In vitro and in vivo comparison of two multiple breath nitrogen washout devices

Background: There are currently several commercially available nitrogen (N 2 ) multiple breath washout (MBW) devices. Individual devices have been tested in lung models and human subjects, but comparative studies including both in vitro and in vivo assessments of devices are lacking. Objective: The aim of this study was to compare the accuracy of two commercially available MBW N2 devices (Exhalyzer D (EcoMedics, AG, Duernten, Switzerland) (EM) and EasyOne Pro LAB (NDD, Zurich, Switzerland) (NDD)) with respect to lung volume measurements. Methods: In vitro measurements were performed using a Soloplex lung model, as described previously by Singer et al (PLoS One, 2012; 7(4):e36083). Functional residual capacity (FRC) was measured under BTPS conditions at 33 different volumes between 2 and 4.2 L by both EM and NDD MBW devices. FRC was also measured in ten healthy adults (median age 23 years (range 19 – 37)) by EM (FRC EM ), NDD (FRC ndd ) and by plethysmography (FRC pleth ) (Vmax Encore PFT system, CareFusion, San Diego, CA, US). Measurements were performed on the same day in randomized order. Results: In the lung model, differences to the actual FRC were relatively small for both devices, with a mean relative FRC EM difference of -4.2% (range -13.6 to 1.5%) and a mean relative FRC NDD difference of 1.1% (range -4.9 to 6.8%). In contrast, FRC measured in vivo differed substantially with a mean relative difference of 14.1% (range -7.3 to 33.3%) for FRC EM and -23.3% (range -35.7 to -8.7%) for FRC NDD compared with FRC pleth (P Conclusion: The lack of agreement between the in vitro and in vivo FRC results underscores the need to perform both in vitro and in vivo validation studies for MBW devices.