Original articleAsthma, lower airway diseasesUsefulness of impulse oscillometry for the assessment of airway hyperresponsiveness in mild-to-moderate adult asthma
Introduction
The measurement of airway hyperresponsiveness (AHR) is integral within the assessment of asthma. Historically, conventional spirometry has been used to quantify the degree of airway obstruction seen after the inhalation of bronchoprovocation agents such as methacholine or histamine.1 Impulse oscillometry (IOS) is a novel effort-independent method of assessing airway resistance by the use of small-amplitude sound waves being superimposed on normal breathing cycles.2 IOS provides an alternative technique to assess changes in airway tone and has been shown to be sensitive to measuring bronchodilatation to salbutamol and ipratropium within asthma and chronic obstructive pulmonary disease populations.[3], [4], [5] Within their unit, the authors have found IOS to be a more sensitive marker than spirometry for bronchodilation to salbutamol and bronchoconstriction to propranolol.[5], [6] Furthermore, owing to the relative simplicity of the technique, within pediatric populations, IOS has been shown to be a useful alternative to spirometry.7 The usefulness of IOS in children has been well demonstrated and has even shown evidence of AHR in the absence of significant changes in spirometry.8 This has allowed IOS parameters to be investigated as potential surrogate markers of AHR instead of spirometry in children.9
Guidelines incorporate a standardized decrease in forced expiratory volume in 1 second (FEV1) of 20% after bronchial provocation (PC20) as evidence of AHR.1 Although IOS provides an alternative means of assessing airway tone after bronchial challenge testing, currently there are no defined criteria as to what a positive bronchial challenge test result would be when using IOS instead of spirometry in adult populations. The purpose of this study was to ascertain the degree of change in IOS measurements seen in patients with asthma undergoing bronchial challenge testing. This would aid in the development of a standardized IOS reference value for potential use in clinical trials.
Section snippets
Methods
A post hoc analysis of a double-blinded, randomized, placebo-controlled trial of propranolol in patients with mild to moderate asthma was performed.10 The Tayside medical research ethics committee (Dundee, Scotland) gave approval before commencement of the trial (10/S0501/22). The study was registered with http://www. clinicaltrials.gov (NCT01074853) and all participants gave written informed consent.
Patients 18 to 65 years old with mild to moderate asthma, FEV1 greater than 80% predicted, and
Results
Within the original study,10 21 participants were randomized, 18 of whom (10 women and 8 men) completed the protocol. All 18 patients were used in this analysis. Mean age was 36 years (SEM 4 years). Baseline characteristics are listed in Table 1.
For methacholine and histamine challenges, at the PC20 threshold, the mean percentages of change in R5 were similar (as a measurement of total airway resistance) at 43.5% (95% confidence interval [CI] 29.4–57.5, P < .001) and 44.9% (95% CI 24.0–65.8, P
Discussion
To the authors' knowledge, this is the first study in adult patients with asthma to directly compare the effects on IOS measurements recorded concurrently with spirometry during methacholine and histamine bronchial challenge testing. Significant effects were observed for all IOS measurements during bronchial challenge testing, with no significant differences observed through the use of methacholine or histamine. The assessment of AHR by PC20 through the FEV1 measurement is a well-established
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Cited by (0)
Disclosures: Authors have nothing to disclose.
Funding: This study was funded by the Chief Scientist Office (Scotland) CZB/4/716+.