Background: Bronchial provocation is often used to confirm asthma. Dyspnea sensation, however, associates poorly with the evoked drop in FEV1. Provocation tests only use the large airways parameter FEV1, although dyspnea is associated with both large- and small airways dysfunction. Aim of this study was to explore if adenosine 5'-monophosphate (AMP) and adenosine evoke an equal dyspnea sensation and if dyspnea associates better with large or small airways dysfunction.
Methods: We targeted large airways with AMP and small airways with dry powder adenosine in 59 asthmatic (ex)-smokers with >= 5 packyears, 14 +/- 7 days apart. All subjects performed spirometry, impulse oscillometry (IOS), and Borg dyspnea score. In 36 subjects multiple breath nitrogen washout (MBNW) was additionally performed. We analyzed the association of the change (Delta) in Borg score with the change in large and small airways parameters, using univariate and multivariate linear regression analyses. MBNW was analyzed separately.
Results: Provocation with AMP and adenosine evoked similar levels of dyspnea. Delta FEV1 was not significantly associated with Delta Borg after either AMP or adenosine provocation, in both univariate and multivariate analyses. In multivariate linear regression, a decrease in FEF25-75 during adenosine provocation was independently associated with an increase in Borg. In the multivariate analyses for AMP provocation, no significant associations were found between Delta Borg and any large or small airways parameters.
Conclusion: AMP and adenosine induce equally severe dyspnea sensations. Our results suggest that dyspnea induced with dry powder adenosine is related to small airways involvement, while neither large nor small airways dysfunction was associated with AMP-induced dyspnea.C