Exercise Induced Pulmonary
Hemorrhage (EIPH) or Bleeding
A certain amount of pulmonary hemorrhage (called EIPH), which is bleeding in the lungs, can occur in any horse engaged in fast or intense exercise. The amount of bleeding can range from just a few red blood cells, detectable only by sensitive tests such as a bronchoalveolar lavage (BAL), to the much more obvious nosebleed. The greater the severity of EIPH, the more the horse's health is affected. Blood in the lungs acts as an irritant resulting in inflammation, and also creates an ideal breeding ground for bacteria.

The most widely accepted theory about the cause of EIPH is that the high blood pressure from heavy exercise coupled with vacuum-like effects that occur during a deep inhalation causes the capillaries to rupture. The only gap in this theory is that it does not explain why almost all of the bleeding occurs in the upper back lobes of the lungs rather than uniformly throughout.

Another theory that helps to explain the location of the bleeding focuses on the anatomy of the running horse. Since a horse's forelegs are not attached to the spine with any bony structures, the action of running causes the shoulders to compress the ribcage. This wave of pressure then spreads outwards causing a shearing force on the tissue in the upper back of the lungs, resulting in bleeding. This type of hemorrhage is similar to the bleeding that occurs from a blunt trauma to the front of the chest or head-that is, the bleeding does not occur at the location of the trauma but on the opposite side of the body. This theory might explain why some horses are more likely to bleed after running on a hard surface, and why some "bleeders" do not respond to Lasix (furosemide).

I have my own additional theory as to why horses bleed. I feel that EIPH occurs because of weakened capillaries secondary to inadequate nutrition. Just as some people bruise easily, some horses bleed easily. The bleeding in horses, however, does not go into the tissues but moves instead into the airways. Many horses also have thick, toxic, and poorly oxygenated blood due to repeated exposure to chemicals and drugs, causing the heart to work harder and the blood pressure to rise. This increased arterial blood pressure, with or without weakened capillary walls, sets the stage for EIPH.

Thanks for reading this preview! The remainder of this section in Holistic Horsekeeping discusses how to diagnose and determine the severity of EIPH as well as how to treat and prevent the condition.

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