Perception of bronchoconstriction and bronchial hyper-responsiveness in asthma

The inter-relationship between the perception of bronchoconstriction, bronc hial hyperresponsiveness and temporal adaptation in asthma is still a matte r of debate. In a total of 52 stable asthmatic patients, 32 without airway obstruction [forced expiratory volume in 1 s (FEV1)/vital capacity (VC) 84. 1% (S.D. 7.9%)], and 20 with airway obstruction [FEV1/VC 60% (4%)], we asse ssed the perception of bronchoconstriction during methacholine inhalation b y using: (i) the slope and intercept of the Borg and VAS (Visual Analog Sca le) scores against the decrease in FEV1, expressed as a percentage of the p redicted value; and (ii) the Borg and VAS scores at a 20% decrease in FEV1 from the lowest post-saline level (PB20) Bronchial hyper-responsiveness was assessed as the provocative concentration of methacholine causing a 20% fa ll in FEV1 (PC20FEV1). The reduction in FEV1 was significantly related to t he Borg and VAS scores, with values for the group mean slope and intercept of this relationship of 0.13 (S.D. 0.08) and -1.1 (3.02) for Borg, and 1.5 (1.19) and -12.01 (35) for VAS. PB20 was 3 (1.75) with Borg scores and 34.6 (20.5) with VAS scores. Compared with the subgroup without airway obstruct ion, the obstructed subgroup exhibited similar slopes. but lower Borg and V AS intercepts. For similar decreases in FEV1 (5-20% decreases from the lowe st post-saline values), the Borg and VAS scores were lower in the non-obstr ucted than in the obstructed subgroup. PC20FEV1 was significantly related t o both Borg PB20 and VAS PB20 when considering all patients. When assessing the subgroups, PC20FEV1 was related to Borg PB20 and VAS PB20 in the non-o bstructed subjects, but not in the obstructed subjects. In neither subgroup was the log of the cumulative dose related to the Borg and VAS scores at t he end of the test. We conclude that, unlike in previous studies, the abili ty to perceive acute bronchoconstriction may be reduced as background airfl ow obstruction increases in asthma. Bronchial hyper-responsiveness did not play a major role in perceived breathlessness in patients without airway ob struction, and even less of a role in patients with obstruction. The cumula tive dose of agonist did not appear to influence the perception of bronchoc onstriction.