BACKGROUND--In the day to day care of obstructive airways diseases (asthma and chronic obstructive pulmonary disease) important decisions such as disease classification and choice of therapy are based on assessment of the bronchodilator response. However, surprisingly little is known of the long term course of the bronchodilator response in patients with obstructive airways disease. METHODS--Data from a multicentre trial were used in which 274 patients aged 18-60 years with airways obstruction were selected with PC20 < 8 mg/ml and FEV1 < 95% CI of predicted. FEV1 was measured before and 20 minutes after 1000 micrograms terbutaline and 40 minutes after an additional 80 micrograms ipratropium bromide. Data were analysed from 185 patients who were followed up for 21 months (five measurements). Four different expressions of bronchodilator response (BDR) were examined for change under long term therapy, long term variability, and prognostic value in predicting response to inhaled corticosteroids. RESULTS--There was a significant reduction in BDR of 117 ml after three months of treatment with a beta 2 agonist plus a corticosteroid (BA + CS), but not after bronchodilators only. Significant reductions with BA + CS were also found in BDR as a percentage of initial FEV1, and in BDR as a percentage of predicted FEV1. Bronchodilator tests were quite variable (SD 186 ml or 11% of initial value) and less than half of the patients could consistently be classified as "irreversible" with recommended cutoff levels. The bronchodilator response at the start of the study proved to be a poor predictor of improvement in FEV1 under BA + CS treatment (correct prediction 60%). CONCLUSIONS--Bronchodilator responses decrease substantially with inhaled corticosteroid therapy, and within subject variability is considerable both in asthma and chronic obstructive pulmonary disease. Dichotomous decisions on whether patients are "irreversible" according to any single bronchodilator measurement should therefore be made with great caution. The bronchodilator response cannot be used accurately as a predictor of response to inhaled corticosteroids in obstructive airways disease.
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