Definition and Prevalence
Exercise-induced bronchospasm (EIB) describes acute, transient airway narrowing that occurs during and most often after exercise. EIB is characterized by symptoms of cough, wheezing, or chest tightness during or after exercise. Exercise is one of the most common triggers of bronchospasm in asthmatic patients, and approximately 80% of persons with chronic asthma have exercise-induced respiratory symptoms. However, EIB also occurs in up to 10% of people who are not known to be atopic or asthmatic. These patients do not have the typical features of chronic asthma (i.e., frequent daytime symptoms, nocturnal symptoms, and impaired lung function), and exercise may be the only stimulus that causes respiratory symptoms.
EIB occurs quite commonly in athletes; prevalence rates of bronchospasm related to exercise in athletes range from 11% to 50% ( Table 16-1 ). Holzer and colleagues found that 50% of a cohort of 50 elite summer athletes had EIB, and Wilber and associates found that 18% to 26% of Olympic winter sport athletes and 50% of cross-country skiers had EIB. The U.S. Olympic Committee reported an 11.2% prevalence of EIB in all athletes who competed in the 1984 Summer Olympics.
| Reference No. | Athletes | EIB Prevalence (%) (Bronchoprovocation Technique) |
|---|---|---|
| 5 | Winter Olympians | 18-26 (exercise) |
| 25 | Elite figure skaters | 41 (EVH) 31 (exercise) |
| 4 | Elite athletes | 50 (EVH) 18 (methacholine) |
| 11 | Collegiate athletes | 39 (EVH) |
Despite numerous studies that investigate the prevalence of EIB in athletes, few studies have investigated the prevalence of EIB in cohorts of athletes without a known history of asthma or EIB. Mannix and associates found that 41 of 212 subjects (19%) in an urban fitness center—none of whom had a previous diagnosis of asthma—had EIB. Rupp and colleagues evaluated 230 middle and high school student athletes, and after excluding those with known EIB, they found that 29% had EIB. These studies suggest that EIB occurs commonly in subjects who are not known to be asthmatic and likely is underdiagnosed clinically.
The prevalence of EIB may be further underestimated because patients with asthma and EIB have been shown to be poor perceivers of symptoms of bronchospasm. Specifically, athletes often have a lack of awareness of symptoms suggestive of EIB. Health care providers and coaches also may not consider EIB as a possible explanation for respiratory symptoms that occur during exercise. Athletes are generally fit and healthy, and the presence of a significant medical problem often is not considered. The athlete is often considered to be “out of shape,” and vague symptoms of chest discomfort, breathlessness, and fatigue are not interpreted as a manifestation of EIB. Athletes themselves are often not aware that they may have a physical problem. Furthermore, if they do recognize they have a medical problem, they often do not want to admit to health personnel that a problem exists because of fear of social stigma or loss of playing time.
Specific Athletic Populations at Risk
Athletes who compete in high-ventilation or endurance sports may be more likely to experience symptoms of EIB than do those who participate in low-ventilation sports ; however, EIB can occur in any setting. EIB is prevalent in endurance sports in which ventilation is increased for long periods of time during training and competition, such as such as cross-country skiing, swimming, and long-distance running. EIB also commonly occurs in athletes who participate in winter sports. In addition, environmental triggers may predispose certain populations of athletes to an increased risk for the development of EIB. Chlorine compounds in swimming pools and chemicals related to ice-resurfacing machinery in ice rinks, such as carbon monoxide and nitrogen dioxide, may put exposed athletic populations at additional risk. These environmental factors may act as triggers and exacerbate bronchospasm in athletes who are predisposed to EIB. Thus it is important for athletes, coaches, and athletic trainers who supervise athletes in these sports to be aware of these important environmental issues.
Clinical Presentation
The clinical manifestations of EIB are extremely variable and can range from mild impairment of performance to severe bronchospasm and respiratory failure. Common symptoms include coughing, wheezing, chest tightness, and dyspnea. More subtle evidence of EIB includes fatigue, symptoms that occur in specific environments (e.g., ice rinks or swimming pools), poor performance for conditioning level, and avoidance of activity ( Box 16-1 ).
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Dyspnea upon exertion
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Chest tightness
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Wheezing
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Fatigue
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Poor performance for level of conditioning
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Avoidance of activity
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Symptoms in specific environments (e.g., ice rinks and swimming pools)
Generally, exercise at a workload representing at least 80% of the maximal predicted oxygen consumption for 5 to 8 minutes is required to generate bronchospasm in most athletes. Typically, athletes experience transient bronchodilation initially during exercise, and symptoms of EIB begin later or shortly after exercise. Symptoms often peak 5 to 10 minutes after exercise ceases and can remain significant for 30 minutes or longer if no bronchodilator therapy is provided. However, some athletes spontaneously recover to baseline airflow within 60 minutes, even in the absence of intervention with bronchodilator therapy. Unfortunately, it is currently impossible to predict which athletes will recover without treatment. Athletes who experience symptoms for extended periods often perform at suboptimal levels for significant portions of their competitive or recreational activities.
Diagnosis
History and Differential Diagnosis
The presence of EIB can be challenging to recognize clinically because symptoms are often nonspecific. A complete history and physical examination should be performed for each athlete with respiratory complaints associated with exercise. However, despite the value of a comprehensive history of the athlete with exertional dyspnea, the diagnosis of EIB based on self-reported symptoms alone has been shown to be inaccurate. Hallstrand and colleagues found that a screening history identified subjects who had symptoms or a previous diagnosis suggestive of EIB in 40% of the participants, but objective testing showed that only 13% of these persons actually had EIB. Similarly, Rundell and associates demonstrated that only 61% of EIB-positive athletes reported symptoms of EIB, whereas 45% of athletes with normal results of objective testing reported symptoms. The poor predictive value of the history and physical examination in the evaluation of EIB strongly suggests that clinicians should perform objective diagnostic testing when EIB is suspected.
Other medical problems that can mimic EIB and should be considered in the initial evaluation of exertional dyspnea include vocal cord dysfunction, gastroesophageal reflux disease, and allergic rhinitis. Cases of cardiac pathology such as arrhythmia, cardiomyopathy, and cardiac shunts are rarer, but these possibilities must be considered as well ( Box 16-2 ). A comprehensive history and examination is recommended to help rule out these other disorders, and specific testing such as echocardiography may be required. A history of specific symptoms in particular environments or during specific activities should be elicited. Timing of symptom onset in relation to exercise and recovery is also helpful. A thorough family and occupational history should be obtained because a family history of asthma increases the risk for development of asthma in other family members.
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Vocal cord dysfunction
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Gastroesophageal reflux disease
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Allergic rhinitis
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Cardiac pathology (e.g., arrhythmias, cardiomyopathy, and shunts)
Objective Testing
Objective testing should begin with spirometry before and after inhaled bronchodilator therapy, which will help identify athletes who have asthma. However, many people who experience EIB have normal baseline lung function. In these patients, spirometry alone is not adequate to diagnose EIB. Significant numbers of false-negative results may occur if adequate exercise and environmental stress are not provided during the evaluation for EIB. When results of a physical examination and spirometry are normal for patients being evaluated for EIB, bronchoprovocation testing is recommended. A positive bronchoprovocation test indicates the need for treatment of EIB. Specific tests have varying positive values, but in general, a change (usually a ≥10% decrease in forced expiratory volume in 1 second [FEV 1 ]) between pretest and posttest values is suggestive of EIB. In a patient with persistent exercise-related symptoms and negative results of a physical examination, spirometry, and bronchoprovocation testing, we recommend reconsidering alternative diagnoses.
Not all bronchoprovocation techniques are equally valuable or accurate in the assessment of EIB in athletes. The International Olympic Committee recommends use of a eucapnic voluntary hyperventilation (EVH) challenge to document EIB in Olympians. EVH involves hyperventilation of a gas mixture of 5% carbon dioxide and 21% oxygen at a target ventilation rate of 85% of the patient’s maximal voluntary ventilation in 1 minute, which is usually calculated as 30 times the baseline FEV 1 . The patient continues to hyperventilate for 6 minutes, and assessment of FEV 1 occurs at specified intervals up to 20 minutes after the test. This challenge test has been shown to have a high specificity for EIB. EVH has also been shown to be more sensitive for detecting EIB than use of methacholine or field- or laboratory-based exercise testing.
Mannitol inhalation is a newer bronchoprovocation technique that has been shown to be effective in diagnosing EIB in athletes. Mannitol inhalation is an osmotic airway challenge that involves inhaling mannitol at increasing concentrations (up to 160 mg). The test is terminated when the last dose of mannitol has been given or the FEV 1 has dropped ≥15% from baseline. The mannitol challenge is portable and can be used for field, clinic, or laboratory testing to identify EIB. Mannitol inhalation correlates well with traditional exercise testing and EVH.
Field-exercise challenge tests that involve having the athlete perform the sport in which he or she is normally involved and assessing FEV 1 after exercise have been shown to be less sensitive than EVH and allow for little standardization of a protocol. Pharmacologic challenge tests, such as the methacholine challenge test, have been shown to have a lower sensitivity than EVH for detection of EIB in athletes and are also not recommended for first-line evaluation of EIB.
Treatment Options
Pharmacologic Therapy
Pharmacologic therapy for EIB ( Table 16-2 ) has been studied extensively. The most common therapeutic recommendation to minimize or prevent symptoms of EIB is the prophylactic use of short-acting bronchodilators (selective β-adrenergic receptor agonists) such as albuterol shortly before exercise. Treatment with two puffs of a short-acting β-agonist shortly before exercise (15 minutes) will provide peak bronchodilation in 15 to 60 minutes and protection from EIB for at least 3 hours in most patients.
| Pharmacologic Therapy | Nonpharmacologic Therapy |
|---|---|
| Short-acting β-agonists | Adequate preexercise warm-up |
| Inhaled corticosteroids Long-acting β-agonists Leukotriene modifiers Cromolyn compounds | Wearing a mask in a cold environment Avoidance of triggers Nasal breathing |
Pharmacologically, long-acting bronchodilators work in a similar manner as short-acting bronchodilators; however, the bronchoprotection afforded by long-acting β-agonists has been shown to last up to 12 hours, whereas that of short-acting agents is no longer significant by 4 hours. Ferrari and associates demonstrated that inhalation of formoterol, a long-acting β-agonist, is effective in protecting asthmatic athletes as early as 15 minutes after dosing. However, tachyphylaxis also has been shown to occur after repeated use of long-acting β-agonists, and thus close follow-up is recommended when using these medications. In addition, controversy about use of long-acting β 2 -agonists as monotherapy in patients with asthma should caution health care providers about the use of these agents alone.
Inhaled corticosteroids are first-line therapy in terms of controller medications for patients who have chronic asthma and also experience EIB. Airway inflammation is also often present in nonasthmatic athletes who have EIB ; therefore, inhaled corticosteroids may be an effective medicine for treatment, but the efficacy of corticosteroids in this cohort has not been studied. Inhaled corticosteroids are also valuable in athletes who train multiple times per day.
Leukotriene modifiers have also been shown to be effective in treating EIB. Leff and colleagues evaluated the ability of montelukast, a leukotriene receptor antagonist, to protect patients with asthma against EIB. Montelukast therapy offered significantly greater protection against EIB than did placebo therapy and was also associated with a significant improvement in the maximal decrease in FEV 1 after exercise. In addition, tolerance to the medication and rebound worsening of lung function after discontinuation of treatment were not seen. In another study, daily zafirlukast treatment protected against EIB for at least 8 hours after regular dosing. Leukotriene modifiers are an effective second-line agent for treatment of EIB.
Mast cell stabilizers have been studied extensively for the prophylaxis of EIB. These medications prevent mast cell degranulation and subsequent histamine release. In a metaanalysis of the prevention of EIB in patients with asthma, nedocromil sodium was found to improve FEV 1 by an average of 16% and to shorten the duration of EIB symptoms to less than 10 minutes. Although these agents are effective, they are often used as a second-line treatment because of their cost, lack of availability in the United States, and their decreased duration of action and efficacy compared with β 2 -agonists.
Nonpharmacologic Therapy
Many athletes find that a period of precompetition warm-up reduces the symptoms of EIB that occur during their competitive activity. Athletes often draw this conclusion without any guidance from health care specialists. It has been shown by investigators that this refractory period does occur in some athletes with asthma and that athletes can be refractory to an exercise task performed within 2 hours of an exercise warm-up. However, the refractory period has not been consistently proved across different athletic populations, and it is currently not possible to identify which athletes will experience this refractory period.
Other nonpharmacologic strategies can be used to help reduce the frequency and severity of symptoms of EIB (see Table 16-2 ). Breathing through the nose rather than the mouth will also help ameliorate EIB by warming, filtering, and humidifying the air, which subsequently reduces airway cooling and dehydration. Wearing a face mask during activity warms and humidifies inspired air when outdoor conditions are cold and dry and is especially valuable to elite and recreational athletes who exercise in the winter. In addition, people with knowledge of triggers (e.g., freshly cut grass) should attempt to avoid them if possible.
Our preferred method for the diagnosis and treatment of EIB is shown in Figure 16-1 . Because the diagnosis of EIB based on symptoms alone is extremely inaccurate, objective testing is necessary to make a confident diagnosis of EIB. We recommend using EVH as the bronchoprovocation test of choice to document EIB; however, EVH may not be available to many health care providers. If EVH is not easily accessible, use of spirometry before and after an adequate exercise challenge is our second-line recommendation. It is essential to ensure that the exercise challenge is strenuous enough to generate adequate ventilation rates in patients who have excellent physical fitness.
In our experience, both pharmacologic and nonpharmacologic approaches are essential to minimizing the adverse effects of EIB. We recommend that athletes who have clinical evidence of EIB be treated with short-acting bronchodilators before exercise and be counseled on the importance of adequate warm-up and avoidance of known triggers. This regimen will prevent significant EIB in more than 80% of athletes. If symptoms persist, especially in athletes with asthma, we recommend adding corticosteroids as maintenance therapy. Although the efficacy of inhaled steroids in nonasthmatic athletes has not been evaluated, we recommend their use in nonasthmatic athletes whose symptoms are not adequately controlled with short-acting bronchodilators. This recommendation is based on evidence of increased inflammation in the airways of subjects without known asthma as a result of hyperventilation and exercise. Alternatively, either leukotriene modifiers or cromolyn compounds can be used in athletes whose EIB is inadequately controlled with β 2 -agonists.
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