A Realistic Validation Study of a New Nitrogen Multiple-Breath Washout System

Abstract

BackgroundFor reliable assessment of ventilation inhomogeneity, multiple-breath washout (MBW) systems should be realistically validated. We describe a new lung model for in vitro validation under physiological conditions and the assessment of a new nitrogen (N2)MBW system.MethodsThe N2MBW setup indirectly measures the N2 fraction (FN2) from main-stream carbon dioxide (CO2) and side-stream oxygen (O2) signals: FN2 = 1−FO2−FCO2−FArgon. For in vitro N2MBW, a double chamber plastic lung model was filled with water, heated to 37°C, and ventilated at various lung volumes, respiratory rates, and FCO2. In vivo N2MBW was undertaken in triplets on two occasions in 30 healthy adults. Primary N2MBW outcome was functional residual capacity (FRC). We assessed in vitro error (√[difference]2) between measured and model FRC (100–4174 mL), and error between tests of in vivo FRC, lung clearance index (LCI), and normalized phase III slope indices (Sacin and Scond).ResultsThe model generated 145 FRCs under BTPS conditions and various breathing patterns. Mean (SD) error was 2.3 (1.7)%. In 500 to 4174 mL FRCs, 121 (98%) of FRCs were within 5%. In 100 to 400 mL FRCs, the error was better than 7%. In vivo FRC error between tests was 10.1 (8.2)%. LCI was the most reproducible ventilation inhomogeneity index.ConclusionThe lung model generates lung volumes under the conditions encountered during clinical MBW testing and enables realistic validation of MBW systems. The new N2MBW system reliably measures lung volumes and delivers reproducible LCI values.

Functional evidence for continued alveolarisation in former preterms at school age?

“…Nitrogen multiple-breath washout All children performed nitrogen MBW (N 2 MBW) according to current consensus [25] using a previously described setup [26,27] (Exhalyzer D; Eco Medics AG). The application of 100% oxygen washes out the lung-resident nitrogen.…”

A new double-tracer gas single-breath washout to assess early cystic fibrosis lung disease

“…The reference lung function test was MBNW performed using validated equipment [18], according to guidelines [17] and is detailed in the online supplementary material. Primary outcome was LCI calculated as the ratio of cumulative expired volume divided by functional residual capacity [19,20].…”

Inter-test reproducibility of the lung clearance index measured by multiple breath washout

“…Investigators report differing findings for the inter-test reproducibility of the LCI due to variability in protocol designs, study population and MBW methodology [5][6][7][8][9][10][11][12][13][14]. Most notably, time intervals between repeated tests range from hours to years, and none report reproducibility for time intervals typically used to clinically track patients with cystic fibrosis (e.g.…”

“…Most notably, time intervals between repeated tests range from hours to years, and none report reproducibility for time intervals typically used to clinically track patients with cystic fibrosis (e.g. quarterly) [6,11,15]. Comparison between studies is further limited by the various methodologies that define reproducibility; coefficient of variation (%CV) [5,7,8], the intra-class correlation coefficient (ICC) [6], the limits of agreement from Bland-Altman plots [5,[9][10][11] or the coefficient of reproducibility [12,13].…”