The Fall 2010 edition of Equine Guelph's Research Update features an article by Natalie Osborne which tackles the subject of respiratory issues with racehorses. A segment of the article discusses furosemide, commercially known as Lasix, which many argue the pros, cons, and effectiveness of.
In her article, Osborne quotes Professor Laurent Viel, a member of Equine Guelph's Department of Clinical Studies, as questioning the effectiveness of Lasix, which is currently permitted for use in the North American standardbred racing industry.
“We wanted to know if Lasix treated or somehow prevented EIPH (Exercise Induced Pulmonary Haemorrhage),” Viel was quoted as saying. “We found that it does neither. Therefore, it becomes questionable if Lasix has any preventative effect at all, meaning the debate should continue as to whether Lasix is a valid pre-racing medication. In my opinion, it would be a great welfare benefit to the horse in treating them for IAD (Inflammatory Airway Disease), as we treat asthmatics with a simple bronchodilator that opens up their airways to their normal, healthy level. Many of these drugs are approved for use in horses and would offer a safer, more effective solution.”
Osborne's article appears below in its entirety.
At a metre and a half in length, horses have one of the longest mammalian airways — three times longer than a human’s. These airways help them obtain the oxygen they need when running…but racehorses and companion horses alike suffer from a myriad of respiratory diseases. To help lead the way to clearer airways, University of Guelph researchers are using a variety of approaches to combat respiratory conditions.
One such condition is exercise induced pulmonary haemorrhage (EIPH), which plagues about 80 per cent of racehorses. It occurs after intense activity, when within seconds a horse’s heart rate more than quadruples to over 200 beats per minute. The huge increase in blood pressure can cause the capillaries in the lung to burst, resulting in nose bleeds and in some cases, potentially fatal haemorrhaging.
Dr. Luis Arroyo and Prof. Laurent Viel, Department of Clinical Studies, and Prof. John Runciman, Department of Engineering, are examining the relationship between EIPH and calcified lesions in the pulmonary artery, which are also found in about 80 per cent of racehorses (the body deposits calcium as an ultimate repair mechanism in an attempt to reinforce tissue weakened by injury or stress).
The main trunk of a horse’s pulmonary artery is four to six centimetres in diameter and responsible for carrying more than 250 litres of blood per minute from the heart to the lungs for oxygenation.
Researchers used MRI and CT scans to build a 3-D image computer model that calculated the stress that this huge volume of blood can cause on arterial walls. They also examined the spatial location of the calcified lesions.
If the research finds that calcium deposits are linked to EIPH, then more resources can go towards understanding and preventing them.
“From our models, we found that the highest stresses were right where the artery branches, and this is also where the calcification always starts,” says Runciman. “The blood flow in racing horses is tortuous; it almost becomes their Achilles’ heel.”
Arteries will stretch to accommodate each pulse of blood from the heart and contract to move the blood along, thereby acting as shock absorbers so the blood pressure in the smallest arteries is minimal, avoiding rupture. A calcified artery is less elastic, losing its shock-absorbing role, which results in a larger, faster pulse wave that has greater impact when it reaches the lungs. Researchers believe this pressure spike is what bursts lung capillaries and causes EIPH.
Their research is taking a new twist. This summer, Arroyo, Runciman and Viel will put catheters in the pulmonary arteries of ex-racers and young, healthy horses to perform inside-out ultrasounds that monitor the animal’s blood flow and pulse wave.
“This is the first time we’ll be looking at live animals,” says Arroyo. “We can examine them both resting and exercising, to see firsthand if and how the calcified lesions affect arterial stiffness and parameters like pulse wave.”
In many cases, existing EIPH seems to be associated with — and perhaps a contributor to — a respiratory condition found in young racehorses called inflammatory airway disease
(IAD). This condition concurrently studied by Viel is similar to asthma in humans, where the airways become overly sensitive to allergens resulting in bronchial constriction, or closure of the airways.
On the racetrack, horses with IAD struggle to get enough oxygen. In an oxygen deprived state, the body’s natural response is to constrict blood vessels. During intense exercise, blood vessels must dilate to accommodate increased blood flow. These counteracting mechanisms could result in the damage and bleeding associated with EIPH.
That’s where research by Viel and graduate student Modest Vengust comes in. They examined the effect of the drug furosemide on the lung. Known commercially as Lasix, it is used on many racehorses and believed to treat EIPH; specifically, fluid in the lung.
Before high blood pressure causes the lung’s small blood vessels to rupture, some of the fluid in the capillaries will be forced out into the lung in an attempt to reduce pressure. Lasix was thought to prevent this accumulation of fluid, called pulmonary oedema, reducing excessive small artery blood pressure.
However, when the researchers put Lasix treated horses on a treadmill to increase their heart rate and blood pressure to racetrack levels, they found that it had no effect on reducing fluid build-up.
Lasix also has many side effects, including dehydration and blood electrolyte imbalance.
“We wanted to know if Lasix treated or somehow prevented EIPH,” says Viel. “We found that it does neither. Therefore, it becomes questionable if Lasix has any preventative effect at all, meaning the debate should continue as to whether Lasix is a valid pre-racing medication. In my opinion, it would be a great welfare benefit to the horse in treating them for IAD, as we treat asthmatics with a simple bronchodilator that opens up their airways to their normal, healthy level. Many of these drugs are approved for use in horses and would offer a safer, more effective solution.”
Some veterinarians also believe that effectively treating IAD early on, could prevent the onset of recurrent airway obstruction (RAO), or 'heaves,' amore advanced respiratory illness of older animals.
RAO is commonly found in hunter-jumpers, ponies, dressage and companion horses. The condition causes frequent allergic respiratory responses which include performance disruptive coughing and animal discomfort. It’s especially prevalent in colder countries like Canada where horses must be stabled for a portion of the year, since mouldy hay and dusty stable conditions are known to induce symptoms.
Prof. Dorothee Bienzle, Department of Pathobiology, is studying Clara cells, the cells that line most of the bronchi in the lung, to understand how the disease progresses. Clara cells produce a protein – Clara cell secretory protein (CCSP) – which reduces the inflammation caused by inhaling harmful dust and fungal spores.
Bienzle found that years of continuous exposure to poor quality air eventually exhausts the Clara cells, which means lower CCSP levels and less ability to limit the inflammatory allergic response. Older horses with advanced RAO produce very little CCSP.
Researchers can measure CCSP levels in the respiratory tract with lung washes, where water is flushed into and then collected from the lung. From these tests, researchers have determined the amount of protein present in normal horses compared to those with severe RAO. This allows them to tell how advanced the disease is based on CCSP levels. They also found that CCSP leaks into the blood of animals with inflamed lungs.
“We’d like to develop a CCSP test for blood, which might be a very good indicator of how severe the disease is,” says Bienzle. “This would allow us to simply take a blood sample and be able to give the animal’s owner an accurate prognosis.”
Over the summer, Bienzle and her team performed lung washes on horses from several nearby farms. The hope was to obtain realistic data by testing animals that are housed in conditions typical to Ontario stables.
Previous studies by Bienzle have identified three types of fungal agents that may be responsible for RAO cases throughout Ontario. She will examine the fungal agents found in the lung washes as well as CCSP levels and the different types of inflammatory cells present in horses with and without RAO.
Research funding has been provided through the funding agencies of Equine Guelph and the Natural Sciences and Engineering Research Council.
(By Natalie Osborne)
This is a great read but
This is a great read but pretty much every trainer and person in the industry knows this. Who made the money on Lasix? The people in charge when it was brought in even knew it is a cover drug and hard on horses and there are better remedies out there. Will there be an investigation into blatant disregard for horses and the betting public? Probably not. Will the lasix program be stopped, probably not, too much at stake. Why was it even allowed in the first place, back in the eighties we knew lasix horses still bled.
Greg Parke
I completely agree that it
I completely agree that it is the high blood pressure during racing that causes EIPH lung bleeding. High blood pressure during racing is normal in healthly horses, but in those with EIPH the pressure rises even higher, causing lung capillaries to burst and leak blood.
It should be remembered that this high blood pressure, or essential hypertension, only occurs in equines and humans and no other mammals. This fact gives the clue as to the underlying cause of EIPH.
Only equines and humans are capable of instantly producing copious sweat for cooling. Sweat liquid is taken directly from the circulating blood supply. This could potentially result in a catastrophic loss of electrolyte in the sweat, but for the fact that the sweat ducts actively recover electrolyte from the sweat before it reaches the surface of the skin.
The sensitive electrolyte recovery mechanism of the sweat ducts is easily disturbed by the normal stresses of training and racing. This results in a swift reaction in the domesticated horse. The reaction is to actively conserve or "lock up" electrolytes, an electrolyte imbalance that is the cause of EIPH.
This reasoning led me, in 2004, to develop the Equiwinner patch. This is a veterinary medical device which prompts the skin cells to generate signals indicating a surplus of the relevant electrolytes, thus undoing the inappropriate "locking up". Over ten thousand horses have now been easily and successfully treated for EIPH with the patches.
For some reason, none of the drugs developed for human use appear to have any effect on horse high blood pressure, and Equine Guelph are to be commended for their research showing that Lasix is not effective. It is possible a drug will be developed at some time in the future, but this may be many years away.