Abstract
Introduction: Positive response to mannitol has been suggested as a specific measure of asthma. Despite the high specificity, the challenge test can only identify a small proportion of asthmatic patients.
Methods: Tidal changes in respiratory mechanics were measured with forced oscillations at 8 Hz in asthmatics [15 responders (PR) and 20 non-responders (NR) based on spirometry data] and 25 healthy subjects (Raine birth cohort study; 22 year follow up) before and after challenge test. Resistance (R) and reactance (X) values were established at transitions of the breathing cycle [at zero-flow (eE and eI)] and at maximum flows (maxI and maxE).
Results: Both healthy and NR subjects had lower baseline R at FRC (eE), maxI and maxE compared to PR (p<0.001, Fig 1). There was no difference in any of the variables in healthy subjects after mannitol, whereas eE and maxI significantly increased in both NR (p=0.026) and PR (p<0.001); however, the elevation was more pronounced in PR. Values at eI were not different between the groups in any condition. Tidal changes in X mirrored that in R in all groups.
Conclusion: Our data suggest that despite the lack of spirometric differences between healthy and NR subjects the within-breath analysis reveals significant alterations in these asthmatics after challenge. Since ReI remained unchanged, the difference between ReE and ReI may be a sensitive measure of hyperresponsiveness to mannitol.
- Copyright ©ERS 2015
