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Exercise-Induced Bronchoconstriction


Definition and Prevalence

Exercise-induced bronchoconstriction (EIB) describes acute, transient airway narrowing that occurs during and 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 bronchoconstriction in asthmatic patients. Approximately 80% of individuals with chronic asthma have exercise-induced respiratory symptoms. However, EIB can also occur 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, impaired lung function), and exercise may be the only stimulus that causes respiratory symptoms.

The mechanism of EIB is characterized by the inspired volumes of relatively low-humidity air. Dry air leads to water loss from the airways, creating an osmotic change on the airway surface. The resultant hyperosmolar environment stimulates mast cell and eosinophil degranulation. The released mediators, predominantly leukotrienes, cause bronchoconstriction and airway inflammation. Inspiring cool air is thought to have a similar effect on the airways, albeit a less potent affect than hyperventilation with dry air.

EIB occurs commonly in athletes. The prevalence rates of exercise-related bronchoconstriction in athletes range from 11% to 50% ( Table 13.1 ). Holzer and colleagues found 50% of a cohort of 50 elite summer athletes had EIB. Wilber and associates found that 18% to 26% of Olympic winter sport athletes and 50% of cross-country skiers had EIB. The US Olympic Committee reported an 11.2% prevalence of EIB in all athletes who competed in the 1984 Summer Olympics.

TABLE 13.1
Prevalence of Exercise-Induced Bronchoconstriction in Selected Studies
Reference No. Athletes EIB Prevalence (Bronchoprovocation Technique)
( ) Winter Olympians 18%–26% (exercise)
( ) Elite figure skaters 41% (EVH)
31% (exercise)
( ) Elite athletes 50% (EVH)
18% (methacholine)
( ) Collegiate athletes 39% (EVH)
EIB , Exercise-induced bronchoconstriction; EVH , eucapnic voluntary hyperventilation.

Despite numerous studies that investigate the prevalence of EIB in athletes, few studies have investigated the prevalence of EIB in cohorts of athletes without 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, 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 bronchoconstriction. Specifically, athletes often suffer from 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 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 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 losing 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 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 occurs commonly in winter sports athletes. In addition, environmental triggers may predispose certain populations of athletes to an increased risk for 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 bronchoconstriction in athletes who are predisposed to EIB. Thus it is important for athletes, coaches, and athletic trainers supervising 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 bronchoconstriction 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 13.1 ).

Box 13.1
Common Symptoms of Exercise-Induced Bronchoconstriction

  • Dyspnea on exertion

  • Chest tightness

  • Wheezing

  • Fatigue

  • Poor performance for level of conditioning

  • Avoidance of activity

  • Symptoms in specific environments (e.g., ice rinks, swimming pools)

In general, exercise at a workload representing at least 80% of the maximal predicted oxygen consumption for 5 to 8 minutes is required to generate bronchoconstriction 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 on 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 screening history identified subjects with symptoms or a previous diagnosis suggestive of EIB in 40% of the participants, but only 13% of these persons actually had EIB after objective testing. Similarly, Rundell and associates demonstrated that only 61% EIB-positive athletes reported symptoms of EIB, whereas 45% of athletes with normal 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 there is a suspicion of EIB.

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. Cardiac pathology such as arrhythmia, cardiomyopathy, and cardiac shunts are more rare, but these possibilities should also be considered ( Box 13.2 ). A comprehensive history and examination is recommended to help rule out these confounding 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 other family members developing asthma.

Box 13.2
Mimics of Exercise-Induced Bronchoconstriction

  • Vocal cord dysfunction

  • Gastroesophageal reflux disease

  • Allergic rhinitis

  • Cardiac pathology (arrhythmias, cardiomyopathy, shunts)

Objective Testing

Objective testing should begin with spirometry before and after inhaled bronchodilator therapy, which will help to 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 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. Specific tests have varying positive values, but in general, a change (usually ≥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 physical examination, spirometry, and bronchoprovocation testing, we recommend reconsidering alternative diagnoses.

Not all bronchoprovocation techniques are equally valuable or accurate in assessing EIB in athletes. The International Olympic Committee recommends eucapnic voluntary hyperventilation (EVH) challenge 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 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 lab- or field-based exercise testing.

In the United States, lab-based exercise testing is widely available, although often less sensitive than EVH. Lab-based exercise testing measures serial lung function tests before and after an exercise challenge. In general, FEV 1 is measured because this value has shown good repeatability. Subjects are first asked to perform spirometry before an exercise challenge to measure the baseline FEV 1 value. Subjects are then asked to exercise, and FEV 1 is measured serially at 5, 10, 15, and 30 minutes after exercise. EIB is diagnosed as a 10% or greater drop in preexercise FEV 1 measured during the 30-minute postexercise phase. Severity of EIB is characterized by the degree of reduction: mild (10% to 25% reduction), moderate (25% to 50% reduction), and severe (≥50% reduction).

In contrast to lab-based testing, field-based exercise testing involves an athlete performing a sport and assessing FEV 1 after exercise. Similar to lab-base testing, field-based testing has been shown to be less sensitive than EVH. Moreover, such field-based exercise testing allows for little protocol standardization. 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

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