Perception of breathlessness during bronchoconstriction induced by antigen, exercise, and histamine challenges

Perception of breathlessness was studied in eight patients with mild, stable asthma after a histamine and exercise challenge performed before and 24 and 48 hours respectively after an antigen challenge. FEV1 and perception of breathlessness, evaluated by Borg's 10 point category scale, were measured after each administration of doubling antigen or histamine concentrations to achieve a greater than 20% fall in FEV1, and after six minutes of steady state exercise at 80% of maximal oxygen consumption (VO2max). The geometric mean provocative concentration of histamine causing a 20% fall in FEV1 (PC20) fell from 1.67 mg/ml before antigen challenge to 0.52 mg/ml 24 hours after the challenge. The median maximal % fall in FEV1 with exercise was 24.9% (range 10.5-40.5%) before and 30.6% (range 13.8-52.3%) 48 hours after antigen challenge. The median maximum % fall in FEV1 after antigen inhalation was 20.1% (range 13.3-35.2%) within the first hour; only two subjects had a late fall in FEV1 (23% and 58%). The median (range) of Borg scores obtained when FEV1 was reduced by 20% did not differ significantly for the three types of acute challenges: 1.25 (0.5-2.5) and 1.0 (0.5-3.0) after histamine tests, 1.0 (0.5-4.1) and 1.55 (0.5-2.0) after exercise, and 1.5 (0-3.0) after antigen challenge. In the two subjects who had a late response to antigen the Borg score was reduced for the same % fall in FEV1 as with the early response. It is concluded that the perception of breathlessness does not differ appreciably during the early response to histamine, antigen exposure, or exercise, but that it is reduced during the late asthmatic response. It was not influenced by previous antigen exposure, despite an increase in airway responsiveness.