Clearing the airway

For years, equine veterinarians Jim Chiapetta, DVM, JD, and Ed Blach, DVM, MS, MBA, were intrigued by a common phenomenon in horses—the nostrils' tendency to collapse during heavy inspiration brought on by strenuous work or exercise. Aware that some human athletes were promoting the use of nasal strips to open airways and increase respiration, the duo developed nasal strips for working horses to similarly improve their performance.

The goal was simple: open the airway to enhance airflow.

"To accomplish this, the nasal strip is worn on the horse's face above the nostrils about an inch and a half," says Howard Erickson, DVM, PhD, emeritus professor of physiology at Kansas State University College of Veterinary Medicine. "At that location, a portion of the nasal passages isn't supported by bone." Three Mylar springs built into the strip help keep the nasal passages open (Photo 1).

Photo 1: An equine nasal strip on a horse.

Do the strips work?

Since the equine nasal strips were developed more than 10 years ago, a growing body of research has examined their effectiveness. Susan Holcombe, VMD, MS, PhD, DACVS, DACVECC; Edward Robinson, BVetMed, PhD; and colleagues at Michigan State University examined nasal passages using videoendoscopy (in one horse) and noted that the nasal strip did open the airway.1 They also carefully measured airway pressures, but they did not quantify exercise-induced pulmonary hemorrhage—bleeding in the lungs—either via endoscopy or bronchoalveolar lavage (BAL).

Nonetheless, their findings revealed a significant effect on airway mechanics during maximal exercise.1 Peak tracheal inspiratory pressure and inspiratory airway resistance were reduced when horses wore the nasal strips while exercising at speeds at and above those that yielded their maximal heart rates. Analysis of these results suggests that the nasal strip increases the diameter of the nasal passage and stability of the soft tissue structures in the nose.

This conclusion was supported by results of endoscopic examination of the nasal valve in one of the horses, which revealed that the strip tented the skin over the nasal valve, pulled the dorsal conchal fold laterally and increased the cross-sectional area of the dorsal meatus, resulting in decreased airway resistance during inspiration. The team concluded that "the nasal strip probably decreases the amount of work required for respiratory muscles in horses during intense exercise and may reduce the energy required for breathing in these horses."1 This was an observation that was substantiated using rigorous laboratory science.

Further investigation

David Poole, PhD, DSc, a professor of physiology at Kansas State University, says he wasn't ready to buy into the idea of an equine nose strip. "When first presented with the strips I was skeptical about their ability to modify upper airway structure and function," he says. "Over several years we'd been measuring the metabolic rate of horses running on the treadmill, and our studies used a facemask to measure pulmonary gas exchange. When we took the facemask off, we paid close attention to the rostral incisive notch region and noticed a partial collapse of the nasal passages.

"Some horses show a pronounced nasal collapse," Poole continues. "We believe that the extent depends on their exact geometry, but there is often an area or region of 3 to 4 centimeters where narrowing occurs, as several researchers have shown."

In fact, 70 percent to 75 percent of breathing resistance in a running horse comes from the nasal passageways. Horses are obligate nasal breathers, their upper airway extending from the opening of the nostrils to the larynx (see Diagram). The nasal passages are continuous, a hollow muscular tube from the nose to the nasopharynx. For exercising horses, this is the primary site of resistance.

Diagram: A line drawing of the nasal system in horses.

"Even a small narrowing of the passages is significant, as the resistance to flow increases to the fourth power of any reduction in airway radius," Poole says. "So I came from the side of being extremely skeptical to understanding the benefit of nasal strips."

When Poole and his colleagues looked at various measurements, including breath-to-breath evaluation of ventilation, breathing frequency and inspired and expired flow profiles, they found clear differences in gas exchange induced by the nasal strip.2 During high-intensity running, the nasal strip could actually decrease the oxygen cost of the exercise.

"The horse's respiratory ability is really enormous," Poole says. "For example, a strong human athlete can reach a maximal oxygen uptake of close to 5 L/min. The estimated oxygen uptake of the respiratory muscles alone in a quality horse during a sprint is close to this value."

Research in human athletes has found that the respiratory muscles will steal cardiac output from the rest of the body. After the heart, they are the first to benefit from cardiac output. When the work of breathing is decreased (e.g., by using a ventilator-assist device in humans), that extra cardiac output that would have gone to the respiratory muscles now goes to the locomotory muscles and improves human performance.3

"We suspect that this may be happening in the running horse when wearing the nasal strip," says Poole. "If so, it can account for some of the improvements in exercise performance noted in equine athletes wearing the nasal strip."

The strips' application in reducing EIPH

The first study that Erickson and his team conducted at Kansas State demonstrated a significant decrease in oxygen consumption when the horses were wearing the nasal strip.4 "Though it doesn't seem like much, it lowers the work of breathing," Erickson says. "By reducing the large swings in airway pressure, the nasal strip reduces pulmonary vessel damage and bleeding into the lungs."

This condition is called exercise-induced pulmonary hemorrhage (EIPH), and in extreme cases, blood can pour from the horse's nostrils. If you can reduce the vascular pressures and decrease the large swings in airway pressures that occur during peak exercise, the vascular "transmural" pressure is reduced, according to Erickson. That's the physiological basis behind the nasal strip's reducing EIPH and potentially improving pulmonary gas exchange.

Thus, the nasal strip has at least two important physiological actions: it decreases EIPH and, as described above, by lowering the oxygen cost of breathing, it may allow more cardiac output to perfuse the exercising locomotory muscles. These effects reduce fatigue and improve exercise tolerance (i.e., increase the time to fatigue).

"We've compared the use of furosemide and the use of the nasal strip, and they both decrease the amount of bleeding (EIPH) to essentially the same extent," Erickson says. "Neither one completely eliminates it."

Whether the nasal strip is better than furosemide or visa versa is equivocal. "In one study we observed that furosemide was better, but in that study the horses were not run to maximum intensity. In another study, when the horses were running at maximum intensity, the results were similar," Erickson says.

A study by McDonough et al. concluded that "two strategies designed to combat both the intravascular (furosemide) and extravascular (nasal strip) components associated with EIPH were demonstrated to be equally efficacious in reducing, although not abolishing, EIPH. Furthermore these treatments enhanced exercise tolerance. Thus, this investigation demonstrates that both airway and vascular pressures contribute to EIPH during maximal exercise in the horse and that both can be 'treated' in a manner that can reduce the severity of EIPH in horses run at high speed to fatigue."5

An additional study by another independent research group showed similar results between furosemide and the nasal strip.6 This study compared the effects of both the nasal strip and furosemide during strenuous exercise and showed that both treatments decreased the severity of pulmonary hemorrhage as compared with a control group. There was further improvement from the nasal strip alone when the treatments were combined. However, no significant difference was seen compared with furosemide alone.

The authors concluded that "both the nasal strip and furosemide attenuate pulmonary hemorrhage in Thoroughbred horses during high-speed sprint exercise. Moreover, the external nasal strip appears to lower the metabolic cost (i.e., oxygen consumption) of supramaximal exertion in horses. Given the purported ergogenic effects of furosemide, the external nasal strip is a valuable alternative for the attenuation of EIPH."6

A study from the University of California-Davis showed that among racehorses exhibiting severe EIPH, the nasal strip was even more beneficial.7 The most severe bleeders had the greatest benefit.

"We noted this finding on the treadmill as well," says Erickson.

According to the UC Davis study, "The mean number of red blood cells in bronchoalveolar lavage fluid was close to statistically significantly (P = 0.054) higher when horses raced without the nasal dilator strip (84.6 cells/µl) than when they raced with it (41.7 cells/µl). In contrast, when severe bleeders raced without the nasal strip (271.0 cells/µl), EIPH was significantly (P = 0.05) higher than when horses raced with the strip (93.8 cells/µl)."

All horses in the UC Davis study were also premedicated with furosemide before racing. Keep in mind that furosemide will reduce the vascular pressures only about 10 percent. But as a diuretic, it also reduces the horse's weight, so the animal is more efficient when it's running.

"I think that enters into the improved exercise tolerance," says Erickson. "Horses will undergo diuresis and lose 20 to 30 pounds with furosemide." It was found that horses lost 13 kg four hours after receiving 0.5 mg/kg of furosemide and 17.2 kg four hours after receiving 1 mg/kg.8

An opposing viewpoint

Offering different results, Goetz et al 2001 demonstrated that "application of an external nasal dilator strip neither improved the exercise-induced arterial hypoxemia and hypercapnia nor diminished the lactate and ammonia production or the incidence of EIPH in Thoroughbred horses performing strenuous exercise."9

Poole, however, takes issue with this study. "When the paper clearly disagreed with us, we were blown away by their poor methodology and the misinterpretation of their own and other scientists results," he says.

One significant difference with this study was the method of measuring EIPH, which was not via BAL.

"The technique used by Goetz and colleagues could not even be expected to detect a reduction in EIPH, as they did not use BAL to measure the red blood cells in the lavage from the respiratory tract," Poole says. "They merely evaluated by eye how much blood was in the large airways and used a very crude rating scale."

Erickson agrees that the use of BAL is key. "About 15 to 20 years ago, as they were using lavage in people, I went to Ireland to visit with Ursala Fogerty, DVM, PhD, at the Irish Equine Center. She did her PhD on BAL, looking at hemosiderin in the BAL fluid," he says. From what he learned, Erickson and his colleagues began using BAL to measure the severity of EIPH. About 150 ml of saline solution is infused into the lungs and about 60 percent of that fluid is then recovered.

"One can actually count the number of red blood cells within the BAL to better quantify the severity of EIPH," Erickson says. Although it is not practical on the racetrack or for the clinical veterinarian (where endoscopy is used), it is a useful method experimentally. "BAL is a well-recognized experimental assessment because of its accuracy in measuring red blood cells within the lavage fluid," he says.

A second difference was the placement of the nasal strips. The paper, when presented as a poster presentation, included a photograph of their horses wearing the nasal strips.

"What was most striking was the misplacement of the nasal strip," Poole says. "They were much higher on the face than specified in the instructions. The correct placement of the strip is just rostral to the nasoincisive notch. When you look at a horse skull, you can clearly see where the nasal passages are unsupported by bone. Remember that the horse needs to generate very high negative pressures to inhale at up to 60 L/s per nostril." This pressure is what generates the compressive forces on the soft tissues, causing nasal passages to narrow.

A third deficiency of this study was in neglecting to measure gas exchange. "The title of their paper proposed some results that were not even tested scientifically within the methodologies of the paper," says Poole. "One was EIPH, and the second was gas exchange (they measured blood gases, which are something else entirely). If you look at the blood gases of the horse, they're hypoxemic, hypercapnic—i.e., low O2, high CO2—because the lungs just can't do as good a job oxygenating the blood as the heart does pumping that blood around the body. Measuring blood gases doesn't reflect gas exchange. Case in point—the Thoroughbred horse running at maximal exercise, about 40 mph, has an oxygen uptake about 150 times higher than a human lung disease (COPD) patient but may have roughly the same blood gases (hypoxemic and hypercapnic). The bottom line is that blood gases don't tell you anything about gas exchange, as the COPD patient has abysmal gas exchange, while that of the Thoroughbred horse is superb."

Conclusion

Based on the research available, it is apparent that use of external nasal strips positively affects both the structure and function of the nasal passages in exercising horses. By resisting their collapse, the nasal strip maintains the diameter of the nasal passageways, thereby reducing upper airway resistance and improving airflow. This has been shown to reduce the severity of EIPH and likely improve overall performance. Once thought to be just a quirky fad, these simple devices may pose a legitimate adjunct or alternative to the use of furosemide in racing horses.

Ed Kane, PhD, is a researcher and consultant in animal nutrition. He is an author and editor on nutrition, physiology and veterinary medicine with a background in horses, pets and livestock. Kane is based in Seattle.

References

1. Holcombe SJ, Berney C, Cornelisse CJ, et al. Effect of commercially available nasal strips on airway resistance in exercising horses. Am J Vet Res 2002;63(8):1101-1105.

2. Poole DC, Kindig CA, Fenton G, et al. Effects of external nasal support on pulmonary gas exchange and EIPH in the horse. J Equine Vet Sci 2000;20(9):579-585.

3. Harms CA, Wetter TJ, McClaran SR, et al. Effects of respiratory muscle work on cardiac output and its distribution during maximal exercise. J Appl Physiol 1998;85(2):609-618.

4. Erickson HH, Epp TS, Poole TC. 2007. Review of alternative therapies for EIPH, in Proceedings. Am Assoc Equine Pract, 2007;68.

5. McDonough P, Kindig CA, Hildreth TS, et al. Effect of furosemide and the equine nasal strip on exercise-induced pulmonary hemorrhage and time-to-fatigue in maximally exercising horses. Equine Comp Ex Physiol 2004;1(3):177-184.

6. Geor RJ, Ommundson L, Fenton G, et al. Effects of an external nasal strip and furosemide on pulmonary hemorrhage in Thoroughbred following high-intensity exercise. Equine Vet J 2001;33(6):577-584.

7. Valdez SC, Nieto JE, Spier SJ, et al. Effect of an external nasal dilator strip on cytologic characteristics of bronchoalveolar lavage fluid in Thoroughbred racehorses. J Am Vet Med Assoc 2004;224(4):558-561.

8. Olsen SC, Coyne CP, Lowe BS, et al. Influence of furosemide on hemodynamic response during exercise in horses. Am J Vet Res 1992;53(5):742-747.

9. Goetz TE, Manohar M, Hassan AS, et al. Nasal strips do not affect pulmonary gas exchange, anaerobic metabolism, or EIIPH in exercising Thoroughbreds. J Appl Physiol 2001;90(6):2378-2385.