Proven Protection for Equine Respiratory Health and Performance
In the Press: Lung Bleeding in Horses
Lung Bleeding in Horses: What do we know so far?
A pressing need exists for large-scale field trials of nasal strips on horses to measure how well they reduce bleeding in the lungs, according to researchers.
Ideally, this assessment should use a technique known as bronchoalveolar lavage, in which a measured amount of saline solution is introduced to the lungs then gathered for analysis.
The bleeding, referred to as exercise-induced pulmonary hemorrhage (EIPH), is seen most commonly in racehorses, but can also occur in greyhounds and healthy human athletes, as well as in patients with conditions such as heart failure.
Investigations using bronchoalveolar lavage indicate that lung bleeding occurs in almost all horses in racing or training.
The 2015 American College of Veterinary Internal Medicine Consensus Statement made the strong recommendation that EIPH in horses be considered a disease rather than a “condition”.
EIPH arises in healthy exercising horses due to high pulmonary capillary pressures and very negative alveolar pressures that build up across the thin blood–gas barrier in the lungs. This barrier ruptures, allowing blood to invade the lungs.
Consequently, the most effective approaches to reducing EIPH have focused on lowering either pulmonary capillary intraluminal pressures through use of the drug furosemide (marketed as Lasix), or alveolar negative pressures by use of nasal strips and long-term management of airway health.
Kansas State University researchers David Poole and Howard Erickson have reviewed scientists’ current understanding of EIPH in the journal Veterinary Medicine: Research and Reports. Poole is professor of exercise physiology in the Department of Kinesiology and Erickson is professor of anatomy and physiology within the university’s veterinary college.
EIPH occurs mainly in Thoroughbreds, Quarter horses and Standardbreds during sprint racing. It also occurs across other high-performance equine athletes.
It is capable of progressively damaging a horse’s lungs, reducing its athletic career.
Horses with either no or mild bleeding have a four-fold higher chance of winning a race as their counterparts with moderate or severe EIPH, the pair wrote.
Bleeding from the nostrils is the most visible form of EIPH, with the condition recognized at least since Elizabethan times.
In 1981, endoscopy revealed that around 70% of horses had significant blood in their airways after racing. “It is now recognized that the vast majority, if not all, performance horses experience EIPH, but fatalities attributed to EIPH are uncommon.”
Thoroughbred horses, they noted, have been bred for speed, with a heart that can be up to 2 percent of their body mass compared with 0.5 to 1 percent for other mammals.
“Notwithstanding the extraordinary dimensions of racehorse lung surface area, the physical constraints of the chest wall have resulted in a structure that is underbuilt in comparison with the heart,” they observed.
“In addition, the necessity for long extrathoracic airways (increasing dead space and airway(s) resistance) and the presence of collapsible nasal passageways provide additional impediments to pulmonary function.”
Visible bleeding from the nose was the original method of diagnosing EIPH and, although considered to be a serious problem, its relatively rare occurrence – between 0.25 and 13 percent of all sprinting horses – lessened concern.
A comprehensive analysis of 250,000 race starts published in 2001 reported the incidence of obvious nose bleeds to be only 0.15%. That investigation and subsequent work noted that nose-bleeding/EIPH was most prevalent in shorter higher intensity races and steeplechases, among older horses, in males, and on cooler days.
Poole and Erickson traversed the diagnosis and prevalence of EIPH before turning to prevention and treatment.
Given the complex cause of EIPH, it was not surprising that it had not been eradicated or that a unified treatment strategy had not been identified, they said.
Therapeutic countermeasures at best reduced, but did not prevent, EIPH and were aimed at either limiting its severity or reducing the resulting harm, which included inflammation and infection as well as possibly fibrosis and venous remodeling.
The pair said the issue was complicated by the fact that weight losses of up to 20kg induced by the diuretic furosemide amounted to a substantial performance enhancer.
“Where permitted in North America, South America, Saudi Arabia and the Philippines, furosemide is the most commonly used race-day EIPH treatment,” they noted.
Discussing nasal strips, the pair said the requirement of horses to breathe through the nose meant that nasal resistance was far more important to inhalation and airflow in horses than in humans.
“During forceful inhalations when galloping, partial collapse of the unsupported nasal passages occurs, and this increases airways resistance.”
Thus, the use of FLAIR nasal strips to stabilize the nasal wall and prevent the partial airway collapse reduced the pressure swings that contributed to capillary pressures near the blood-gas barrier, thereby reducing EIPH by up to 50% as assessed by bronchoalveolar lavage.
Other interventions have been developed, but few have stood up to scientific scrutiny, they noted.
In conclusion, they said EIPH resulted from catastrophic mechanically induced rupture of the thin blood–gas barrier in the lungs.
Anything that increased the positive capillary intravascular pressures or the negative alveolar pressures would exacerbate EIPH.
“In terms of therapeutic countermeasures that have scientifically proven efficacy in reducing but not abolishing EIPH, furosemide is by far the most widely used.
“Given the likelihood that furosemide will be banned in North America as a race-day drug in the near future, there is an urgent need for an effective alternative.
“At present, perhaps, the best candidate for race-day alleviation of EIPH is the nasal strip, use of which is gaining in popularity.”
They suggested that resistance to use of the nasal strip as an alternative to furosemide in the racing industry likely resulted from the overarching fact that nasal strips did not increase performance sufficiently, or at least not to the extent that furosemide did with the big weight loss it produced.
“At present, there is a pressing need for large-scale field trials of the nasal strip ideally using bronchoalveolar lavage to measure reductions in EIPH severity.”
They said immunomodulation therapy and the use of conjugated estrogens were avenues deserving of closer scientific scrutiny.
Longer breaks between races, investigating dehydration strategies to mimic the effects of furosemide, and, in the longer term, selective breeding programs aimed at reducing the prevalence of EIPH, were worthy of serious consideration and investigation, they said.