Exercise-Induced Bronchoconstriction

BreAnna Kinghorn, MD

Introduction/Etiology/Epidemiology

•Exercise-induced bronchoconstriction (EIB) involves acute, transient airway narrowing that occurs during and after exercise.

•EIB is most often defined by ≥10% decline in forced expiratory volume in 1 second (FEV₁) at spirometry after exercise provocation.

•EIB occurs in 90% of individuals with asthma.

•EIB also can occur in individuals without a known diagnosis of asthma.

•Prevalence of EIB is higher in the competitive athlete population (30%–70%) than the nonathlete population (≤10%).

Pathophysiology

•Breathing dry and/or cold air causes airway narrowing via osmotic and thermal consequences of evaporative water loss from the airway surface.

•Dry or cold air in the distal airways causes hyperemia of bronchial vasculature and airway edema, which further causes airway narrowing.

•Airway narrowing causes cough.

•Although the events that trigger EIB and the role of inflammatory cells are not fully understood, a hyperosmolar environment is thought to trigger the release of inflammatory mediators, including histamine, tryptase, and leukotrienes from eosinophils and mast cells.

•Several studies have demonstrated that individuals who are prone to EIB have increased levels of exhaled nitric oxide, increased airway leukotriene levels, greater expression of mast cell genes, and/or peripheral eosinophilia.

Clinical Features

•Clinical manifestations can range from mild impairment to severe bronchospasm and, rarely, respiratory failure.

•Symptoms include coughing, wheezing, chest tightness, and dyspnea.

•More subtle symptoms include fatigue, abdominal discomfort, poor performance, and avoidance of activities.

•Exercise duration for a minimum of 5–8 minutes at 80% of maximum predicted oxygen consumption typically generates bronchospasm.

Differential Diagnosis

(Note: Children may have EIB [Figure 41-1] in addition to any of the disorders listed here.)

•Unrecognized or poorly controlled asthma

•Anxiety

Figure 41-1. Diagnostic flowchart for exercise-induced bronchoconstriction (EIB). Reprinted with permission from Krafczyk MA, Asplund CA. Exercise-induced bronchoconstriction: diagnosis and management. Am Fam Physician. 2011;84(4):427– 434. Copyright © 2011 American Academy of Family Physicians. All Rights Reserved.

•Vocal cord dysfunction

•Exercise-induced laryngomalacia

•Exercise-induced anaphylaxis

•Exercise-induced reflux

•Central airway obstruction arrhythmias

•Pulmonary or cardiac shunt

Diagnostic Considerations

Comprehensive History and Physical Examination

•Obtaining a history alone has been shown to lead to under- and over-diagnosis of EIB.

—Rule out other etiologic origins, including vocal cord dysfunction, arrhythmias, and pulmonary or cardiac shunt.

—Obtain a complete family history, including asthma or relatives with atopy.

Pulmonary Function Testing

While spirometry is the most important pulmonary function test, there are other tests that can be considered when evaluating a patient with exercise-related respiratory symptoms, including some that are more sensitive and/or less effort-dependent than spirometry alone. For the purpose of this review, discussion will be limited to the use of spirometry in the diagnosis of EIB.

Spirometry

•All patients with suspected EIB should perform spirometry.

—Assess the patient for baseline airway obstruction (ratio of FEV₁ to forced vital capacity up to the lower limit of normal for age).

Bronchodilator Responsiveness

•Identify bronchodilator responsiveness, defined as an increase of ≥12% in FEV₁ after inhalation of a short-acting bronchodilator.

Bronchoprovocation Techniques

•FEV₁ decrease ≥10% from a pre-exercise level is diagnostic of EIB, with an FEV₁ decline of ≥50% considered to indicate severe EIB.

•Indirect testing: Exercise, eucapnic voluntary hyperpnea, inhaled powdered mannitol, or nebulized hypertonic saline (see Table 41-1)

—Elicits inflammatory response to release mediators and provokes airway smooth muscle constriction

—Measurements obtained 5, 10, 15, and 30 minutes after exercise

• Direct challenges: Methacholine or histamine

—Acts directly with airway smooth muscle receptors to cause constriction independent of airway inflammation