Exercise-induced pulmonary hemorrhage

EIPH often occurs in horses that race at high speeds, with the number of affected race horses increasing in proportion to the speed and intensity of the exercise. It may occur in racing Thoroughbreds (flat racing, steeplechasing or jump racing), American Quarter Horses (incidence of 50–75%), Standardbreds (incidence of 40–60%), Arabians, and Appaloosas. EIPH also occurs in eventers, jumpers, polo ponies, endurance horses, draft horses that pull competitively, and horses taking part in Western speed events such as barrel racing, reining and cutting. It is rare in endurance horses or draft breeds. The lowest intensities of exercise which may cause EIPH are intense trotting (40–60% maximal oxygen uptake) and cantering at speeds of 16–19 miles per hour (26–31 km/h). EIPH occurs less frequently in stallions than mares or geldings. Approximately 43 to 75% of horses have blood in the trachea and bronchi following a single post-race endoscopic examination. In one study, all horses endoscoped on at least three separate occasions following racing had EIPH at least once. Epistaxis (blood coming from one or both nostrils) is much less common, occurring in 0.25–13% of cases. In a survey of over 220,000 horse starts in UK Flat and National Hunt (jump) racing, 185 cases of epistaxis were identified (0.83 per 1000 starts). Similar frequencies have been reported in Japan (1.5 per 1000 starts) and South Africa (1.65 per 1000 starts), whereas a higher frequency has been reported in Korean (8.4 per 1000 starts). Unless a horse has severe EIPH, with blood present at the nostrils (known as epistaxis), the main sign is usually poor athletic performance; other signs are generally subtle and not easy to detect. Frequent swallowing and coughing in the immediate post-exercise recovery period, and poor appetite post-performance may be suggestive of EIPH. A definitive diagnosis can only be made by endoscopic examination of the trachea. In the case where no blood is visible in the trachea, EIPH in the small airways may still be present and can be confirmed by a bronchoalveolar lavage. Impaired arterial blood gas (oxygen) tensions during intense exercise, increased blood lactate, and rarely death have been noted (likely due to ruptured chordae tendinae or a different mechanism of lung hemorrhage). Epistaxis is diagnosed when blood is visible at either or both nostrils during or following exercise. To confirm whether the blood is coming from the upper or lower airway requires further examination by endoscopy, although in some cases it is not possible to determine the location. In the majority of epistaxis cases, the blood originates from the lung. Epistaxis during or following exercise can less commonly occur as a result of upper airway hemorrhage, for example following head trauma, subepiglottic cysts, atrial fibrillation, or guttural pouch mycoses. EIPH reduces a horse's racing performance. Severe EIPH (epistaxis) shortens a horse's racing career. Moderate to severe EIPH is associated with a worsened finishing position in a race, and finishing farther behind the winner. Horses with mild EIPH earn more prize money than those with more severe EIPH. While single bouts of EIPH may not even be apparent to the rider, owner or trainer of a horse unless an endoscopic examination is undertaken, the effect on performance within a single race appears to be significant but relatively subtle. In a 2005 study, horses finishing races with grade 4 EIPH were on average 6 metres behind those finishing with grade 0. However, the effect of repeated bouts of EIPH that occur with daily training may lead to more significant changes and a greater degree of tissue damage over time with consequent loss of lung function. As only one in ten cases of EIPH have epistaxis (bleeding from the nostrils), and as epistaxis can have causes other than EIPH, various diagnostic tools are used to diagnose EIPH.