Asthma, thermally induced asthma: Asthma that is "triggered" by vigorous physical activity. Exercise-induced asthma tends particularly to affect children and young adults (because of their high level of physical activity) but can occur at any age.

Exercise-induced asthma is initiated by the process of respiratory heat exchange (the fall in airway temperature during rapid breathing followed by rapid reheating with lowered ventilation). The more heat transferred, the cooler the airways become, the more rapidly they rewarm, and the more the bronchi are narrowed.

Exercise-induced asthma is common. People with chronic asthma can develop symptoms whenever they are exposed to a "trigger" of the asthma, such as a virus, pollen, dust, or cigarette smoke. About 80 to 90 percent of people who have chronic asthma have exercise-induced asthma. And about 35 to 40 percent of people with seasonal allergies also have exercise-induced asthma and symptoms worsen during the spring and fall.

Acute attacks of exercise-induced asthma can often be avoided by warming up before strenuous activity. Of note, cold dry air is believed to trigger exercise-induced asthma. Exercising outdoors in the winter or mouth breathing can set off the asthma attack. Some doctors recommend indoor swimming as an ideal form of exercise because the warm, humid air keeps the airways from drying and cooling.

Exercise-induced asthma is monitored using a peak-flow meter. This hand-held device measures air flow (how fast air is blown out of the lungs). Patients can use peak-flow meters to measure their own air flow regularly. This allows patients to obtain a much earlier indication of an oncoming attack.

If need be, exercise-induced asthma can also be managed by avoiding the offending allergic triggers and using medications up to an hour before exercising. Medications used (bronchodilators) help to relax the muscle spasm of the airways, permitting improved air flow. Other medications can be used to prevent the lining of the airways from swelling in response to cold air or allergic triggers. Inhaled cortisone-related medications are sometimes also used to reduce inflammation and swelling in the airways.

While in the past, athletes were forced out of competition because of exercise-induced asthma, today they can frequently get back in the stride with their peers.