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.