Exercise-induced asthma and exercise-induced bronchoconstriction

• Exercise-induced asthma and exercise- induced bronchoconstriction are the terms commonly used to describe the transient narrowing of the airways that follows vigorous exercise in a dry environment.¹ The term exercise-induced asthma is preferred when describing the response in clinically recognised asthmatics. Exercise-induced bronchoconstriction is the preferred term when describing the same response in people who do not have any other signs or symptoms of asthma.² Both names however are frequently used to describe the response to exercise whether there is a clinical diagnosis of asthma or not.
• Exercise-induced asthma/exercise induced bronchoconstriction is defined as a reduction in forced expiratory volume in one second (FEV₁) of 10% or more from the value measured before exercise.
• Exercise-induced asthma occurs in around 50-65% of people with asthma who are being treated with inhaled corticosteroids; a fall in FEV₁ of 30% or more is regarded as severe.^3,4 Severe exercise-induced asthma is accompanied by arterial hypoxemia and lung hyperinflation, and requires medical attention.
• In Australia, exercise-induced bronchoconstriction has become increasingly recognised in school children⁵ and in elite athletes who have normal lung function.^6,7

Knowing the severity of exercise-induced asthma is useful for selecting the type of medication and in particular the dose and duration of treatment with ICS.8-11

Pathogenesis

• As inspired air is heated and humidified during exercise, water is evaporated from the airway surface. This process can cause exercise-induced asthma or exercise-induced bronchoconstriction.¹² The cooler and dryer the inspired air, the more severe the symptoms.
• Breathing warm humid air can prevent airway dehydration so that exercise does not provoke an attack of asthma.
• In elite athletes performing endurance summer sports, the levels of allergen they inhale during training may increase the risk of exercise-induced bronchoconstriction.¹³ In elite swimmers, environmental irritants arising from exposure to chlorine and its products is thought to contribute to the development of ‘twitchy' airways, a feature of asthma.^14,15
• The pathogenesis of exercise-induced bronchoconstriction in winter athletes may relate to injury of the airway epithelial surface from conditioning large volumes of cold dry air.¹⁶ This is thought to lead to increased responsiveness of bronchial smooth muscle and subsequently symptoms of asthma and exercise-induced bronchoconstriction.¹⁷

Content Created (Thursday, 16 November 2006)