Exercise-induced pulmonary hemorrhage
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.
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.
[13] 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[14] with consequent loss of lung function.
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.
A variety of causes have been proposed, but EIPH is most likely a multi-factorial condition, involving airway, vascular, inflammatory, blood, cardiac, locomotory, and remodelling components.
Other contributing factors may include upper airway obstruction, increased blood viscosity, abnormalities of cardiac origin (small cross-sectional area of atrioventricular valves, stiff valves, slow left ventricular relaxation time, right tricuspid valve regurgitation), preferential distribution of blood flow to the dorsocaudal lung regions, mechanical trauma, lower airway obstruction, inflammation, abnormalities of blood coagulation, inhomogeneity of ventilation and locomotory trauma.
This theory is based on the fact that, during galloping, the absence of any bone attachment of the forelegs to the spine in the horse causes the shoulder to compress the cranial rib cage.
[33] The alternate expansion and compression at the microscopic level in adjacent areas of lung tissue creates shear stress and capillary disruption.
The theory predicts that hemorrhage would be more severe on hard track surfaces, but it does not explain why EIPH can occur in horses during swimming exercise.
In the case of horses that consistently demonstrate greater severity of EIPH this is most likely due to congenital factors, such as very high pulmonary vascular pressures.
In horses that experience isolated episodes of increased severity of EIPH, possible contributing factors may include, amongst others, pulmonary infection or atrial fibrillation, inflammation, longer distances, longer duration of exercise, hard surfaces, steeplechasing/hurdling, increased length of career, breed (i.e. Thoroughbred greater than Standardbred), time in training/racing, genetics, and cold temperatures.
Furosemide (trade name: Lasix) administered prior to racing or strenuous exercise in Thoroughbred and Standardbred racehorses reduces the severity EIPH in 68% of horses.
Other vascular agents such as nitric oxide (NO), n-nitro-l-arginine methyl ester (L-Name), nitroglycerin, NO + phosphodiesterase inhibitors (e.g., sildenafil), and endothelin receptor antagonists have no effect, and in some cases worsen of the EIPH.
Equine nasal strips are a non-pharmacological option with strong scientific support for the prophylactic reduction of exercise-induced pulmonary hemorrhage (EIPH).
Numerous studies [35] [36][37][38][39][40] have hypothesized—and Holcombe et al. (2002) [41] confirmed—that the strip’s spring-like action prevents collapse of the soft tissues within the nasal cavity.
Moreover, the nasal strip elicits a proportionately greater reduction in inspiratory resistance and EIPH as exercise duration and intensity increases.
[35,37,38,40] Nasal strips are widely approved for flat and harness racing in North America, multiple international jurisdictions, and by all major non-racing regulatory bodies.
Other anti-inflammatory agents, such as hesperidin-citrus bioflavinoids, vitamin C, NSAIDs such as phenylbutazone, corticosteroids, heated water vapor therapy, cromoglicic acid or nedocromil, have no beneficial effects in reducing EIPH severity.
Other ineffective treatments include leukocyte elastase protease inhibitors, the EIPH Patch, hyperbaric oxygen therapy, pentoxyfylline, guanabenz, clonidine, snake venom, and enalapril.
Horses that undergo surgical correction for upper airway dysfunction are rested, and are under environmentally controlled environments with reduced dust may see some benefit.
In conclusion, administering furosemide (Lasix) four hours before racing and wearing equine nasal strips (FLAIR®) are the only treatments scientifically proven to effectively reduce EIPH in horses.
