Exercise-Induced Bronchoconstriction.

Abstract

Definition Transient narrowing of the airways only after exercise in individuals with or without underlying asthma. Epidemiology Current literature suggests that the prevalence of exercise-induced bronchoconstriction (EIB) is significantly higher in athletes than in the general population at any age and equally between genders. These rates are highest among athletes in cold weather, indoor sports, swimmers, and in endurance athletes (1,2,4). Mechanism Mechanism not established with certainty, several proposed theories (1,2). The key stimulus is airway dehydration due to increased ventilation, resulting in a loss of heat, drying of the airways, as well as increased intracellular osmolarity. This triggers the release of inflammatory mediators, leading to airway smooth muscle contraction and airway edema (1,2). Mechanical stress/injury to airway epithelium plays a role in the acute response to exercise as well as in the development of airway remodeling in athletes through their effects on smooth muscle contractile properties causing hypersensitivity leading to bronchoconstriction (1,2). Transient immunosuppression also may develop in athletes during periods of intense training, with increased susceptibility to respiratory infections (especially viral), which may increase airway response to exercise acutely and affect overall asthma control (1,2). Diagnosis History of characteristic symptoms induced by 10 to 15 min of intense exercise, which dissipates upon activity cessation (late-phase response can occur 4 to 8 h after exercise) and documentation of variable airflow limitations, by means of bronchodilator reversibility testing or bronchoprovocation tests (respiratory symptoms alone have poor predictive value). Exercise challenge tests — an athlete must reach >90% of peak heart rate at 2 min and maintain this level for another 6 min. This allows for adequate associated ventilation rate >85% maximum voluntary ventilation (at least 17.5 times the resting forced expiratory volume [FEV1]). FEV1 is measured at 5, 10, 15, and 30 min after exercise, and then these values are compared with preexercise results. This test should be done with cool, dry air, and clinicians should consider performing the challenge test specific to the athlete’s sport (1,2,4). ○ Mild — FEV1 decrease of 10% to <25% ○ Moderate — FEV1 decrease of 25% to 50% ○ Severe — FEV1 decrease ≥50% Bronchoprovocation testing: direct versus indirect testing, direct = inhaled methacholine — acts on airway smooth muscle to cause bronchoconstriction. Indirect challenges (preferred by the International Olympic Committee [IOC]) include eucapnic voluntary hyperpnea (recommended), hyperosmolar tests with saline or mannitol, and laboratory or field exercise tests (2). Athletes may have a positive response to only one type of test, and airway hyperresponsiveness can normalize within a few weeks after stopping intense training; therefore, a more accurate diagnosis may require conducting more than one type of testing. Differential Diagnosis (Consider if provocation testing is inconclusive or poor response to therapy) Exercise-induced glottic or supraglottic laryngeal obstruction Vocal cord dysfunction Chronic allergic rhinitis Gastroesophageal reflux Hyperventilation syndrome Chronic lung disease, including asthma General deconditioning Swimming-induced pulmonary edema Exercise-induced arterial hypoxemia Other cardiovascular conditions Management: Nonpharmacological and Pharmacotherapy Education Mechanical barriers: face mask, scarf Preexercise warm-up (low-intensity or variable-intensity precompetitive exercise) Evaluate for underlying persistent asthma by performing spirometry measurements before and after administration of a short-acting bronchodilator to demonstrate the presence of reversible airflow. Exhaled nitric oxide measured during a single breath exhalation also may be used as an adjunct or as an alternative to spirometry. Avoid exercise close to busy roads in high allergen exposure environments. Provide short-acting B2 agonists rescue therapy 5 to 15 min before exercise. ○ Regular use may increase airway responsiveness to bronchoconstriction stimuli and lead to tolerance, thus decreasing their bronchoprotective effects due to down-regulation of the B2 receptor (tachyphylaxis). Inhaled corticosteroid (ICS) daily if athlete needs to use a rescue B2 agonist more than twice per week, or if baseline lung function is below normal — it may take more than 2 to 4 wk after initiation to see maximal improvement (1–3). ○ Consider ICS if rescue medication is needed more than twice per month. Second-line therapy is leukotriene receptor antagonist. If uncontrolled with a low dose of inhaled glucocorticoid, prescribe a combined inhaled glucocorticoid and inhaled long-acting B2 agonist or add a leukotriene receptor antagonist to inhaled glucocorticoid after checking general measures and contribution of coexisting conditions. Weak recommendations for low-salt diet, fish oil, and ascorbic acid (1). Athletes with documented asthma or EIB should review and adhere to antidoping regulations.