Unaltered perception of dyspnoea during treatment with long-acting beta(2)-agonists

There is the possibility that during treatment with inhaled long-acting bet a (2)-agonists that a loss of perception of dyspnoea might occur and that t he forced expiratory volume in one second (FEV1) might fall precipitously d uring bronchial provocation. This study investigated these possibilities du ring methacholine provocation, continued until there was greater than or eq ual to 30% fall in FEV1, mimicking a moderate asthma attack. Nineteen asthmatic patients were asked to score their dyspnoea as a Borg sc ore during provocation with methacholine. One hour prior to this provocatio n, the patients used the last morning dose of 14 days treatment with either formoterol (twice daily 24 mug by Turbuhaler (R)), salmeterol (twice daily 100 mug by Diskhaler (TM)) and placebo in a double-blind, randomized, doub le-dummy, cross-over design. The perception of dyspnoea, expressed as the Borg score divided by the chan ge in FEV1 at greater than or equal to 30% fall in FEV1, was similar on the three test days at 0.067, 0.076 and 0.074%(-1) after formoterol, salmetero l and placebo treatment, respectively (p=0.16). The slope of the methacholi ne dose response curve did not differ (P=0.52). In conclusion, no suggestion was found for an abnormal perception of dyspno ea or an exaggerated fall in forced expiratory volume in one second during provocation with methacholine under long-acting beta (2)-agonist treatment.