Potential masking effect on dyspnoea perception by short- and long-acting beta2-agonists in asthma.

Asthma patients evaluate the effect of medication treatment through the degree of their asthma symptoms, which might be affected by their ability to perceive these symptoms. It has been suggested that beta2-agonists may mask the effects of an increase in airway inflammation. This study compared the perception of histamine-induced bronchoconstriction during monotherapy with short- or long-acting beta2-agonists. Asthmatic patients (68 male and 60 female, mean age 35+/-11 yrs, forced expiratory volume in one second (FEV1) 86+/-15% of the reference value, provocative concentration causing a 20% fall in FEV1 (PC20) geometric mean 0.97 mg x mL(-1) (95% confidence interval (CI): 0.73-1.30)) were selected and randomly allocated to use either a short-acting (salbutamol, n=41) or long-acting beta2-agonist (formoterol, n=46) or placebo (n=41) for 12 weeks. Perception of dyspnoea provoked by histamine-induced bronchoconstriction was measured at the start and every 4 weeks thereafter. Subjects quantified their sensation of breathlessness during the challenge tests on a modified Borg scale at the start of the study and every 4 weeks thereafter. The sensitivity to changes in FEV1 was analysed by the linear regression slope (alpha) Borg versus % fall in FEV1. The absolute perceptual magnitude (PS20) was determined by the perception score at the 20% fall in FEV1. Although the geometric mean PC20 decreased significantly within the group using short-acting beta2-agonists (in the group with initial PC20 > or = 2 mg x mL(-1) there was a drop from 5.26-1.94 mg x mL(-1); p=0.013), repeated measurement analysis showed no difference in the course of time of perception (both slope alpha and PS20) between the three medication groups. This study showed that chronic use of short- or long-acting beta2-agonists in asthmatics for a period of 12 weeks, did not significantly change the perception of histamine-induced bronchoconstriction compared with placebo. Further investigation is required to establish whether this suggests that these drugs do not mask a deterioration of asthma.