The Inflammatory Basis of Exercise-Induced Bronchoconstriction

Abstract

Exercise-induced bronchoconstriction (EIB) is common in individuals with asthma, and may be observed even in the absence of a clinical diagnosis of asthma. Exercise-induced bronchoconstriction can be diagnosed via standardized exercise protocols, and anti-inflammatory therapy with inhaled corticosteroids (ICS) is often warranted. Exercise-related symptoms are commonly reported in primary care; however, access to standardized exercise protocols to assess EIB are often restricted because of the need for specialized equipment, as well as time constraints. Symptoms and lung function remain the most accessible indicators of EIB, yet these are poor predictors of its presence and severity. Evidence suggests that exercise causes the airways to narrow as a result of the osmotic and thermal consequences of respiratory water loss. The increase in airway osmolarity leads to the release of bronchoconstricting mediators (eg, histamine, prostaglandins, leukotrienes) from inflammatory cells (eg, mast cells and eosinophils). The objective assessment of EIB suggests the presence of airway inflammation, which is sensitive to ICS in association with a responsive airway smooth muscle. Surrogate tests for EIB, such as eucapnic voluntary hyperpnea or the osmotic challenge tests, cause airway narrowing via a similar mechanism, and a response indicates likely benefit from ICS therapy. The complete inhibition of EIB with ICS therapy in individuals with asthma may be a useful marker of control of airway pathology. Furthermore, inhibition of EIB provides additional, useful information regarding the identification of clinical control based on symptoms and lung function. This article explores the inflammatory basis of EIB in asthma as well as the effect of ICS on the pathophysiology of EIB.