Exercise-induced bronchoconstriction: prevalence, pathophysiology, patient impact, diagnosis and management
Exercise-induced bronchoconstriction (EIB) was previously known as exercise-induced asthma or exercise-induced bronchospasm, before being named EIB in 1970. It is defined as acute, transient, reversible airway narrowing, occurring during or soon after exercise. Most cases occur in patients with asthma, but EIB has also been experienced by individuals without asthma, including some elite athletes.
EIB is estimated to occur in approximately 90% of people with asthma, and is more likely to manifest in patients with poorly controlled asthma. The prevalence in the general population is estimated at 5–20%, but few population studies differentiate between patients with asthma and those without. The prevalence in children is generally higher, at 3–35%, and those living in urban environments are 1.6 times more likely to experience EIB than those in more rural areas. High-performance athletes are also at increased risk, due to prolonged inhalation of cold, dry air and airborne pollutants. Among elite or Olympic-level athletes, the prevalence of EIB has been estimated at 30–70%.
Present theories suggest that hyperventilation during exercise leads to water loss via evaporation, dehydrating the airway surfaces and initiating the mast cell-mediated signalling cascade, which results in the contraction of bronchial smooth muscle. Breathing cold air further increases the dehydration effect, and therefore athletes performing in cold weather conditions demonstrate the highest rates of EIB.
Unless well managed, EIB can limit patients’ ability to exercise, depriving them of the well-known health benefits of regular exercise. In patients without asthma, nonpharmacological treatments for EIB include pre-warming and humidifying air during exercise (e.g. by breathing through a face mask) and utilising a warm-up period. If symptoms continue, use of short-acting beta-agonists, leukotriene receptor antagonists or chromones should be considered. In patients with asthma, EIB may indicate poor asthma control, and therefore attention should be focused on optimising asthma management.