The utility of moment ratios and abbreviated endpoints of the multiple breath washout test in preschool children with cystic fibrosis

MRI and Pulmonary Function Tests' Results as Ventilation Inhomogeneity Markers in Children and Adolescents with Cystic Fibrosis

Magnetic resonance imaging (MRI) of the chest is becoming more available in the detection and monitoring of early changes in lung function and structure in patients with cystic fibrosis (CF). The aim of this study was to assess the relationship between pulmonary function tests (PFT) and perfusion deficits in CF children measured by MRI. We performed a retrospective analysis of the perfusion lung MRI scans and the results of spirometry, oscillometry, body plethysmography, single-breath carbon monoxide uptake, and multiple-breath washout technique (MBW). There were statistically significant correlations between the MRI perfusion scores and MBW parameters (2.5% LCI, M1/M0, M2/M0), spirometry parameters (FEV1, FVC, FEF25/75), reactance indices in impulse oscillometry (X5Hz, X10Hz), total lung capacity (TLC) measured in single breath carbon monoxide uptake, markers of air-trapping in body plethysmography (RV, RV/TLC), and the diffusing capacity of the lungs for carbon monoxide. We also observed significant differences in the aforementioned PFT variables between the patient groups divided based on perfusion scores. We noted a correlation between markers of functional lung deficits measured by the MRI and PFTs in CF children. MRI perfusion abnormalities were reflected sooner in the course of the disease than PFT abnormalities.

Model-based Bayesian inference of the ventilation distribution in patients with cystic fibrosis from multiple breath washout, with comparison to ventilation MRI

BACKGROUND

Indices of ventilation heterogeneity (VH) from multiple breath washout (MBW) have been shown to correlate well with VH indices derived from hyperpolarised gas ventilation MRI. Here we report the prediction of ventilation distributions from MBW data using a mathematical model, and the comparison of these predictions with imaging data.

METHODS

We developed computer simulations of the ventilation distribution in the lungs to model MBW measurement with 3 parameters: σ_V, determining the extent of VH; V₀, the lung volume; and V_D, the dead-space volume. These were inferred for each individual from supine MBW data recorded from 25 patients with cystic fibrosis (CF) using approximate Bayesian computation. The fitted models were used to predict the distribution of gas imaged by ³He ventilation MRI measurements collected from the same visit.

RESULTS

The MRI indices measured (I_1/3, the fraction of pixels below one-third of the mean intensity and I_CV, the coefficient of variation of pixel intensity) correlated strongly with those predicted by the MBW model fits (r=0.93,0.88 respectively). There was also good agreement between predicted and measured MRI indices (mean bias ± limits of agreement: I_1/3:-0.003±0.118 and I_CV:-0.004±0.298). Fitted model parameters were robust to truncation of MBW data.

CONCLUSION

We have shown that the ventilation distribution in the lung can be inferred from an MBW signal, and verified this using ventilation MRI. The Bayesian method employed extracts this information with fewer breath cycles than required for LCI, reducing acquisition time required, and gives uncertainty bounds, which are important for clinical decision making.

Cystic fibrosis year in review 2020: Section 2 pulmonary disease, infections, and inflammation

The outlook for those with cystic fibrosis (CF) has never been brighter with ever increasing life expectancy and the approval of the highly effective CFTR modulators, such as elexacaftor/tezacaftor/ivacaftor. With that being said, the progressive pulmonary decline and importance of lung health, infection, and inflammation in CF remains. This review is the second part in a three-part CF Year in Review 2020. Part one focused on the literature related to CFTR modulators while part three will feature the multisystem effects related to CF. This review focuses on articles from Pediatric Pulmonology, including articles from other journals that are of particular interest to clinicians. Herein, we highlight studies published during 2020 related to CF pulmonary disease, infection, treatment, and diagnostics.

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.

Pediatric pulmonology year in review 2020: Physiology

Pulmonary physiology is a core element of pediatric pulmonology care and research. This article reviews some of the notable publications in physiology that were published in Pediatric Pulmonology in 2020.

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.