Relation of the perception of airway obstruction to the severity of asthma

Background-Patients with a poor perception of their symptoms of asthma seem to have an increased risk of an asthma attack. The influence of factors su ch as airway calibre, bronchial hyperresponsiveness, age and sex on the "pe rceptiveness" of a patient are poorly understood. It is of clinical importa nce to identify patients who are likely to have a poor perception of their symptoms. We have studied the perception of bronchoconstriction by asthmati c patients during a histamine provocation test and analysed the influence o f bronchial obstruction, hyperresponsiveness, sex, and age. We were particu larly interested to establish whether there was any difference in perceptio n between subjects with a greater or lesser severity of asthma (expressed a s bronchial obstruction, hyperresponsiveness). Methods-One hundred and thirty four patients with allergic asthma underwent a histamine provocation test. The FEV1 was measured after each inhalation of histamine. Subjects were asked to rate subjective quantification of the sensation of breathlessness on a visual analogue scale (VAS). The relations hip between changes in VAS values and the reduction in FEV1 as a percentage of the baseline value was analysed by determining the linear regression sl ope (a) between the two parameters and indicates the perception of airway o bstruction. Multiple regression analysis was performed to investigate the e ffect of baseline FEV1, bronchial hyperresponsiveness, sex and age on the " perceptiveness" for bronchoconstriction. Results-The median value of the slope a (indicating the perception of airwa y obstruction) was 0.91 (25-75th percentile: 0.48-1.45), Age and sex had no influence on the perception of bronchoconstriction. Both initial bronchial tone (baseline FEV1) and bronchial hyperresponsiveness (PC20)showed a sign ificant correlation with the perception of bronchoconstriction. The regress ion coefficients for FEV1 and 2log PC20 in the multiple regression model we re 0.20 and 0.10. Patients who had a low baseline FEV1 and/or a high bronch ial responsiveness to histamine were more likely to show a low perceptivene ss for bronchoconstriction during the challenge test. Conclusions-Low baseline FEV1 and high bronchial responsiveness are associa ted with a low degree of "perceptiveness" for bronchoconstriction. This sug gests that patients with a more severe degree of asthma either show adaptat ion of "perceptiveness" for airway obstruction or that low perceptiveness l eads to more severe asthma.