Day-to-day variability indices improve utility of oscillometry in paediatric asthma

Background Oscillometry may provide the feasible and sensitive tool for objective remote monitoring of paediatric asthma. Methods Observational study of school-aged healthy, well-controlled and poorly-controlled asthma performing daily home-based oscillometry for 3–4 months, alongside objective measures of asthma control (Asthma Control Questionnaire weekly and Asthma Control Test monthly), medication use and exacerbations. Day-to-day variability calculated as coefficient of variation (CV) for resistance at 5 Hz (R5), reactance at 5 Hz (X5) and area under reactance curve (AX). Our objective was to examine feasibility, whether day-to-day variability was increased in asthma and correlations with asthma control and exacerbation burden. Clinical exacerbation patterns were examined using principal component analysis and k-means clustering of oscillometry, symptoms, breathing parameters and adherence. Results Feasibility was 74.9±16.0% in health (n=13, 93.7±16.2 days) and 80.6±12.9% in asthma (n=42, 101.6±24.9 days; 17 well-controlled and 27 poorly-controlled asthma). Increased day-to-day variability in all oscillometry indices occurred in asthma versus health (all p≤0.002), with CV R5 the best discriminator (area under receiver operating characteristics curve 0.88, p<0.001). CV R5 increased during exacerbation and correlated with all asthma control measures and exacerbation burden. Correlations remained when examining non-exacerbation oscillometry data. Two exacerbation patterns were found based on oscillometry data in the pre-exacerbation period, characterised by severity of impairment of R5, X5, AX and CV R5 (n=12, more severe). Findings were similar using post-exacerbation period oscillometry data (n=8, more severe). Symptoms did not differ across exacerbation patterns. Conclusions Home-based oscillometry monitoring was highly feasible over extended periods in school-aged asthmatics. Day-to-day oscillometry variability was increased in asthma compared with health, reflected asthma control and exacerbation burden and identified differing exacerbation patterns. Data are available upon reasonable request. All data relevant to the study are included in the article or uploaded as supplementary information. Further data may be available upon reasonable request to the corresponding author.