Exercise-Induced Asthma

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Summary of practice points

 Level of evidence
ICS treatment as monotherapy twice daily for 8 to12 weeks reduces severity of exercise-induced asthma and after treatment 50% of people will no longer require any prophylactic medication pre-exercise. II
ICS in combination with a LABA is recommended to prevent exercise-induced asthma for those with abnormal spirometry and persistent symptoms. The duration of the protective effect of LABAs is reduced with daily use (either alone or in combination with ICS). Thus, in the middle of a dosing period, extra doses of the combination or a SABA may be required to protect against exercise-induced asthma. I
Single doses of short- or long-acting beta2 agonist, sodium cromoglycate or nedocromil sodium may significantly inhibit or even prevent exercise-induced asthma when taken immediately before exercise. I
LABAs alone are only recommended to prevent exercise-induced asthma if used less than 3 times per week because the duration of their protective effect against exercise is reduced when they are taken daily. Daily doses may lead to excessive use of beta agonists. II
Leukotriene antagonists reduce both the severity and the duration of exercise-induced asthma. Tolerance does not develop to daily use of these drugs. II
Respiratory symptoms during exercise are poor indicators of presence of exercise-induced asthma, therefore, objective testing is recommended. IV
Being physically fit can increase the intensity of exercise required to provoke exercise-induced asthma, although exercise-induced asthma can still occur. I 

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

Practice tip

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

Impact on quality of life, asthma and sporting performance

Exercise-induced asthma/exercise-induced bronchoconstriction should not be allowed to interfere significantly with quality of life because treatment is so successful in preventing the problem.

  • Because exercise-induced asthma/exercise-induced bronchoconstriction occurs after exercise, it should not provide a physiological limitation to exercise performance. However, there are some minor changes in lung function during exercise18 and, in competitive sport, these may contribute to performance.
  • When exercise is performed within one hour of recovering from exercise-induced asthma/exercise-induced bronchoconstriction, approximately 50% of people become refractory and will have significantly less exercise-induced asthma/exercise-induced bronchoconstriction a second time.19
  • There is no evidence that exercise-induced asthma/exercise-induced bronchoconstriction impacts on asthma control but it may be regarded as a sign that asthma is not well controlled.

Detection

The best question to elicit a history of exercise-induced asthma/exercise-induced bronchoconstriction is to ask: "Do you feel more breathless/wheezy/symptomatic five to ten minutes after you stop exercise than during exercise?"

  • People without asthma will also get short of breath if they exercise hard enough, but the symptoms subside rapidly after the exercise stops.
  • In someone with exercise-induced asthma/exercise-induced bronchoconstriction the symptoms get worse for the next 5 to 10 minutes before spontaneous recovery occurs over the next 30 minutes.
  • Recovery from exercise-induced asthma/exercise-induced bronchoconstriction can be aided by the use of a bronchodilator to reverse the airway narrowing.
  • Exercise-induced asthma/exercise-induced bronchoconstriction cannot be excluded on the basis of a negative test to inhalation of methacholine and histamine, particularly in people with normal spirometry.20 Leukotrienes and prostaglandins are considerably more potent in causing bronchial smooth muscle contraction than histamine and methacholine21 and they are the most important mediators of the airway narrowing provoked by exercise.
Practice points
  • Respiratory symptoms during exercise are poor indicators of the presence of exercise-induced asthma, therefore, objective testing is recommended. (IV)
  • Being physically fit can increase the intensity of exercise required to provoke exercise-induced asthma, although exercise-induced asthma can still occur. (I)

Assessment of lung function

Forced expiratory volume in one second (FEV1) is the best measurement to identify exercise-induced asthma/exercise-induced bronchoconstriction and to assess its severity. A peak flow meter can be used but the measurement has greater variability than FEV1. Repeated measurements are usually made before exercise and then repeated at least 3 times within 10 minutes of ceasing exercise. 

When testing for exercise-induced asthma in the field, exercise should be: 22

  • Strenuous (> 85% maximum heart rate)
  • Preferably running
  • Performed for six minutes in children and eight minutes in adults
  • Take place in an environment that is dry or at least has less than 10 mg of water per litre of air (represented by a common room air temperature of 23C with 40% humidity).

Several laboratory tests are used as surrogates for exercise to detect exercise-induced asthma/exercise-induced bronchoconstriction:

  • Eucapnic voluntary hyperpnea: the major advantage of this test is that the duration, intensity, ventilation and temperature of the inspired air can be adjusted to simulate the sport and environmental conditions in which it is performed if necessary. False negative results for exercise-induced asthma/exercise-induced bronchoconstriction are uncommon.23,24
  • Hyperosmolar aerosols of salt and sugar.25,26
  • Inhalation of a dry powder preparation of mannitol is now available as a challenge test for airway hyperresponsiveness: the mannitol test provides an alternative to testing by exercise, eucapnic voluntary hyperpnoea and inhaled hypertonic saline in the diagnosis of exercise-induced asthma and exercise-induced bronchoconstriction.26-28

Under- and over-diagnosis

Exercise-induced asthma/exercise-induced bronchoconstriction may be under-diagnosed due to:

  • Poor perception of symptoms unless the FEV1 falls 20% or more
  • Post-exercise breathlessness not considered abnormal.

Exercise-induced asthma/exercise-induced bronchoconstriction may be over-diagnosed because:

  • People who are overweight and unfit become breathless easily
  • Cough after exercise commonly occurs in non-asthmatics when they exercise heavily in cool dry air
  • Winter athletes commonly exhibit cough, breathlessness, wheeze and mucus production29
  • A person, usually an athlete, may have vocal cord dysfunction.30

Practice tips

  • Normal values for spirometry should not exclude a diagnosis of exercise-induced asthma/exercise-induced bronchoconstriction.
  • Classic symptoms of asthma such as waking at night or early in the morning are not common in athletes who may only have exercise-induced asthma/exercise-induced bronchoconstriction. Objective measurement is recommended before a firm diagnosis is made (especially for those who require permission to inhale a beta2 agonist before a sporting event).6,31
  • Exercise-induced asthma/exercise-induced bronchoconstriction is often one of the first signs of asthma 32-34 and one of the last to go with treatment.8
  • Early identification and treatment of exercise-induced asthma/exercise-induced bronchoconstriction may prevent later development of clinically recognised asthma and changes in lung function.

Effect of training

Asthma severity, as reflected by exercise-induced asthma, is not altered by training, but the threshold for respiratory symptoms can increase. This means that after training, the person is likely to:

  • have less exercise-induced asthma
  • be less breathless
  • be less anxious about activity
  • feel good
  • be less dependent on treatment
  • lose less time from school.

Some athletes find warm up prevents them getting exercise-induced asthma during the main game. This beneficial effect may be due to improved delivery of water to the airway surface by the bronchial circulation.

Treatment strategies to manage exercise-induced asthma

Drugs that reduce airway inflammation, inhibit the release of mediators or inhibit the contractile effects of these mediators can be used to manage exercise-induced asthma.35

  • Inhaled corticosteroids (ICS): have been shown to significantly reduce the severity of exercise-induced asthma and completely inhibit exercise-induced asthma in 50% of cases following 8-12 weeks treatment.4,9,36,37,11 Sodium cromoglycate, nedocromil sodium or a bronchodilator can be used immediately before exercise (or as rescue medication) until the full effect of ICS is realised. This ICS alone approach is suggested for asthmatics with normal lung function for whom a bronchodilator is not indicated. It is recommended because successful treatment results in 50% of people no longer having exercise-induced asthma and thus the need for pre-exercise medication is avoided.
  • Long-acting beta2 agonist (LABA) in combination with ICS: can be used successfully for prevention of exercise-induced asthma in patients with abnormal spirometry and/or more persistent symptoms.37 The duration of the protective effect of the LABA against exercise induced asthma is reduced when they are taken daily, even in combination with ICS.35,37-41 As a result of this reduction in duration of protection, it would be expected that over time patients will use extra inhalations of SABA before exercise or if breakthrough exercise-induced asthma occurs.
  • Long-acting beta2 agonist (LABA) alone: can be used successfully for prevention of exercise-induced asthma.42-44 LABAs can be effective for up to 12 hrs when they are used intermittently (less than 3 times a week)45 but the duration of the protective effect is reduced when these drugs are used daily.39,46,47 Further, recovery time from breakthrough exercise-induced asthma can be prolonged when LABA are used daily.41
  • Short-acting beta2 agonist (SABA): provide about 80% protection for up to 2 hrs when given immediately before exercise.48,43 SABAs are also effective rescue therapy provided they are not being used to excess. Single-dose LABA or SABA treatment can be beneficial, particularly in young people with normal lung function and no other significant asthma symptoms.
  • Sodium cromoglycate and nedocromil sodium: are less effective than beta agonists in preventing exercise-induced asthma. They provide 50-60% protection for only 1-2 hours, but have some advantages over beta2 agonists.49-51 They do not induce tolerance and can be used several times in a day. The dose can be adjusted and the protective effect is immediate.52
  • Leukotriene receptor antagonists: are also used to control exercise-induced asthma and provide 50-60% protection when given as tablets for up to 24 hrs.53,54 They do not induce tolerance55,47 and recovery from any residual exercise-induced asthma is rapid, usually occurring within 15 minutes.53,41
Practice points
  • ICS treatment for 8-12 weeks reduces severity of exercise-induced asthma and after treatment 50% of people will no longer require medication pre-exercise. (II)
  • Single doses of short- or long-acting beta2 agonist, sodium cromoglycate or nedocromil sodium may significantly inhibit or even prevent exercise-induced asthma when taken immediately before exercise. (I)
  • LABAs are best used intermittently to prevent exercise-induced asthma because the duration of their protection against exercise is reduced when they are taken daily, whether alone or in combination with inhaled corticosteroids. (II)
  • Leukotriene antagonists reduce severity and duration of exercise-induced asthma. Tolerance does not develop to daily use of these drugs. (II)

Drug-free strategies

People with exercise-induced asthma may benefit from the following advice:

  • Be as fit as possible so that the threshold for exercise-induced asthma is increased (many forms of exercise will not be of sufficient intensity to cause an attack of asthma).56
  • Exercise in a warm humid environment.
  • Do not perform exercise in environment with a high level of allergens (pollen season) or a high level of particulate matter or irritant gases.
  • Consider breathing with a mask or through the nose.
  • Warm up: this may prevent exercise-induced asthma during the main game.

Practice tips

  • Tolerance to LABA is very common and manifests itself as a reduction in the duration of the protective effect. This means that extra treatment may be needed in the middle of a dosing period.
  • It is important to have a strategy for treatment of exercise-induced asthma that does not rely on excessive use of SABAs or LABAs.35, 57
  • There is little difference in exercise-induced asthma between adults and children, although young children do tend to recover from exercise-induced asthma faster than older children or adults.58

Use of asthma medications in competitive sport

Many sporting bodies require objective evidence of exercise-induced asthma/exercise-induced bronchoconstriction in order for athletes to use asthma medications during competition.

  • The International Olympic Committee now requires documentation of asthma or exercise-induced bronchoconstriction as a prerequisite for permission to use an inhaled beta2 agonist.31
  • Regulations regarding the use of certain medications in sport may depend on the different sporting bodies. If a sporting organisation allows the therapeutic use of prohibited substances, the athlete must strictly adhere to the approval procedures. Healthcare providers should advise patients to check with their sport's relevant sporting organisation.
  • The Australian Sports Anti-Doping Authority provides information about Therapeutic Use Exemptions for athletes who suffer from medical conditions requiring treatment with prohibited substances. Go to http://www.asada.gov.au/ or call the ASADA tollfree hotline: 1800 020 506 to check the status of substances. The hotline is a confidential service for athletes and their support staff that offers information on the status of Australian pharmaceutical medications and substances in sport.