures above 90 mmHg
- •High-speed sprint exercise frequently exceeds the pulmonary arterial pressure threshold at which haemorrhage occurs