Exercise-induced shortness of breath not always caused by asthma

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."

For the other patients, the testing revealed several different physical causes of the EID. Fifteen patients had mild physical conditions that caused inefficient, abnormal breathing patterns - they breathed too fast and too shallow to maximize their lung capacity. Weinberger noted that these physical abnormalities, which included minor degrees of scoliosis, were generally not otherwise problematic for the patients and only caused breathing problems during vigorous exercise. Airway problems that hinder breathing during exercise were diagnosed for another 15 patients - 13 had vocal cord dysfunction and two had a condition known as laryngomalacia. One patient had hyperventilation. The most unusual diagnosis was a rare heart abnormality known as supra-ventricular tachycardia. UI pediatric cardiologists identified this exercise-induced cardiac arrhythmia from the patient's electrocardiogram recorded during exercise testing and Ian Law, M.D., UI assistant professor (clinical) of pediatrics and a pediatric cardiac electrophysiologist at UI Children's Hospital of Iowa, was subsequently able to correct the abnormality.

The exercise test did not reproduce shortness of breath in 25 patients, so the researchers were not able to determine the cause of their EID. However, none of these patients showed the classic signs of asthma during the treadmill test.

"The biggest benefits to these patients were getting them off medication that was not doing them any good and eliminating the anxiety that is often associated with shortness of breath," Weinberger said.

Weinberger noted that the treadmill test with continuous respiratory and cardiac monitoring used in the UI study takes longer than a simple exercise test, and requires specialized equipment and experience, but it does provides definitive diagnoses.

"We get answers, which is what the patients and parents want," he said.

In addition to Weinberger, who was senior author on the study, the research team included Mutasim Abu-Hasan, M.D., UI assistant professor (clinical) of pediatrics, and Beatrice Tannous, M.D., who was a pediatric resident at UI Children's Hospital of Iowa at the time of the study and who now works as a pediatrician in the Washington, D.C. area.