Intra-breath oscillometry detects ventilation inhomogeneity in Cystic Fibrosis children

Abstract

Background: Ventilation inhomogeneity (VI) is measured in patients with Cystic Fibrosis (CF) by lung clearance index (LCI) using the Multiple Breath Washout (MBW). In young children, feasibility is often low within busy clinical settings. Intra-breath oscillometry (IB-OSC) measures respiratory system reactance (Xrs), which is determined by the same physiological principles. Given the high feasibility of IB-OSC in young children (>80%), we aimed to explore whether Xrs variables reflected VI as measured by LCI. Methods: Paired measurements of IB-OSC (TremoFLO C-100, 10Hz signal) and Nitrogen (N2) MBW (Exhalyzer D) were performed in 97 children with CF. Abnormal LCI was defined as ≥7.1. IB-OSC Xrs variables at end-expiration (XeE), end-inspiration (XeI), volume-dependence of Xrs (ΔX) and ΔX corrected for tidal volume (ΔX/VT) were compared between those with normal and abnormal LCI. Receiver operator characteristic (ROC) analysis was performed to identify cut-off values to detect abnormal LCI. Results: 115 acceptable paired IB-OSC and MBW measurements were achieved by 85 children (male 61%, median age 7.8yrs [25th-75th% 5.8-11.9]). 52 (45%) measurements of LCI were abnormal. All Xrs variables where significantly decreased (more negative) in children with abnormal LCI compared to normal (XeE -2.98v-0.81; XeI -2.10v-1.00; ΔX -0.25v0.12; ΔX/VT -0.54v0.22; all p<0.001). Cut-off values for ΔX and ΔX/VT provided the best sensitivity and specificity for detecting abnormal LCI. Conclusion: These results suggest that novel IB-OSC variables can detect abnormal VI as measured by N2 MBW-LCI. This technique may allow us to detect and monitor early changes to lung function in busy CF clinics more easily.