Validation of commercial devices for measurement of lung clearance index (LCI) and functional residual capacity (FRC) in school-aged children

Abstract

SF 6 Multiple Breath Washout (MBW) using Mass Spectrometry (MS) is sensitive to lung disease in cystic fibrosis (CF). We compared LCI and FRC on 2 commercial nitrogen washout (N 2 -WO) systems to SF 6 -WO in CF patients and controls. Methods: Children performed N 2 -WO as per manufacturer guidelines on the ndd EasyOne Pro ® LAB (ndd Medizintechnik AG) and the Eco Medics Exhalyzer ® D (Eco Medics AG) and SF 6 -WO on AMIS 2000 MS on the same day in random order. FRC and LCI were reported as the mean of 3 technically acceptable runs per device. Results: 42 children with CF, mean age 13.7y(7-18y) and 30 controls 14.9y(12-18y) were measured. Failure rates were; children with CF: Exhalyzer 22, EasyOne 3; controls: Exhalyzer 11. In CF, LCI from the Exhalyzer was significantly higher than LCI measured by MS (mean diff 0.76; 95% CI 0.39;1.13) and LCI measured by EasyOne significantly lower than MS (-0.72; -0.19;-1.24). These differences were not seen in controls. On Bland Altman analysis 95% limits of agreement (LoA) in controls were similar for LCI and FRC irrespective of equipment and narrower than in CF. In children with CF, 95% LoA were wider for EasyOne-MS than Exhalyzer-MS for LCI, and reverse for FRC. Conclusion: This is the first study to compare 2 N 2 -WO devices against MS in vivo. LCI varies significantly with device. Narrower LoA for Exhalyzer-MS suggest better agreement than EasyOne-MS.