Fitness, For Parents, Science

Exercise-Induced Asthma (And How to Deal With It)

For me, going back to school has had both positive and negative effects on my life.  Among the positive ones has been that it has forced me to do a lot of research and to write articles/papers about various different topics related to sports science.  I recently was asked to write a report on exercise-induced asthma, a condition that is common in athletes, including youth soccer players and many of the individuals that I work with in my business.  Below is the report (plus several relevant references).  Hope you like it and find it useful!

Exercise-induced asthma is a condition in which vigorous physical activity triggers acute airway narrowing in people with heightened airway reactivity (McFadden & Gilbert, 1994).  Narrowing of the airway is commonly called “bronchospasm” as it implies spasm or constriction of the smooth muscle that lines the airway.  This constriction can make breathing difficult or in severe cases, almost impossible.  Exercise-induced asthma can also be caused by an accumulation of mucous within the airway.  In unusual circumstances, exposure to antigens, oxidant air pollutants, or respiratory viruses may increase vulnerability of the airway to the extent that episodes of airway obstruction can follow even minimal exertion (McFadden & Gilbert, 1994).

Individuals suffering from exercised-induced asthma generally report being short of breath, commonly termed “dyspnea” (Powers & Howley, 2014).  Dyspnea is the most obvious and common symptom of exercise-induced asthma.  The most common exercise situation in which dyspnea due to airway constriction occurs is when, following strenuous activity (accompanied with an increase in minute ventilation), exercise continues at a lower intensity and minute ventilation falls, which prompts a re-warming of the airway (National Asthma Education Program, 1991).

The prevalence of exercise-induced symptoms in patients with asthma has been reported to range from 40 to 90 percent (McFadden & Gilbert, 1994, Jones et. al., 1962).  Interestingly, although exercise may be a common (or commonly-occurring) trigger of airway restriction, in many cases exercise may not be the only trigger (McFadden & Gilbert, 1994).  The wide range of incidence of exercise-induced symptoms owes itself to several different factors.  Among them are the intensity of the exercise that elicits a response, which may be much higher in trained versus untrained individuals.  Second, there is a lack of standardization of the exercise tests used to detect a response.  Several different types of exercise tests are used by physicians and respirologists, with different exercise modes (bicycle, running, calisthenics) and intensities being used.  Finally, it can also be very difficult in a laboratory to standardize the environmental variables that control the magnitude of the airway obstruction (McFadden & Gilbert, 1994).

Ventilation and the heat content of inspired air can have a significant effect on the nature of the response and airway restriction in individuals with exercise-induced asthma.  As a general rule, the more strenuous the work, the greater the ventilation required to meet metabolic demands and the more intense the asthma attack.  Some studies have demonstrated that running (high intensity) limits airflow more than jogging (moderate intensity), which in turn limits airflow more than walking (low intensity) (Strauss et. al., 1978, Deal et. al., 1979).  Temperature and humidity of the inspired air is also an exacerbating factor or airway restriction.  Airway obstruction is maximized when the inspired air (and thus the temperature) is cold or dry and minimized when the air is warm and humid (Strauss et. al., 1977).

Some preventative steps can be undertaken to reduce the incidence as well as the severity of exercise-induced asthma “attacks.”  First, a long a properly conducted warm-up will help to gradually warm and raise the temperature of inspired air.  Studies have demonstrated that, when bouts of exercise are performed repeatedly within a period of 40 minutes or less, the bronchial narrowing progressively decreases. A person can thus limit the obstructive consequences of vigorous activity by first undertaking a short warm-up period (Weiler-Ravell & Godfrey, 1981).  Unfortunately, this limitation in the obstruction of the airway following progressive warm-up is only effective against the exercise stimulus (increase in ventilation / cold air) and is not effective against other irritants in the air that may also cause airway constriction (Weiler-Ravell & Godfey, 1981).

A second preventative step to attenuate and eliminate the effects of exercise-induced asthma is the use of medication.  Aerosols of β 2 -adrenergic-agonist drugs, cromolyn, and nedocromil used 10 to 15 minutes before exertion, as needed, are the most common therapies (Tullett et. al., 1985, Roberts et. al., 1985).     Both of these medications have anti-inflammatory effects.  They act by blockading chloride channels and the modulation of mast cell mediator release and eosinophil recruitment, effects which limit the inflammation and irritation that causes the airways to constrict (www.meded.ucsd.edu).    Typically, 1-2 inhalations of β 2 -adrenergic-agonists can attenuate the symptoms of exercise-induced asthma for up to 12 hours, which is more than enough time to allow individuals to complete their desired exercise session (www.meded.ucsd.edu).  Of course, individuals suffering from exercise-induced asthma can never be “cured” in the sense that the condition will always be present.  The symptoms of the disease, however, can be controlled through a combination of proper warm-up and administration of anti-inflammatory medication.

References:

Deal, E.C., McFadden, E.R., Ingram, R.H., Strauss, R.H., Jaeger, J.J. (1979).  Role of respiratory heat exchange in production of exercise-induced asthma. Journal of Applied Physiology, 46:467-475.

Jones, R.S., Buston, M.H., Wharton, M.J. (1962).  The effect of exercise on ventilatory function in the child with asthma. British Journal of Disorders of the Chest, 56:78-86.

McFadden, E.R., Gilbert, I.A.  (1994). Exercise induced asthma.  The New England Journal of Medicine, 330.19: 1362-1367.

Roberts, J.A., Thomson, N.C. (1985).  Attenuation of exercise-induced asthma by pretreatment with nedocromil sodium and minocromil. Clinical Allergy, 15: 377-381.

Strauss, R.H., McFadden, E.R., Ingram, R.H., Deal, E.C., Jaeger, J.J. (1978).  Influence of heat and humidity on the airway obstruction induced by exercise in asthma. Journal of Clinical Investigation, 61:433-440.

Strauss, R.H., McFadden, E.R., Ingram, R.H., Jaeger, J.J. Enhancement of exercise-induced asthma by cold air. New England Journal of Medicine, 297:743-747.

Tullett, W.M., Tan, K.M., Wall, R.T., Patel, K.R. (1985). Dose-response effect of sodium cromoglycate pressurized aerosol in exercise induced asthma. Thorax, 40: 41-44.

Unknown (2015).  Pharmacologic management of asthma.  Retrieved from: https://meded.ucsd.edu/isp/1998/asthma/html/medguide.html.

Weiler-Ravell, D., Godfrey, S. (1981). Do exercise-and antigen-induced asthma utilize the same pathways? Antigen provocation in patients rendered refractory to exercise-induced asthma. Journal of Allergy and Clinical Immunology, 67:391-397.

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