It's a great-looking morning, clear and dry. You're due at the office in 90 minutes, but there's time for a quick run. For the first few minutes, you feel great; your limbs begin to loosen and you're able to quicken the pace. But just as you're about to hit your training stride, this run turns into a frightening experience. Your breathing becomes constricted, and you can't seem to take in enough air. These gasps are interrupted by coughing spasms, but you can't clear your lungs. That sense of well-being you had just moments ago is suddenly replaced by anxiety.

What is asthma?
Although the above scenario may sound dramatic, for millions of asthma sufferers it is frighteningly real. Asthma is an inflammatory (swelling) disease that blocks the airway. In asthma, airways are hyper-reactive, or "twitchy," and obstructive episodes can be triggered by infections (colds, bronchial or sinus infections, etc.), allergens (substances that provoke allergies), irritants (smog and tobacco smoke), and even emotional factors. Exercise, however, is one of the most common causes of asthma.

Exercise-induced asthma (EIA) is quite common in people with asthma, affecting about 90% of them. It is also common in people with a history of allergies, such as hay fever or eczema. However, EIA can occur in people with no known history of allergy or asthma.

What are the symptoms?
The onset of wheezing is the classical sign of an attack, but it may not be present or the only symptom. Other things to look for are coughing, chest pain, and feeling out of breath, which some people mistake as being out of shape. An obstructive episode can last up to 2 hours. In about one-third of unfortunate victims, a "late phase" attack takes place 3 to 6 hours after exercise. Typically, exercises that provoke asthma are fairly intense, have to be sustained for 6 to 12 minutes, and often have to take place in a certain setting or under certain "modulating" conditions, such as in smog or on a grassy field during hay fever season.

How does exercise cause asthma?
During intensive exercise, the amount of air taken in compared with that at rest may increase by 30 times. This large volume of air must be heated and humidified as it travels to the lungs to deliver oxygen. It is believed that the stress of this demand on the airways triggers the asthmatic episode. This stress provokes certain inflammatory cells, which then release various substances leading to airway constriction (or bronchospasm), swelling, and mucous plugging of the airways (see figure). Not all exercises provoke an attack and the same exercise may not always produce the same symptoms. Exercising in cold and dry air is likely to cause an attack, whereas a warm humid environment (such as an indoor swimming pool) may be somewhat protective.

There's good news . . .
Many medications are available for the treatment of asthma. Inhaled medications, which expand the airways, are the mainstay of prevention and treatment.

Strategies can also be used to allow people with EIA to exercise freely. One simple measure is to breathe moist, humid air. For example, this can be accomplished through nasal breathing or by using a face mask in cold weather exercise. Additionally, choosing sports with intermittent short exercise bursts, such as baseball and football, is a good strategy. These activities are not likely to provoke asthma as compared with sustained high-intensity workouts. Avoiding allergens, pollutants, and choosing the proper environment can be beneficial for many.

By using preventative strategies and medications as needed, most people with EIA can participate in exercise safely and enjoyably.

William L. Cappiello, M.D.
Santa Clara, California