In vitroandin vivofunctional residual capacity comparisons between multiple-breath nitrogen washout devices

Abstract

Functional residual capacity (FRC) accuracy is essential for deriving multiple-breath nitrogen washout (MBNW) indices, and is the basis for device validation. Few studies have compared existing MBNW devices. We evaluated in vitro and in vivo FRC using two commercial MBNW devices, the Exhalyzer D (EM) and the EasyOne Pro LAB (ndd), and an in-house device (Woolcock in-house device, WIMR).FRC measurements were performed using a novel syringe-based lung model and in adults (20 healthy and nine with asthma), followed by plethysmography (FRCpleth). The data were analysed using device-specific software. Following the results seen with ndd, we also compared its standard clinical software (ndd v.2.00) with a recent upgrade (ndd v.2.01).WIMR and EM fulfilled formal in vitro FRC validation recommendations (>95% of FRC within 5% of known volume). Ndd v.2.00 underestimated in vitro FRC by >20%. Reanalysis using ndd v.2.01 reduced this to 11%, with 36% of measurements ≤5%. In vivo differences from FRCpleth (mean±sd) were 4.4±13.1%, 3.3±11.8%, −20.6±11% (p<0.0001) and −10.5±10.9% (p=0.005) using WIMR, EM, ndd v.2.00 and ndd v.2.01, respectively.Direct device comparison highlighted important differences in measurement accuracy. FRC discrepancies between devices were larger in vivo, compared to in vitro results; however, the pattern of difference was similar. These results represent progress in ongoing standardisation efforts.

Difference between SF6 and N2 multiple breath washout kinetics is due to N2 back diffusion and error in N2 offset

“…Previous studies reporting differences between SF 6 and N 2 LCI (11,12) used different breathing assemblies, breathing patterns, and software algorithms. Even when using the same device for N 2 -MBW, there are differences noted with different software versions (20). The magnitude of differences we observed in our study is similar to differences observed by other investigators.…”

“…A number of studies have identified differences between LCI derived from these two different techniques (11,12) and between different devices using the same technique (20). None of these studies obtained truly simultaneous measurements; results could be influenced by differences in breathing assemblies, subject breathing pattern, and software algorithms used to analyze data.…”

Controlledversusfree breathing for multiple breath nitrogen washout in healthy adults

“…We studied 27 non-smoking, healthy volunteers (22 at the RNSH site, 5 at the WIMR site) with a median age of 34 (range 19–65) years and spirometry/lung volumes within the limits of normal ( table 1 ). Since MBNW parameters are likely to be device- and protocol-specific [ 17 , 18 ], we were unable to compare all measurements to a single set of reference equations. However, MBNW indices from the free breathing protocol were within the ranges of normal derived from the same testing device ( supplementary table S1 ) [ 9 ].…”

“…However the between-session coefficient of repeatability (equal to 1.96× sd of the mean differences) of LCI, S cond and S acin was greater in our study, which may reflect the different time between sessions (weeks/months versus days). There is a paucity of repeatability data in health, and previous reports may not be generalisable due to persistent between-device differences [ 17 , 18 , 26 ]. Nevertheless, the excellent between-session repeatability for FRC and LCI [ 25 , 27 – 29 ] but poor repeatability in S acin and S cond [ 25 , 28 ] has been noted with the free breathing protocol by other investigators, regardless of device, tracer gas or disease.…”

“…Third, our results only apply to a healthy population tested on a single MBNW device. There are likely to be differences between equipment [ 17 , 18 ] and between populations ( e.g. children, older adults, lung disease) that limit the generalisability of our results.…”