Static hyperinflation is associated with ventilatory limitation and exercise tolerance in adult cystic fibrosis

Change in the 6-min walk test among 71 patients with cystic fibrosis treated with elexacaftor/tezacaftor/ivacaftor

BACKGROUND

Elexacaftor/tezacaftor/ivacaftor (ETI) has led to substantial improvements in the clinical outcome of people with cystic fibrosis (pwCF). However, its effects on exercise capacity remain uncertain.

METHODS

This retrospective cohort study included 71 pwCF who started ETI between March 2020 and September 2022. The best performance on the 6-min walk test (6MWT), defined as the peak walking distance achieved, was compared between the 12 months preceding ETI initiation and the first 14 months of treatment. Pulmonary function tests (PFT) and Cystic Fibrosis Questionnaire-Revised (CFQ-R) were analyzed at treatment initiation and after 12 months.

RESULTS

After starting ETI, the 6MWT was performed at a median interval of 356 [296-380] days. The mean 6-min walk distance (6MWD) was 641 m ± 85.5 at baseline. After treatment, the 6MWD showed a significant absolute increase of 15.8 m (P = 0.007). Improvement was greater in pwCF with a percent predicted FEV1 (ppFEV1) ≤40, showing a mean increase of 37.8 m (P = 0.009), and in those without prior CFTR modulator therapy with an increase of 21.6 m (P = 0.016). After 12 months, the absolute increase in ppFEV1 was 15.8 (P < 0.001). The absolute changes from baseline in CFQ-R physical and respiratory scores were 17.9 (P < 0.001) and 27 points (P < 0.001), respectively. No correlation was found between changes in 6MWT and changes in PFT results.

CONCLUSIONS

ETI improved exercise capacity in pwCF, as evidenced by a significant increase in the 6MWD. ETI was also associated with improvements in physical-related quality of life. Changes in PFT results cannot predict changes in 6MWT results after ETI therapy.

Identifying limitations to exercise with incremental cardiopulmonary exercise testing: a scoping review

Cardiopulmonary exercise testing (CPET) is a comprehensive and invaluable assessment used to identify the mechanisms that limit exercise capacity. However, its interpretation remains poorly standardised. This scoping review aims to investigate which limitations to exercise are differentiated by the use of incremental CPET in literature and which criteria are used to identify them. We performed a systematic, electronic literature search of PubMed, Embase, Cochrane CENTRAL, Web of Science and Scopus. All types of publications that reported identification criteria for at least one limitation to exercise based on clinical parameters and CPET variables were eligible for inclusion. 86 publications were included, of which 57 were primary literature and 29 were secondary literature. In general, at the level of the cardiovascular system, a distinction was often made between a normal physiological limitation and a pathological one. Within the respiratory system, ventilatory limitation, commonly identified by a low breathing reserve, and gas exchange limitation, mostly identified by a high minute ventilation/carbon dioxide production slope and/or oxygen desaturation, were often described. Multiple terms were used to describe a limitation in the peripheral muscle, but all variables used to identify this limitation lacked specificity. Deconditioning was a frequently mentioned exercise limiting factor, but there was no consensus on how to identify it through CPET. There is large heterogeneity in the terminology, the classification and the identification criteria of limitations to exercise that are distinguished using incremental CPET. Standardising the interpretation of CPET is essential to establish an objective and consistent framework.

Assessment of hyperinflation: comparison of Global Lung Function Initiative and European Community for Steel and Coal lung volume reference equations

Background

Assessment of static hyperinflation severity is crucial to identify COPD patients eligible for lung volume reduction. The current recommendation of residual volume ≥175% predicted may need to be reconsidered owing to potential differences between the Global Lung Function Initiative (GLI) and the European Community for Steel and Coal (ECSC) reference equations for residual volume and concerns about using percentage of predicted.

Methods

We compared the residual volume reference values derived from the GLI and ECSC equations using mathematically simulated data and used a receiver operating characteristic curve to establish a new GLI-derived z-score cut-off for residual volume using body plethysmography data from patients with severe COPD.

Results

The GLI reference equation for residual volume consistently yields a lower predicted residual volume for individuals with an average or below-average height (females ≤163 cm and males ≤177 cm). Our clinical cohort consisted of 1011 patients with COPD (graded using the Global Initiative for Chronic Obstructive Lung Disease (GOLD) criteria as 38% GOLD 3 and 59% GOLD 4). In this cohort, a GLI-derived residual volume z-score of ≥2.9 could accurately replace the ECSC-derived 175% predicted cut-off and a z-score of ≥3.5 was established for the 200% predicted cut-off.

Conclusion

There are substantial differences in predicted residual volume values between the GLI and ECSC equations, with the GLI generally yielding a lower predicted residual volume in the majority of individuals. A GLI-derived residual volume z-score of ≥2.9 could be used to replace the currently used cut-off of ≥175% predicted to identify potential lung volume reduction candidates.

Dynamic Hyperinflation While Exercising-A Potential Predictor of Pulmonary Deterioration in Cystic Fibrosis

BACKGROUND

Lung function deterioration in cystic fibrosis (CF) is typically measured by a decline in the forced expiratory volume in one second (FEV1%), which is thought to be a late marker of lung disease. Dynamic hyperinflation (DH) is seen in obstructive lung diseases while exercising. Our aim was to assess whether DH could predict pulmonary deterioration in CF; a secondary measure was the peak VO2.

METHODS

A retrospective study was conducted of people with CF who performed cardiopulmonary exercise tests (CPETs) during 2012-2018. The tests were classified as those demonstrating DH non-DH. Demographic, genetic, and clinical data until 12.2022 were extracted from patient charts.

RESULTS

A total of 33 patients aged 10-61 years performed 41 valid CPETs with valid DH measurements; sixteen (39%) demonstrated DH. At the time of the CPETs, there was no difference in the FEV1% measurements between the DH and non-DH groups (median 83.5% vs. 87.6%, respectively; p = 0.174). The FEV1% trend over 4 years showed a decline in the DH group compared to the non-DH group (p = 0.009). A correlation was found between DH and the lung clearance index (LCI), as well as the FEV1% (r = 0.36 and p = 0.019 and r = -0.55 and p = 0.004, respectively). Intravenous (IV) antibiotic courses during the 4 years after the CPETs were significantly more frequent in the DH group (p = 0.046). The peak VO2 also correlated with the FEV1% and LCI (r = 0.36 and p = 0.02 and r = -0.46 and p = 0.014, respectively) as well as with the IV antibiotic courses (r = -0.46 and p = 0.014).

CONCLUSIONS

In our cohort, the DH and peak VO2 were both associated with lung function deterioration and more frequent pulmonary exacerbations. DH may serve as a marker to predict pulmonary deterioration in people with CF.

The role of inspiratory capacity and tidal flow in diagnosing exercise ventilatory limitation in Cystic Fibrosis

BACKGROUND

Exercise ventilatory limitation conventionally defined by reduced breathing reserve (BR) may underestimate the effect of lung disease on exercise capacity in patients with mild to moderate obstructive lung diseases.

OBJECTIVE

To investigate whether ventilatory limitation may be present despite a normal BR in Cystic Fibrosis (CF).

METHODS

Twenty adult CF patients (age 16-58y) with a wide range of pulmonary obstruction severity completed a symptom-limited incremental exercise test on a cycle ergometer. Operating lung volumes were derived from inspiratory capacity (IC) measurement during exercise and exercise tidal flow volume loop analysis.

RESULTS

six patients had a severe airway obstruction (FEV₁<45% predicted) and conventional evidence of ventilatory limitation (low BR). Fourteen patients had mild to moderate-severe airway obstructive (FEV₁ 46-103% predicted), and a normal BR [12-62 L/min, BR% (17-40)]. However, dynamic respiratory mechanics demonstrated that even CF patients with mild to moderate-severe lung disease had clear evidence of ventilatory limitation during exercise. IC was decreased by (median) 580 ml (range 90-1180 ml) during exercise, indicating dynamic hyperinflation. Inspiratory reserve volume at peak exercise was 445 ml (241-1350 ml) indicating mechanical constraint on the respiratory system. The exercise tidal flow met or exceeded the expiratory boundary of the maximal flow volume loop over 72% of the expiratory volume (range 40-90%), indicating expiratory flow limitation.

CONCLUSION

Reduced BR as a sole criterion underestimates ventilatory limitation during exercise in mild to moderate-severe CF patients. Assessment of dynamic respiratory mechanics during exercise revealed ventilatory limitation, present even in patients with mild obstruction.

Nasal high-flow therapy as an adjunct to exercise in patients with cystic fibrosis: A pilot feasibility trial

BACKGROUND

Exercise tolerance in people with CF and advanced lung disease is often reduced. While supplemental oxygen can improve oxygenation, it does not affect dyspnoea, fatigue or comfort. Nasal high-flow therapy (NHFT), thanks to its pathophysiological mechanisms, could improve exercise tolerance, saturation and dyspnoea. This study explores the feasibility of conducting a clinical trial of using NHFT in patients with CF during exercise.

METHODS

A pilot, open-label, randomized crossover trial was performed, enroling 23 participants with CF and severe lung disease. Participants completed two treadmill walking test (TWT) with and without NHFT at 24-48 h interval. Primary outcome was trial feasibility, and exploratory outcomes were TWT distance (TWTD), SpO₂, transcutaneous CO₂, dyspnoea and comfort.

RESULTS

Recruitment rate was 2.4 subjects/month with 1.3:1 screening-to-randomization ratio. No adverse events caused by NHFT were observed. Tolerability was good and data completion rate was 100%. Twenty subjects (91%) were included in the exploratory study. Mean difference in TWTD on NHFT was 19 m (95% CI [4.8 - 33.1]). S_pO₂ was similar, but respiratory rate and mean tcCO₂ were lower on NHFT (mean difference = -3.9 breaths/min 95% CI [-5.9 - -1.9] and -0.22 kPa 95% CI [-0.4 - 0.04]). NHFT reduced exercise-induced dyspnoea and discomfort.

CONCLUSION

Trials using NHFT in patients with CF during exercise are feasible. NHFT appears to improve walking distance, control respiratory rate, CO₂, dyspnoea and improve comfort. A larger trial with a longer intervention is feasible and warranted to confirm the impact of NHFT in training programmes for patients with CF.

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.

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.

Within-breath changes in respiratory system impedance in children with cystic fibrosis

BACKGROUND

The aim of this study was to assess within-breath respiratory system impedance by the forced oscillation technique (FOT) in children with cystic fibrosis (CF) and relate it to the underlying lung disease.

METHODS

Thirty-three children with CF (median [range] age 12.0 [6-17] years) underwent FOT at 8 Hz during tidal breathing, multiple breath nitrogen washout (LCI), spirometry (FEV1), body plethysmography (RV/TLC), and magnetic resonance imaging (MRI). FOT outcomes included: mean inspiratory, expiratory, and whole breath resistance (R8_INSP , R8_EXP , R8_TOT ) and reactance (X8_INSP , X8_EXP , X8_TOT ), and the differences between X8_INSP and X8_EXP (ΔX8). Morphological changes were evaluated by MRI using CF-specific morphological scores. Spearman correlation was performed to examine the correlation between FOT indices and other parameters.

RESULTS

FEV1 was negatively correlated with R8_EXP (r = -0.52, P = 0.002) and ΔX8 (r = -0.55, P = 0.001), and positively correlated with and X8_EXP (r = 0.56, P < 0.001). RV/TLC was positively correlated with R8_EXP (r = 0.43, P = 0.013), and ΔX8 (r = 0.54, P = 0.001) and negatively correlated with X8_EXP (r = -0.54, P = 0.001). We found poor correlation between FOT parameters and LCI and no correlation between FOT parameters and MRI scores.

CONCLUSION

In children with CF, changes in within-breath FOT parameters are consistent with peripheral obstruction and dynamic airway compression, while they are not associated with ventilation heterogeneities and morphological alterations.