Exercise-induced bronchoconstriction (EIB) occurs commonly in patients with asthma but also can affect individuals without asthma. EIB is particularly common in populations of athletes. Common symptoms include cough, dyspnea, chest tightness, and wheezing; however, there can be a variety of more subtle symptoms. In this article, the clinical presentation of EIB as well as the diagnosis and treatment of EIB are outlined.
Key points
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Exercise-induced bronchoconstriction (EIB) occurs in individuals with and without chronic asthma.
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The symptoms of EIB are often subtle and difficult to differentiate from normal manifestations of intense exercise.
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Diagnosis of EIB based on subjective symptoms alone is extremely inaccurate.
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Objective testing is strongly recommended to document a diagnosis of EIB.
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Treatment of EIB with a short-acting bronchodilator before exercise is 80% effective.
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If short-acting bronchodilators are used daily for prophylaxis, controller agents such as inhaled steroids should also be added.
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Adjunctive treatment approaches (adequate warm-up, allergen avoidance, dietary modification, etc.) may also be helpful.
Introduction
Exercise-induced bronchoconstriction (EIB) describes acute, transient airway narrowing that is provoked by exercise. EIB is characterized by symptoms of cough, wheezing, shortness of breath, fatigue, and/or chest tightness during or after exercise. Exercise is a very common trigger of bronchoconstriction in asthmatics, and 80% of all individuals with chronic asthma experience exercise-induced respiratory symptoms at some point. EIB also occurs in up to 10% of subjects who are not known to be atopic or asthmatic. This cohort does not have the typical features of chronic asthma (ie, nocturnal symptoms, multiple triggers, impaired lung function), and exercise may be the only trigger that causes such individuals respiratory symptoms.
EIB also occurs quite commonly in athletes, and prevalence rates of bronchoconstriction related to exercise in cohorts of athletes range from 11% to 50%. This wide variability in reported prevalence rates, in part, is a consequence of variable testing methods, thresholds for diagnosis, and participant populations. EIB is prevalent in endurance sports in which ventilatory load is increased for extended periods of time during training and competition (ie, soccer, lacrosse, swimming, long-distance running) ; however, EIB can occur in any setting. EIB also occurs commonly in cold weather and winter sports athletes. In addition, environmental triggers may predispose certain populations of athletes to an increased risk for development of EIB. Chloramine compounds in swimming pools and chemicals related to ice-resurfacing machinery in ice rinks may put exposed athletic populations at additional risk. Athletic fields in urban or high-traffic areas for vehicles may be more likely to cause EIB symptoms.
Despite how prevalent EIB is, the actual prevalence of EIB may actually be underestimated for multiple reasons. Patients with asthma and EIB have been shown to be poor perceivers of symptoms of bronchospasm. Athletes, specifically, often suffer from lack of awareness of symptoms suggestive of EIB. Furthermore, if they do recognize they have a medical problem, they often do not want to admit to health personnel that a problem exists due to fear of social stigma or losing playing time. In addition to this lack of self-perception, health care providers, parents, and coaches also may not consider EIB as a possible explanation for respiratory symptoms occurring 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 pathologic problem.
Introduction
Exercise-induced bronchoconstriction (EIB) describes acute, transient airway narrowing that is provoked by exercise. EIB is characterized by symptoms of cough, wheezing, shortness of breath, fatigue, and/or chest tightness during or after exercise. Exercise is a very common trigger of bronchoconstriction in asthmatics, and 80% of all individuals with chronic asthma experience exercise-induced respiratory symptoms at some point. EIB also occurs in up to 10% of subjects who are not known to be atopic or asthmatic. This cohort does not have the typical features of chronic asthma (ie, nocturnal symptoms, multiple triggers, impaired lung function), and exercise may be the only trigger that causes such individuals respiratory symptoms.
EIB also occurs quite commonly in athletes, and prevalence rates of bronchoconstriction related to exercise in cohorts of athletes range from 11% to 50%. This wide variability in reported prevalence rates, in part, is a consequence of variable testing methods, thresholds for diagnosis, and participant populations. EIB is prevalent in endurance sports in which ventilatory load is increased for extended periods of time during training and competition (ie, soccer, lacrosse, swimming, long-distance running) ; however, EIB can occur in any setting. EIB also occurs commonly in cold weather and winter sports athletes. In addition, environmental triggers may predispose certain populations of athletes to an increased risk for development of EIB. Chloramine compounds in swimming pools and chemicals related to ice-resurfacing machinery in ice rinks may put exposed athletic populations at additional risk. Athletic fields in urban or high-traffic areas for vehicles may be more likely to cause EIB symptoms.
Despite how prevalent EIB is, the actual prevalence of EIB may actually be underestimated for multiple reasons. Patients with asthma and EIB have been shown to be poor perceivers of symptoms of bronchospasm. Athletes, specifically, often suffer from lack of awareness of symptoms suggestive of EIB. Furthermore, if they do recognize they have a medical problem, they often do not want to admit to health personnel that a problem exists due to fear of social stigma or losing playing time. In addition to this lack of self-perception, health care providers, parents, and coaches also may not consider EIB as a possible explanation for respiratory symptoms occurring 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 pathologic problem.
Diagnosis
The clinical manifestations of EIB are extremely variable and can range from impairment of athletic performance (most cases) to severe bronchospasm and respiratory failure (less common, yet still possible). Common symptoms include coughing, wheezing, chest tightness, and dyspnea. More subtle evidence of EIB includes fatigue, symptoms that occur in specific environments (eg, ice rinks or swimming pools), poor performance for conditioning level (running/swimming slower than expected times), and avoidance of activity (very common in school-aged children) ( Box 1 ).
Dyspnea on exertion
Chest tightness
Wheezing
Fatigue
Poor performance for conditioning level
Avoidance of activity
Symptoms in specific environments
Generally, exercise at a workload representing at least 80% of the maximal predicted oxygen consumption for 5 to 8 minutes is required to generate an episode of EIB. If the onset of symptoms occurs more quickly after starting exercise, then EIB is less likely. Typically, most people experience transient bronchodilation initially during exercise, and symptoms of EIB begin later or shortly after exercise. Symptoms may manifest after exercise ceases and can remain significant for 30 minutes or longer if no bronchodilator therapy is provided. Some patients spontaneously recover to baseline airflow within 60 minutes, even in the absence of intervention with bronchodilator therapy, which is clearly not recommended. Individuals who experience symptoms for extended periods frequently perform at suboptimal levels for significant portions of their competitive or recreational activities.
The presence of EIB can be challenging to recognize clinically, because symptoms are often nonspecific. Complete history and physical examination should be performed on each patient with respiratory complaints associated with exercise. However, despite the value of a comprehensive history in the patient with exertional respiratory symptoms, the diagnosis of EIB based on self-reported symptoms alone has been shown to be extremely inaccurate ; this is likely due to the lack of specificity of symptoms and the fact that in most cases the physical examination will be normal. 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 there is a clinical suspicion of EIB.
Other medical problems that commonly mimic EIB and that need to be considered in the initial evaluation include vocal cord dysfunction, gastroesophageal reflux disease, and allergic rhinitis/sinus disease ( Box 2 ). Cardiac pathology such as arrhythmia, cardiomyopathy, and cardiac shunts are much less common, but need to be considered as well. A comprehensive history and examination is recommended to help rule out these other disorders, and specific testing such as echocardiography, allergy testing, and/or videolaryngostroboscopy 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.
Vocal cord dysfunction
Gastroesophageal reflux disease
Allergic rhinitis/sinus disease
Cardiac pathology (arrhythmias, cardiomyopathy, shunts)
Objective testing should begin with spirometry before and after inhaled bronchodilator therapy, which will help identify athletes whose lung function was impaired at rest. However, most 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 in the evaluation for EIB. In patients being evaluated for EIB who have a normal physical examination and normal spirometry, bronchoprovocation testing is recommended. A positive bronchoprovocation test indicates the need for treatment of EIB. A decrease of 10% or (greater forced expiratory volume in 1 second [FEV 1 ]) between pretest and post-test values is diagnostic of EIB. In a patient with persistent exercise-related symptoms and negative physical examination, spirometry, and bronchoprovocation testing, alternative diagnoses other than EIB should be considered.
The International Olympic Committee recommends eucapnic voluntary hyperventilation (EVH) as the bronchoprovocation test of choice to document EIB in Olympians. EVH involves hyperventilation of a gas mixture of 5% CO 2 and 21% O 2 at a target ventilation rate of 85% of the patient’s maximal voluntary ventilation in 1 minute (MVV). The MVV is usually calculated as 35 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 methacholine or field- or lab-based exercise testing. However, the major limitation of EVH is that it is not widely available.
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% or greater 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. There are some potential limitations in using mannitol to identify airway hyperresponsiveness. As with any osmotic challenge, mannitol inhalation will frequently provoke a person to cough. Excessive coughing has the potential to affect the mannitol dose deposited in the lower airway, which could lead to a false-negative test result.
Treadmill or ergometer-based testing in pulmonary function laboratories are effective methods for diagnosing EIB but may result in false-negatives if the exercise stimulus is not intense enough. The optimal exercise challenge is 8 minutes in duration and allows the patient to achieve greater than 90% of maximum predicted heart rate by 2 minutes into the challenge and maintain it for the remaining 6 minutes of the challenge.
Field-exercise challenge tests that involve athletes performing the sport in which they are normally involved and assessing lung function pre- and post-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 ( Table 1 ).
