Exercise-induced pulmonary hemorrhage (EIPH) occurs in most
racehorses and is observed in many other horses used in equine
sports (eg, polo, barrel racing, 3-day events) that require
strenuous exercise for short periods of time. Epistaxis is
observed in a small proportion (~5%) of horses with EIPH. Blood
in the tracheobronchial tree is identified in 45–75% of
racehorses via endoscopic examination, and hemorrhage is
detected by cytologic examination of bronchoalveolar lavage in
>90% of racehorses. Proposed pathophysiologic mechanisms for
pulmonary hemorrhage include high pulmonary vascular pressures
during maximal exercise, neovascularization secondary to
pulmonary inflammation, and intrathoracic shear forces generated
during exercise. Some research suggests EIPH results from
thickening of pulmonary vein walls, resulting in decreased
luminal diameter and increased intravascular pressure at the
level of the pulmonary capillaries. Endoscopic observation of
blood in the airways 30–90 min after exercise provides d