Variability of monthly nitrogen multiple-breath washout during one year in children with cystic fibrosis

An update on multiple breath washout in children with cystic fibrosis

INTRODUCTION

Cystic fibrosis (CF) is an autosomal recessive disorder caused by mutations in the CF transmembrane regulator (CFTR) gene, leading to progressive lung disease and systemic complications. Lung disease remains the primary cause of morbidity and mortality, making early detection of lung function decline crucial. The Lung Clearance Index (LCI), derived from the multiple breath washout (MBW) test, has emerged as a sensitive measure for identifying early airway disease.

AREAS COVERED

This review examines the technical aspects and clinical relevance of LCI, its advantages over traditional lung function tests, and its application in CF clinical trials. A focused literature review highlights LCI's utility in evaluating treatment efficacy and its potential integration into routine CF care.

EXPERT OPINION

LCI is more sensitive than spirometry for detecting early lung function decline and is predominantly used in pediatric settings. Its use is expanding in adult CF populations as advances in treatment allow adults to maintain stable lung function. In clinical trials, LCI is widely recognized as an outcome measure. While implemented into clinical care in many centers in Europe, this is not yet the case in North America. Faster testing protocols and point-of-care interpretation tools will support LCI's integration into routine CF monitoring.

Correlation Between Lung Clearance Index (LCI) and Forced Expiratory Volume (FEV1) in Children with Cystic Fibrosis (CF): A Cross-sectional Study

Background: The Lung Clearance Index (LCI) serves as a non-uniform ventilation index utilized for monitoring pulmonary function in patients with cystic fibrosis (CF). Lung Clearance Index exhibits higher sensitivity compared to forced expiratory volume in 1 second (FEV1) for early detection of lung disease and does not necessitate active patient cooperation, as required for FEV1 measured through spirometry. Presently, FEV1 is the standard parameter employed for monitoring lung function in CF patients. Objectives: The objective of this study was to assess the correlation between LCI and FEV1 in patients with cystic fibrosis. Methods: This cross-sectional study enrolled children aged 6 to 18 years with confirmed CF diagnosis, who were referred to the CF clinic at Children's Medical Center Hospital (Tehran, Iran). Participants completed consent forms and subsequently underwent pulmonary function tests. Lung Clearance Index was calculated using the exhaling-D device via the Multiple Breath Washout (MBW) method, followed by FEV1 assessment through spirometry. Results: The study included 52 patients with an average age of 12 years, among whom 52% were males. The mean ± standard deviation of FEV1 and LCI were 80.2% ± 25.3 and 8.9 ± 2.8, respectively. A significant inverse relationship was observed between these two parameters in the study (r = -0.49, P = 0.001). Conclusions: These findings further underscore the potential utility of LCI, which offers ease of administration and demonstrates high reliability and accuracy compared to FEV1 for monitoring pulmonary function in CF patients.

Turning lung clearance index on its head. Reference data for SF6 multiple-breath washout derived ventilation distribution efficiency

Cystic fibrosis (CF) lung disease is characterized by increased ventilation inhomogeneity (VI), as measured by multiple-breath washout (MBW). Lung clearance index (LCI) is the most reported VI outcome. This study aimed to evaluate historically published reference equations for sulfur hexafluoride (SF6) MBW outcomes, to data collected using updated commercial SF6MBW equipment, and to produce device-specific equations if necessary. SF6MBW was performed in 327 healthy children aged 0.1-18.4 yr [151 (46%) girls], 191 (58.4%) <3 yr. z-Scores were calculated from published reference equations (FRC and LCI) and multivariate linear regression was performed to produce device-specific reference equations. Due to increasing residual standard deviations with increasing LCI values, investigation of methods for improvement were investigated, based on the relationship between VI and dead space ventilation (VD/VT; dead space volume/tidal volume) in a cohort of 59 healthy children, 26 children with CF (n = 138 test occasions), and 49 adults with lung disease. Historical SF6MBW reference equations were unsuitable for EXHALYZER D data. In contrast to LCI and log10(LCI), 1/LCI (ventilation distribution efficiency; VDE) was linearly related to VD/VT, with z-scores linearly related to its absolute values. Reference equations were reported for VDE and log10(FRC). Significant predictors for VDE and log10(FRC), respectively, were log10(age) and sex, and log10(height), sex, and posture. VDE is potentially a better index of VI than LCI, particularly in more advanced CF lung disease and also for longitudinal monitoring. Further confirmatory clinical studies, particularly longitudinal imaging studies of structural or ventilatory changes, are warranted.NEW & NOTEWORTHY Lung clearance index (LCI) is the most used outcome from the multiple-breath washout test. As known for decades, the LCI is not linearly related to dead space ventilation, giving difficulties interpreting changes over time and in clinical trials. We present a new and improved outcome based on LCI, the ventilation distribution efficiency (VDE), which solves this problem by being linearly related to dead space ventilation. A pediatric age range reference equation for VDE is presented.

Variability of clinically measured lung clearance index in children with cystic fibrosis

RATIONALE

The lung clearance index (LCI) is increasingly being used in the clinical surveillance of patients with cystic fibrosis (CF). However, there are limited data on long-term variability and physiologically relevant changes in LCI during routine clinical surveillance.

OBJECTIVES

To evaluate the long-term variability of LCI and propose a threshold for a physiologically relevant change.

METHODS

In children aged 4-18 years with CF, LCI was measured every 3 months as part of routine clinical surveillance during 2011-2020 in two centers. The variability of LCI during periods of clinical stability was assessed using mixed-effects models and was used to identify thresholds for physiologically relevant changes.

RESULTS

Repeated LCI measurements of acceptable quality (N = 858) were available in 100 patients with CF; for 74 patients, 399 visits at clinical stability were available. The variability of repeated LCI measurements over time expressed as the coefficient of variation (CV%) was 7.4%. The upper limit of normal (ULN) for relative changes in LCI between visits was 19%.

CONCLUSION

We report the variability of LCI in children and adolescents with CF during routine clinical surveillance. According to our data, a change in LCI beyond 19% may be considered physiologically relevant. These findings will help guide clinical decisions according to LCI changes.

Multiple breath washout: measuring early manifestations of lung pathology

The multiple breath washout (MBW) test measures the efficiency of gas mixing in the lungs and has gained significant interest over the past 20 years. MBW outcomes detect early lung function impairment and peripheral airway pathology, through its main outcome measure lung clearance index (LCI). LCI measures the number of lung turnovers required to washout an inert tracer gas. MBW is performed during normal (tidal) breathing, making it particularly suitable for young children or those who have trouble performing forced manoeuvres. Additionally, research in chronic respiratory disease populations has shown that MBW can detect acute clinically relevant changes before conventional lung function tests, such as spirometry, thus enabling early intervention. The development of technical standards for MBW and commercial devices have allowed MBW to be implemented in clinical research and potentially routine clinical practice. Although studies have summarised clinimetric properties of MBW indices, additional research is required to establish the clinical utility of MBW and, if possible, shorten testing time. Sensitive, feasible measures of early lung function decline will play an important role in early intervention for people living with respiratory diseases.

Educational aim

To describe the multiple breath washout test, its applications to lung pathology and respiratory disease, as well as directions for future research.

A Short extension to multiple breath washout provides additional signal of distal airway disease in people with CF: A pilot study

BACKGROUND

Adding a slow vital capacity (SVC) to multiple breath washout (MBW) allows quantification of otherwise overlooked signal from under/un-ventilated lung units (UVLU) and may provide a more comprehensive assessment of airway disease than conventional lung clearance index (LCI_2.5).

METHODS

We conducted a pilot study on people undergoing MBW tests: 10 healthy controls (HC) and 43 cystic fibrosis (CF) subjects performed an SVC after the standard end of test. We term the new outcome LCI with Short extension (LCI_ShX). We assessed (i) CF/ HC differences, (ii) variability (iii) effect of pulmonary exacerbation (PEx)/treatment and (iv) relationship with CF computed tomography (CFCT) scores.

RESULTS

HC/ CF group differences were larger with LCI_ShX than LCI_2.5 (P<0.001). Within the CF group UVLU was highly variable and when abnormal it did not correlate with corresponding LCI_2.5. Signal showed little variability during clinical stability (n = 11 CF; 2 visits; median inter-test variability 2.6% LCI_ShX, 2.5% LCI_2.5). PEx signal was significantly greater for LCI_ShX both for onset and resolution. Both MBW parameters correlated significantly with total lung CT scores and hyperinflation but only LCI_ShX correlated with mucus plugging.

CONCLUSIONS

UVLU captured within the LCI_ShX varies between individuals; the lack of relationship with LCI_2.5 demonstrates that new, additional information is being captured. LCI_ShX repeatability during clinical stability combined with its larger signal around episodes of PEx may lend it superior sensitivity as an outcome measure. Further studies will build on this pilot data to fully establish its utility in monitoring disease status.

Longitudinal course of clinical lung clearance index in children with cystic fibrosis

BACKGROUND

Although the lung clearance index (LCI) is a sensitive marker of small airway disease in individuals with cystic fibrosis (CF), less is known about longitudinal changes in LCI during routine clinical surveillance. Here, our objectives were to describe the longitudinal course of LCI in children with CF during routine clinical surveillance and assess influencing factors.

METHODS

Children with CF aged 3-18 years performed LCI measurements every 3 months as part of routine clinical care between 2011 and 2018. We recorded clinical data at every visit. We used a multilevel mixed effect model to determine changes in LCI over time and identify clinical factors that influence LCI course.

RESULTS

We collected LCI measurements from 1204 visits (3603 trials) in 78 participants, of which 907 visits had acceptable LCI data. The average unadjusted increase in LCI for the entire population was 0.29 (95% CI 0.20-0.38) LCI units·year^-1. The increase in LCI was more pronounced in adolescence (0.41 (95% CI 0.27-0.54) LCI units·year^-1). Colonisation with either Pseudomonas aeruginosa or Aspergillus fumigatus, pulmonary exacerbations, CF-related diabetes and bronchopulmonary aspergillosis were associated with a higher increase in LCI over time. Adjusting for clinical risk factors reduced the increase in LCI over time to 0.24 (95% CI 0.16-0.33) LCI units·year^-1.

CONCLUSIONS

LCI measured during routine clinical surveillance is associated with underlying disease progression in children with CF. An increased change in LCI over time should prompt further diagnostic intervention.

A short-term evaluation of a prototype disposable Oscillating Positive Expiratory Pressure (OPEP) device in a cohort of children with cystic fibrosis

Background

Oscillating Positive Expiratory Pressure (OPEP) devices are important adjuncts to airway clearance therapy in patients with cystic fibrosis (CF). Current devices are typically reusable and require daily, or often more frequent, cleaning to prevent risk of infection by acting as reservoirs of potentially pathogenic organisms. In response, a daily disposable OPEP device, the UL-OPEP, was developed to mitigate the risk of contamination and eliminate the burdensome need for cleaning devices.

Methods

A convenience sample of 36 participants, all current OPEP device users, was recruited from a paediatric CF service. For one month, participants replaced their current OPEP device with a novel daily disposable device. Assessment included pre- and post-intervention lung function by spirometry, as well as Lung Clearance Index. Quality of life was assessed using the Cystic Fibrosis Questionnaire – Revised, while user experience was evaluated with a post-study survey.

Results

31 participants completed the study: 18 males; median age 10 years, range 4–16 years. Lung function (mean difference ± SD, %FEV1 = 1.69 ± 11.93; %FVC = 0.58 ± 10.04; FEV1: FVC = 0.01 ± 0.09), LCI (mean difference ± SD, 0.08 ± 1.13), six-minute walk test, and CFQ-R were unchanged post-intervention. Participant-reported experiences of the device were predominantly positive.

Conclusions

The disposable OPEP device maintained patients’ lung function during short term use (≤ 1 month), and was the subject of positive feedback regarding functionality while reducing the risk of airway contamination associated with ineffective cleaning.

Registration

The study was approved as a Clinical Investigation by the Irish Health Products Regulatory Authority (CRN-2209025-CI0085).

Supplementary Information

The online version contains supplementary material available at 10.1186/s12890-021-01525-3.

Lung Clearance Index to Track Acute Respiratory Events in School-Age Children with Cystic Fibrosis

Rationale: The lung clearance index (LCI) is responsive to acute respiratory events in preschool children with cystic fibrosis (CF), but its utility to identify and manage these events in school-age children with CF is not well defined.Objectives: To describe changes in LCI with acute respiratory events in school-age children with CF.Methods: In a multisite prospective observational study, the LCI and FEV₁ were measured quarterly and during acute respiratory events. Linear regression was used to compare relative changes in LCI and FEV₁% predicted at acute respiratory events. Logistic regression was used to compare the odds of a significant worsening in LCI and FEV₁% predicted at acute respiratory events. Generalized estimating equation models were used to account for repeated events in the same subject.Measurements and Main Results: A total of 98 children with CF were followed for 2 years. There were 265 acute respiratory events. Relative to a stable baseline measure, LCI (+8.9%; 95% confidence interval, 6.5 to 11.3) and FEV₁% predicted (-6.6%; 95% confidence interval, -8.3 to -5.0) worsened with acute respiratory events. A greater proportion of events had a worsening in LCI compared with a decline in FEV₁% predicted (41.7% vs. 30.0%; P = 0.012); 53.9% of events were associated with worsening in LCI or FEV₁. Neither LCI nor FEV₁ recovered to baseline values at the next follow-up visit.Conclusions: In school-age children with CF, the LCI is a sensitive measure to assess lung function worsening with acute respiratory events and incomplete recovery at follow-up. In combination, the LCI and FEV₁ capture a higher proportion of events with functional impairment.

Time to get serious about the detection and monitoring of early lung disease in cystic fibrosis

Structural and functional defects within the lungs of children with cystic fibrosis (CF) are detectable soon after birth and progress throughout preschool years often without overt clinical signs or symptoms. By school age, most children have structural changes such as bronchiectasis or gas trapping/hypoperfusion and lung function abnormalities that persist into later life. Despite improved survival, gains in forced expiratory volume in one second (FEV₁) achieved across successive birth cohorts during childhood have plateaued, and rates of FEV₁ decline in adolescence and adulthood have not slowed. This suggests that interventions aimed at preventing lung disease should be targeted to mild disease and commence in early life. Spirometry-based classifications of 'normal' (FEV₁≥90% predicted) and 'mild lung disease' (FEV₁ 70%-89% predicted) are inappropriate, given the failure of spirometry to detect significant structural or functional abnormalities shown by more sensitive imaging and lung function techniques. The state and readiness of two imaging (CT and MRI) and two functional (multiple breath washout and oscillometry) tools for the detection and monitoring of early lung disease in children and adults with CF are discussed in this article.Prospective research programmes and technological advances in these techniques mean that well-designed interventional trials in early lung disease, particularly in young children and infants, are possible. Age appropriate, randomised controlled trials are critical to determine the safety, efficacy and best use of new therapies in young children. Regulatory bodies continue to approve medications in young children based on safety data alone and extrapolation of efficacy results from older age groups. Harnessing the complementary information from structural and functional tools, with measures of inflammation and infection, will significantly advance our understanding of early CF lung disease pathophysiology and responses to therapy. Defining clinical utility for these novel techniques will require effective collaboration across multiple disciplines to address important remaining research questions. Future impact on existing management burden for patients with CF and their family must be considered, assessed and minimised.To address the possible role of these techniques in early lung disease, a meeting of international leaders and experts in the field was convened in August 2019 at the Australiasian Cystic Fibrosis Conference. The meeting entitiled 'Shaping imaging and functional testing for early disease detection of lung disease in Cystic Fibrosis', was attended by representatives across the range of disciplines involved in modern CF care. This document summarises the proceedings, key priorities and important research questions highlighted.

The assessment of short- and long-term changes in lung function in cystic fibrosis using 129Xe MRI

INTRODUCTION

Xenon-129 (129Xe) ventilation magnetic resonance imaging (MRI) is sensitive to detect early cystic fibrosis (CF) lung disease and response to treatment. 129Xe-MRI could play a significant role in clinical trials and patient management. Here we present data on the repeatability of imaging measurements and their sensitivity to longitudinal change.

METHODS

29 children and adults with CF and a range of disease severity were assessed twice, a median (interquartile range (IQR)) of 16.0 (14.4-19.5) months apart. Patients underwent 129Xe-MRI, lung clearance index (LCI), body plethysmography and spirometry at both visits. 11 patients repeated 129Xe-MRI in the same session to assess the within-visit repeatability. The ventilation defect percentage (VDP) was the primary metric calculated from 129Xe-MRI.

RESULTS

At baseline, mean±sd age was 23.0±11.1 years and forced expiratory volume in 1 s (FEV1) z-score was -2.2±2.0. Median (IQR) VDP was 9.5 (3.4-31.6)% and LCI was 9.0 (7.7-13.7). Within- and inter-visit repeatability of VDP was high. At 16 months there was no single trend of 129Xe-MRI disease progression. Visible 129Xe-MRI ventilation changes were common, which reflected changes in VDP. Based on the within-visit repeatability, a significant short-term change in VDP is >±1.6%. For longer-term follow-up, changes in VDP of up to ±7.7% can be expected, or ±4.1% for patients with normal FEV1. No patient had a significant change in FEV1; however, 59% had change in VDP >±1.6%. In patients with normal FEV1, there were significant changes in ventilation and in VDP.

CONCLUSIONS

129Xe-MRI is a highly effective method for assessing longitudinal lung disease in patients with CF. VDP has great potential as a sensitive clinical outcome measure of lung function and end-point for clinical trials.

Multiple breath washout in bronchiectasis clinical trials: is it feasible?

Background

Evaluation of multiple breath washout (MBW) set-up including staff training, certification and central "over-reading" for data quality control is essential to determine the feasibility of MBW in future bronchiectasis studies.

Aims

To assess the outcomes of a MBW training, certification and central over-reading programme.

Methods

MBW training and certification was conducted in European sites collecting lung clearance index (LCI) data in the BronchUK Clinimetrics and/or i-BEST-1 studies. The blended training programme included the use of an eLearning tool and a 1-day face-to-face session. Sites submitted MBW data to trained central over-readers who determined validity and quality.

Results

Thirteen training days were delivered to 56 participants from 22 sites. Of 22 sites, 18 (82%) were MBW naïve. Participant knowledge and confidence increased significantly (p<0.001). By the end of the study recruitment, 15 of 22 sites (68%) had completed certification with a mean (range) time since training of 6.2 (3-14) months. In the BronchUK Clinimetrics study, 468 of 589 (79%) tests met the quality criteria following central over-reading, compared with 137 of 236 (58%) tests in the i-BEST-1 study.

Conclusions

LCI is feasible in a bronchiectasis multicentre clinical trial setting; however, consideration of site experience in terms of training as well as assessment of skill drift and the need for re-training may be important to reduce time to certification and optimise data quality. Longer times to certification, a higher percentage of naïve sites and patients with worse lung function may have contributed to the lower success rate in the i-BEST-1 study.

Prospective longitudinal association between repeated multiple breath washout measurements and computed tomography scores in children with cystic fibrosis

BACKGROUND

Progression of structural lung disease (SLD) is a major risk factor for morbidity in patients with cystic fibrosis (CF). We studied changes in SLD and correlations with spirometry and nitrogen multiple breath washout (N₂MBW) outcomes to explore associations in contemporary evolution between structural and functional abnormalities in CF lung disease.

METHODS

Spirometry-controlled chest-CTs using PRAGMA-CF for scoring extent of SLD, spirometry, and N₂MBW were performed at two-year intervals in school-age children with CF.

RESULTS

Fifty-seven children aged 6-18 years were included. No significant progression in mean PRAGMA-CF scores was observed. Half of the children showed improvement in the proportion of bronchiectasis (%Bx). Lung Clearance Index (LCI) and the second moment ratio (M2) increased significantly and baseline values correlated significantly with SLD at follow-up (p ≤ 0.0002). The correlation between the change in M2 (∆M2) and the change in total SLD was R = 0.27 (p = 0.048). We found high negative predictive values (100%) for ∆M2<10% to exclude progression in SLD. For stable or improving values of LCI and M2, the predicted probability for progression in SLD was 16% and 14%, respectively (upper 95% confidence limit: 33%). Evolution in N₂MBW and CT outcomes was discordant in half of the children.

CONCLUSIONS

We found no progression in SLD over 2 years in school-age children with CF, in contrast to both LCI and M2, which along with discordant outcomes in half of the children underlines that N₂MBW and CT assess different aspects of CF lung disease. However, stable outcomes from N₂MBW were associated with stable structural lung disease.

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.

An 8 week open-label interventional multicenter study to explore the lung clearance index as endpoint for clinical trials in cystic fibrosis patients ≥8 years of age, chronically infected with Pseudomonas aeruginosa

BACKGROUND

Forced expiratory volume in 1 second (FEV₁) is the only parameter currently recognized as a surrogate endpoint in cystic fibrosis (CF) trials. However, FEV₁ is relatively insensitive to changes in the small airways of patients with milder lung disease. This pilot study aimed to explore the lung clearance index (LCI) as a marker for use in efficacy trials with inhaled antibiotics in CF.

METHODS

This open-label, single-arm study enrolled CF patients with Pseudomonas aeruginosa infection, who were treated with tobramycin (28-day on/off regime). FEV₁, LCI and bacterial load in sputum (CFU) were assessed at baseline, after 1, 4 and 8 weeks of treatment.

RESULTS

All patients (n = 17) showed elevated LCI of > 11 despite 3 patients having normal FEV₁ (> 90% predicted) at baseline. Overall, LCI improved in 8 (47%) patients and FEV₁ in 9 (53%) patients. At week 4, LCI improved by 0.88, FEV₁ increased by 0.52%, and P. aeruginosa reduced by 30,481.3 CFU/mL. These changes were however statistically non-significant. Six adverse events occurred in 5/17 (29.4%) patients, most of which were mild-to-moderate in severity.

CONCLUSIONS

Due to the low evaluable sample size, no specific trend was observed related to the changes between LCI, FEV₁ and CFU. Based on the individual data from this study and from recently published literature, LCI has been shown to be a more sensitive parameter than FEV₁ for lung function. LCI can be hypothesized to be an appropriate endpoint for efficacy trials in CF patients if the heterogeneity in lung function is limited by enrolling younger patients or patients with more milder lung disease and thus, limiting the ventilation inhomogeneities.

TRIAL REGISTRATION

The study is registered with ClinicalTrials.gov, identifier: NCT02248922.

Exercise capacity and ventilation inhomogeneity in cystic fibrosis: A cross-sectional study

BACKGROUND

Lung clearance index (LCI_2.5 ) is a marker of overall lung ventilation inhomogeneity and has proven to be able to detect early peripheral damage in subjects with cystic fibrosis (CF), with greater sensitivity than conventional spirometry. Combining its sensitivity with the output of an incremental exercise testing, we hypothesized that any sign of ventilation inhomogeneity in subjects without severe airflow obstruction and with a normal exercise tolerance could be relevant for the CF team, tracking early lung disease and potential exercise limiting factors.

METHODS

Patients with CF in clinical stable conditions were recruited between 2015 and 2017. Available spirometry, nitrogen multiple-breath washout test and symptoms-limited exercise testing performed as parts of patients' annual routine evaluation were considered for this cross-sectional study. To describe the relationship between exercise intensity and ventilation inhomogeneity, a linear regression analysis was performed using backward elimination based on Akaike information criteria.

RESULTS

Seventy-seven patients (38 females) were included. S_acin and LCI_2.5 were significantly higher in patients with an overall reduced exercise tolerance. Peak work developed during exercise was associated with body mass index (b = 5.25; 95% confidence interval [CI] = 1.53-8.98), forced expiratory volume in 1 second (FEV₁ ; b = 3.71; 95% CI = 1.96-5.46), Pseudomonas aeruginosa chronic infection (b = -8.84; 95% CI = -15.84 to -1.84) but not with LCI_2.5 .

CONCLUSION

Exercise capacity and airflow obstruction are associated in this Italian CF cohort. Considering the greater discriminatory power of LCI_2.5 over FEV₁ and peak work, the Godfrey protocol without gas analysis cannot provide detailed information about lung function or efficiency. However, this incremental protocol without gas exchange measures can still provide the CF team with information about exercise tolerance and disability.

Cystic fibrosis year in review 2018, part 1

Cystic fibrosis research and case reports were robust in the year 2018. This report summarizes research and cases related to Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) modulator therapies, inflammation and infection, epidemiology and the physiologic, and imaging assessment of disease.

Applications of lung clearance index in monitoring children with cystic fibrosis

A sensitive, reproducible and feasible measure of lung function for monitoring the respiratory health is a prerequisite for the optimization of management of the patients with cystic fibrosis (CF). Spirometry has been considered the method of choice, although it is applicable only in children older than 6 years of age, as good cooperation is necessary for its proper performance. However, over the last 15 years, scientific interest in gas dilution techniques and particularly in multiple breath wash out (MBW) method has been revived. The most commonly reported index of MBW is lung clearance index (LCI). The aim of this review is to present the most recent developments in the application of LCI as a monitoring index of respiratory status of CF patients. LCI is a sensitive and reproducible marker of ventilation inhomogeneity. It is more sensitive than spirometry and, unlike spirometry; it can be performed across the whole pediatric age range. Since it is dependent on body size, until at least the age of 6 years, the relative and not the absolute changes are more appropriate for providing clinically meaningful conclusion on ventilation inhomogeneity. Until now, MBW has been mainly used as a research tool. Based on the currently available data LCI cannot safely predict high-resolution computed tomography findings in children with CF, especially in infants. It can be used as an end-point measure for the assessment of beneficial effect of interventions. However, its utility as an outcome measure for the efficacy of therapeutic interventions seems to be dependent on the pathophysiologic mechanisms that underlie each intervention. It seems that more studies, especially longitudinal ones, are required in order to fully clarify the clinical usefulness of LCI, not only in the research setting, but also in every day practice of CF clinic.

[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.

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.