Longitudinal tracking of intra-breath respiratory impedance in preschool children

Abstract

Background Longitudinal measurements of intra-breath respiratory impedance (Zrs) in preschool-aged children may be able to distinguish abnormal lung function trajectories in children with a history of wheezing compared to healthy ones. Methods Children from a prospective, longitudinal community-based cohort performed annual intra-breath oscillometry (IB-OSC) measurements from age 3-years to 7-years. IB-OSC was performed using a single 10 Hz sinusoid while clinically asymptomatic. Linear mixed-effects models were developed to explore the effects of wheezing phenotypes, growth, and sex on seven IB-OSC outcome variables over time: resistance at end-expiration (ReE), resistance at end-inspiration (ReI), the tidal change in resistance (∆R=ReE-ReI), reactance at end-expiration (XeE), reactance at end-inspiration (XeI), the tidal change in reactance (∆X=XeE-XeI), and ∆X normalised by tidal volume (∆X/VT). Results Eighty-five children produced 375 acceptable IB-OSC measurements. Subjects were classified into one of three wheeze groups: never (n=36), transient (n=35), or persistent (n=14). After adjusting for height, children with persistent wheezing, compared to those who never wheezed, had -0.669 hPa∙s∙L-1 XeE (95% confidence interval [CI] -1.102 to -0.237, p<0.01), -0.465 hPa∙s∙L-1 ∆X (95%CI -0.772 to -0.159, p<0.01) and +1.433 hPa∙s∙L-1 ∆X/VT (95%CI +0.492 to +2.374, p<0.01). Increasing subject height had a significant effect on all IB-OSC resistance and reactance variables when adjusted for the effect of preschool wheezing. Conclusions IB-OSC is feasible for tracking lung function in preschool-aged children, and intra-breath reactance outcomes may allow abnormal lung function to be identified early in asymptomatic children with a history of persistent wheeze.