Managing Exercise-Induced Pulmonary Hemorrhage in Racehorses

Racehorses must be healthy and at their peak fitness to be successful. One commonly combated health condition—exercise-induced pulmonary hemorrhage, or EIPH—can be performance-limiting and even deadly among these athletes. And as racehorse medication reform has taken center stage in recent years, the racing world has been rife with controversy over whether to allow horses in America to race while medicated to help control the condition, or to implement a medication-free racing policy, as some racing jurisdictions overseas have.

During the "Current Controversies" session at the 2013 American Association of Equine Practitioners' Convention, held Dec. 7-11 in Nashville, Tenn., Rick Arthur, DVM, looked back at the condition's history, what it does to the horse, and how veterinarians currently treat it.

Arthur, of the University of California, Davis, and the equine medical director for the California Horse Racing Board, explained that two very famous racehorses and prominent sires, Eclipse and Herod, were bleeders. Their bloodlines factor strongly in subsequent generations, so it’s not surprising that many horses competing on today’s racetracks exhibit EIPH.

Arthur said that veterinarians originally thought that the bleeding derived from injury to the blood vessel-rich area within the head. But, in 1974, with the advent of a simple fiber-optic scope, Robert Cook, FRCVS, PhD, identified that the bleeding was coming from the blood vessels within the lungs. This discovery modified how veterinarians approach this syndrome, both diagnosis and treatment. John Pascoe, BVSc, PhD, Dipl. ACVS, and colleagues coined the term "exercise-induced pulmonary hemorrhage" after conducting research Thoroughbred and Standardbred racetracks in the late 1970s, in which they examined horses post-race using a fiber-optic endoscope, Arthur added.

Bleeding is apparent in 40-80% of affected horses on a single examination post-race, depending on endoscope length and other factors, and the condition is evident in 85% or more of horses examined multiple times. But Arthur stressed that the most notable feature is found with cytological (looking at cells beneath a microscope) exam of cells obtained from the trachea during endoscopy; 100% of samples were found to have signs of EIPH. He said that all racehorses bleed, but some are more seriously affected than others.

Arthur explained that studies in Hong Kong carried out in the mid-1980s demonstrated pronounced pathological cellular structure changes in EIPH horses’ lungs, primarily in the dorsal-caudal (top, back) portions of the lung. Similarly, he said, veterinarians have learned they can identify physiological changes with nuclear scintigraphy and lung function tests in horses with advanced EIPH. Both the structure and function of the lung can change in chronic EIPH cases, he said.

Veterinarians grade bleeders on a 0 to 4 scale (in which 4 is most severely affected), describing how much of the trachea’s circumference is streamed with blood. Arthur said the grading scale correlates to performance: The more the trachea is occluded with blood, the worse the horse performs. He noted that EIPH episodes occur not only during races but also training gallops.

Arthur explained that a galloping horse takes up to 130 to 150 breaths per minute and his heart beats a maximum of 220 to 240 beats per minute. The heart beats so rapidly that the left side of the heart (atrium) doesn’t have time to fill, causing blood to back up into the lungs. This increased pressure leads to the blood capillaries breaking and blood entering into the lungs' interstitial spaces (areas between cells). The body’s normal response eventually results in interstitial (surrounding the cells) fibrosis. This scarring in the lung fields compromises the long-term athletic potential of racing athletes, he said, by creating areas of less efficient air exchange through the lungs.

Historically, veterinarians have used furosemide to manage bleeders. Arthur reported it is quite effective in reducing bleeding, particularly in Grade 3 and 4 individuals. He pointed out that in addition experiencing a profound effect on the cardiovascular system, horses can run three to five lengths faster than horses not medicated with furosemide; “to not race on furosemide is a competitive disadvantage.” This has caused nearly all trainers to put their racehorses on this medication.

“The question that remains,” said Arthur, “is whether or not furosemide can alter long-term pathological changes associated with EIPH.”

Considerable research has been done on EIPH over the last 30 years, Arthur concluded, but there is still much to do.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.

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