October 14, 2019

Bleeders - the facts, fiction and future direction

October 14, 2019/ Webmaster

By Dr. David Marlin

Bleeders - the facts, fiction and future directionWe are now approaching half a century since Bob Cook pioneered the use of the flexible fibreoptic endoscope, which allowed examination of the respiratory tract in the conscious horse. One of the impo…

We are now approaching half a century since Bob Cook pioneered the use of the flexible fibreoptic endoscope, which allowed examination of the respiratory tract in the conscious horse. One of the important outcomes of this technique was that it opened the door to the study of ‘bleeding’ or exercise-induced pulmonary haemorrhage (EIPH). But nearly 50 years on the irony is perhaps that whilst we have become good at describing the prevalence of EIPH and some of the factors that appear to increase the severity of EIPH within individual horses, we still lack a clear understanding of the condition and how to manage it. I use the term manage rather than treat or prevent as our knowledge of EIPH must show us that EIPH cannot be stopped entirely; it is a consequence of intense exercise. The other irony is that in the past 50 years, by far the majority of research into the management of EIPH has focussed on the use of the diuretic furosemide. Whilst we have good evidence from controlled studies that furosemide reduces the severity of EIPH on a single occasion, we still lack good evidence to suggest that furosemide is effective when used repeatedly during training and or racing; and there is also evidence to the contrary.

Let’s review some basic facts about EIPH, which should not be contentious.

EIPH is the appearance of blood in the airways associated with exercise.
EIPH occurs as a result of moderate to intense exercise. In fact, EIPH has been found after trotting when deep lung wash (bronchoalveolar lavage or BAL) is done after exercise.
EIPH most often involves the smallest blood vessels (capillaries) but can sometimes and less commonly be due to the rupture of larger blood vessels.
The smallest blood vessels are extremely thin. Around 1/100th the thickness of a human hair. But this extremely thin membrane is also what allows racehorses such as thoroughbreds, standardbreds and Arabs to use oxygen at such a high rate and is a major reason for their athleticism.
EIPH is a progressive condition. The chance of seeing blood in the trachea after exercise increases with time in racing.
EIPH is variable over time, even when horses are scoped after the same type of work.
If you ‘scope a horse after three gallops in a row, you can expect to see blood in the trachea on at least one occasion.
EIPH damage to the lungs starts at the back and top, and over time moves forward and down and is approximately symmetrical.
Following EIPH the lung becomes fibrotic (as scar tissue), stiffer and does not work as well. The iron from the blood is combined with protein and stored permanently in the lung tissue where it can cause inflammation.
High blood pressure within the lung is a contributing factor in EIPH. Horses with higher blood pressure appear to suffer worse EIPH.
There is also evidence that upper airway resistance and breathing pattern can play a role in EIPH.
Airway inflammation and poor air quality may increase the severity of EIPH within individual horses.
Increasing severity of EIPH appears to have an increasing negative effect on performance.
Visible bleeding (epistaxis) has a very clear and marked negative effect on performance.

In order to make progress in the management of EIPH (i.e., to minimise the severity of EIPH in each individual), there are certain steps that trainers can take based on the information we have to date.

These include:

Ensuring good air quality in stables
Regular respiratory examination and treatment of airway inflammation
Reduced intensity of training during periods of treatment for moderate to severe airway inflammation
Extended periods of rest and light work with a slower return to work for horses following viral infection
Addressing anything that increases upper airway resistance (e.g., roaring, gurgling)
Avoiding intense work in cold weather
Avoiding extremes of going
Limiting number of training days in race preparation and increasing interval between races

FUTURE OPPORTUNITIES IN UNDERSTANDING AND MANAGING EIPH

We have to accept EIPH as a normal consequence of intense exercise in horses. Our aim should be to reduce the severity to a minimum in each individual horse. However, there are areas in which we still need a much greater scientific understanding.

What actually causes the capillaries to leak or rupture?…

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March 22, 2019

EIPH: An Australian Perspective with Worldwide Implications

March 22, 2019/ Web Master

Exercise-induced pulmonary haemorrhage (EIPH) is a common disease of racehorses. The precise cause of EIPH is yet to be fully determined, but a well-accepted theory is that lung blood vessels rupture in response to the extremely high blood pressure …

By Ellie Crispe and Guy Lester

Exercise-induced pulmonary haemorrhage (EIPH) is a common disease of racehorses. The precise cause of EIPH is yet to be fully determined, but a well-accepted theory is that lung blood vessels rupture in response to the extremely high blood pressure and low airway pressure experienced during strenuous exercise. The barrier that separates the airway from the blood vessels is ultra-thin to facilitate the efficient exchange of gases, but this predisposes to breakage. The condition is most frequently described in Thoroughbred and Standardbred racehorses, but it has also been identified in racing Appaloosas and Quarter Horses, as well as horses involved in other high intensity athletic activities, including showjumpers, 3-day eventers, barrel racers, steeplechasers and polo horses.

EIPH is not unique to horses and has been reported in human athletes, as well as racing greyhounds and camels. Our group at Murdoch University in Perth Australia has had an interest in EIPH, which has led to three recent publications in the Equine Veterinary Journal.1-3

How common is EIPH?

Blood from both nostrils—also known as epistaxis—is the most obvious manifestation of EIPH and occurs between 1.5 and 8.4/1000 race starts, varying with racing jurisdiction. Epistaxis represents a severe manifestation of EIPH, and basing surveys on its presence vastly underestimates the true prevalence of lung haemorrhage. There are several techniques used to diagnose EIPH, but endoscopy of the trachea 30-120 minutes after racing or galloping is a common and reliable method. Occurrence and severity of pulmonary haemorrhage is typically graded using a 0-4 scale. Using endoscopy, we reported a prevalence of EIPH post-race in Australian thoroughbreds racing on turf tracks of around 55%, with most positive horses having low to moderate volumes of blood in the trachea. EIPH is less common if horses are examined after trialling, and reduced further if examined after track gallops. The prevalence of EIPH increases when horses are examined on multiple occasions after racing, and in fact all horses in our research population that had seven monitored race-starts experienced EIPH on at least one occasion.

What is the effect of EIPH on race-day performance?

It is generally considered that EIPH has a negative impact on racing performance, but evidence for this assertion is surprisingly lacking. We performed 3,794 post-race endoscopy exams on over 1,500 Australian horses and reported that inferior race-day performance was limited to horses with severe EIPH (grades 3 and 4); this reflected only 6.3% of all examinations. Horses with the highest grades of EIPH (grade 4) were less likely to finish in the first three, finished further from the winner, were less likely to collect race earnings, were slower over the final stages of the race, and were more likely to be overtaken by other competitors in the home straight than horses without EIPH. Interestingly, horses with EIPH grade 1 or 2 were more likely to overtake others in the home straight, compared to horses without EIPH (grade 0).

It is highly unlikely that low-grade EIPH (grade 1 or 2) confers an athletic advantage; a plausible explanation is that horses that are ridden competitively to the finish are functioning at their maximal physiological limit, compared to horses that are eased up, and overtaken, during the finishing stages of the race because they are not in prize contention or are affected by interference in the home straight. Another interesting finding was that horses with moderate to severe EIPH (grades 3 or 4) raced the early and mid-sections of the race faster than horses without EIPH. It is possible that these horses reach the breaking threshold of the small lung blood vessels at an earlier stage in the race compared to horses that start the race slower, compounding the severity thereafter. A study of barrel racing horses reported that horses with the most severe grade of EIPH were faster than horses without EIPH, a finding which may also reflect this rapid acceleration increasing the risk of EIPH. It may be wise for trainers to instruct jockeys riding horses with a history of moderate to severe EIPH to refrain from racing in this manner.

What is the effect of a one-off diagnosis of EIPH over a horse’s career?…