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. Effects on performance 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. Diagnosis 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. Endoscopy EIPH is most commonly diagnosed by endoscopic examination of the trachea and larger bronchi, with the optimal timing for endoscopy being 60–90 minutes after hard exercise. This post-exercise delay allows time for blood within the lungs to travel to the trachea. Blood can usually be detected in the trachea or bronchi for 1–3 days after an episode of EIPH, but may be present for up to a week.