In individuals with asthma, the use of minimal clinically important differences (MCIDs) derived from impulse oscillometry (IOS) can be used to measure and evaluate patients’ small airway function, according to study findings published in the European Respiratory Journal.
Although IOS can non-invasively and passively measure small airway function in patients with asthma, well-established MCID values based on IOS-derived measures are not available. Investigators in Germany therefore sought to establish MCIDs based on often-used IOS measures in patients with asthma (ie, frequency dependence of resistance [FDR] and area of reactance [AX]) and to confirm these MCID values using patient-reported outcome measures (PROMs) for asthma control and quality of life.
The study involved 235 adult participants (aged 19 to 79) with mild to severe asthma who had participated in All Age Asthma, a multicenter, longitudinal, cohort study (ALLIANCE; ClinicalTrials.gov Identifier: NCT02419274). As part of the ALLIANCE study of adults, all participants underwent pulmonary function testing that included IOS at baseline and at a 1-year follow-up. All of the participants exhibited poor symptom control and a high frequency of exacerbations at baseline, which improved at the 1-year follow-up.
Participants completed IOS testing based on current recommendations of the European Respiratory Society (ERS). The decline in airway resistance from 5 to 20 Hz was expressed as the FDR, which was considered an index for the resistance seen in small airways. AX was measured as well, as an indicator of airway compliance and possible peripheral airway obstruction. After IOS, the participants underwent spirometry, which included measuring forced expiratory volume in 1 second (FEV1).
[T]his study provides MCID for IOS-derived measures of small airway function in asthma. The MCID values were determined based on a statistical approach and validated according to patients reported outcomes measures for symptom control and quality of life.
The researchers used participants’ IOS data to statistically determine IOS-based MCID cut-off values for FDR and AX (a decline of ≥0.06 kPa/L/s for FDR; a decline of ≥0.65 kPa/L for AX). The researchers then sought to validate these MCIDs by determining whether patients who had changes beyond these MCID cutoffs showed greater improvements in PROMs than those who had not.
Patient-reported outcome measures were evaluated using the Asthma Control Test (ACT), the Asthma Control Questionnaire 7 (ACQ-7), and the Asthma Quality of Life Questionnaire (AQLQ). The predetermined MCID values for these PROMs were 3.0 points for the ACT, 0.5 points for the ACQ-7, and 0.5 points for the AQLQ.
The investigators also used multivariable analyses to determine how their IOS-based MCIDs compared to the standard MCID of FEV1 in predicting improvements in PROMs.
Using the IOS-derived MCID cut-off values, researchers found that participants with improvements beyond the MCIDs for both FDR and AX experienced greater improvements in their PROMs than did participants who experienced either unchanged or worsened FDR or AX. Among individuals with improved FDR and AX, the mean improvements reported in PROMs were beyond the established MCID values for ACQ and AQLQ scores, and they approximated the MCID value for ACT score. Further, per multivariable analyses, the MCID for FDR was a stronger predictor of all PROMs compared with the MCID for FEV1.
Study limitations include the lack of standardization surrounding the use of IOS testing and measures and the fact that the study involved only 1-year changes in MCIDs.
“In conclusion, this study provides MCID for IOS-derived measures of small airway function in asthma. The MCID values were determined based on a statistical approach and validated according to patients reported outcomes measures for symptom control and quality of life,” the study authors noted. “It is noteworthy that both IOS measures [ie, FDR and AX] were independent predictors above and beyond the conventional measure of FEV1,” they added, suggesting that IOS measures be used as “potential endpoints in future clinical trials and routine care.”
Disclosure: Some of the study authors have declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.