How do patients with either asthma or COPD perceive acute bronchodilation?

Abstract

The purpose of this study was to assess the perception of bronchodilation, as a change in shortness of breath on a bipolar visual analogue scale (VAS), in 16 asthmatics and 20 subjects with COPD. Bronchodilation was gradually induced by five consecutive terbutaline inhalations (cumulated dose 800 μg). The subjects were categorized into high and low perceivers, on the basis of a cut-off of 25% VAS line length (after the fifth inhalation). The quality of perception was studied on a within-subject basis by linear regression analysis of VAS ratings against changes in lung function, and was characterized in terms of strength of correlation (squared correlation coefficient, r2(, slope, aud VAS axis intercept. Fourteen out of 16 asthmatics, and 13 out of 20 COPD subjects, were high perceivers. In the COPD group, the high perceivers had a larger objective response - particularly in inspiratory vital capacity - than the low perceivers. The strongest correlation between subjective and objective response was obtained in asthmatics when the improvement in shortness of breath was evaluated against the decrease in specific inspiratory resistance (median r2 = 0.831). In COPD low perceivers, subjective and objective response were unrelated, while COPD high perceivers differed from the asthmatics by larger intercepts. The perceptual characteristics were unrelated to the degree of baseline obstruction, whilst a modest relationship (r = 0.51) was found between the increase in forced expiratory volume in one second (FEV1) and r2 of the VAS/ΔFEV1 analysis. In conclusion, having characterized the perception of terbutaline-induced bronchodilation, we found that some COPD subjects differed from the asthmatics in that they perceived at a low level, without relationship between VAS ratings and objective response. Other COPD subjects compared well with the asthmatics in terms of strength and slope of the VAS/change in lung function relationship, but differed by a larger intercept, suggesting the presence of a placebo effect.