Assessing bronchodilator responsiveness.

This report concerns the difficulty in distinguishing variation due to drug effects from the spontaneous daily variation in baseline levels of pulmonary function in the evaluation of bronchodilator responsiveness in asthmatic children. Both prospective and retrospective studies were employed to assess the importance of the influence of the baseline level of function from which change is measured on the degree of responsiveness observed. It was found that for baseline levels up to approximately 90% of the predicted normal value, all patients had the capacity to respond significantly to a bronchodilator. However, there was no limit of baseline function below which a significant response did not occur.