Exercise Induced Pulmonary Hemorrhage (EIPH) occurs when the tiny blood vessels (capillaries) within the lungs of a horse burst during exercise, causing bleeding in the lungs. “Exercise-Induced”, meaning caused by exercise. “Pulmonary”, meaning the lungs. “Hemorrhage”, meaning bleeding.
Basic Lung Anatomy and Physiology:
Before we dive deeper into EIPH, let's review the basic anatomy and physiology of the lungs.
Image of air pathway of horse.
A horse’s lungs inhale oxygen first through the nostrils, then past the epiglottis, then trachea, then bronchioles, and then alveoli (alveolar sacs). Once the oxygen reaches the alveolar sacs, oxygen is diffused into the blood across an extremely thin layer of tissue that lines the blood vessels within the lungs.
The layer between the open space in the lungs and the blood vessel wall is about 1/100th the width of a human hair– once again, an extremely thin layer. This thin layer is important because it allows oxygen to pass through this layer from the lung space and into the blood more easily than a thicker layer. However, this reduces the durability of these blood vessels within the lungs.
Prevalence of EIPH
Between 40-75% of thoroughbred racehorses experience EIPH during racing (Sullivan & Hinchcliff, 2015; McGilvary & Cardwell, 2021). But EIPH is not just limited to racehorses. Barrel racers (66%, Gold et al. 2018), show jumpers (50%, Bonomo et al. 2019), polo ponies (30%, Sullivan & Hinchcliff 2015), endurance horses (50%, Tarancon et al. 2019), draft pulling horses (26%, Burns et al. 2023), Three-Day Event horses (40%, Ainsworth & Hackett 2004), pony club event horses (10%, Ainsworth & Hackett 2004) experience EIPH during competition. The incidence of EIPH is likely higher in these different sport horses, but the data is limited due to the lack of research of EIPH incidence in these different sport horses compared to thoroughbred racehorses.
Data taken from studies cited above (references linked at bottom of article).
The main method to determine the presence and severity of EIPH is via pulmonary endoscopy (otherwise known as “scoping”). A vet or trainer may take an endoscope (a thick snake-like wire with a camera on the end) up a horse’s nostril, past their epiglottis, and down their trachea. With endoscopic exams, the severity of EIPH (if any) can be determined and monitored in a specific horse following exercise.
Image of endoscopic examination of lungs.
There are different grades of severity of EIPH in horses, as shown in the image below. The distribution of EIPH severity are as follows:
Grade 0 - No bleeding visible in trachea.
Grade 1 - Less than quarter of trachea covered with visible blood.
Grade 2 - Between quarter and half of trachea covered with visible blood.
Grade 3 - More than half of trachea covered with blood.
Grade 4 - More than 90% of trachea covered with blood (This grade is not depicted in the image below)
Epistaxis - The worst grade of EIPH is epistaxis, when a horse’s lungs bleed so severely that blood is present coming out of the nostrils of the horse. Sometimes it may take 30-60 minutes following hard exercise while their head is down to eat or graze when blood can be visible dripping out of the nostril. These cases of epistaxis are often not life threatening and it is extremely rare a horse develops further complications such as infection or severe blood loss where the horse’s life is threatened. In some very severe cases, epistaxis occurs in the middle of hard exercise where blood is violently blown out of the horse’s nostrils with each breath (it is these cases that often result in death of the horse).
Keep in mind that these grades of EIPH are not universal and may vary depending on the study you are reading. Many studies use a scale of 4 grades in addition to Epistaxis. It is likely that the “Grade 3” shown in the image above would likely be a grade 4 (“severe”) in some studies.
The prevalence of each grade of EIPH varies across studies. This data across different sport horses is likely not reliable enough to be worth reporting as of now due to small sample sizes and lack of studies overall– except thoroughbred racehorses because EIPH in those sport horses have been extensively studied for decades. However, there is a consistent trend of the majority of EIPH cases being grade 2 or less. The more severe the EIPH, the less common the prevalence.
In Hinchcliff et al. (2005), thoroughbred racehorses in Australia (where Lasix is banned on race day) were scoped after their races to measure the severity of their EIPH. 44.6% had no EIPH. 36.7% had grade 1 EIPH. 13.5% had grade 2 EIPH. 3.3% had grade 3. 1.7% had grade 4. 1.7% had epistaxis. Epistaxis seems to occur in about 1-3% within all EIPH cases in thoroughbred racehorses according to numerous studies (Hinchcliff 2015).
Data taken from Hinchcliff et al. (2005) in Australian thoroughbred racehorses following race without Lasix.
The harder the horse exercises, the more likely the horse will experience more severe grades of EIPH, if any EIPH is present. (If you want to see the prevalence of the different grades of EIPH in the other sport horses I mentioned, I have linked the studies below for you to read yourself. If you have trouble accessing the full article, feel free to email me - gallopscience@gmail.com)
The big takeaway here is that EIPH in horses is fairly common across all disciplines. Additionally, the vast majority of EIPH cases (over 97% of cases) cannot be seen unless you do an endoscopic examination of your horse’s trachea/airways. This is important for horse owners and trainers to understand because your horse may be bleeding every time they exercise and you won’t ever know it.
Veterinarians and researchers have concluded EIPH is not painful due to the lack of nerves in the alveoli of the lungs, but in severe EIPH cases may invoke the horse to coughing, respiratory distress, and frequent swallowing.
How much does EIPH affect Athletic Performance
How common EIPH actually is in horses that exercise may be frightening to many horse owners and trainers. However, EIPH grades of 1 or less (which are the most common grades of EIPH cases across sport horses including racehorses) do not seem to affect performance or the horse’s career longevity. Once again, this area of research with other sport horses is very small, so I am not able to say how much EIPH affects other sport horse’s performance. However, this topic has been extensively studied in thoroughbred racehorses, which can provide some insight for owners and trainers of other sport horse disciplines.
According to Sullivan & Hinchcliff (2015), a single episode of an EIPH grade 1-3 does not seem to impact career longevity in thoroughbred racehorses, whereas a grade 4 or epistaxis may. In Hinchcliff et al. (2005), racehorses with an EIPH grade of 2 or higher were 4-times less likely to win and 2-times less likely to win or finish in the top 3 of their race compared to horses with an EIPH grade of 1 or less. Racehorses with an EIPH grade of 1 or less were 3-times more likely to be in the top 90th percentile for race earnings. Meanwhile, a study by Crispe et al. (2019) with a large sample size found that only a grade 3 or higher of EIPH had a significant impact on performance whereas a grade 2 or less did not.
In an article from the Paulick Report, Dr. Warwick Bayly comments on the results of an ongoing epidemiological study of EIPH prevalence in two year old thoroughbred racehorses racing without Lasix across the United States he and his colleagues have been conducting:
‘“If you're worried about EIPH from the perspective of interfering with performance, we found it had some impact on performance just like what's been shown before [in previous research], but only on really severe EIPH cases,” he said. “Less than 10 percent of horses had any association with not running well as a result of EIPH.”’ (Paulick Report 2023).
If you want more details on the results of this study involving 2 year old racehorses racing without Lasix, check out this article: https://www.thoroughbreddailynews.com/from-dust-to-dust-do-terrible-racetrack-barns-exacerbate-eiph/
It is important to note that there are horses that experience severe EIPH, even epistaxis, but still perform well and even win races. Although, one can guess on how much better than horse can be if they did not experience EIPH.
Horses that experience moderate to severe EIPH are more likely to have worsened EIPH the next time they undergo hard exercise. This is because when the blood vessels in the lungs break, they are not able to completely be repaired. Scar tissue may develop in replacement of the blood vessels, which is a weaker tissue. Some treatments involving stem cells have been promising in enhancing the recovery of the lungs following an EIPH episode. But more research is needed.
Because EIPH can get progressively worse with repeated severe episodes, prevention of bleeding not only becomes critical for short term athletic performance, but also long-term performance.
If you suspect your horse bled during a race, usually they will have abnormal fatigue and drop back from their position quickly about halfway through their race. The horses that pass them in the final 400-600m of the race are less likely to be bleeders. These findings have also been found in scientific literature, where Crispe et al. (2017) found that horses that had higher faster average speed in the early/mid portion of the race were more likely to be grade 3 or higher bleeders. Meanwhile, horses with grades 1 and 2 are more likely to run down their competitors from the back or mid-pack in the final 400m of the race compared to horses without any EIPH.
If you monitor your horse’s heart rate after a workout or race, if the horse’s heart rate takes a longer time to drop following that exercise, they may be experiencing EIPH.
Potential Causes of EIPH
The concept many people fail to realize is that EIPH is a symptom caused and influenced by several factors. EIPH is likely not caused by one single variable. Those factors that influence EIPH prevalence and severity will be covered in this article.
Why Pulmonary Hemorrhage is “Exercise-Induced”
When a horse exercises, their heart rate rises and their stroke volume (the amount of blood pumped per heart beat) increases. As heart rate increases, the speed of flow of blood increases, which then increases the stress on the blood vessel walls. The body can help blunt these stresses by dilating (increasing the width of) the blood vessels in the body. However, how readily the blood vessels dilate and the max width of each blood vessel is limited. The harder the horse exercises, the higher their heart rate will get, the faster the blood will flow through the blood vessels, and the more resistance/stress is put upon the walls of the blood vessels. Given the blood vessels of the lungs are very small and frail as previously explained, they are more likely to rupture during exercise.
Additionally, as the horse exercises, they are taking deeper breaths, and have a higher breath-rate the faster they gallop– in other words “pleural pressure” within the lungs increases the harder the horse exercises. With each breath, the alveolar sacs within the lungs expand and deflate. These mechanisms are constantly stretching and compressing these tiny blood vessels within the lungs, further increasing the stress on these blood vessels. This environment the blood vessels of the lungs are experiencing during exercise increase the risk of them breaking, causing the lungs to bleed. With all of this in mind, it makes it all the more incredible that there are sport horses, especially racehorses, undergoing vigorous exercise and do not bleed at all (at least visibly in the trachea).
It is important to note that EIPH does not occur only during maximally hard exercise. It can occur during submaximal, easy-moderate exercise intensities as well in some horses.
The Spleen
The horse is unique in that they can store up to 30% of their red blood cells in their spleen. During fight or flight response, or during hard exercise, the spleen will release these red blood cells into the spleen. With more red blood cells in circulation, oxygen delivery from the lungs to the muscles is enhanced, enhancing the horse’s endurance. However, when the spleen releases red blood cells into the overall circulation, blood volume can increase to as much as 20%. This sudden and large increase in blood volume can drastically increase blood pressure.
The release of more red blood cells into blood circulation also increases the blood’s viscosity (thickness, stickiness) which puts more resistance on the blood vessel walls. This combination of increased blood viscosity and blood pressure adds more stress on the blood vessel walls. Making them more prone to breaking. Because of this, researchers found an association between higher hematocrit (the proportion of red blood cells to blood plasma) and a higher risk of developing EIPH in Standardbred horses exercising on a treadmill (Lo Feudo et al. 2022).
Lung Inflammation and Asthma
Lung inflammation has been associated with EIPH in racehorses (Newton & Wood 2002; Michelotto et al. 2011; McKane & Slocombe 2010). However, whether the inflammation was a cause or effect of EIPH is unclear. Other studies have failed to find this association (Silva et al. 2017; Hinchcliff et al. 2015). How asthma or lung inflammation is measured varies across studies, so this may have contributed to these contradicting results.
Lung inflammation can weaken the integrity of the blood vessel walls within the lungs. Lung inflammation can also constrict the airways, increasing pleural pressure. These factors can possibly increase the risk of EIPH. As for the mixed results of whether lung inflammation increases the risk of EIPH, these findings further emphasize that EIPH is multifactorial.
One study found that mild equine asthma was present in 80% of racehorses and negatively impacted racing performance (Ivester et al. 2018). Another study also found that lung inflammation has the ability to decrease exercise capacity and performance in standardbred horses (Stucchi et al. 2020). So whether EIPH is influenced by lung inflammation or not, this variable should not be ignored.
Temperature
A handful of studies have found that horses racing in colder temperatures were associated with higher prevalence of EIPH (Crispe et al. 2016; Crispe et al. 2018; Lapointe et al. 1994; Hinchcliff et al. 2010; Leguillette et al. 2016). It is unknown if temperature acclimation plays a role. Hinchcliff et al. 2010 found that horses racing in <20 C° (68 F°) were 1.9 times more likely to have an EIPH grade greater than 1 and a two-fold increase in having a grade 2 or higher. Exercising in lower temperatures has been shown to cause airway inflammation and increase blood pressure in the pulmonary circuit in humans, horses, and other animals (Giesbrecht 1995; Davis et al. 2006; Chauca & Bligh 1976; Davis et al. 2007), which may serve as a possible explanation for this phenomenon.
Cardiac Arrhythmias (Atrial fibrillation)
Cardiac arrhythmias (abnormal heart rhythms) during exercise has been associated with increased risk of developing EIPH– particularly atrial fibrillation (AF). Nath et al. (2022) found that AF was associated with EIPH prevalence and severity. This area of research is relatively new and needs more evidence to definitively conclude a direct causal relationship between cardiac arrhythmias and EIPH risk. The idea is that during exercise, if the heart has several abnormal heart beats in a period of time, the blood flow from the lungs to the heart becomes interrupted. This can cause a “back-up” of blood flow within the lungs, drastically increasing the pressure on the blood vessel walls in the lungs and can cause them to burst.
There are several causes of cardiac arrhythmias such as fatigue, lung inflammation, unsoundness, stress, genetics, etc. Horses are unique in that they seem to have cardiac arrhythmias more frequently during exercise than humans. In many horses, these arrhythmias seem to occur without cause and do not impair health or performance of the horse. Experts in equine cardiology are still trying to define what is considered “abnormal/concerning” cardiac arrhythmias and “normal” cardiac arrhythmias.
Genetics
There have been a few studies that have shown epistaxis is heritable, likely suggesting that EIPH overall is genetic (Velie et al. 2014; Weideman et al. 2004; Welsh 2014). However, these genetic links do not explain all EIPH cases. More definitive research is needed in this area.
Speed and Racing Strategy
As mentioned before, horses that had higher faster average speed in the early/mid portion of the race were more likely to be grade 3 or higher bleeders. Meanwhile, horses with grades 1 and 2 are more likely to run down their competitors from the back or mid-pack in the final 400m of the race compared to horses without any EIPH (Crispe et al. 2018). This is observed by racehorse trainers as well, solidifying this finding. Scientific literature has also shown that a rapid acceleration of speed causes higher pressure in the blood vessels of the lungs compared to a more gradual increase of speed over the course of an exercise to the same speeds (Manohar 1994). This suggests that faster acceleration may increase the likelihood of a horse experiencing more severe EIPH.
Lasix
Lasix has been repeatedly shown to decrease the severity of EIPH and is the only substance to have repeatedly shown such significant reductions in EIPH severity in research (Sullivan et al. 2014). But how does Lasix work?
Remember back to “The Spleen” section above. Again emphasizing that during hard exercise the spleen releases a large portion of red blood cells into circulation. This causes a large and sudden increase in blood volume which increases stress on the blood vessel walls within the lungs. Lasix (also known as Furosemide or Salix) is a diuretic, meaning it reduces blood volume by forcing the body to urinate by excreting water from the blood (keep in mind that about 70% of the blood is water). Lasix works by saturating sodium transporters in the horse’s blood so electrolytes like sodium, along with chlorine and calcium, are urinated out along with water. About 3cc of Lasix can cause the horse to urinate over 20lbs of urine from their body in the span of 4 hours. This reduction in blood volume can decrease blood pressure at rest and during exercise. The decreased blood volume Lasix causes puts much less stress on the blood vessel walls, reducing their likelihood to burst. In other words, Lasix can counteract the mechanisms of the spleen that contributes to EIPH.
Keep in mind, Lasix does not eliminate EIPH, it only reduces the severity of it. This once again emphasizes that EIPH does not have one lone cause (such as high blood volume). Lasix only has the capacity to eliminate EIPH if the horse is already a grade 1-2 bleeder. Horses can still have severe EIPH with Lasix. In some horses, Lasix does not reduce EIPH severity at all. There are still some horses that can have a grade 4 or even epistaxis with Lasix despite receiving Lasix before exercise. This once again furthers the point that EIPH has multiple causes.
Many racehorse trainers in countries where Lasix is not allowed before racing (Europe, Australia, Japan, etc) will prevent their horses from drinking water the day they race. This is for the same reason Lasix is used, to reduce the amount of water (within the plasma) in the blood to reduce the horse’s blood volume. Some trainer’s will “sponge” the horse’s mouth with water to still eliminate their sensation of thirst leading up to their race. Despite Lasix being banned on race-day in these countries, many trainers still give their horse’s Lasix before high-speed workouts during training (which is legal) to prevent them from bleeding. This is to prevent excessive long-term lung damage from EIPH in these horses. Some trainers only give Lasix to known “bad-bleeders” during training. Others give it to all their horses no matter what out of prevention.
During the early to mid 1900’s, some veterinarians and trainers found that draining a bucket or two of the blood from the horse’s jugular vein the day before a race boosted some of those horse’s performances. This is likely due to, again, reducing blood volume and thus reducing the severity of EIPH. This practice has obviously not been used in decades with advancements in horse welfare.
The more you use Lasix on a horse, the more the horse’s body may build a tolerance to the pharmaceutical. Smart veterinarians and trainers will start out giving horses small doses of Lasix over time (around 3cc). A horse that has been racing for years and given Lasix frequently throughout their career may be given 10cc prior to a workout.
Electrolytes
Electrolytes include calcium, potassium, sodium, chlorine, and magnesium. These molecules are important for the body’s hydration because they help retain water within the cells and blood. Electrolytes also have other mechanisms such as aiding in muscle contractions and maintaining the pH (acidity) of bodily fluids.
What do electrolytes have to do with EIPH? Again, electrolytes help retain water within the blood, thus helping retain blood volume. Higher blood volume can cause higher blood pressure during exercise and put strain on the blood vessels within the lungs as previously explained. This is not to say that you should withhold essential electrolytes from your horse to prevent or reduce their EIPH, but maybe not overload them with it.
Many old-timer racehorse trainers have observed that alfalfa can increase risk of EIPH. The original thought is that alfalfa can be dusty, which can inflame the airways. But this observation is more likely due to alfalfa’s high calcium content (an electrolyte that retains water in blood).
Other trainers have been known to withhold salt and other electrolyte supplements from horse’s on race day because of their own experiences with high blood pressure; with their doctors advising they should reduce salt from their diet to improve their blood pressure. Again, this is because excessive salt (containing two electrolytes, sodium and chlorine) intake causes water retention, increasing blood volume, and has the potential to increase blood pressure.
It is important to mention racehorse trainers that do retain water and/or electrolytes prior to races or give lasix will often give their horse’s electrolyte IV’s, supplements, or pastes following their races to aid in their recovery and welfare.
Electrolytes are necessary for optimum athletic performance, but overdoing them may not be beneficial due to these reasons. Many fortified grains already contain the optimum balance of electrolytes your horse needs depending on the horse’s workload and sweat-rate.
There are many equine supplements on the market claiming to reduce or eliminate EIPH without any scientific basis backing their product or their ingredients. If a supplement claims to reduce EIPH and contains any electrolytes (calcium, potassium, sodium, chlorine, magnesium), be suspicious. In fact, be suspicious over any supplements with ingredients that have little scientific basis behind what the supplement company claims they do. Lasix is the only substance that has proven through dozens of peer reviewed research papers to legitimately reduce EIPH severity (Sullvian et al. 2014).
FLAIR Nosestrips
Image of FLAIR nosestrip on racehorse.
Remember back to when I mentioned “pleural pressure.” Pleural pressure is the amount of pressure put upon the walls of the lungs (and their blood vessels) when the horse is breathing. Given how rapidly horses are capable of breathing during exercise (taking over 2 breaths per second during a high speed gallop), the size of the horse’s lungs, and that the horse can only breathe through their nostrils, a horse’s pleural pressure compared to other animals is extremely high. This pressure alone can put much strain on the lung’s blood vessels.
I mentioned Lasix is the only scientifically proven “substance” to reduce the severity of EIPH. Nose strips are also the only proven “product” that has been proven to reduce the severity of EIPH in a few scientific research articles.
Nose strips allow a wider opening for air to flow through the nostrils, also preventing the nostrils from collapsing during inhalation. This allows pleural pressure within the lungs to be reduced.
There have been three studies performed on nasal strips effectiveness of reducing EIPH:
“Effect of an external nasal dilator strip on cytologic characteristics of bronchoalveolar lavage fluid in Thoroughbred race- horses” (Valdez et al. 2004)
“Effects of an external nasal strip and frusemide on pulmonary haemorrhage in Thoroughbreds following high intensity exercise” (Geor et al. 2001)
“Effect of furosemide and the equine nasal strip on exercise-induced pulmonary haemorrhage and time-to-fatigue in maximally exercising horses” (McDonough et al. 2007).
All three of these studies demonstrate nasal strips have the ability to reduce EIPH severity. However, it is important to mention that the study by Geor et al. (2001) and McDonough et al. (2007) were funded by CNS, Inc.- the company that patented and owns FLAIR Nosestrips (https://www.sec.gov/Archives/edgar/data/814258/000089710101500081/cns010440_10k.htm).
The study by Valdez et al. (2004) does not specify their funding but did use FLAIR Nosestrips in their study. All of these studies have small sample sizes (which is common in equine research), so achieving statistical significance can be challenging unless the effectiveness of the treatment is very strong. Take whatever you want with this information.
Then again, like Lasix, horses can still experience severe EIPH, even epistaxis, with FLAIR nose strips.
Image of racehorse experiencing epistaxis with FLAIR nosestrip (this horse did not receive Lasix).
Miscellaneous
Since Lasix was banned in 2 year old and stakes races in thoroughbred racing within the United States, some trainers and vets have looked for non-medication alternatives to help EIPH that are legal before racing. Two of these include a vitamin C and/or L-arginine IV solution (or “jug”). Both this vitamin and amino acid alone can cause a diuretic effect when given in large quantities, which may help against EIPH the same way Lasix does. Although these natural substances may not be as strong of a diuretic as Lasix. Additionally, vets are not allowed to administer IV’s within 24 hours of a race, so the effect of the diuretic may wane over the 24 hours as opposed to Lasix being administered 4 hours before the horse races.
Abnormal Throat Function
Various throat dysfunctions, such as recurrent laryngeal dysfunction, dorsal displacement of soft palate, and entrapped epiglottis have been shown to impair horse performance, especially racehorses (Erck-Westergren et al. 2017).
Photos of different types of airway dysfunction in the horse. (Photo from FLAIR equine nasal strips)
These throat abnormalities are fairly common amongst performance horses, but many cannot be identified unless a throat endoscopy is performed while the horse is exercising (when the function of the airways is challenged) compared to analyzing throat function when the horse is at rest.
Upper airway obstruction has been shown to increase the risk of EIPH in several studies (Courouce-Malblanc et al. 2010; Joo et al. 2021; Mucciacito Junior et al. 2021; Mason et al. 2012; Ducharme et al. 2010). However, Davidson et al. (2011), Burns et al. (2023), and Lo Fuedo et al. (2022) found no significant association between airway function and EIPH risk.
In the study by Mucciacito Junior et al. (2021), researchers analyzed over 3,000 thoroughbred racehorses’ upper airways for throat abnormalities and EIPH severity post-race (some were treated with lasix, others not). Researchers found that horses with dorsal soft palate displacement were significantly more likely to experience more prevalent and severe EIPH than horses with no throat abnormalities. However, there was no difference in the prevalence or severity of EIPH in horses with left-sided laryngeal hemiplegia (LLH) than horses with no throat abnormalities.
The results from this study does not necessarily conclude that LLH does not put a horse more at risk for EIPH at all. This is also the case with the other studies that did not find a significant association with airway abnormalities and EIPH risk (Davidson et al. 2011, Burns et al. 2023, and Lo Fuedo et al. 2022). Again, as the theme of this entire article, EIPH is multifactorial. Other variables may have increased the risk for EIPH, thus causing a lack of statistical significance in this study to show LLH alone increases EIPH risk. That being said, it is even more interesting that racehorses with horses with dorsal soft palate displacement did in fact have significantly higher EIPH risk. Impaired airway function may increase the pressures within the lungs, thus increasing the risk for the blood vessels within the lungs to burst, causing EIPH.
How about horses that underwent surgery to correct their airway abnormalities? Mason et al. (2012) found that thoroughbred racehorses that underwent prosthetic laryngoplasty with ventriculocordectomy (PLVC) surgery to treat left-sided laryngeal hemiplegia (LLH) were more likely to experience more severe EIPH (especially epistaxis) and tracheal mucus following races compared to racehorses with assumed normal airway function and did not undergo throat surgery. The researchers hypothesize that the surgery may have been inefficient to restore airway function and airway pressures within the respiratory tract and may increase airway inflammation (Ramzan et al. 2008; Tetens et al. 1996). As a result, the pressures within the alveoli are higher and blood vessels within the lungs are more likely to break, thus increasing the risk of EIPH (McKane & Slocombe 2010; Ducharme & Hiraga 1999; Jackson et al. 1997; West et al. 1993). It is not clear whether EIPH was worse pre vs post the surgery in these racehorses. Also keep in mind surgeries for different airway disorders have different effects on performance and the original severity of the airway dysfunction as well as the skill of the veterinarian performing the surgery also factor into post-surgery performance outcomes.
Conclusion:
In every equine discipline, there are horses that experience bleeding in their lungs due to exercise (EIPH).
EIPH has several potential causes such as high blood pressure, high pleural pressure, high blood volume, respiratory inflammation, cold air temperature, cardiac arrhythmias, throat abnormalities, and genetics.
Over 75% of thoroughbred racehorses without Lasix have an EIPH grade of 1 or less following a race, which may not impact athletic performance.
Lasix is a very scientifically proven option to reduce severity, but not always completely eliminate, EIPH in horses. Flair Nosestrips and other non-pharmascudical diuretics (legal for competition) may also be helpful investments. Don’t fall for sham supplements.
References:
“Associations between Exercise Induced Pulmonary Hemorrhage (EIPH) and Fitness Parameters Measured by Incremental Treadmill Test in Standardbred Racehorses” (Lo Feudo et al. 2022).
"Association between exercise-induced pulmonary hemorrhage and performance in Thoroughbred racehorses” (Hinchcliff et al. 2005)
“Exercise Induced Pulmonary hemorrhage; risk factors, clinical signs, and prevention” (Rendel 2016)
“Prevalence of Exercise-Induced Pulmonary Hemorrhage, Tracheal Mucus and Recurrent Laryngeal Neuropathy in competitive Draft Pulling Horses” (Burns et al. 2023)
“Occurrence of exercise-induced pulmonary haemorrhage in show jumping horses” (Bonomo et al. 2019) https://www.sciencedirect.com/science/article/abs/pii/S1090023318306944
“Exercise-Induced Pulmonary Hemorrhage in barrel racing horses in the Pacific Northwest region of the United States” (Gold et al. 2018) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5866954/
“Update on Exercise-Induced Pulmonary Hemorrhage” (Sullivan & Hinchcliff 2015)
“Prevalence of exercise induced pulmonary hemorrhage in competing endurance horses” (Tarancon et al. 2019)
“Training related risk factors for exercise induced pulmonary haemorrhage
in British National Hunt Racehorses” (McGilvary & Cardwell, 2021)
“EIPH: postrace endoscopic evaluation of standardbreds and thoroughbreds” (Birks et al. 2002)
“Bar shoes and ambient temperature are risk factors for exercise-induced pulmonary haemorrhage in Thoroughbred racehorses” (Crispe et al. 2016)
“Evidence of an association between inflammatory airway disease and EIPH in young Thoroughbreds during training” (Newton et al. 2002) https://doi.org/10.1111/j.2042-3306.2002.tb05459.x
“Exercise-induced pulmonary haemorrhage in Thoroughbred racehorses: a longitudinal study” (Crispe et al. 2018)
“The Relationship between Lung Inflammation and Aerobic Threshold in Standardbred Racehorses with Mild-Moderate Equine Asthma” (Stucchi et al. 2020)
“Descriptive analysis of longitudinal endoscopy for exercise-induced pulmonary haemorrhage in Thoroughbred racehorses training and racing at the Hong Kong Jockey Club” (Preston et al. 2015)
“Pulmonary inflammation due to exercise-induced pulmonary haemorrhage in Thoroughbred colts during race training” (Michelotto et al. 2011) https://pubmed.ncbi.nlm.nih.gov/22108190/
“An observational study of environmental exposures, airway cytology, and performance in racing thoroughbreds” (Ivester et al. 2018)
- Dr. Laurent Couëtil
“Experimental mild pulmonary inflammation promotes the development of exercise-induced pulmonary haemorrhage” (Mckane and Slocombe 2010)
“A systematic review and meta-analysis of the efficacy of furosemide for exercise-induced pulmonary haemorrhage in Thoroughbred and Standardbred racehorses” (Sullivan et al. 2014)
“Heritability of epistaxis in the Australian Thoroughbred racehorse population” (Velie et al. 2014)
“A genetic analysis of epistaxis as associated with EIPH in the Southern African Thoroughbred” (Weideman et al. 2004)
“Heritability analyses of musculoskeletal conditions and exercise-induced pulmonary haemorrhage in Thoroughbred racehorses” (Welsh 2014)
“Associations between postrace atrial fibrillation and measures of performance, racing history and airway disease in horses” (Nath et al. 2022)
“The association between exercise-induced pulmonary haemorrhage and race-day performance in Thoroughbred racehorses” (Crispe et al. 2019)
“Risk factors for exercise-induced pulmonary haemorrhage in Thoroughbred racehorses” (Hinchcliff et al. 2010)
“A survey of exercise-induced pulmonary haemorrhage in Quebec standardbred racehorses” (Lapointe et al. 1994)
“Tracheobronchoscopic Assessment of Exercise-Induced Pulmonary Hemorrhage and Airway Inflammation in Barrel Racing Horses” (Leguillette et al. 2016)
“Influx of neutrophils and persistence of cytokine expression in airways of horses after performing exercise while breathing cold air” (Davis et al. 2007)
“Evaluation of race distance, track surface and season of the year on exercise-induced pulmonary haemorrhage in flat racing thoroughbreds in Brazil” (Costa & Thomassian 2006)
“Risk factors for exercise-induced pulmonary haemorrhage in Thoroughbred racehorses” (Hinchcliff et al. 2010)
“Exercise-Induced Pulmonary Hemorrhage in the racing apollosa horse” (Hillige et al. 1985)
“Frequency of and risk factors for epistaxis associated with exercise-induced pulmonary hemorrhage in horses” (Takahashi et al. 2001)
“Pulmonary vascular pressures of Thoroughbreds increase rapidly and to a higher level with rapid onset of high-intensoty exercise than slow onset” (Manohar 1994)
“The respiratory system in a cold environment” (Giesbrecht 1995)
https://pubmed.ncbi.nlm.nih.gov/7487830/#:~:text=Acute%20or%20chronic%20cold%20exposure,secretions%20and%20decreased%20mucociliary%20clearance.
“Cold air-induced late phase bronchoconstriction in horses” (Davis et al. 2006)
“Influx of neutrophils and persistence of cytokine expression in airways of horses after performing exercise while breathing cold air” (Davis et al. 2007)
“An additive effect of cold exposure and hypoxia on pulmonary artery pressure in sheep” (Chauca & Bligh 1976)
“Respiratory diseases and their effects on respiratory function and exercise capacity” (Erck-Westergren et al. 2013)
“Cohort study examining long-term respiratory health, career duration and racing performance in racehorses that undergo left-sided prosthetic laryngoplasty and ventriculocordectomy surgery for treatment of left-sided laryngeal hemiplegia” (Mason et al. 2013)
“Experimental mild pulmonary inflammation promotes development of exercise-induced pulmonary hemorrhage” (McKane & Slocombe 2010)
“Efficacy of prosthetic laryngoplasty with and without bilateral ventriculocordectomy as treatments for laryngeal hemiplegia in racehorses” (Tetens et al. 1996)
“Lower respiratory tract disease in Thoroughbred racehorses: analysis of endoscopic data from a UK training yard” (Ramzan et al. 2008)
“Upper airway disease: does it affect lower airway mechanisms and pulmonary haemodynamics?” (Ducharme & Hiraga 1999)
“Effects of airway obstruction on transmural pulmonary artery pressure in exercising racehorses” (Jackson et al. 1997)
“Stress failure of pulmonary capillaries in racehorses with exercise induced pulmonary hemorrhage” (West et al. 1993)
“Relation between Exercise-induced pulmonary hemorrhage and findings in upper airway and trachea in Thoroughbred racehorses” (Mucciacito Junior et al. 2021)
“Upper and Lower Airways Evaluation and Its Relationship with Dynamic Upper Airway Obstruction in Racehorses” (Lo Fuedo et al. 2022)
“Physiological measurements and prevalence of lower airway diseases in Trotters with dorsal displacement of the soft palate” (Courouce-Malblanc et al. 2010)
“Asthmatic Disease as an underlying cause of dorsal displacement of the soft palate in horses” (Joo et al. 2021)
“Dynamic endoscopy of the upper-airway– What is significant?” (Trope 2013)
“Upper airway obstruction partial asphyxia as possible cause of exercise-induced pulmonary hemorrhage in the horse: An hypothesis” (Cook 1988)
“Exercising blood gas analysis, dynamic upper respiratory track obstruction, and post exercising bronchoalveolar lavage cytology: A comparative study in poor performing horses” (Davidson et al. 2011)
Extra:
EIPH Risk Factors- epidemiology
EIPH is Genetic -
From Dust to Dust: Do “Terrible” Racetrack Barns Exasperate EIPH? -TDN
https://www.thoroughbreddailynews.com/from-dust-to-dust-do-terrible-racetrack-barns-exacerbate-eiph/
Study shows less than 10% of 2yo runners experience severe EIPH regardless of Lasix administration- Paulick Report, Dr. Bayly
“Effect of bedding on the incidence of Exercise Induced Pulmonary Hemorrhage in racehorses in Hong Kong” (Mason et al. 1984)
“The effect of herbal supplementation on the severity of exercise induced pulmonary haemorrhage” (McDonough et al. 2007) Yunnan Paiyao and Single Immortal were not any more effective to a placebo (corn starch) in reducing EIPH.
“New Furosemide research reveals unexpected impacts of the medication” - Paulick Report - KER research on Lasix urination quanity with 3-10cc of Lasix and effects on drinking dehydration.