Exercise Induced Asthma

EXERCISE INDUCED ASTHMA 

Exercise induced bronchospasm (EIB) is defined as airway obstruction following physical exertion. 

However, as exercise is not an independent risk factor for developing asthma, the term exercise induced asthma is potentially misleading.  Exercise only induces symptoms of asthma (i.e. bronchoconstriction, wheezing, etc.) in those who already have the disease or are predisposed to have the disease.

 

Incidence and Prevalence 
 

Prevalence estimates: ~ 10-20%; in pts with symptomatic asthma, estimates range from 40 – 90% (likely > 80%); 40% of children with allergic rhinitis; approximately 10% of the general population without a history of asthma;11% of the 1984 US Olympic team had EIA and about 40% were unaware that they had the condition.. 

 

Pathogenesis 
 

Onset of exercise induced bronchoconstriction is a result of changes in temperature  and water vapor content of air in the respiratory tree during exercise. Increasing ventilation leads to a decrease in temperature and humidification of air (or, a decrease in conditioning of air) as it enters the bronchial tree. Decreased temperature and increased evaporation of water leads to increased osmolar load which places greater demand on mucosal and epithelial lining cells of the bronchial tree. In addition, increased mast cell activity in this setting leads to increased narrowing of airways (i.e. obstruction).

Related theories propose that increased heating and transudation of fluid across the respiratory mucosa (secondary to hyperemia) itself leads to decreased airway diameter and that there is actually minimal bronchoconstriction that occurs.

Ultimately, the underlying physiology is likely due to a combination of the above factors given the beneficial effects of bronchodilators such as albuterol, leukotriene receptor antagonists such as montelukast and inflammatory modulators such as cromolyn.

 

Clinical Features 
 

Wheezing, coughing, shortness of breath and chest tightness  
 

Bronchospasm usually arises 10-15 minutes after beginning exercise and peaks about 10 minutes after the exercise is completed. Symptoms may last for 60 minutes.

Some patients may not manifest symptoms until the exercise is completed.  
  

 

Diagnosis

Often can be diagnosed based on the following alone (i.e. no pulmonary function test needed):

1. History of asthma

2. Development of typical symptoms following exercise 

3. Symptoms resolve with, or are prevented by, pretreatment with short acting beta agonists

    
 

Definitive diagnosis: exercise challenge test

6-8 minutes on ergometer or treadmill à decrease in FEV1 > 15%

Other alternatives: cold air hyperventilation test, methacholine challenge; neither simulates exercise as well as the exercise challenge test

 

Differential diagnosis:

1. central airway obstruction

2. vocal cord dysfunction

3. laryngotracheomalacia

4. parenchymal pulmonary disease

5. GERD

6. coronary artery disease

7. CHF

 

Management 
 

General:

1. Ensure that exercise is not avoided

2. Breathe through loosely fitting scarf or mask when exercising in cold, dry weather

3. Ensure patients know how to use metered dose inhaler

4. Warm up prior to exercise; appropriate timing places refractory period during time of exercise

5. Encourage nasal breathing to improve air conditioning prior to entering bronchial tree

6. Avoid exercise when air pollution index is poor and when environmentl allergens are most prevalent

7. Some forms of exercise are better than others: running is particularly problematic; swimming is good

 

Monitoring:

1. Routine assessment of symptom control and exercise tolerance

2. Regular measurements of peak expiratory flows, compare to baseline

3. If symptoms worsen or if precise measurements required, perform exercise

    challenge test and compare to baseline if available

 

Pharmacologic Therapy:

1. Short term beta agonist such as albuterol via Metered Dose Inhaler (MDI). Because of short period of airway reactivity, prophylaxis is successful. Use 15-30 minutes prior to the activity.  Approximately 90% effectiveness.  
 

2. Long acting beta agonist via MDI or Diskhaler such as salmeterol. Up to 9 hours of coverage and convenient for children that are in school and not allowed to carry inhalers. Allows for spontaneous activity by the child.  
 

3. Cromolyn by MDI 15- 30 minutes prior to activity. Approximately 70 % effectiveness.  
 

4. Single dose inhaled steroids are not protective although long-term use will  decrease the incidence of EIA.

 

References

  1. Milgrom H. and Taussig L.M. Keeping Children with Exercise-Induced Asthma Active. Pediatrics 1999
  2. Randolph C. Exercise Induced Bronchospasm in Children. Clinic Rev Allerg Immunol 2008
  3. Storms W.W. Exercise Induced Brochospasm. Current Sports Medicine Reports 2009
  4. Wood P.R. and Hill V.L Practical Management of Asthma. Peds in Review 2009

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