Multiple breath nitrogen washout: a feasible alternative to mass spectrometry

Multiple breath washout and oscillometry after allogenic HSCT: a scoping review

Pulmonary chronic graft-versus-host disease (cGVHD) is a substantial cause of pulmonary morbidity and mortality post-haematopoietic stem cell transplantation (HSCT). Current spirometry-based monitoring strategies have significant limitations. Understanding the utility of novel peripheral airway function tests - multiple breath washout (MBW) and oscillometry - is critical in efforts to improve detection, facilitate earlier intervention and improve outcomes. In this scoping review, we identified 17 studies investigating MBW or oscillometry, or both, after allogenic HSCT. Despite small study numbers limiting the ability to draw firm conclusions, several themes were evident. Detectable peripheral airway abnormality in MBW occurred in a substantial proportion prior to HSCT. MBW indices post-HSCT were more frequently abnormal than spirometry when reporting group data and among those with extrapulmonary cGVHD and pulmonary cGVHD. Changes in MBW indices over time may be more indicative of pulmonary complications than absolute values at any given time point. Oscillometry indices were often normal at baseline, but more frequently abnormal in those who developed pulmonary cGVHD. Pooling currently available individual participant data across these studies may improve our ability to formally compare their respective sensitivity and specificity at specific time points and assess the trajectory of MBW and oscillometry indices over time.

Nitrogen-based lung clearance index: a valid physiological biomarker for the clinic

Multiple breath washout (MBW) testing is increasingly used as a physiological measurement in the clinic, due in part to the availability of commercial equipment and reference values for MBW indices. Commercial N₂ washout devices are usually based on indirect measurement of N₂ concentration (C_N2), by directly measuring either molar mass and O₂ and CO₂, or molar mass and CO₂. We aim to elucidate the role of two potential pitfalls associated with N₂-MBW testing that could override its physiological content: indirect N₂ measurement and blood-solubility of N₂. We performed MBW in 12 healthy adult subjects using a commercial device (MBW_indirect) with simultaneous direct gas concentration measurements by mass spectrometry (MBW_direct) and compared C_N2 between MBW_direct and MBW_indirect. We also measured argon concentration during the same washouts to verify the maximal effect gas solubility can have on N₂-based functional residual capacity (FRC) and lung clearance index (LCI). Continuous N₂ concentration traces were very similar for MBW_indirect and MBW_direct, resulting in comparable breath-by-breath washout plots of expired concentration and in no significant differences in FRC_N2, LCI_N2, S_cond, and S_acin between the two methods. Argon washouts were slightly slower than N₂ washouts, as expected for a less diffusive and more soluble gas. Finally, comparison between LCI_N2 and LCI_Ar indicates that the maximum impact from blood-tissue represents less than half a LCI unit in normal subjects. In conclusion, we have demonstrated by direct measurement of N₂ and twice as soluble argon, that indirect N₂ measurement can be safely used as a meaningful physiological measurement.NEW & NOTEWORTHY The physiological content of N₂ multibreath washout testing has been questioned due to N₂ indirect measurement accuracy and N₂ blood solubility. With direct measurement of N₂ and twice as soluble argon, we show that these effects are largely outweighed by ease of use.

Contemporary N2 and SF6 multiple breath washout in infants and toddlers with cystic fibrosis

INTRODUCTION

Multiple breath washout (MBW) is used for early detection of cystic fibrosis (CF) lung disease, with SF₆ MBW commonly viewed as the reference method. The use of N₂ MBW in infants and toddlers has been questioned for technical and physiological reasons, but a new correction of the N₂  signal has minimized the technical part. The present study aimed to assess the remaining differences and the contributing mechanisms for the differences between SF₆ and N₂ MBW,corrected-such as tidal volume reduction during N₂ washout with pure O₂ .

METHOD

This was a longitudinal multicenter cohort study. SF₆ MBW and N₂ MBW were performed prospectively at three CF centers in the same visits on 154 test occasions across 62 children with CF (mean age: 22.7 months). Offline analysis using identical algorithms to the commercially available program provided outcomes of N_2,original and N_2,corrected for comparison with SF₆ MBW.

RESULTS

Mean functional residual capacity, FRC_N2,corrected was 14.3% lower than FRC_{N2, original} , and 1.0% different from FRC_SF6 . Lung clearance index, LCI_N2,corrected was 25.2% lower than LCI_N2,original , and 7.3% higher than LCI_SF6 . Mean (SD) tidal volume decreased significantly during N₂ MBW_corrected , compared to SF₆ MBW (-13.1 ml [-30.7; 4.6], p < 0.0001, equal to -12.0% [-25.7; 1.73]), but this tidal volume reduction did not correlate to the differences between LCI_N2,corrected and LCI_SF6 . The absolute differences in LCI increased significantly with higher LCI_SF6 (0.63/LCI_SF6 ) and (0.23/LCI_SF6 ), respectively, for N_2,original and N_2,corrected , but the relative differences were stable across disease severity for N_2,corrected , but not for N_2,original .

CONCLUSION

Only minor residual differences between FRC_N2,corrected and FRC_SF6 remained to show that the two methods measure gas volumes very similar in this age range. Small differences in LCI were found. Tidal volume reduction during N₂ MBW did not affect differences. The corrected N₂ MBW can now be used with confidence in young children with CF, although not interchangeably with SF₆ .

The effect of O2 and CO2 cross-sensitivity sensor error in the Eco Medics Exhalyzer D device on measures of conductive and acinar airway function

Introduction

The multiple breath nitrogen washout (MBNW) test provides important clinical information in obstructive airways diseases. Recently, a significant cross-sensitivity error in the O₂ and CO₂ sensors of a widely used commercial MBNW device (Exhalyzer D, Eco Medics AG, Duernten, Switzerland) was detected, which leads to overestimation of N₂ concentrations. Significant errors in functional residual capacity (FRC) and lung clearance index (LCI) have been reported in infants and children. This study investigated the impact in adults, and on additional important indices reflecting conductive (S_cond) and acinar (S_acin) ventilation heterogeneity, in health and disease.

Methods

Existing MBNW measurements of 27 healthy volunteers, 20 participants with asthma and 16 smokers were reanalysed using SPIROWARE V 3.3.1, which incorporates an error correction algorithm. Uncorrected and corrected indices were compared using paired t-tests and Bland–Altman plots.

Results

Correction of the sensor error significantly lowered FRC (mean difference 9%) and LCI (8–10%) across all three groups. S_cond was higher following correction (11%, 14% and 36% in health, asthma and smokers, respectively) with significant proportional bias. S_acin was significantly lower following correction in the asthma and smoker groups, but the effect was small (2–5%) and with no proportional bias.

Discussion

The O₂ and CO₂ cross-sensitivity sensor error significantly overestimated FRC and LCI in adults, consistent with data in infants and children. There was a high degree of underestimation of S_cond but minimal impact on S_acin. The presence of significant proportional bias indicates that previous studies will require reanalysis to confirm previous findings and to allow comparability with future studies.

O₂ and CO₂ cross-sensitivity sensor error in the Exhalyzer D device significantly overestimates FRC and LCI in adults, consistent with infants and children. Importantly, there was a high degree of underestimation of S_cond, but minimal impact on S_acin.https://bit.ly/3HcH3Tp

Correction of sensor crosstalk error in Exhalyzer D multiple-breath washout device significantly impacts outcomes in children with cystic fibrosis

RATIONALE

Nitrogen multiple-breath washout is an established technique to assess functional residual capacity and ventilation inhomogeneity in the lung. Accurate measurement of gas concentrations is essential for the appropriate calculation of clinical outcomes.

OBJECTIVES

We investigated the accuracy of oxygen and carbon dioxide gas sensor measurements used for the indirect calculation of nitrogen concentration in a commercial multiple-breath washout device (Exhalyzer D, Eco Medics AG, Duernten, Switzerland) and its impact on functional residual capacity and lung clearance index.

METHODS

High precision calibration gas mixtures and mass spectrometry were used to evaluate sensor output. We assessed the impact of corrected signal processing on multiple-breath washout outcomes in a dataset of healthy children and children with cystic fibrosis using custom analysis software.

RESULTS

We found inadequate correction for the cross sensitivity of the oxygen and carbon dioxide sensors in the Exhalyzer D device. This results in an overestimation of expired nitrogen concentration, and consequently multiple-breath washout outcomes. Breath-by-breath correction of this error reduced the mean (SD) cumulative expired volume by 19.6 (5.0)%, functional residual capacity by 8.9 (2.2)%, and lung clearance index by 11.9 (4.0)%. It also substantially reduced the level of the tissue nitrogen signal at the end of measurements.

CONCLUSIONS

Inadequate correction for cross sensitivity in the oxygen and carbon dioxide gas sensors of the Exhalyzer D device leads to an overestimation of functional residual capacity and lung clearance index. Correction of this error is possible and could be applied by re-analyzing the measurements in an updated software version.

Longitudinal assessment of lung clearance index to monitor disease progression in children and adults with cystic fibrosis

Background

Lung clearance index (LCI) is a valuable research tool in cystic fibrosis (CF) but clinical application has been limited by technical challenges and uncertainty about how to interpret longitudinal change. In order to help inform clinical practice, this study aimed to assess feasibility, repeatability and longitudinal LCI change in children and adults with CF with predominantly mild baseline disease.

Methods

Prospective, 3-year, multicentre, observational study of repeated LCI measurement at time of clinical review in patients with CF >5 years, delivered using a rapid wash-in system.

Results

112 patients completed at least one LCI assessment and 98 (90%) were still under follow-up at study end. The median (IQR) age was 14.7 (8.6–22.2) years and the mean (SD) FEV₁ z-score was −1.2 (1.3). Of 81 subjects with normal FEV₁ (>−2 z-scores), 63% had raised LCI (indicating worse lung function). For repeat stable measurements within 6 months, the mean (limits of agreement) change in LCI was 0.9% (−18.8% to 20.7%). A latent class growth model analysis identified four discrete clusters with high accuracy, differentiated by baseline LCI and FEV₁. Baseline LCI was the strongest factor associated with longitudinal change. The median total test time was under 19 min.

Conclusions

Most patients with CF with well-preserved lung function show stable LCI over time. Cluster behaviours can be identified and baseline LCI is a risk factor for future progression. These results support the use of LCI in clinical practice in identifying patients at risk of lung function decline.

Improved agreement between N2 and SF6 multiple-breath washout in healthy infants and toddlers with improved EXHALYZER D sensor performance

Recent studies indicate limited utility of nitrogen multiple-breath washout (N₂MBW) in infancy and advocate for using sulfur hexafluoride (SF₆) MBW in this age-group. Modern N₂MBW systems, such as EXHALYZER D (ECO MEDICS AG, Duernten, Switzerland), use O₂ and CO₂ sensors to calculate N₂ concentrations (in principle, N₂% = 100 - CO₂% - O₂%). High O₂ and CO₂ concentrations have now been shown to significantly suppress signal output from the other sensor, raising apparent N₂ concentrations. We examined whether improved EXHALYZER D N₂ signal, accomplished after thorough examination of this CO₂ and O₂ interaction on gas sensors and its correction, leads to better agreement between N₂MBW and SF₆MBW in healthy infants and toddlers. Within the same session, 52 healthy children aged 1-36 mo [mean = 1.30 (SD = 0.72) yr] completed SF₆MBW and N₂MBW recordings (EXHALYZER D, SPIROWARE version 3.2.1) during supine quiet sleep. SF₆ and N₂ 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 N₂MBW provided by ECO MEDICS AG. Applying the improved N₂ signal significantly reduced mean [95% confidence interval (CI)] differences between N₂MBW and SF₆MBW recorded functional residual capacity (FRC) and lung clearance index (LCI): for FRC, from 26.1 (21.0, 31.2) mL, P < 0.0001, to 1.18 (-2.3, 4.5) mL, P = 0.5, and for LCI, from 1.86 (1.68, 2.02), P < 0.001, to 0.44 (0.33, 0.55), P < 0.001. Correction of N₂ signal for CO₂ and O₂ interactions on gas sensors resulted in markedly closer agreement between N₂MBW and SF₆MBW outcomes in healthy infants and toddlers.NEW & NOTEWORTHY Modern nitrogen multiple-breath washout (N₂MBW) systems such as EXHALYZER D use O₂ and CO₂ sensors to calculate N₂ concentrations. New corrections for interactions between high O₂ and CO₂ concentrations on the gas sensors now provide accurate N₂ signals. The correct N₂ signal led to much improved agreement between N₂MBW and sulfur hexafluoride (SF₆) MBW functional residual capacity (FRC) and lung clearance index (LCI) in 52 sleeping healthy infants and toddlers, suggesting a role for N₂MBW in this age-group.

The differing physiology of nitrogen and tracer gas multiple-breath washout techniques

Background

Multiple-breath washout techniques are increasingly used to assess lung function. The principal statistic obtained is the lung clearance index (LCI), but values obtained for LCI using the nitrogen (N₂)-washout technique are higher than those obtained using an exogenous tracer gas such as sulfur hexafluoride. This study explored whether the pure oxygen (O₂) used for the N₂ washout could underlie these higher values.

Methods

A model of a homogenous, reciprocally ventilated acinus was constructed. Perfusion was kept constant, and ventilation adjusted by varying the swept volume during the breathing cycle. The blood supplying the acinus had a standard mixed-venous composition. Carbon dioxide and O₂ exchange between the blood and acinar gas proceeded to equilibrium. The model was initialised with either air or air plus tracer gas as the inspirate. Washouts were conducted with pure O₂ for the N₂ washout or with air for the tracer gas washout.

Results

At normal ventilation/perfusion (V′/Q′) ratios, the rate of washout of N₂ and exogenous tracer gas was almost indistinguishable. At low V′/Q′, the N₂ washout lagged the tracer gas washout. At very low V′/Q′, N₂ became trapped in the acinus. Under low V′/Q′ conditions, breathing pure O₂ introduced a marked asymmetry between the inspiratory and expiratory gas flow rates that was not present when breathing air.

Discussion

The use of pure O₂ to washout N₂ increases O₂ uptake in low V′/Q′ units. This generates a background gas flow into the acinus that opposes flow out of the acinus during expiration, and so delays the washout of N₂.

Differences in lung clearance index between nitrogen and exogenous tracer gas multiple-breath washout tests can be explained by the oxygen used to wash out nitrogen generating convective flows of gas into low ventilation/perfusion unitshttps://bit.ly/3l0xq0G

Multiple breath washout (MBW) testing using sulfur hexafluoride: reference values and influence of anthropometric parameters

BACKGROUND

Multiple breath washout (MBW) using sulfur hexafluoride (SF₆) has the potential to reveal ventilation heterogeneity which is frequent in patients with obstructive lung disease and associated small airway dysfunction. However, reference data are scarce for this technique and mostly restricted to younger cohorts. We therefore set out to evaluate the influence of anthropometric parameters on SF₆-MBW reference values in pulmonary healthy adults.

METHODS

We evaluated cross-sectional data from 100 pulmonary healthy never-smokers and smokers (mean 51 (SD 20), range 20-88 years). Lung clearance index (LCI), acinar (S_acin) and conductive (S_cond) ventilation heterogeneity were derived from triplicate SF₆-MBW measurements. Global ventilation heterogeneity was calculated for the 2.5% (LCI_2.5) and 5% (LCI₅) stopping points. Upper limit of normal (ULN) was defined as the 95th percentile.

RESULTS

Age was the only meaningful parameter influencing SF₆-MBW parameters, explaining 47% (CI 33% to 59%) of the variance in LCI, 32% (CI 18% to 47%) in S_acin and 10% (CI 2% to 22%) in S_cond. Mean LCI increases from 6.3 (ULN 7.4) to 8.8 (ULN 9.9) in subjects between 20 and 90 years. Smoking accounted for 2% (CI 0% to 8%) of the variability in LCI, 4% (CI 0% to 13%) in S_acin and 3% (CI 0% to 13%) in S_cond.

CONCLUSION

SF₆-MBW outcome parameters showed an age-dependent increase from early adulthood to old age. The effect was most pronounced for global and acinar ventilation heterogeneity and smaller for conductive ventilation heterogeneity. No influence of height, weight and sex was seen. Reference values can now be provided for all important SF₆-MBW outcome parameters over the whole age range.

TRIAL REGISTRATION NUMBER

NCT04099225.

Multiple breath washout quality control in the clinical setting

BACKGROUND

Multiple breath washout (MBW) is increasingly used in the clinical assessment of patients with cystic fibrosis (CF). Guidelines for MBW quality control (QC) were developed primarily for retrospective assessment and central overreading. We assessed whether real-time QC of MBW data during the measurement improves test acceptability in the clinical setting.

METHODS

We implemented standardized real-time QC and reporting of MBW data at the time of the measurement in the clinical pediatric lung function laboratory in Bern, Switzerland, in children with CF aged 4-18 years. We assessed MBW test acceptability before (31 tests; 89 trials) and after (32 tests; 96 trials) implementation of real-time QC and compared agreement between reviewers. Further, we assessed the implementation of real-time QC at a secondary center in Zurich, Switzerland.

RESULTS

Before the implementation of real-time QC in Bern, only 58% of clinical MBW tests were deemed acceptable following retrospective QC by an experienced reviewer. After the implementation of real-time QC, MBW test acceptability improved to 75% in Bern. In Zurich, after the implementation of real-time QC, test acceptability improved from 38% to 70%. Further, the agreement between MBW operators and an experienced reviewer for test acceptability was 84% in Bern and 93% in Zurich.

CONCLUSION

Real-time QC of MBW data at the time of measurement is feasible in the clinical setting and results in improved test acceptability.

What Is Most Suitable for Children With Cystic Fibrosis-The Relationship Between Spirometry, Oscillometry, and Multiple Breath Nitrogen Washout

INTRODUCTION

In cystic fibrosis (CF), pathological lung changes begin early in life. The technological progress currently gives many diagnostic possibilities. However, pulmonary function testing in children remains problematic.

OBJECTIVES

Our study aimed to correlate the results of impulse oscillometry (IOS) with those of multiple breath nitrogen washout (MBNW) in our pediatric CF population. We also compared those parameters between the groups with and without spirometric features of obturation.

METHODS

We collected 150 pulmonary function test sets, including spirometry, IOS, and MBNW in patients with CF aged 12.08 ± 3.85 years [6-18]. The study group was divided into two subgroups: IA (without obturation) and IB (with obturation). We also compared Sacin, Scond, and oscillometry parameters of 20 patients aged 14-18 years who reached the appropriate tidal volume (VT) during MBNW.

RESULTS

Statistical analysis showed a negative correlation between lung clearance index (LCI) and spimoetric parameters. Comparison of subgroups IA (n = 102) and IB (n = 48) indicated a statistically significant difference in LCI (p < 0.001) and FEV1z-score (p < 0.001), FEV1% pred (p < 0.001), MEF25z-score (p < 0.001), MEF50 z-score (p < 0.001), MEF75 z-score (p < 0.001), R5% pred (p < 0.05), and R20% pred (p < 0.01). LCI higher than 7.91 was found in 75.33% of the study group, in subgroup IB-91.67%, and IA-67.6%.

CONCLUSIONS

LCI derived from MBNW may be a better tool than IOS for assessing pulmonary function in patients with CF, particularly those who cannot perform spirometry.

Evaluation of a multiple breath nitrogen washout system in children

INTRODUCTION

The multiple breath nitrogen washout (MBW) test offers a sensitive measure of airway function. In this study we aim to (a) assess the validity of the EasyOne Pro LAB (MBW_ndd ) in an in vitro lung model, (b) assess the feasibility, repeatability, and reproducibility of MBW_ndd and (c) compare outcomes with the Exhalyzer D (MBW_EM ) and body plethysmography.

METHODS

In vitro, functional residual capacity (FRC) measurements were assessed using a lung model under quasi-physiological conditions and compared to measured FRC. In vivo plethysmography and MBW were performed in a prospective study of children at two visits (n = 45 healthy; n = 41 cystic fibrosis [CF]). Bland-Altman plots were used to compare agreement between FRC and lung clearance index (LCI) measurements.

RESULTS

In vitro FRC_ndd measurements were repeatable but lung volumes were underestimated (mean relative difference -5.4% (limits of agreement [LA] -9.6%; -1.1%), 95% confidence interval (CI) -6.27; -4.45). In vivo, compared to plethysmography, FRC_ndd was consistently lower (-19.3% [-40.5; 1.9], 95% CI [-23.9; -14.7]), and showed a volume dependency. LCI_ndd values were also higher in children with smaller lung volumes. The within-test coefficient of variation of the FRC_ndd and LCI_ndd were 4.9% in health, and 5.6% and 6.9% in CF respectively. LCI_ndd was reproducible between-visits (mean relative difference [LA] -3.7% [-14.8, -7.5; 95% CI -6.6; -0.73] in health [n = 17] and 0.34% [-13.2, 22.8; 95% CI -5.0; 5.69] in CF [n = 23]). When calculated using the same algorithm, LCI_ndd was similar to LCI_EM in health.

CONCLUSIONS

MBW_ndd measurements are feasible, repeatable, and reproducible, however, MBW-derived outcomes are not interchangeable with MBW_EM .

Lung compartment analysis assessed from N2 multiple-breath washout in children with cystic fibrosis

BACKGROUND

Compartment analysis (CA) based on nitrogen multiple-breath washout (N₂ MBW) has been shown to allow the assessment of specific volume and ventilation of faster- and slower-ventilating lung compartments of the lung in adults with cystic fibrosis (CF). The aim of this study was to extend previous findings into the pediatric age range.

METHODS

Cross-sectional multicenter observational study in children with CF and healthy controls (HC) was done with the assessment of N₂ MBW and spirometry. A two-lung compartment model-based analysis (CA) was used to estimate size and function of faster- and slower-ventilating lung compartments from N₂ MBW.

RESULTS

A total of 125 children with CF and 177 HC, median age 10.8 (range, 2.8-18.9) years, were included in the analysis. CA could be calculated in 66 (53%) children with CF compared with 48 (27%) HC (P < .0001). The proportion of the slower-ventilating lung compartment was significantly smaller in children with CF (53.5%; 95% confidence interval [CI]: 51.9%-55.7%) compared with HC (62.2%; 95% CI: 59.0%-65.0%) The regional specific ventilation of the slower compartment (rV_T ,slow/rFRC,slow, %) was significantly lower in children with CF (4.9%; 95% CI: 4.5-5.9) compared with HC (9.7%, 95% CI: 9.2-10.9), and showed inverse correlation to lung clearance index (r²  = -.65; P < .0001), S_acin  × VT (r²  = -.36; P = .003) and S_cond  × VT (r²  = -.51; P < .0001). There was no significant difference in pulmonary parameters between children with CF with and without feasible CA.

CONCLUSION

CA is less feasible in children than in adults and correlated to other MBW parameters. The clinical value of CA is still unclear and is yet to be established.

Differences in lung clearance index and functional residual capacity between two commercial multiple-breath nitrogen washout devices in healthy children and adults

Multiple-breath nitrogen washout (MBNW) and its clinical parameter lung clearance index (LCI) are gaining increasing attention for the assessment of small airway function. Measurement of LCI relies on accurate assessment of functional residual capacity (FRC). The EasyOne Pro LAB (ndd) and Exhalyzer D (EM) are two commercially available MBNW devices. The aim of the study was to compare these two devices in vitro and in vivo in healthy subjects with regard to FRC, LCI and secondary outcome parameters and to relate FRC_MBNW to FRC measured by body plethysmography (pleth) and helium dilution technique. MBNW measurements were performed using a lung model (FRC between 500 and 4000 mL) in vitro and in 38 subjects aged 6–65 years followed by helium dilution and pleth in vivo using fixed and relaxed breathing techniques. In vitro accuracy within 5% of lung model FRC was 67.3% for ndd, FRC was >5% higher for EM in all tests. In vivo, FRC_pleth ranged from 1.2 to 5.6 L. Mean differences (limits of agreement) between FRC_pleth and FRC_MBNW were −7.0%, (−23.2 to 9.2%) and 5.7% (−11.2 to 22.6%) using ndd and EM, respectively. FRC_ndd was consistently lower than FRC_EM (−11.8% (−25.6 to 2%)). LCI was comparable between the two devices (−1.3% (−21.9 to 19.3%)). There was a difference of >10 % in LCI in 12 of 38 subjects. Using the most recent software updates, both devices show relevant deviations in FRC measurement both in vitro and in vivo and individual differences in LCI in a significant proportion of subjects. The devices are therefore not interchangeable.

MBNW measurements with the Exhalyzer D and EasyOne Pro LAB cannot be used interchangeably for FRC and LCI measurements. FRC measured on both devices showed deviations from in vitro and in vivo measurements.https://bit.ly/2xyyUuJ

Lung clearance index-triggered intervention in children with cystic fibrosis - A randomised pilot study

HYPOTHESIS

Using increase in the lung clearance index (LCI) as a trigger for bronchoalveolar lavage (BAL) and associated antimicrobial treatment might benefit clinical outcomes in children with cystic fibrosis (CF).

METHODS

A 2-year, longitudinal, interventional, randomized, controlled pilot study with quarterly visits in 5-18 years old children with CF. LCI and z-scores for the forced expired volume in 1 s (zFEV₁) and body mass index (zBMI) were obtained at every visit, CF Questionnaire-revised (CFQ-R) yearly and BAL and chest computed tomography at first and last visit. Children in the intervention group had BAL performed if LCI increased >1 unit from a fixed baseline value established at first visit. If the presence of a pathogen was documented in the BAL fluid, treatment was initiated/altered accordingly.

RESULTS

Twenty-nine children with CF were randomized to the control (n = 14) and intervention group (n = 15). The median (interquartile range) number of BAL procedures per child was 2.5 (2.0; 3.0) and 6.0 (4.0; 7.0) in the control and intervention group, respectively. There was no significant difference between groups in slope for the primary outcome LCI; difference was 0.21 (95% confidence interval: -0.45; 0.88) units/year. Likewise, there was no significant difference between groups in slope for the secondary outcomes zFEV₁, zBMI, CFQ-R respiratory symptom score and the proportion of total disease and trapped air on chest computed tomography.

CONCLUSIONS

LCI-triggered BAL and associated antimicrobial treatment did not benefit clinical outcomes in a small cohort of closely monitored school-age children with CF.

Lung clearance index in healthy volunteers, measured using a novel portable system with a closed circuit wash-in

Introduction

Lung clearance index (LCI) is a sensitive measure of early lung disease, but adoption into clinical practice has been slow. Challenges include the time taken to perform each test. We recently described a closed-circuit inert gas wash-in method that reduces overall testing time by decreasing the time to equilibration. The aim of this study was to define a normative range of LCI in healthy adults and children derived using this method. We were also interested in the feasibility of using this system to measure LCI in a community setting.

Methods

LCI was assessed in healthy volunteers at three hospital sites and in two local primary schools. Volunteers completed three washout repeats at a single visit using the closed circuit wash-in method (0.2% SF₆ wash-in tracer gas to equilibrium, room air washout).

Results

160 adult and paediatric subjects successfully completed LCI assessment (95%) (100 in hospital, 60 in primary schools). Median coefficient of variation was 3.4% for LCI repeats and 4.3% for FRC. Mean (SD) LCI for the analysis cohort (n = 53, age 5–39 years) was 6.10 (0.42), making the upper limit of normal LCI 6.8. There was no relationship between LCI and multiple demographic variables. Median (interquartile range) total test time was 18.7 (16.0–22.5) minutes.

Conclusion

The closed circuit method of LCI measurement can be successfully and reproducibly measured in healthy volunteers, including in out-of-hospital settings. Normal range appears stable up to 39 years. With few subjects older than 40 years, further work is required to define the normal limits above this age.

Feasibility and clinical applications of multiple breath wash-out (MBW) testing using sulphur hexafluoride in adults with bronchial asthma

Ventilation heterogeneity is frequent in bronchial asthma and can be assessed using multiple breath wash-out testing (MBW). Most data is available in paediatric patients and using nitrogen as a tracer gas. We aimed to evaluate sulphur hexafluoride (SF₆) MBW in adult asthmatics. Spirometry, whole-body plethysmography, impulse oscillometry and SF₆-MBW were prospectively performed. MBW parameters reflecting global (lung clearance index, LCI), acinar (S_acin) and conductive (S_cond) ventilation heterogeneity were derived from three consecutive wash-outs. LCI was calculated for the traditional 2.5% and an earlier 5% stopping point that has the potential to reduce wash-out times. 91 asthmatics (66%) and 47 non-asthmatic controls (34%) were included in final analysis. LCI_2.5 and LCI₅ were higher in asthmatics (p < 0.001). Likewise, S_acin and S_cond were elevated (p < 0.001 and p < 0.01). Coefficient of variation was 3.4% for LCI_2.5 and 3.5% for LCI₅ in asthmatics. Forty-one asthmatic patients had normal spirometry. ROC analysis revealed an AUC of 0.906 for the differentiation from non-asthmatic controls exceeding diagnostic performance of individual and conventional parameters (AUC = 0.819, p < 0.05). SF₆-MBW is feasible and reproducible in adult asthmatics. Ventilation heterogeneity is increased as compared to non-asthmatic controls persisting in asthmatic patients with normal spirometry. Diagnostic performance is not affected using an earlier LCI stopping point while reducing wash-out duration considerably.

Nitrogen offset in N2 multiple washout method

In a recent study of the nitrogen multiple breath washout (MBW) method to measure lung clearance index (LCI) using the Exhalyzer device (Eco Medics AG, Dürnten, Switzerland), Bayfieldet al. [1] reported an N₂ offset signal of ∼1.4%, slightly higher than reported in several previous studies. There was no similar offset using sulfur hexafluoride as the tracer gas measured with the Innocor device (Innovision ApS, Glamsbjerg, Denmark), a finding that is in line with previous reports. The results of this and other studies are extremely important as the Exhalyzer is the device that is currently used in ≥100 cystic fibrosis centres in the European Cystic Fibrosis Society Clinical Trial Network and the Cystic Fibrosis Foundation Therapeutics Development Network in various drug trials [2].

An offset in the nitrogen signal significantly affects LCI measured by the N₂ MBW methodhttp://bit.ly/35hwOuH

Normative data for multiple breath washout outcomes in school-aged Caucasian children

Background

The multiple breath nitrogen washout (N2MBW) technique is increasingly used to assess the degree of ventilation inhomogeneity in school-aged children with lung disease. However, reference values for healthy children are currently not available. The aim of this study was to generate reference values for N2MBW outcomes in a cohort of healthy Caucasian school-aged children.

Methods

N2MBW data from healthy Caucasian school-age children between 6 and 18 years old were collected from four experienced centres. Measurements were performed using an ultrasonic flowmeter (Exhalyzer D, Eco Medics AG, Duernten, Switzerland) and were analysed with commercial software (Spiroware version 3.2.1, Eco Medics AG). Normative values and upper limits of normal (ULN) were generated for lung clearance index (LCI) at 2.5% (LCI2.5%) and at 5% (LCI5%) of the initial nitrogen concentration and for moment ratios (M1/M0 and M2/M0). A prediction equation was generated for functional residual capacity (FRC).

Results

Analysis used 485 trials from 180 healthy Caucasian children aged from 6 to 18 years old. While LCI increased with age, this increase was negligible (0.04 units·year–1 for LCI2.5%) and therefore fixed ULN were defined for this age group. These limits were 7.91 for LCI2.5%, 5.73 for LCI5%, 1.75 for M1/M0 and 6.15 for M2/M0, respectively. Height and weight were found to be independent predictors of FRC.

Conclusion

We report reference values for N2MBW outcomes measured on a commercially available ultrasonic flowmeter device (Exhalyzer D, Eco Medics AG) in healthy school-aged children to allow accurate interpretation of ventilation distribution outcomes and FRC in children with lung disease.

Simultaneous sulfur hexafluoride and nitrogen multiple-breath washout (MBW) to examine inherent differences in MBW outcomes

Multiple-breath washout (MBW) can be performed with different gases (sulfur hexafluoride (SF_6­) and nitrogen (N₂)) and different devices, all of which give discrepant results. This study aimed to confirm previously reported differences and explore factors influencing discrepant results; equipment factors or the physical properties of gases used.

Inherent differences in simultaneous SF₆ and N₂ washout on the mass spectrometer show why results are never comparablehttp://bit.ly/34k52Oo

Preschool Multiple-Breath Washout Testing. An Official American Thoracic Society Technical Statement

BACKGROUND

Obstructive airway disease is nonuniformly distributed throughout the bronchial tree, although the extent to which this occurs can vary among conditions. The multiple-breath washout (MBW) test offers important insights into pediatric lung disease, not available through spirometry or resistance measurements. The European Respiratory Society/American Thoracic Society inert gas washout consensus statement led to the emergence of validated commercial equipment for the age group 6 years and above; specific recommendations for preschool children were beyond the scope of the document. Subsequently, the focus has shifted to MBW applications within preschool subjects (aged 2-6 yr), where a "window of opportunity" exists for early diagnosis of obstructive lung disease and intervention.

METHODS

This preschool-specific technical standards document was developed by an international group of experts, with expertise in both custom-built and commercial MBW equipment. A comprehensive review of published evidence was performed.

RESULTS

Recommendations were devised across areas that place specific age-related demands on MBW systems. Citing evidence where available in the literature, recommendations are made regarding procedures that should be used to achieve robust MBW results in the preschool age range. The present work also highlights the important unanswered questions that need to be addressed in future work.

CONCLUSIONS

Consensus recommendations are outlined to direct interested groups of manufacturers, researchers, and clinicians in preschool device design, test performance, and data analysis for the MBW technique.

Lung clearance index for early detection of pulmonary complications after allo-HSCT in children

BACKGROUND

Pulmonary chronic graft-vs-host disease (cGvHD) after hematopoietic stem cell transplantation (HSCT) is characterized by impairment of the small airways. Assessment of lung clearance index (LCI) gained from multiple breath washout (MBW) is more sensitive than spirometry in detection of small airways disease. The aim of this study was to describe the development of LCI during the first year after pediatric HSCT and how LCI relates to other pulmonary function parameters and cGvHD.

METHODS

This prospective, longitudinal study included 28 pediatric HSCT-recipients. Spirometry, Sulfur hexafluoride MBW and diffusion capacity of the lungs were performed before and at 3, 6, 9, and 12 months after HSCT. Respiratory symptoms and signs of cGvHD were recorded at each visit.

RESULTS

Before HSCT, 47.8% had abnormal LCI and 12.5% had abnormal forced expiratory volume in 1 second (FEV₁ )_. Patients with persisting respiratory symptoms 12 months post-HSCT had higher median LCI (factor 5.7, P = 0.0018) and lower FEV₁ z-scores (-1.5, P = 0.033) post-HSCT compared to patients free of respiratory symptoms. Overall, post-HSCT LCI values were 3.49 times higher and FEV₁ was 2.31 z-scores lower in eight patients with cGvHD in any organ system compared with patients without cGvHD (P = 0.0089 and P < 0.0001). LCI values during the first 3 months were not predictive of pulmonary cGvHD.

CONCLUSION

LCI is a sensitive marker for cGvHD and high LCI values were associated with persisting respiratory symptoms after 1 year. Further evaluation of MBW in early detection of HSCT-related pulmonary complications require larger patient cohorts and closer follow-up during the first months after HSCT.

Lung clearance index in subjects with cystic fibrosis in Italy

The Lung Clearance Index (LCI) is an index derived from washout recordings, able to detect early peripheral airway damage in subjects with cystic fibrosis (CF) with a greater sensitivity than spirometry.

LCI is a marker of overall lung ventilation inhomogeneity; in fact, as pulmonary ventilation worsens, the number of tidal breaths and the expiratory volumes required to clear the lungs of a marker gas are increased, as documented by a greater value.

In the field of CF, LCI allows indirect investigation of the small airways (< 2 mm) the site where, from a pathophysiologic point of view, the disease begins due to the defect of the CF transmembrane-conductance regulator (CFTR) protein. Infant pulmonary function changes seem to occur before clinically overt symptoms of lower respiratory illness occur.

When performing the test, it is important to refer to the American Thoracic Society and European Respiratory Society consensus statements and apply a strict standardization.

In Italy the first tests were carried out in 2014 for research purpose and now approximately 10 centers are collecting data and are experiencing a consistency in repeating exams.

Currently in Italian centers children at pre-school age are the main target: in this population it is important to have a sensitive and feasible test, non-invasive, that can be performed at tidal volume without sedation, and requiring minimal cooperation and coordination, and that can be used longitudinally over time. Another target could be the transplanted subjects to detect early signs of lung function decline.

The content of this paper captures the experience and discussions among some of the Italian centers where LCI is currently used for research and/or in clinical practice about the method and the need to have a common approach.

The aim of this paper is not to describe the methodology of MBW, but to inform the pediatric community about the possible application of LCI in CF.

[Lung clearance index in cystic fibrosis]

INTRODUCTION

Small airways' involvement in cystic fibrosis (CF) pulmonary disease is a very early event, which can progress sub-clinically and insidiously since it is poorly reflected by commonly used lung function tests.

STATE OF ART

Sensitive and discriminative tools are available to investigate small airways function. However their complexity and/or invasiveness has confined their use to research purposes and to some specialized research teams. By contrast, the multiple breath washout (MBW) test is more affordable and non-invasive. Lung clearance index (LCI), which is the most used derived parameter, is reproducible and much more sensitive than spirometry in detecting small airways disease. However, MBW is operator dependent.

PERSPECTIVES

The recent commercialization of devices assessing LCI launches MBW as a potential tool in routine clinical care, although its use currently remains mostly dedicated to research purposes. However, important differences in LCI between various equipment settings raise a number of theoretical questions. Specific algorithms should be refined and more transparent. Standardization of MBW is still an ongoing process. Whether other MBW derived indices can prove superior over LCI deserves further study.

CONCLUSIONS

In CF, LCI is now a well-established outcome in research settings to detect early lung function abnormalities and new treatment effects, especially in patients with mild lung disease. In these patients, LCI seems an attractive tool for clinicians too. Yet, further investigation is needed to define clinically significant changes in LCI and to which extent this index can be useful in guiding clinical decisions remains to be studied.

Comparison of lung clearance index determined by washout of N2 and SF6 in infants and preschool children with cystic fibrosis

BACKGROUND

Multiple-breath washout (MBW) has been shown to detect early impairment of lung function in children with cystic fibrosis (CF). Nitrogen (N₂) or sulfur hexafluoride (SF₆) can be used as tracer gas for MBW. Recent data indicated higher lung clearance index (LCI) values measured with N₂-MBW than concurrent SF₆-MBW in older children and adults, however, a comparison in infants and younger children, as well as to other outcome measures of CF lung disease is pending.

METHODS

N₂- and SF₆-MBW were performed consecutively in 31 sedated infants and preschool children with CF (mean age, 2.3 ± 0.8 years) and 20 controls (mean age, 2.3 ± 1.1 years) using the Exhalyzer D system. Children with CF also underwent chest magnetic resonance imaging (MRI).

RESULTS

Mean difference (95% CI) in LCI between N₂- and SF₆-MBW was 1.1 ± 0.4 (0.9 to 1.3) in controls and 2.1 ± 1.9 (1.4 to 2.8) in CF. Agreement between N₂- and SF₆-LCI was poor in children with CF. N₂-LCI and SF₆-LCI correlated with MRI, however N₂-LCI showed a higher concordance with MRI than SF₆-LCI. The absolute difference between N₂- and SF₆-LCI values increased with the severity of CF lung disease as determined by MRI scores.

CONCLUSION

N₂-LCI values were higher than SF₆-LCI values in infants and preschool children with CF and controls. Better concordance of N₂-LCI than SF₆-LCI with chest MRI scores point towards of a higher sensitivity of N₂-LCI to detect early lung disease in children with CF.

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

Measurement of lung clearance index (LCI) by multiple breath washout (MBW) is a sensitive method for monitoring lung disease in patients with cystic fibrosis (CF). To compare nitrogen MBW (N2-MBW) and sulfur hexafluoride MBW (SF6-MBW), we connected these two gas analysis systems in series to obtain truly simultaneous measurements, with no differences other than the gas used. Nonsmoking healthy controls (HC) and subjects with CF were recruited at two institutions. The Exhalyzer-D (for N2-MBW measurement) was connected in series with the Innocor (for SF6-MBW measurement). Subjects washed in SF6 from a Douglas bag with tidal breathing and washed out SF6 and nitrogen with 100% oxygen provided as bias flow. Washout of both gases was continued past the LCI point (1/40th of equilibration concentration) in triplicate. N2-MBW resulted in higher cumulative exhaled volume, functional residual capacity (FRC), and LCI when compared with SF6-derived parameters in HC subjects ( P < 0.0001 for all comparisons). All N2-MBW parameters were also significantly higher than SF6-MBW parameters in subjects with CF ( P < 0.01 for all comparisons). After recalculation with a common FRC, N2-MBW LCI was higher than SF6-MBW LCI in subjects with CF (19.73 vs. 11.39; P < 0.0001) and in HC (8.12 vs. 6.78; P < 0.0001). Adjusting for N2 back diffusion and an offset error in the nitrogen measurement resulted in near complete agreement between the two methodologies. We found significant differences in LCI and FRC measurements using two different gases for MBW. This may have significant implications for the future use and interpretation of LCI data in clinical trials and routine clinical care.

NEW & NOTEWORTHY This study provides important insights into the differences between the two techniques used for measuring lung clearance index (LCI): N2 and SF6 multiple breath washout. Differences between measurements made by these two methods in subjects with cystic fibrosis and healthy controls could be explained by nitrogen back diffusion and N2 offset error. This is important for use and interpretation of LCI data as an outcome measure for clinical trials and in routine clinical care.

Effect of intermittent inspiratory leaks on measurement of lung clearance index using nitrogen and sulfur hexafluoride

Even small air leaks can have a significant impact on LCI measured using N2. This is particularly the case for leaks that occur towards the end of washout. In contrast, leaks generally have a much smaller impact on LCI measured by SF6. http://ow.ly/az7b30lG5Ku.

Feasibility and challenges of using multiple breath washout in COPD

Background

Lung clearance index (LCI), derived from multiple-breath washout (MBW), is a well-established assessment of ventilation inhomogeneity in cystic fibrosis but has not been widely applied in other conditions characterized by heterogeneous airways disease, such as COPD. The aim of this study was to evaluate the sensitivity, repeatability, and practicality of LCI in patients with COPD.

Methods

Fifty-four COPD patients completed MBW using nitrogen as the washout tracer gas (MBW_N2, measured using an Exhalyzer™ device), spirometry, and plethysmography. Twenty patients repeated MBW_N2, MBW_SF6 (using a separate Innocor™ gas analyzer to measure washout of the exogenous trace sulphur hexafluoride), and spirometry at a second visit ≥24 hours later.

Results

Mean (SD) COPD LCI measured by nitrogen washout (LCI_N2) was 12.1 (2.2); mean (SD) LCI Z-score 5.8 (2.0). LCI_N2 increased across Global Initiative for Obstructive Lung Disease stages 1 to 3 and was abnormal (Z-score >1.65) in all COPD patients, including those with forced expiratory volume in 1 second (FEV₁) ≥80% predicted. LCI was repeatable (median intra-test coefficient of variation 4.1%) and reproducible (limits of agreement -1.8 to 1.6) after mean of 16 days. Functional residual capacity (FRC) measurements were significantly greater using nitrogen than SF₆ or plethysmography: mean FRC measured by nitrogen washout (FRC_N2) 139% predicted versus FRC measured by plethysmography 125% predicted, p<0.0001.

Conclusion

LCI is most suitable as a measure of early airways disease in COPD in those with well-preserved FEV₁, with similar repeatability and limitations to that observed in cystic fibrosis. Using the Exhalyzer system to perform MBW_N2, however, appeared to substantially over-read FRC. This discrepancy needs addressing before FRC_N2 measurements made using this device can be reliably deployed.

Comparison of different analysis algorithms to calculate multiple-breath washout outcomes

Lung clearance index (LCI) is the main outcome of the multiple-breath washout (MBW) test. Current recommendations for LCI acquisition are based on low-grade evidence. The aim of this study was to challenge those recommendations using alternative methods for LCI analysis. Nitrogen MBW measurements from school-aged children, 20 healthy controls, 20 with cystic fibrosis (CF) and 17 with primary ciliary dyskinesia (PCD), were analysed using 1) current algorithms (standard), 2) three alternative algorithms to detect with higher precision the end of MBW testing and 3) two alternative algorithms to determine exhaled tracer gas concentrations. LCI values, intra-test repeatability, and ability to discriminate between health and lung disease were compared between these methods. The analysis methods strongly influenced LCI (mean±sd overall differences (%) between standard and alternative analysis methods: -4.9±5.7%; range: -66-19%), but did not improve intra-test variability. Discrimination between health and disease was comparable as areas under the receiver operator curves were not greater than that from standard analysis. This study supports current recommendations for LCI calculation in children. Alternative methods influence LCI estimates and hamper comparability between MBW setups. Alternative algorithms, whenever used, should be carefully reported.

Infant multiple breath washout using a new commercially available device: Ready to replace the previous setup?

INTRODUCTION

Multiple breath washout (MBW) is a sensitive test to measure lung volumes and ventilation inhomogeneity from infancy on. The commonly used setup for infant MBW, based on ultrasonic flowmeter, requires extensive signal processing, which may reduce robustness. A new setup may overcome some previous limitations but formal validation is lacking.

AIM

We assessed the feasibility of infant MBW testing with the new setup and compared functional residual capacity (FRC) values of the old and the new setup in vivo and in vitro.

METHODS

We performed MBW in four healthy infants and four infants with cystic fibrosis, as well as in a Plexiglas lung simulator using realistic lung volumes and breathing patterns, with the new (Exhalyzer D, Spiroware 3.2.0, Ecomedics) and the old setup (Exhalyzer D, WBreath 3.18.0, ndd) in random sequence.

RESULTS

The technical feasibility of MBW with the new device-setup was 100%. Intra-subject variability in FRC was low in both setups, but differences in FRC between the setups were considerable (mean relative difference 39.7%, range 18.9; 65.7, P = 0.008). Corrections of software settings decreased FRC differences (14.0%, -6.4; 42.3, P = 0.08). Results were confirmed in vitro.

CONCLUSION

MBW measurements with the new setup were feasible in infants. However, despite attempts to correct software settings, outcomes between setups were not interchangeable. Further work is needed before widespread application of the new setup can be recommended.

Leaks during multiple-breath washout: characterisation and influence on outcomes

Nitrogen multiple-breath washout (N₂MBW) is increasingly used in patients with cystic fibrosis. The current European Respiratory Society/American Thoracic Society consensus statement for MBW recommends the rejection of measurements with leaks. However, it is unclear whether this is necessary for all types of leaks. Here, our aim was to 1) model and 2) apply air leaks, and 3) to assess their influence on the primary MBW outcomes of lung clearance index and functional residual capacity.

We investigated the influence of air leaks at various locations (pre-, intra- and post-capillary), sizes, durations and stages of the washout. Modelled leaks were applied to existing N₂MBW data from 10 children by modifying breath tables. In addition, leaks were applied to the equipment during N₂MBW measurements performed by one healthy adolescent.

All modelled and applied leaks resulted in statistically significant but heterogeneous effects on lung clearance index and functional residual capacity. In all types of continuous inspiratory leaks exceeding a certain size, the end of the washout was not reached. For practical application, we illustrated six different “red flags”, i.e. signs that enable easy identification of leaks during measurements.

Air leaks during measurement significantly influence N₂MBW outcomes. The influence of leaks on MBW outcomes is dependent on the location, relation to breath cycle, duration, stage of washout and size of the leak. We identified a range of signs to help distinguish leaks from physiological noise.

The influence of leaks on nitrogen MBW outcomes is complex, dynamic and dependent on the size, duration, location and position of leaks during the washout and breathing cyclehttp://ow.ly/PbHV30hB91H

Multiple breath washout testing in adults with pulmonary disease and healthy controls - can fewer measurements eventually be more?

BACKGROUND

Multiple breath washout (MBW) became a valuable research tool assessing ventilation heterogeneity. However, routine clinical application still faces several challenges. Deriving MBW parameters from three technically acceptable measurements according to current recommendations prolongs test times. We therefore aimed to evaluate reporting only duplicate measurements in healthy adults and pulmonary disease.

METHODS

One hundred and fifty-three subjects prospectively underwent conventional lung function testing and closed-circuit SF₆-MBW. Three technically acceptable MBW-measurements were obtained in 103 subjects.

RESULTS

Lung clearance index (LCI) differed significantly among 19 controls (7.4 ± 0.8), 19 patients with sarcoidosis (8.1 ± 1.2), 32 with bronchial asthma (9.2 ± 1.9) and 33 with COPD (10.8 ± 2.2, p < 0.001). Within-test repeatability was high (coefficient of variation between 2.5% in controls and 3.6% in COPD) and remained unchanged when only including the first two measurements. Likewise, LCI remained stable with mean absolute changes ranging from 0.9 ± 0.8% in controls to 1.5 ± 0.9% in COPD (p = 0.1). Mean test time reduction differed significantly between groups reaching 200 s in COPD (p = 0.01).

CONCLUSIONS

Duplicate SF₆-MBW-measurements are sufficient in adult patients with pulmonary disease and healthy controls. LCI values and intra-test repeatability are not affected reducing total test time statistically significant. Our findings have the potential to further facilitate application of MBW in research and clinical routine.

TRIAL REGISTRATION

NCT03176745 , June 2, 2017 retrospectively registered.

Fractional exhaled nitric oxide and multiple breath nitrogen washout in preschool healthy and asthmatic children

INTRODUCTION

Objectively assessing pulmonary disease is challenging in preschool children with asthma. We evaluated the feasibility of measuring fractional exhaled nitrogen oxide (FeNO) and multiple breath nitrogen washout (N₂MBW) in children. We compared their capacities for discriminating between children with asthma and healthy controls.

METHODS

We measured FeNO and N₂MBW-derived indices of lung clearance (LCI_2.5) and conductive and acinar ventilation heterogeneity (S_cond and S_acin) in 65 preschool children; 35 with physician-diagnosed asthma and 30 healthy. FeNO was measured with a portable device (sampling time, 6 s). We employed data quality control guidelines on N₂MBW. Feasibility was evaluated in a maximum of 8 attempts for both methods. Atopic co-morbidity and first-degree disposition were evaluated with the ISAAC-questionnaire.

RESULTS

FeNO and N₂MBW testing were feasible in 45% and 91% of children, respectively. Feasibility was highly age-dependent. In children under 4 years old, FeNO was not feasible, but N₂MBW was 85% feasible. Children with asthma had significantly elevated S_cond values (median; 95% CI) (0.024; 0.020; 0.029) compared to healthy controls (0.019; 0.016; 0.023), but similar FeNO, LCI_2.5 and S_acinvalues.

CONCLUSION

The feasibility of measuring FeNO was highly age-dependent and not applicable in children under age 4. N₂MBW was feasible in the majority of preschool children. S_cond, but not FeNO, could discriminate between children with asthma and healthy controls.

Correcting for tissue nitrogen excretion in multiple breath washout measurements

Nitrogen excreted from body tissues impacts the calculation of multiple breath nitrogen washout (MBWN2) outcomes. The aim of this study was to determine the effect of tissue N2 on MBWN2 outcomes in both healthy subjects and patients with CF and to assess whether it is possible to correct for tissue N2. The contribution of tissue N2 to MBWN2 outcomes was estimated by comparing MBWN2-derived functional residual capacity (FRCN2) to FRC measured by body plethysmography (FRCpleth) and by comparing MBW outcome measures derived from MBWN2 and sulfur hexafluoride MBW (MBWSF6). Compared to plethysmography and MBWSF6, MBWN2 overestimated FRC and lung clearance index (LCI). Application of mathematical tissue N2 corrections reduced FRCN2 values closer to FRCpleth in health and reduced LCIN2 in both health and CF, but did not explain all of the differences observed between N2-dependent and -independent techniques. Use of earlier washout cut-offs could reduce the influence of tissue N2. Applying tissue N2 corrections to LCIN2 measurements did not significantly affect the interpretation of treatment effects reported in a previously published interventional trial. While tissue N2 excretion likely has an impact on MBWN2 outcomes, better understanding of the nature of this phenomenon is required before routine correction can be implemented into current MBWN2 protocols.

In vitro and in vivo functional residual capacity comparisons between multiple-breath nitrogen washout devices

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 (FRC_pleth). 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 FRC_pleth (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.

Multiple-breath washout devices are not yet comparablehttp://ow.ly/bB7b30eAs0c

The effect of inert gas choice on multiple breath washout in healthy infants: differences in lung function outcomes and breathing pattern

The detrimental effects on breathing pattern during multiple breath inert gas washout (MBW) have been described with different inhaled gases [100% oxygen (O₂) and sulfur hexafluoride (SF₆)] but detailed comparisons are lacking. N₂- and SF₆-based tests were performed during spontaneous quiet sleep in 10 healthy infants aged 0.7-1.3 yr using identical hardware. Differences in breathing pattern pre and post 100% O₂ and 4% SF₆ exposure were investigated, and the results obtained were compared [functional residual capacity (FRC) and lung clearance index (LCI)]. During 100% O₂ exposure. mean inspiratory flow ("respiratory drive") decreased transiently by mean (SD) 28 (9)% ( P < 0.001), and end-tidal CO₂ (carbon dioxide) increased by mean (SD) 0.3 (0.4)% units ( P < 0.05) vs. air breathing prephase. During subsequent N₂ washin (i.e., recovery phase), the pattern of change reversed. No significant effect on breathing pattern was observed during SF₆ testing. In vitro testing confirmed that technical artifacts did not explain these changes. Mean (SD) FRC and LCI in vivo were significantly higher with N₂ vs. SF₆ washout: 216 (33) vs. 186 (22) ml ( P < 0.001) and 8.25 (0.85) vs. 7.55 (0.57) turnovers ( P = 0.021). Based on these results, SF₆ based MBW is the preferred methodology for tests in this age range. NEW & NOTEWORTHY Inert gas choice for multiple breath inert gas washout (MBW) in infants has important consequences on both breathing pattern during test performance and the functional residual capacity and lung clearance index values obtained. Data suggest the detrimental effect of breathing pattern of 100% O₂ and movement of O₂ across the alveolar capillary membrane, with direct effects on MBW outcomes. SF₆ MBW during infancy avoids this and can be further optimized by addressing the sources of technical artifact identified in this work.

Small airways disease: time for a revisit?

It is increasingly acknowledged that delays in the diagnosis of chronic inflammatory lung conditions have hampered our understanding of pathogenesis and thus our ability to design efficacious therapies. This is particularly true for COPD, where most patients are diagnosed with moderate-to-severe airflow obstruction and little is known about the inflammatory processes present in early disease. There is great interest in developing screening tests that can identify those most at risk of developing COPD before airflow obstruction has developed for the purpose of research and clinical care. Landmark pathology studies have suggested that damage to the small airways precedes the development of airflow obstruction and emphysema and, thus, presents an opportunity to identify those at risk of COPD. However, despite a number of physiological tests being available to assess small airways function, none have been adopted into routine care in COPD. The reasons that tests of small airways have not been utilized widely include variability in test results and a lack of validated reference ranges from which to compare results for some methodologies. Furthermore, population studies have not consistently demonstrated their ability to diagnose disease. However, the landscape may be changing. As the equipment that delivers tests of small airways become more widely available, reference ranges are emerging and newer methodologies specifically seek to address variability and difficulty in test performance. Moreover, there is evidence that while tests of small airways may not be helpful across the full range of established disease severity, there may be specific groups (particularly those with early disease) where they might be informative. In this review, commonly utilized tests of small airways are critically appraised to highlight why these tests may be important, how they can be used and what knowledge gaps remain for their use in COPD.

Developments in multiple breath washout testing in children with cystic fibrosis

BACKGROUND

Lung clearance index (LCI) is becoming recognized as an important addition in the monitoring of pediatric cystic fibrosis (CF). The non-invasive technique is easy to perform in all ages, reproducible and increasingly being used in clinical trials. There is interest in utilizing it within the clinic setting but its current use is mostly as a research tool. The procedure is highly dependent on skilled operators and a relaxed testing environment is key to obtaining good quality measurements.

CONCLUSIONS

Standardization of LCI is part of an ongoing collaborative, multicenter process. This review describes the background to LCI, discusses technical issues and limitations and provides examples of its utility in clinical and research contexts.

Agreement between multiple-breath nitrogen washout systems in children and adults

BACKGROUND

Comparability of multiple breath washout (MBW) systems has been little explored. We assessed agreement in lung clearance index (LCI) from two similar, commercial nitrogen MBW setups in patients with Cystic Fibrosis (CF) and controls.

METHODS

The EasyOne Pro (NDD) and Exhalyzer D (EM) were randomly applied in 85 adults (34 with CF) and 97 children (47 with CF and normal forced expiratory volume in one second). We assessed differences between setups in LCI, lung volumes and breathing pattern and diagnostic performance for detecting abnormal lung function.

RESULTS

Compared to NDD, EM measured higher LCI, functional residual capacity and cumulative expired volume while respiratory rate was lower. Mean difference (limits of agreement) in LCI was 1.30 (-2.34 to 4.94). In CF, prevalence of abnormal LCI was greater in children and similar in adults using EM compared to NDD.

CONCLUSIONS

Agreement of MBW outcomes between setups is poor and explained by nitrogen measurement techniques and breathing pattern.