Exercise-induced pulmonary hemorrhage (EIPH) describes a condition that occurs when horses bleed into their lungs during racing or any other vigorous exercise.
When severe, EIPH causes horses to perform poorly and for many horses this ends their athletic career. Some horses die from this condition.
The reason why horses bleed is poorly understood, therefore no fully effective medication or management is available. Teams of researchers are working to identify the causes of EIPH with the hope that soon, effective medication can be developed and horse owners can know more about how to manage horses with the condition.
Bleeding appears to be related to the speed of exercise with greater risk in horses exercising at maximum speed and effort. Recent research shows that the pulmonary artery blood pressures increase dramatically during heavy exercise because of the need for oxygen by the rapidly contracting muscles.
According to one important theory, locomotory impact can produce lung tissue damage resulting in localized bruising and bleeding from the lungs. Many other factors may contribute, including age of the horse, airway inflammatory conditions, small airway disease, capillary pressure within the lungs, track surface, training methods, and body and lung conformation.
Recently researchers at the Equine Veterinary Hospital at Michigan State found scarring around blood vessels in the lungs of EIPH-affected Thoroughbred racehorses. Their theory is that this scarring around blood vessels obstructs these veins causing blood to back up into the lung, causing vessel rupture which causes the horse to bleed..
Currently these researchers are investigating the cause of the scarring by beginning to identify molecules in the vein walls that may be responsible for this scarring. They found that vigorous exercise causes changes in the molecular content of vein walls that may be responsible for the scarring. Future studies are needed to evaluate the role of these molecules in causing EIPH.