The clinical utility of lung clearance index in early cystic fibrosis lung disease is not impacted by the number of multiple-breath washout trials

Repeatability of lung clearance index in infants with cystic fibrosis and recurrent wheeze

OBJECTIVES

To describe the short- and medium-term repeatability of lung clearance index at 2.5% (LCI_2.5 ) in infants and calculate the number of patients needed to enroll in a study (N) using LCI_2.5 as a primary outcome.

METHODS

An 8-month follow-up observational study was employed for assessing short-term [coefficient of repeatability (CR) and intraclass correlation (ICC)] and medium-term repeatability (Bland-Altman method) of LCI_2.5 in infants with cystic fibrosis (CF) or recurrent wheeze (RW) measured by the nitrogen multiple-breath washout test (N₂ -MBW). Using these variability data, the N to reach 90% test power at the level of statistical significance (0.05) was calculated.

RESULTS

Forty infants with CF and 21 with RW were enrolled. Initial N₂ -MBW testing was successful in 33 and 17 patients, respectively. Follow-up data were available for 23 and 11 infants, respectively. Short-term repeatability of LCI_2.5 was high (CR = 1.10 and 1.04 in CF and RW patients, respectively; ICC = 0.88 and 0.83 in CF and RW patients, respectively). The between-subject standard deviation was <13% of the actual LCI_2.5 value. In clinically stable patients, LCI_2.5 did not significantly change during the 8-month follow-up. Mean LCI_2.5 change was -0.08 (1% of baseline) in CF and -0.05 (0.6%) in RW, with 95% limits of agreement being (-1.70; 1.53) in CF and (-1.51; 1.40) in RW patients. N = 23 infants if both intragroup differences of LCI_2.5 and minimal difference to be detected would be 2.0.

CONCLUSION

N₂ -MBW may be a reproducible tool with reasonable test power to detect differences in infant studies.

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.

Shedding light into the black box of infant multiple-breath washout

BACKGROUND

Multiple-breath inert gas washout (MBW) is a sensitive technique to assess lung volumes and ventilation inhomogeneity in infancy. Poor agreement amongst commercially available setups and a lack of transparency in the underlying algorithms for the computation of infant MBW outcomes currently limit the widespread application of MBW as a surveillance tool in early lung disease.

METHODS

We determined all computational steps in signal processing and the calculation of MBW outcomes in the current infant WBreath/Exhalyzer D setup (Exhalyzer D device, Eco Medics AG; WBreath software version 3.28.0, ndd Medizintechnik AG; Switzerland). We developed a revised WBreath version based on current consensus guidelines and compared outcomes between the current (3.28.0) and revised (3.52.3) WBreath version. We analyzed 60 visits from 40 infants with cystic fibrosis (CF) and 20 healthy controls at 6 weeks and 1 year of age.

RESULTS

Investigation into the algorithms in WBreath 3.28.0 revealed discrepancies from current consensus guidelines, which resulted in a potential overestimation of functional residual capacity (FRC) and underestimation of lung clearance index (LCI). We developed a revised WBreath version (3.52.3), which overall resulted in 6.7% lower FRC (mean (SD) -1.78 (0.99) mL/kg) and 14.1% higher LCI (1.11 (0.57) TO) than WBreath version 3.28.0.

CONCLUSION

Comprehensive investigation into the signal processing and algorithms used for analysis of MBW measurements improves the transparency and robustness of infant MBW data. The revised software version calculates outcomes according to consensus guidelines. Future work is needed to validate and compare outcomes between infant MBW setups.

Reflex zone stimulation reduces ventilation inhomogeneity in cystic fibrosis: A randomised controlled cross-over study

BACKGROUND

The reflex zone stimulation technique (RST) activates complex motor responses and has a positive impact on the locomotor system. This technique may also indirectly affect breathing; however, the use of this technique as adjunct of the treatment of cystic fibrosis (CF) has not yet been characterised.

METHODS

We performed a randomised controlled single-centre interventional trial to evaluate the short-term effects of RST on lung function in 21 paediatric CF patients with normal baseline spirometry. The effect of 30 min of RST was compared to that of sham therapy in a crossover design. The interventions were performed in random order and planned 6 months apart. The primary outcome was a change in global ventilation inhomogeneity after intervention, assessed by lung clearance index (LCI_2.5 ) derived from a nitrogen multiple breath washout test. Secondary outcomes included changes in regional ventilation inhomogeneity (indices of acinar [Sacin*Vt] and conductive airway [Scond*Vt] inhomogeneity) and spirometry parameters (inspiratory capacity, forced vital capacity, and forced expiratory volume in 1 s). Trunk deformity was assessed by physiotherapists at study entry.

RESULTS

After the RST intervention, the LCI_2.5 (p = .004) and Scond*Vt (p = .009) decreased significantly, while inspiratory capacity increased (p = .012). In the sham-therapy group, none of the parameters changed significantly. Trunk deformity was seen in 76.5% of all patients, and 92.9% of those with trunk deformity showed a decrease in LCI_2.5 after RST.

CONCLUSION

RST has multiple positive short-term effects on lung function, especially in CF patients with trunk deformities.

Nocturnal non invasive ventilation in normocapnic cystic fibrosis patients: a pilot study

BACKGROUND AND AIM

In patients with cystic fibrosis (CF) non-invasive ventilation (NIV) improves lung mechanics and gas exchange, and decreases the work of breathing. Domiciliary NIV is mainly used in hypercapnic patients with severe disease, because it counteracts the progression of lung functional impairment and it is often used as a useful "bridge" to lung transplantation. However, to date, there are no standardized criteria to indicate the effect of a precocious starting of NIV in patients with functional ventilation inhomogeneity without hypercapnia. In this pilot study we assessed whether an early NIV treatment might influence functional and clinical outcomes in CF patients.

METHODS

Six normocapnic CF patients were treated for one year with NIV. At baseline and after 1 year of NIV treatment, arterial gas analysis, spirometry, MBW to derive LCI, nocturnal cardio-respiratory polygraphy (PG), and Pittsburgh Sleep Quality Index (PSQI) were perfomed in all enrolled patients.

RESULTS

After one year, despite spirometric and LCI values remain statistically not modified, the number of infectious exacerbations was reduced by 50%.

CONCLUSIONS

These results suggest that nocturnal NIV improves clinical conditions of stable CF patients. Finally, we suggest that this procedure can be useful to counteract the progression of lung disease even in normocapnic patients.

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.

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.

The role of geographical location and climate on recurrent Pseudomonas infection in young children with Cystic Fibrosis

OBJECTIVES

To determine the association between residence and climate with risk of Pseudomonas aeruginosa (Pa) and other respiratory outcomes.

METHODS

We performed regular bronchoalveolar lavage and upper airway cultures in young children with CF to identify Pa infection. Children were classified for residence as regional or metropolitan. Bronchiectasis was detected on periodic chest computed tomography scans. Multilocus sequence typing determined Pa genotype. Lung function was assessed using Multiple Breath Washout.

RESULTS

Of infants diagnosed with CF between 2006 and 2017, 129 were included in the study. Seven patients moved between metropolitan and regional Victoria and were excluded from analysis. Of the remaining 122 subjects, seventy-four (61%) children resided in metropolitan areas and over half (54%) were male. There were 83 Pa episodes in the 122 children who lived consistently in a geographical location. The incidence rate was 0.15 episodes per person-years. We found weak evidence of a 15% increase in the rate of Pa episodes with increasing average annual maximum temperature (95%CI (0.98, 1.36); p = .086), while the rate of Pa acquision decreased with average annual 3 pm humidity (IRR = 0.96; 95%CI(0.92, 1.0008); p = .054). The rate of Pa episodes was 2.1 times higher in regional participants (95%CI (1.4, 3.1); p = .001) and risk of second episode was more than five times greater (HR 5.7; 95%CI 1.9, 17); p = .002). No difference between regions in lung clearance index and presence of bronchiectasis was detected.

CONCLUSION

Regional residence is associated with risk of acquiring recurrent infection with Pseudomonas aeruginosa in young children with CF.