Exercise-Induced Bronchoconstriction

Posted by • February 13th, 2015

Asthma or asthma-like conditions can limit the ability of athletes to perform. This article reviews the diagnosis and treatment of asthma and exercise-induced bronchoconstriction in athletes.

The term exercise-induced bronchoconstriction describes the transient narrowing of the airways after exercise, a phenomenon that occurs frequently among athletes who may not have a diagnosis of asthma or even have any respiratory symptoms.

Clinical Pearls

– Describe a key factor in the pathogenesis of exercise-induced bronchoconstriction.

The mechanism of exercise-induced bronchoconstriction has not been established with certainty; both airway cooling resulting from conditioning of inspired air and postexercise rewarming of airways have been proposed as mechanisms. However, the key stimulus is probably airway dehydration as a result of increased ventilation, resulting in augmented osmolarity of the airway-lining fluid. This is thought to trigger the release of mediators — such as histamine, cysteinyl leukotrienes, and prostaglandins — from airway inflammatory cells, which leads to airway smooth-muscle contraction and airway edema.

How is asthma or exercise-induced bronchoconstriction in athletes diagnosed?

The demonstration of more than 10% diurnal variability in peak expiratory flows measured twice daily over a period of 2 weeks, or more than 12% (and >200 ml) variability in forced expiratory volume in 1 second (FEV1) over time or after 4 weeks of treatment, is consistent with a diagnosis of asthma or exercise-induced bronchoconstriction. The likelihood of airways to narrow can also be demonstrated, if airflow limitation is present, by a more than 12% (and >200 ml) change in the FEV1 after inhalation of an aerosolized beta2-agonist; if the baseline airway caliber is normal, this likelihood can be assessed as the presence of airway hyperresponsiveness documented with the use of bronchoprovocation testing. These tests include direct challenges (e.g., with inhaled methacholine), which act on airway smooth muscle to cause bronchoconstriction, and indirect challenges, such as eucapnic voluntary hyperpnea (particularly recommended for athletes), hyperosmolar tests with saline or mannitol, and laboratory or field exercise tests. However, athletes may have a positive response to only one of these types of tests, and airway responsiveness can normalize a few weeks after they stop intense training. Therefore, more than one type of test may be needed, and ideally the testing should be performed during a period of intense training.

Figure 1. Diagnosis of Asthma and Exercise-Induced in Athletes.

Morning Report Questions

Q: What general measures are recommended for the management of exercise-induced bronchoconstriction?

A: As for all patients with asthma, education about asthma self-management is essential; this should include advice about environmental measures, inhaler-use technique, and the use of an asthma action plan for the management of exacerbations, in addition to regular follow-up. Mechanical barriers such as face masks, although they are not always well tolerated, can help reduce the effects of cold air exposure in winter-sports athletes or the inhalation of particulate air pollutants. A pre-exercise warm-up
(i.e., low-intensity or variable-intensity precompetitive exercise) can result in a reduction in exercise-induced bronchoconstriction in more than half of persons. However, whenever possible, it is preferable for sensitized athletes not to exercise close to busy roads or during periods of high allergen exposure. Measures to reduce chloramine formation in chlorinated pools, improve ventilation of pool environments, and reduce exposure to other indoor and outdoor pollutants, including ozone, particulate matter, and nitrogen oxides, should also be promoted.

Q: What pharmacologic therapies are commonly used?

A: The most common management strategy for athletes with asthma or exercise-induced bronchoconstriction who are exercising daily is daily treatment with inhaled glucocorticoids, with short-acting inhaled beta2-agonists used occasionally before exercise. Inhaled glucocorticoids are the mainstay of asthma therapy in athletes, as they are in nonathletes; these agents are allowed by sports authorities. Apart from helping to control asthma and improve pulmonary function, an additional benefit of treatment with inhaled glucocorticoids is a progressive reduction, with regular use, in airway responses to various stimuli, including exercise. If low doses of inhaled glucocorticoids do not achieve asthma control, the addition of another controller drug should be considered, preferably a long-acting inhaled beta2-agonist. Leukotriene-receptor antagonists are also an option for maintenance treatment, and the combination of inhaled glucocorticoids and leukotriene-receptor antagonists may provide additional protection.

Table 1. Specific Issues in the Management of Asthma in Athletes.

Table 2. Treatment of Asthma and Exercise-Induced Bronchoconstriction in Athletes.

Table 3. Current Antidoping Status of Asthma Medications.

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