Criteria for the determination of clinically important and statistically significant positive responses to inhaled bronchodilator have been established. However, the significance of and mechanisms responsible for acute decrements, or paradoxical responses, in the volume exhaled in the first second of forced expiration, forced vital capacity, and peak expiratory flowrate have received little attention. METHOD: In order to assess the finding of a paradoxical response to the acute inhalation of a bronchodilator, we reviewed the pulmonary function tests (ie, spirometry and flow-volume loops) of all patients cared for in the Pulmonary Unit of Massachusetts General Hospital from January 1982 to February 1987 who showed an apparent paradoxical response to bronchodilator during testing. RESULTS: The apparent paradoxical response of 48 of the 51 patients (94%) whose records were studied was in fact due to poor test performance with poor reproducibility. Only 3 patients (1 with asthmatic bronchitis and 2 with asthma) showed true reproducible paradoxical responses. These responses may have been due to increases in airway resistance, decreases in muscle tone of large airways, or decreases in elastic recoil. CONCLUSION: An apparent paradoxical response to the acute inhalation of a bronchodilator is an uncommon finding (120 7% of 1681 patients, with 95% confidence limits 6-8%) and is usually due to poor reproducibility of test results that is most likely due to poor performance and thus is not a true paradoxical response. However, a small number of patients may have a reproducible decrement, a true paradoxical response, that is a manifestation of an abnormal change in lung mechanics.
Shepherd et al. (Tue,) studied this question.