TY - JOUR T1 - Comparison of indirect measurements of multiple breath nitrogen washout with mass spectrometry JF - European Respiratory Journal JO - Eur Respir J DO - 10.1183/13993003.congress-2019.PA791 VL - 54 IS - suppl 63 SP - PA791 AU - Chantal Darquenne AU - Rebecca J. Theilmann AU - Sylvia Verbanck Y1 - 2019/09/28 UR - http://erj.ersjournals.com/content/54/suppl_63/PA791.abstract N2 - Background: Multiple breath nitrogen washouts (MBW) and derived lung clearance index (LCI) are increasingly used in clinical applications, due in part to the availability of commercial equipment. These devices are usually based on indirect measurements of N2 concentration (CN2), by measuring O2 and CO2 or molar mass and CO2.Aim: To compare N2 washout tracings and LCI from a commercial MBW device using molar mass and CO2 measurement, with direct CN2 measurements by mass spectrometry (MS).Methods: MBW were performed in triplicate in 12 healthy adult subjects (6M/6F; age: 50±13yr) with 1-liter tidal breathing using a commercial device (MBWdevice). Simultaneous CN2 measurements were obtained with a MS (MBWMS) by inserting a sampling line in the mouthpiece.Results: Mean expired alveolar CN2 was significantly higher throughout the MBWdevice compared to the MBWMS, with an average difference of 0.94±0.35(SD)% (p<0.001). The LCI (mean±SD) calculated from the raw MBWdevice trace was 7.8±0.7, and after offsetting mean expired CN2 by 0.94%, LCI became 6.2±0.4. The latter LCI value fell within the normal range for a device with instrumental dead space of 15ml, whereas the former exceeded LCI upper limit of normal [1]. Corresponding syringe tests showed no significant difference in expired CN2 between MBWdevice and MBWMS (0.03±0.03; P>0.1).Conclusion: Indirect measurements of CN2 were consistently higher than those by mass spectrometry, resulting in a considerable overestimation of LCI. Syringe MBW data suggest a potential role of humidity in exhaled gases on the overestimation of CN2.Reference:1. Verbanck et al. Thorax 2012;67:689-695.This work was funded by grant 5R01 HL135496-02 from NHLBI/NIH.FootnotesCite this article as: European Respiratory Journal 2019; 54: Suppl. 63, PA791.This is an ERS International Congress abstract. No full-text version is available. Further material to accompany this abstract may be available at www.ers-education.org (ERS member access only). ER -