Improved Agreement Between N and SF Multiple-breath Washout in Healthy Infants and Toddlers with Improved EXHALYZER D Sensor Performance

Recent studies indicate limited utility of nitrogen multiple-breath washout (NMBW) in infancy and advocate for using sulfur hexafluoride (SF) MBW in this age-group. Modern NMBW systems, such as EXHALYZER D (ECO MEDICS AG, Duernten, Switzerland), use O and CO sensors to calculate N concentrations (in principle, N% = 100 - CO% - O%). High O and CO concentrations have now been shown to significantly suppress signal output from the other sensor, raising apparent N concentrations. We examined whether improved EXHALYZER D N signal, accomplished after thorough examination of this CO and O interaction on gas sensors and its correction, leads to better agreement between NMBW and SFMBW in healthy infants and toddlers. Within the same session, 52 healthy children aged 1-36 mo [mean = 1.30 (SD = 0.72) yr] completed SFMBW and NMBW recordings (EXHALYZER D, SPIROWARE version 3.2.1) during supine quiet sleep. SF and N SPIROWARE files were reanalyzed offline with in-house software using identical algorithms as in SPIROWARE with or without application of the new correction factors for NMBW provided by ECO MEDICS AG. Applying the improved N signal significantly reduced mean [95% confidence interval (CI)] differences between NMBW and SFMBW recorded functional residual capacity (FRC) and lung clearance index (LCI): for FRC, from 26.1 (21.0, 31.2) mL, < 0.0001, to 1.18 (-2.3, 4.5) mL, = 0.5, and for LCI, from 1.86 (1.68, 2.02), < 0.001, to 0.44 (0.33, 0.55), < 0.001. Correction of N signal for CO and O interactions on gas sensors resulted in markedly closer agreement between NMBW and SFMBW outcomes in healthy infants and toddlers. Modern nitrogen multiple-breath washout (NMBW) systems such as EXHALYZER D use O and CO sensors to calculate N concentrations. New corrections for interactions between high O and CO concentrations on the gas sensors now provide accurate N signals. The correct N signal led to much improved agreement between NMBW and sulfur hexafluoride (SF) MBW functional residual capacity (FRC) and lung clearance index (LCI) in 52 sleeping healthy infants and toddlers, suggesting a role for NMBW in this age-group.