A comparison of breathlessness during spontaneous asthma and histamine-induced bronchoconstriction.

The aim of the study was to investigate the possibility that the scoring of breathlessness during histamine bronchial provocation testing might be used to identify asthmatic subjects who sense dyspnea poorly during spontaneous bronchoconstriction. The perception of dyspnea caused by asthma and histamine-induced bronchoconstriction was studied in 17 subjects (10 female and 7 male). All of the subjects had a positive histamine challenge test; the concentration of histamine required to cause a 20% fall in FEV1 (PC20) averaged 3.0 mg/ml. The histamine challenge test was performed with scoring of dyspnea on a modified Borg scale. The subjects subsequently recorded peak expiratory flows (PEF) and dyspnea scores (Borg scale) at home 4 times daily for a 7-d period. We found that the intensity of dyspnea sensed during histamine-induced bronchoconstriction was very variable among subjects. The Borg score for a 20% fall in FEV1 ranged from 0 to 9. However, there was a correlation between the minimum FEV1 and the corresponding Borg score (r = -0.63; p < 0.01). For most subjects, there was no correlation between the magnitude of breathlessness during spontaneously occurring bronchoconstriction and the accompanying decline in PEF. Among subjects there was no relationship between the ability to sense breathlessness during induced and spontaneous bronchoconstriction. Therefore, the sensation of breathlessness during histamine-induced bronchoconstriction cannot be used to identify the asthmatics who perceive dyspnea poorly.