3 July, 2012
– Dr John Hodsdon
Perhaps the most widely recognized of all disorders affecting racehorses is “bleeding/epistaxis” or Exercise Induced Pulmonary Hemorrhage (EIPH). We now know that most racehorses bleed at some time during their careers. In fact some horses might bleed every time they undertake strenuous exercise. It also occurs in other disciplines such as 3 day eventers, polo ponies, steeplechasers. The common dominator is strenuous exercise.
Although this condition has been recognized for over 300 years we still have more questions than answers with regards to the cause and prevention of EIPH. Research in the last 30-40yrs has shed more light on why horses bleed, however to date there is still no consensus regarding the true cause of it. The prevention of EIPH is just as controversial mainly due to the use of Lasix and its performance enhancing affects.
Epistaxis (bleeding from the nose) occurs in 0.5 to 2% of race horse depending on different studies. EIPH in its true form (presence of blood in the trachea/lower airways) occurred in a higher number of horses, with 50-60% of race horses having evidence of bleeding in the trachea when scoped 60-90min after strenuous exercise. On bronchoalveolar lavage (BAL, lung wash) nearly all race horses had Hemosiderin (Red Cell breakdown product) in lung macrophages indicating that at some stage a degree of bleeding had occurred in the past.
This tells us that EIPH occurs in most racehorses, however the severity of bleeding varies greatly between horses and tends to worsen with age.
Numerous causes have been proposed for EIPH, including small airway disease, upper airway obstruction, exercise induced hyperviscosity of the blood, mechanical stresses of respiration and locomotion, redistribution of blood flow in the lungs, alveolar pressure fluctuation, and pulmonary hypertension. The above mentioned causes will have an effect, however the most popular theory at present is “pulmonary capillary stress failure”.
In summary the capillaries forming the blood gas barrier rupture due to the high pressure environments that exist in the lungs during strenuous exercise. The blood pressure within the lung increases dramatically during exercise, 2 to 3 times higher than in other species. This is primarily due to cardiac function, when cardiac output and heart rate are high there is naturally an increase in blood pressure, however at maximum output there isn’t sufficient relaxation of the left ventricle to allow rapid filling at normal filling pressure.
Pulmonary blood pressure therefore increases to facilitate blood flow from the lungs to the heart. Further cardiac issues that might increase pulmonary blood pressure during strenuous exercise relate to the AV valve within the heart, during high cardiac output the ventricular pressure may result in regurgitation through the AV valve, and its cross-sectional area when open, may be too small to allow rapid filling without an increase in pressure.
Large changes and fluctuations in lung airway pressure further contribute to the stress on the blood gas barrier. During inspiration a large negative pressure is needed for air flow into the lungs. This, combined with the high positive blood pressure results in extreme forces on the blood gas barrier and the capillaries within, causing them to rupture and bleed into the lungs.
Further issues like upper airway obstruction (roaring, laryngeal hemiplasia) and small airway disease further increase the required size of the negative pressure required for airflow into the lungs therefore exacerbating the problem.
Does EIPH alter athletic ability?
This is still a contentious issue surrounding EIPH as most horses at some stage will bleed to a certain degree. Mild bleeding has minimal or no effect on performance, but severe bleeding will impair performance as the blood will flood the alveoli and small airways preventing the normal exchange of oxygen and carbon dioxide. It is also suspected that repeated bleeds contribute to the development of chronic inflammatory airway disease which is associated with decreased athletic performance. So the effect on performance is related to the degree of hemorrhage. At present there is no method for measuring how much bleeding occurs and what level of bleeding significantly affects performance.
A hot subject at present is Lasix use in the USA, where it can still be used in racing, and is used as the main underlying treatment for EIPH. Lasix works as a diuretic, increasing urine production and therefore decreasing blood volume. During exercise, due to the decreased blood volume, you will also have a decreased pulmonary blood pressure therefore reducing the stress placed on the pulmonary capillaries, and the severity of bleeding. It doesn’t stop the bleeding just the severity of it.
The main controversy surrounding the use of Lasix is whether the drug actually enhances a horse’s ability in any other way. Two research studies done in the USA clearly showed that Lasix is associated with superior racing performance. However the results can be interpreted in two different ways. One school of thought was that the improvement was due to the decrease in the severity of the bleed, while the other stated it was related to the acute weight loss just prior to the race.
Weight loss comes from water loss through urination. Up to 8-10kg weight loss can be expected if feed and water are restricted until after the race, which could be seen as the equivalent of removing that weight in handicap. The truth most likely lies in between the two schools of thought, however as we can’t quantify and relate the severity of the bleed to performance, this can’t be verified.
The Equine Nasal Strip is another product that has shown some promise in reducing EIPH. As stated previously upper airway restriction/obstruction results in an increase in the intra thoracic negative pressure which exacerbates the stress on pulmonary capillaries. Nearly 40-50% of the total pulmonary resistance may result from the nasal passages, and since horses are obligatory nasal breathers, by reducing nasal resistance by maintaining the patency of the nares during strenuous exercise, you will decrease the required negative intra thoracic pressure for airflow into the lungs.
Some of the other popular treatments range from coagulants, conjugated estrogens, inspired water vapour, Cromolyn Sodium, immune products and herbal/nutritional supplements.
The complete prevention or cure of this condition is unlikely due to the large percentage of race horses experiencing EIPH of some degree during strenuous exercise. However the severity of the bleeds need to be controlled and treated, to limit the inflammatory response to blood in the lungs, and stop chronic inflammatory airway disease. Virtually every trainer, owner, groom and vet has a preferred treatment for EIPH illustrating that there is no one universally successful or accepted treatment.
Bosch Hoek Equine Hospital is a state of the art Equine hospital situated in the beautiful Kwa-Zulu Natal Midlands of South Africa. Our primary goal is to offer clients and their horses world class care and expertise for both surgical and medical conditions with a rehabilitation centre to match.
If you require our services or would like to discuss anything please call one of us on the numbers below:
Dr Helen Tiffin 082 966 9324
Dr Jenny Lawrence 082 836 9897
Dr Anna Bowker 082 849 3456 (away until August)
Dr John Hodsdon 072 165 7122
|Dr John Hodsdon
Equine Veterinarian BVSc
John qualified at Onderstepoort in 2003 after which he headed over to the UK where he spent 8yrs in busy equine practices, predominantly in the Suffolk/Essex region. John has a keen interest in lameness, diagnostics and surgery. Being a former Maritzburg boy, he and his young family have now returned to KZN on a permanent basis. His UK equine experience has brought a new dynamic to the practice and complements the existing vets. When John is not busy with horses, he can be found being entertained by his 3 young daughters … who no doubt will be asking Daddy for a pony very soon!