Asthma is the most common cause of exercise-induced shortness of breath in children and adolescents. While a diagnosis of asthma is often correct, University of Iowa pediatric pulmonary physicians caution that other unrelated conditions also can cause shortness of breath during exercise.
In cases where the asthma diagnosis is questionable, the UI experts recommend further testing to identify the true cause of exercise-induced shortness of breath.
"Asthma usually responds well to treatment, and people with asthma who are well treated can have normal exercise tolerance," said Miles Weinberger, M.D., professor of pediatrics in the UI Roy J. and Lucille A. Carver College of Medicine and director of the Pediatric Allergy and Pulmonary Division at Children's Hospital of Iowa. "However, if the asthma medication doesn't work and the patient has normal lung function when measured before exercise, it is probably not asthma.
"If a patient is not responding to the simplest measure, such as use of a bronchodilator inhaler, and there are no other asthmatic symptoms, the exercise-induced shortness of breath, also known as dyspnea, requires further detailed evaluation," he added.
Weinberger and his colleagues examined 142 patients who were troubled by exercise-induced dyspnea (EID) but did not show other signs of asthma or were not responding to asthma medications. The team monitored respiration and heart function continuously while patients exercised on a treadmill vigorously enough to reproduce their usual symptoms. Sophisticated equipment allowed breath-by-breath analysis of oxygen use, carbon dioxide production and other important lung capabilities. A significant drop in a major measurement of lung function, called the "one-second forced expiratory volume," confirmed a diagnosis of asthma.
Under these conditions, exercise testing reproduced the symptoms troubling the patient in 117 cases, Although EID had previously been attributed to asthma in 98 of these patients, only 11 patients were shown to have asthma as the cause of their exercise-induced symptoms. For the majority of the other patients, not only did the testing definitively demonstrate the absence of asthma, but the sophisticated respiratory and heart measurements also revealed the true cause of the shortness of breath during exercise. The findings are published in the March issue of Annals of Allergy, Asthma and Immunology. In the study, the most common cause of exercise-induced dyspnea was simply that the patients had reached their natural limits for exercising, and their shortness of breath was an entirely normal response to vigorous exercise. Despite the varying levels of cardiovascular conditioning for the 74 patients in this group, each patient had interpreted their normal physiologic shortness of breath as being abnormal.
"Being kids, they thought they should be able to do anything they want without limits," Weinberger said. "We were able to reassure the patients and parents that there was no abnormality and advise the type of cardiovascular conditioning or athletic training that would enable them to be physically active without the natural anxiety that occurs with dyspnea."