Single-breath washout and association with structural lung disease in children with cystic fibrosis

Looking beyond LCI: Multiple breath washout phase III slope derived indices and their application in chronic respiratory disease in children

The multiple breath washout (MBW) test is widely reported in the context of Lung Clearance Index (LCI). LCI reflects global ventilation inhomogeneity but does not provide information regarding the localization of disease along the respiratory tree. The MBW-derived normalized phase III slope (SnIII) indices (Scond and Sacin), instead, can distinguish between convective-dependent and diffusion-convection-dependent ventilation inhomogeneity considered to occur within the conductive and acinar airways, respectively. In cystic fibrosis, Scond tends to become abnormal even earlier than LCI and spirometry. The value of Scond and Sacin in clinical practice has been recently explored in other respiratory conditions, including asthma, primary ciliary dyskinesia, bronchopulmonary dysplasia, bronchiolitis obliterans, and sickle cell disease. In this narrative review we offer an overview on the theoretical background, potentialities, and limitations of SnIII analysis in children, including challenges and feasibility aspects. Moreover, we summarize current evidence on the use of SnIII-derived indices across different groups of pediatric chronic respiratory disease and we highlight the gaps in knowledge that need to be addressed in future studies.

Evaluation of the Double-Tracer Gas Single-Breath Washout Test in a Pediatric Field Study

BACKGROUND

The early life origins of chronic pulmonary diseases are thought to arise in peripheral small airways. Predictors of ventilation inhomogeneity, a proxy of peripheral airway function, are understudied in schoolchildren.

RESEARCH QUESTION

Is the double-tracer gas single-breath washout (DTG-SBW) measurement feasible in a pediatric field study setting? What are the predictors of the DTG-SBW-derived ventilation inhomogeneity estimate in unselected schoolchildren?

STUDY DESIGN AND METHODS

In this prospective cross-sectional field study, a mobile lung function testing unit visited participating schools in Switzerland. We applied DTG-SBW, fraction of exhaled nitric oxide (Feno), and spirometry measurements. The DTG-SBW is based on tidal inhalation of helium and sulfur-hexafluoride, and the phase III slope (SIIIHe-SF6) is derived. We assessed feasibility, repeatability, and associations of SIIIHe-SF6 with the potential predictors of anthropometrics, presence of wheeze (ie, parental report of one or more episode of wheeze in the prior year), Feno, FEV1, and FEV1/FVC.

RESULTS

In 1,782 children, 5,223 DTG-SBW trials were obtained. The DTG-SBW was acceptable in 1,449 children (81.3%); the coefficient of variation was 39.8%. SIIIHe-SF6 was independently but weakly positively associated with age and BMI. In 276 children (21.2%), wheeze was reported. SIIIHe-SF6 was higher by 0.049 g.mol.L-1 in children with wheeze compared with those without and remained associated with wheeze after adjusting for age and BMI in a multivariable linear regression model. SIIIHe-SF6 was not associated with Feno, FEV1, and FEV1/FVC.

INTERPRETATION

The DTG-SBW is feasible in a pediatric field study setting. On the population level, age, body composition, and wheeze are independent predictors of peripheral airway function in unselected schoolchildren. The variation of the DTG-SBW possibly constrains its current applicability on the individual level.

TRIAL REGISTRATION

ClinicalTrials.gov; No.: NCT03659838; URL: www.

CLINICALTRIALS

gov.

Cystic fibrosis year in review 2019: Section 2 pulmonary disease and infections

During the year 2019, research and case reports or series in the field of cystic fibrosis (CF) were in abundance. To adequately address the large body of CF research published during 2019, the CF year in review will be divided into three sections. This report is the second section, focusing specifically on new research related to pulmonary disease and infections. Additional sections will concentrate on CF transmembrane conductance regulator modulators and the multisystem effects of CF. It is an exciting time to be providing care for patients and their families with CF with all the exciting new discoveries that will be shared in these reviews.

State-of-the-art review of lung imaging in cystic fibrosis with recommendations for pulmonologists and radiologists from the "iMAging managEment of cySTic fibROsis" (MAESTRO) consortium

OBJECTIVE

Imaging represents an important noninvasive means to assess cystic fibrosis (CF) lung disease, which remains the main cause of morbidity and mortality in CF patients. While the development of new imaging techniques has revolutionised clinical practice, advances have posed diagnostic and monitoring challenges. The authors aim to summarise these challenges and make evidence-based recommendations regarding imaging assessment for both clinicians and radiologists.

STUDY DESIGN

A committee of 21 experts in CF from the 10 largest specialist centres in Italy was convened, including a radiologist and a pulmonologist from each centre, with the overall aim of developing clear and actionable recommendations for lung imaging in CF. An a priori threshold of at least 80% of the votes was required for acceptance of each statement of recommendation.

RESULTS

After a systematic review of the relevant literature, the committee convened to evaluate 167 articles. Following five RAND conferences, consensus statements were developed by an executive subcommittee. The entire consensus committee voted and approved 28 main statements.

CONCLUSIONS

There is a need for international guidelines regarding the appropriate timing and selection of imaging modality for patients with CF lung disease; timing and selection depends upon the clinical scenario, the patient's age, lung function and type of treatment. Despite its ubiquity, the use of the chest radiograph remains controversial. Both computed tomography and magnetic resonance imaging should be routinely used to monitor CF lung disease. Future studies should focus on imaging protocol harmonisation both for computed tomography and for magnetic resonance imaging. The introduction of artificial intelligence imaging analysis may further revolutionise clinical practice by providing fast and reliable quantitative outcomes to assess disease status. To date, there is no evidence supporting the use of lung ultrasound to monitor CF lung disease.

Correlation of computed tomography findings and lung function in children and adolescents with cystic fibrosis

BACKGROUND

The timely and appropriate monitoring of pulmonary status is of utmost importance for patients with cystic fibrosis (CF). Computed tomography (CT) has been used in clinical and research settings for tracking lung involvement in CF patients. However, as CT delivers a considerable amount of radiation, its sequential use in CF patients remains a concern. The application of CT, therefore, should take into account its potential risks. This review aims to understand whether and to what extent the CT findings correlate with the findings from other monitoring tools in CF lung disease.

DATA SOURCES

PubMed was searched for articles about the correlation of chest CT findings with spirometric indices and with lung clearance index in children and adolescents with CF. The most relevant articles were reviewed and are presented herein.

RESULTS

Most studies have shown that forced expiratory volume in the first second (FEV₁) and other spirometric indices correlate moderately with CT structural lung damage. However, at the individual level, there were patients with FEV₁ within the normal range and abnormal CT and vice versa. Furthermore, longitudinal studies have indicated that the deterioration of structural lung damage does not occur in parallel with the progression of lung function. Lung clearance index is a better predictor of CT findings.

CONCLUSIONS

In general, the existing studies do not support the use of lung function tests as surrogates of chest CT.

Abnormal Lung Clearance Index in Cystic Fibrosis Children with Normal FEV1 and Single-Breath Nitrogen Washout Test

Single- and multiple-breath washout tests (SBW and MBW) measure ventilation inhomogeneity, but the relationship between them is unclear. Forty-three subjects with cystic fibrosis (CF) and healthy controls (HC) 8-21 years of age were recruited (CF = 30 and HC = 13) and performed nitrogen MBW, vital capacity SBW, spirometry, and plethysmography. Mean phase III slope from SBW (SIII) and lung clearance index (LCI) were significantly different between CF and HC (p = 0.017 and p < 0.0001, respectively). Based on Pearson correlation, SIII and LCI showed strong correlation (ρ = 0.81, p < 0.0001). Both SIII and LCI significantly correlated with spirometry (all p < 0.05). Among CF subjects with normal FEV₁ (≥ 80%; n = 17), 76% (n = 13) had normal SIII but abnormal LCI. We conclude that LCI can be abnormal despite normal SIII and FEV₁ in CF children. Although LCI and SIII showed strong correlation, our results suggest that LCI is a better test to detect ventilation inhomogeneity in CF children with normal FEV₁.

Pediatric pulmonology year in review 2019: Physiology

Pulmonary physiologic assessments are critical for the care and study of pediatric respiratory disease. In 2019, there were numerous contributions to this topic in Pediatric Pulmonology.

Limitations of regional ventilation inhomogeneity indices in children with cystic fibrosis

BACKGROUND

S_cond is a multiple breath washout (MBW) index that measures convection-dependent ventilation inhomogeneity (CDI) arising within conductive airways, but the calculation method is unreliable in subjects with advanced cystic fibrosis (CF) lung disease. A new CDI index, S_cond *, has been proposed for use in adults with CF and moderate to severe ventilation inhomogeneity. We aimed to evaluate the most appropriate CDI index in children and adolescents with CF and various degrees of inhomogeneity, and from that the most appropriate diffusion-convection-interaction index (S_acin or S_acin *).

METHODS

S_cond , S_acin  and the alternative indices, S_cond *, and S_acin * were retrospectively calculated in subjects with CF aged 3 to 18 years and age-matched controls, who underwent sulfur hexafluoride MBW between 2003 and 2015. The upper limit of normal was based on 95th percentile of the control population.

RESULTS

One hundred and twenty-seven subjects with CF (44% male; mean age ± SD: 7.5 years ± 4.9) and 94 controls (53% male; 7.9 years ± 5.1) were included in the final analysis. All measures of ventilation inhomogeneity were significantly higher in children with CF. As predicted, S_cond reached a maximum value at lung clearance index (LCI) values of approximately 9. In subjects with LCI ≥ 9 S_cond * showed good correlation with LCI, whilst S_cond had no relationship with LCI (Spearman rank correlation S_cond */LCI, 0.49; P < .01; S_cond /LCI, -0.068; P = .46). In subjects with mild disease (LCI < 9) S_cond was more frequently abnormal than S_cond * (37% vs 16%; P = .01).

CONCLUSIONS

S_cond and S_acin are sensitive indices of early regional inhomogeneity, but are of no value when LCI ≥ 9. In these subjects, S_cond * & S_acin * are potential alternatives.