Exercise-induced hyperventilation: a pseudoasthma syndrome

Exercise-induced asthma is common and generally responds well to an inhaled beta2 agonist.

We examined the physiologic changes in airflow and gas exchange that occurred during standardized treadmill exercise in patients previously diagnosed with exercise-induced asthma whose histories appeared atypical or where conventional treatment, including an inhaled beta2 agonist, was ineffective.

During a 1-year period 32 patients, aged 8 to 18, met these criteria. All had been previously diagnosed as having exercise-induced asthma. Exercise consisted of treadmill running at a time when the patients had received no inhaled beta2 agonist, cromolyn, or nedocromil for at least 4 hours. Spirometry was done before and at 2, 5, 10, and 15 minutes after exercise; oxygen saturation was monitored by pulse oximetry; and end-tidal CO2 was monitored with nasal cannula.

Despite their previous diagnoses of exercise-induced asthma, 11 patients who described chest tightness during exercise had decreases in FEV1 less than 15% with all but one of those less than 10% (mean decrease 5.6%) but demonstrated decreases in end-tidal CO2 greater than in all of the other 21 patients (mean 23.2 versus 9.8%, P < .01). Only 4 patients had unequivocal evidence for bronchospasm with cough and wheezing accompanying chest tightness in association with decreases in FEV1 from 18 to 22%. Seventeen patients had neither their symptoms reproduced nor physiologic abnormalities.

These data show that chest discomfort perceived as dyspnea during vigorous exercise may be associated with hypocapnia from hyperventilation without bronchospasm in children and adolescents previously misdiagnosed and treated as having exercise-induced asthma.