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Exercise Induced Pulmonary Haemorrhage
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Exercise Induced Pulmonary Haemorrhage (EIPH) refers to the presence of blood in the airways following exercise. The condition occurs in athletic horses and also in racing greyhounds and human athletes.
Up to 80% all racehorses will have blood in their trachea after a race, however, only around 1% will show epistaxis after racing. The exact etiology is unknown, but impact forces of the hooves striking the ground is thought to play a role as this is thought to rupture capillaries in the dorsocaudal area of the lung. Because only around 5% or less of horses show epistaxis, the condition is undetected in most.
It is thought that high transmural pressures in the lungs leads to pulmonary capillary stress failure. The horse has very high pulmonary vascular pressures during intense exercise; commonly exceeding 100mmHg in the pulmonary artery. During expiration the high positive pressures in the pulmonary blood vessels pushing out are opposed by high positive airway pressures pushing back, which does not place undue stress on the thin blood vessel walls. However, during inspiration the high positive pressures in the pulmonary blood vessels pushing out are met by negative pressures distending the blood vessel and placing increased stress on the walls. Studies have shown that significant EIPH occurs above a mean pulmonary artery pressure of around 80-95 mmHg.
This condition is thought to be more prevalent in mares and gelding, than in stallions. It is also thought to be associated with increasing age and airway inflammation.
Typical signs include frequent swallowing or coughing immediately post exercise, with or without the presence of epistaxis. The condition may also be associated with poor performance.
Definitive diagnosis is via endoscopic examination of the trachea following exercise. In severe cases blood may be visible in the trachea immediately after exercise. The most common current practice is to perform endoscopy of the trachea around 30–60 minutes after exercise. Haemorrhage most commonly originates in the dorsocaudal lung lobes, therefore it may take some time to reach the trachea by mucociliary clearance, gravity and ventilation. Blood may be visible in the trachea for several days following an intense exercise. The amount of blood visible in the trachea at the time of examination is most commonly graded on a 0 (no blood) to 4 (airways awash with blood) scale.
Bronchoalveolar lavage (BAL) can also be of diagnostic use. If blood is not visible in the trachea, then examination of the smaller airways in the lung may reveal hemorrhage. In this procedure sedation is commonly used and the endoscope is advanced into the smaller bronchi. BAL is performed and if a horse has experienced EIPH then the fluid that is recovered will be serosanguinous. Upon cytology there will be red blood cells and macrophages will contain haemosiderin, indicating haemorrhage has occurred. The number of red blood cells present can be quantified using a haemocytometer.
Radiographs and pulmonary scintigraphy can be used but are mainly used to exclude other differentials of bleeding.
Treatment and Control
Many treatments have been suggested such as rest, bronchodilators, anti-inflammatories, diuretics, concentrated equine serum and nasal strips. Research has been undertaken to assess which of these work. Currently it is thought that rest, bronchodilators and anti-inflammatories have no effect on the condition, but that diuretics, concentrated equine serum and nasal strips do help.
Hillidge, CJ; Whitlock TW (May 1986). "Sex variation in the prevalence of exercise-induced pulmonary haemorrhage in racing quarter horses". Research in Veterinary Science 40 (3): 406–407.
Meyer, T.S., Fedde, M.R., Gaughan, E.M., Langsetmo, I. and Erickson, H.H. (1998) Quantification of exercise-induced pulmonary haemorrhage with bronchoalveolar lavage. Equine Vet J 30, 284-288.
Newton, JR; Wood JL (September 2002). "Evidence of an association between inflammatory airway disease and EIPH in young Thoroughbreds during training". Equine Veterinary Journal Supplement. Equine exercise physiology 6 (34): 417–424.
Smyth, B (2008) Respiratory System Study Guide, Royal Veterinary College.
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