Perception of bronchoconstriction and bronchial hyper-responsiveness in asthma

Abstract

The inter-relationship between the perception of bronchoconstriction, bronchial hyper-responsiveness and temporal adaptation in asthma is still a matter 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 assessed the perception of bronchoconstriction during methacholine inhalation by using: (i) the slope and intercept of the Borg and VAS (Visual Analog Scale) scores against the decrease in FEV1, expressed as a percentage of the predicted 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% fall in FEV1 (PC20FEV1). The reduction in FEV1 was significantly related to the 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 obstruction, the obstructed subgroup exhibited similar slopes, but lower Borg and VAS intercepts. For similar decreases in FEV1 (5–20% decreases from the lowest post-saline values), the Borg and VAS scores were lower in the non-obstructed than in the obstructed subgroup. PC20FEV1 was significantly related to 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-obstructed 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 the end of the test. We conclude that, unlike in previous studies, the ability to perceive acute bronchoconstriction may be reduced as background airflow obstruction increases in asthma. Bronchial hyper-responsiveness did not play a major role in perceived breathlessness in patients without airway obstruction, and even less of a role in patients with obstruction. The cumulative dose of agonist did not appear to influence the perception of bronchoconstriction.