Ventilatory response to nitrogen multiple-breath washout in infants

Hyperoxic ventilatory response in infants is related to nocturnal hypoxaemia

Background

The carotid bodies primarily serve as oxaemia sensors that affect tidal breathing. Their function has not yet been studied in infants with nocturnal hypoxaemia. This cross-sectional study aimed to characterise the hyperoxic ventilatory response (HVR) in infants and its relationship to nocturnal hypoxaemia.

Methods

The HVR was analysed in term infants aged <24 months with childhood interstitial lung disease (chILD), those with severe recurrent wheezing (wheeze), and nonrespiratory controls. The HVR timing was characterised using hyperoxia response time (HRT1), and HVR magnitude was characterised by the relative change in minute volume between normoxia and 30-s hyperoxia (VE_dH30). Time spent with an arterial haemoglobin oxygen saturation (SpO2) <90% during overnight monitoring (t90) was estimated.

Results

HVR data were available for 23 infants with chILD, 24 wheeze and 14 control infants. A significant decrease in minute volume under 30 s of hyperoxia was observed in all patients. HRT1 was shorter in chILD (5.6±1.2 s) and wheeze (5.9±1.5 s) groups than in the controls (12.6±5.5 s) (ANOVA p<0.001). VE_dH30 was increased in the chILD group (24.3±8.0%) compared with that in the controls (14.7±9.2%) (p=0.003). t90 was abnormal in the wheeze (8.0±5.0%) and chILD (32.7±25.8%) groups and higher in the chILD group than in the controls (p<0.001). HRT1 negatively correlated with t90 in all groups.

Conclusion

Significant differences in HVR timing and magnitude were noted in the chILD, wheeze and control groups. A relationship between nocturnal hypoxaemia and HRT1 was proposed. HVR characterisation may help identify patients with abnormal nocturnal SpO2.

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 .

A multimodal approach to detect and monitor early lung disease in cystic fibrosis

Introduction: In the early stages, lung involvement in cystic fibrosis (CF) can be silent, with disease progression occurring in the absence of clinical symptoms. Irreversible airway damage is present in the early stages of disease; however, reliable biomarkers of early damage due to inflammation and infection that are universally applicable in day-to-day patient management have yet to be identified.Areas covered: At present, the main methods of detecting and monitoring early lung disease in CF are the lung clearance index (LCI), computed tomography (CT), and magnetic resonance imaging (MRI). LCI can be used to detect patients who may require more intense monitoring, identify exacerbations, and monitor responses to new interventions. High-resolution CT detects structural alterations in the lungs of CF patients with the best resolution of current imaging techniques. MRI is a radiation-free imaging alternative that provides both morphological and functional information. The role of MRI for short-term follow-up and pulmonary exacerbations is currently being investigated.Expert opinion: The roles of LCI and MRI are expected to expand considerably over the next few years. Meanwhile, closer collaboration between pulmonology and radiology specialties is an important goal toward improving care and optimizing outcomes in young patients with CF.

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 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.

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.

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.

Novel methodology to perform sulfur hexafluoride (SF6)-based multiple-breath wash-in and washout in infants using current commercially available equipment

Multiple-breath inert gas washout (MBW) is ideally suited for early detection and monitoring of serious lung disease, such as cystic fibrosis, in infants and young children. Validated commercial options for the MBW technique are limited, and suitability of nitrogen (N2)-based MBW is of concern given the detrimental effect of exposure to pure O2 on infant breathing pattern. We propose novel methodology using commercially available N2 MBW equipment to facilitate 4% sulfur hexafluoride (SF6) multiple-breath inert gas wash-in and washout suitable for the infant age range. CO2, O2, and sidestream molar mass sensor signals were used to accurately calculate SF6 concentrations. An improved dynamic method for synchronization of gas and respiratory flow was developed to take into account variations in sidestream sample flow during MBW measurement. In vitro validation of triplicate functional residual capacity (FRC) assessments was undertaken under dry ambient conditions using lung models ranging from 90 to 267 ml, with tidal volumes of 28-79 ml, and respiratory rates 20–60 per minute. The relative mean (SD, 95% confidence interval) error of triplicate FRC determinations by washout was −0.26 (1.84, −3.86 to +3.35)% and by wash-in was 0.57 (2.66, −4.66 to +5.79)%. The standard deviations [mean (SD)] of percentage error among FRC triplicates were 1.40 (1.14) and 1.38 (1.32) for washout and wash-in, respectively. The novel methodology presented achieved FRC accuracy as outlined by current MBW consensus recommendations (95% of measurements within 5% accuracy). Further clinical evaluation is required, but this new technique, using existing commercially available equipment, has exciting potential for research and clinical use.

Multiple-Breath Washout as a Lung Function Test in Cystic Fibrosis. A Cystic Fibrosis Foundation Workshop Report

The lung clearance index (LCI) is a lung function parameter derived from the multiple-breath washout (MBW) test. Although first developed 60 years ago, the technique was not widely used for many years. Recent technological advances in equipment design have produced gains in popularity for this test among cystic fibrosis (CF) researchers and clinicians, particularly for testing preschool-aged children. LCI has been shown to be feasible and sensitive to early CF lung disease in patients of all ages from infancy to adulthood. A workshop was convened in January 2014 by the North American Cystic Fibrosis Foundation to determine the readiness of the LCI for use in multicenter clinical trials as well as clinical care. The workshop concluded that the MBW text is a valuable potential outcome measure for CF clinical trials in preschool-aged patients and in older patients with FEV1 in the normal range. However, gaps in knowledge about the choice of device, gas, and standardization across systems are key issues precluding its use as a clinical trial end point in infants. Based on the current evidence, there are insufficient data to support the use of LCI or MBW parameters in the routine clinical management of patients with CF.

2014 year in review: Cystic fibrosis

In this article, we highlight cystic fibrosis (CF) research published in Pediatric Pulmonology during 2014, as well as related articles published in other journals.

The effect of gas exchange on multiple-breath nitrogen washout measures of ventilation inhomogeneity in the mouse

Inert-gas washout measurements using oxygen, in the lungs of small animals, are complicated by the continuous process of oxygen consumption (V̇o2). The multiple-breath nitrogen washout (MBNW) technique uses the alveolar slope to determine measures of ventilation inhomogeneity in the acinar (Sacin) and conducting (Scond) airway regions, as well as overall inhomogeneity, as determined by the lung clearance index (LCI). We hypothesized that measured ventilation inhomogeneity in the mouse lung while it is alive is in fact an artifact due to the high V̇o2 in proportion to alveolar gas volume (Va), and not ventilation inhomogeneity per se. In seven male C57BL/6 mice, MBNW was performed alive and postmortem to derive measures with and without the effect of gas exchange, respectively. These results were compared with those obtained from an asymmetric multibranch point mathematical model of the mouse lung. There was no statistical difference in Sacin and LCI between alive and postmortem results (Sacin alive = 0.311 ± 0.043 ml(-1) and Sacin postmortem = 0.338 ± 0.032 ml(-1), LCI alive = 7.0 ± 0.1 and LCI postmortem = 7.0 ± 0.1). However, there was a significant decrease in Scond from 0.086 ± 0.005 ml(-1) alive to 0.006 ± 0.002 ml(-1) postmortem (P < 0.01). Model simulations replicated these results. Furthermore, in the model, as V̇o2 increased, so did the alveolar slope. These findings suggests that the MBNW measurement of Scond in the mouse lung is confounded by the effect of gas exchange, a result of the high V̇o2-to-Va ratio in this small animal, and not due to inhomogeneity within the airways.