A novel non-invasive method allowing for discovery of pathologically relevant proteins from small airways.

BACKGROUND: There is a lack of early and precise biomarkers for personalized respiratory medicine. Breath contains an aerosol of droplet particles, which are formed from the epithelial lining fluid when the small airways close and re-open during inhalation succeeding a full expiration. These particles can be collected by impaction using the PExA® method (Particles in Exhaled Air), and are derived from an area of high clinical interest previously difficult to access, making them a potential source of biomarkers reflecting pathological processes in the small airways. RESEARCH QUESTION: Our aim was to investigate if PExA method is useful for discovery of biomarkers that reflect pathology of small airways. METHODS AND ANALYSIS: Ten healthy controls and 20 subjects with asthma, of whom 10 with small airway involvement as indicated by a high lung clearance index (LCI ≥ 2.9 z-score), were examined in a cross-sectional design, using the PExA instrument. The samples were analysed with the SOMAscan proteomics platform (SomaLogic Inc.). RESULTS: Two hundred-seven proteins were detected in up to 80% of the samples. Nine proteins showed differential abundance in subjects with asthma and high LCI as compared to healthy controls. Two of these were less abundant (ALDOA4, C4), and seven more abundant (FIGF, SERPINA1, CD93, CCL18, F10, IgM, IL1RAP). sRAGE levels were lower in ex-smokers (n = 14) than in never smokers (n = 16). Gene Ontology (GO) annotation database analyses revealed that the PEx proteome is enriched in extracellular proteins associated with extracellular exosome-vesicles and innate immunity. CONCLUSION: The applied analytical method was reproducible and allowed identification of pathologically interesting proteins in PEx samples from asthmatic subjects with high LCI. The results suggest that PEx based proteomics is a novel and promising approach to study respiratory diseases with small airway involvement.

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.

Tobacco smoke exposure in early life and adolescence in relation to lung function.

Maternal smoking during pregnancy is associated with impaired lung function among young children, but less is known about long-term effects and the impact of adolescents' own smoking. We investigated the influence of maternal smoking during pregnancy, secondhand smoke exposure and adolescent smoking on lung function at age 16 years.The BAMSE (Barn/Child, Allergy, Milieu, Stockholm, Epidemiology) birth cohort collected information on participants' tobacco smoke exposure through repeated questionnaires, and measured saliva cotinine concentrations at age 16 years. Participants performed spirometry and impulse oscillometry (IOS) at age 16 years (n=2295).Exposure to maternal smoking during pregnancy was associated with reduced forced expiratory volume in 1 s (FEV1)/forced vital capacity (FVC) ratio of -1.1% (95% CI -2.0 to -0.2%). IOS demonstrated greater resistance at 5-20 Hz (R5-20) in participants exposed to maternal smoking during pregnancy. Adolescents who smoked had reduced FEV1/FVC ratios of -0.9% (95% CI -1.8 to -0.1%) and increased resistance of 6.5 Pa·L-1·s (95% CI 0.7 to 12.2 Pa·L-1·s) in R5-20 Comparable associations for FEV1/FVC ratio were observed for cotinine concentrations, using ≥12 ng·mL-1 as a cut-off for adolescent smoking.Maternal smoking during pregnancy was associated with lower FEV1/FVC ratios and increased airway resistance. In addition, adolescent smoking appears to be associated with reduced FEV1/FVC ratios and increased peripheral airway resistance.

Early-Life Exposure to Traffic-related Air Pollution and Lung Function in Adolescence.

RATIONALE: Exposure to air pollution during infancy has been related to lung function decrements in 8-year-old children, but whether the negative effects remain into adolescence is unknown. OBJECTIVES: To investigate the relationship between long-term air pollution exposure and lung function up to age 16 years. METHODS: A total of 2,278 children from the Swedish birth cohort BAMSE (Children, Allergy, Milieu, Stockholm, Epidemiological Survey) performed spirometry at age 16 years. Levels of outdoor air pollution from local road traffic were estimated (nitrogen oxides [NOx] and particulate matter with an aerodynamic diameter of <10 µm [PM10]) for residential, daycare, and school addresses during the lifetime using dispersion modeling. Associations between exposure in different time windows and spirometry indexes were analyzed by linear regression and mixed effect models. MEASUREMENTS AND MAIN RESULTS: Exposure to traffic-related air pollution during the first year of life was associated with FEV1 at age 16 years of -15.8 ml (95% confidence interval [CI], -33.6 to 2.0 for a 10 µg/m(3) difference in NOx), predominately in males (-30.4 ml; 95% CI, -59.1 to -1.7), and in subjects not exposed to maternal smoking during pregnancy or infancy. Later exposures appeared to have had an additional negative effect. High exposure during the first year of life was also associated with odds ratios for FEV1 and FVC less than the lower limit of normal (LLN) (defined as a z-score < -1.64 SD) of 3.8 (95% CI, 1.3-10.9) and of 4.3 (95% CI, 1.2-15.0), respectively. The results for PM10 were similar to those for NOx. CONCLUSIONS: Exposure to traffic-related air pollution in infancy is negatively associated with FEV1 at age 16 years, leading to increased risk of clinically important deficits.

Consensus statement for inert gas washout measurement using multiple- and single- breath tests.

Inert gas washout tests, performed using the single- or multiple-breath washout technique, were first described over 60 years ago. As measures of ventilation distribution inhomogeneity, they offer complementary information to standard lung function tests, such as spirometry, as well as improved feasibility across wider age ranges and improved sensitivity in the detection of early lung damage. These benefits have led to a resurgence of interest in these techniques from manufacturers, clinicians and researchers, yet detailed guidelines for washout equipment specifications, test performance and analysis are lacking. This manuscript provides recommendations about these aspects, applicable to both the paediatric and adult testing environment, whilst outlining the important principles that are essential for the reader to understand. These recommendations are evidence based, where possible, but in many places represent expert opinion from a working group with a large collective experience in the techniques discussed. Finally, the important issues that remain unanswered are highlighted. By addressing these important issues and directing future research, the hope is to facilitate the incorporation of these promising tests into routine clinical practice.

Nationwide lung function monitoring from infancy in newborn-screened children with cystic fibrosis.

Background: Cystic fibrosis (CF) lung disease starts in infancy and can be assessed for structural lung abnormalities using computed tomography or magnetic resonance scans, or for lung function impairment using multiple breath washout (MBW). However, in infancy these two methods are not well correlated. Trajectories of CF lung disease assessed by MBW in infants and toddlers remain poorly described, which is why we aimed to 1) describe the trajectory of lung function, 2) explore risk factors for progression and 3) explore the real-life effect of lumacaftor/ivacaftor. Methods: This was a nationwide observational cohort study (2018-2021) using data collected as part of the routine clinical surveillance programme (including MBW and monthly endo-laryngeal suction sampling for bacterial pathogens) in children born after implementation of newborn screening for CF (May 2016). Lumacaftor/ivacaftor commenced from age 2 years in children homozygous for F508del. Ventilation distribution efficiency (VDE), recently described to have advantages over lung clearance index (LCI), was reported as the primary MBW outcome after z-score calculations based on published reference data. Mixed effect linear regression models were the main statistical analyses performed in this study. Results: 59 children, aged 2-45 months, contributed with 211 MBW occasions (median (interquartile range (IQR)) 3 (2-5) MBW occasions per child) with a median (IQR) follow-up time of 10.8 (5.2-22.3) months. An overall mean annual deterioration rate of -0.50 (95% CI -0.78- -0.22) z-VDE was observed, starting from an estimated mean z-VDE of -1.68 (95% CI -2.15- -1.22) at age 0.0 years (intercept). Pseudomonas aeruginosa "ever" (n=14, MBWs 50) had a significantly worse z-VDE trajectory versus P. aeruginosa "never" (mean difference 0.53 (95% CI 0.16-0.89) per year; p=0.0047) and lumacaftor/ivacaftor treatment (n=22, MBWs 46) significantly improved the trajectory of z-VDE (mean difference 1.72 (95% CI 0.79-2.66) per year; p=0.0004), leading to a stable mean z-VDE trajectory after start of treatment. Conclusions: Infants and toddlers with CF demonstrated progressive deterioration in z-VDE over the first years of life. P. aeruginosa isolation "ever" was associated with an accelerated deterioration in lung function, while lumacaftor/ivacaftor therapy significantly improved and stabilised the trajectory.

Ventilation inhomogeneity in children with primary ciliary dyskinesia.

BACKGROUND: The lung clearance index (LCI) derived from the multiple breath inert gas washout (MBW) test reflects global ventilation distribution inhomogeneity. It is more sensitive than forced expiratory volume in 1 s (FEV(1)) for detecting abnormal airway function and correlates closely with structural lung damage in children with cystic fibrosis, which shares features with primary ciliary dyskinesia (PCD). Normalised phase III slope indices S(cond) and S(acin) reflect function of the small conducting and acinar airways, respectively. The involvement of the peripheral airways assessed by MBW tests has not been previously described in PCD. METHODS: A cross-sectional MBW study was performed in 27 children and adolescents with verified PCD, all clinically stable and able to perform lung function tests. LCI, S(cond) (n=23) and S(acin) (n=23) were derived from MBW using a mass spectrometer and sulfur hexafluoride as inert marker gas. MBW indices were compared with present age, age at diagnosis and spirometry findings, and were related to published normative values. RESULTS: LCI, S(cond) and S(acin) were abnormal in 85%, 96% and 78% of patients with PCD and in 81%, 93% and 79%, respectively, of 13/27 subjects with normal FEV(1). LCI and S(acin) correlated significantly while S(cond) did not correlate with any other lung function parameters. None of the lung function measurements correlated with age or age at diagnosis. CONCLUSIONS: PCD is characterised by marked peripheral airway dysfunction. MBW seems promising in the early detection of lung damage, even in young patients with PCD. The relationship of MBW indices to the outcome of long-term disease and their role in the management of PCD need to be assessed.

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 N2,original and N2,corrected for comparison with SF6 MBW. RESULTS: Mean functional residual capacity, FRCN2,corrected was 14.3% lower than FRCN2, original , and 1.0% different from FRCSF6 . Lung clearance index, LCIN2,corrected was 25.2% lower than LCIN2,original , and 7.3% higher than LCISF6 . Mean (SD) tidal volume decreased significantly during N2 MBWcorrected , 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 LCIN2,corrected and LCISF6 . The absolute differences in LCI increased significantly with higher LCISF6 (0.63/LCISF6 ) and (0.23/LCISF6 ), respectively, for N2,original and N2,corrected , but the relative differences were stable across disease severity for N2,corrected , but not for N2,original . CONCLUSION: Only minor residual differences between FRCN2,corrected and FRCSF6 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 .

Improved agreement between N2 and SF6 multiple-breath washout in healthy infants and toddlers with improved EXHALYZER D sensor performance.

Recent studies indicate limited utility of nitrogen multiple-breath washout (N2MBW) in infancy and advocate for using sulfur hexafluoride (SF6) MBW in this age-group. Modern N2MBW systems, such as EXHALYZER D (ECO MEDICS AG, Duernten, Switzerland), use O2 and CO2 sensors to calculate N2 concentrations (in principle, N2% = 100 - CO2% - O2%). High O2 and CO2 concentrations have now been shown to significantly suppress signal output from the other sensor, raising apparent N2 concentrations. We examined whether improved EXHALYZER D N2 signal, accomplished after thorough examination of this CO2 and O2 interaction on gas sensors and its correction, leads to better agreement between N2MBW and SF6MBW in healthy infants and toddlers. Within the same session, 52 healthy children aged 1-36 mo [mean = 1.30 (SD = 0.72) yr] completed SF6MBW and N2MBW recordings (EXHALYZER D, SPIROWARE version 3.2.1) during supine quiet sleep. SF6 and N2 SPIROWARE files were reanalyzed offline with in-house software using identical algorithms as in SPIROWARE with or without application of the new correction factors for N2MBW provided by ECO MEDICS AG. Applying the improved N2 signal significantly reduced mean [95% confidence interval (CI)] differences between N2MBW and SF6MBW recorded functional residual capacity (FRC) and lung clearance index (LCI): for FRC, from 26.1 (21.0, 31.2) mL, P < 0.0001, to 1.18 (-2.3, 4.5) mL, P = 0.5, and for LCI, from 1.86 (1.68, 2.02), P < 0.001, to 0.44 (0.33, 0.55), P < 0.001. Correction of N2 signal for CO2 and O2 interactions on gas sensors resulted in markedly closer agreement between N2MBW and SF6MBW outcomes in healthy infants and toddlers.NEW & NOTEWORTHY Modern nitrogen multiple-breath washout (N2MBW) systems such as EXHALYZER D use O2 and CO2 sensors to calculate N2 concentrations. New corrections for interactions between high O2 and CO2 concentrations on the gas sensors now provide accurate N2 signals. The correct N2 signal led to much improved agreement between N2MBW and sulfur hexafluoride (SF6) MBW functional residual capacity (FRC) and lung clearance index (LCI) in 52 sleeping healthy infants and toddlers, suggesting a role for N2MBW in this age-group.

Newly developed multiple-breath washout reference equations from the CHILD Cohort Study: implications of poorly fitting equations.

Using inappropriate reference equations would provide incorrect estimate of z-scores, which would cause misdiagnosis. Appropriate representative normative reference data must be available to correctly interpret individual lung function results. https://bit.ly/3dcNZ5p.

Asthma and allergy patterns over 18 years after severe RSV bronchiolitis in the first year of life.

BACKGROUND: An increased prevalence of asthma/recurrent wheeze (RW), clinical allergy and allergic sensitisation up to age 13 years has previously been reported in subjects hospitalised with respiratory syncytial virus (RSV) bronchiolitis in their first year of life compared with matched controls. A study was undertaken to examine whether these features persist into early adulthood, to report longitudinal wheeze and allergy patterns, and to see how large and small airway function relates to RSV infection and asthma. METHODS: Follow-up at age 18 years was performed in 46 of 47 subjects with RSV and 92 of 93 controls. Assessments included questionnaire, clinical examination, skin prick tests, serum IgE antibodies to inhaled allergens, blood eosinophils, fraction of exhaled nitric oxide (FeNO), spirometry, multiple breath washout (lung clearance index, LCI) and dry air hyperventilation challenge. RESULTS: Increased prevalence of asthma/RW (39% vs 9%), clinical allergy (43% vs 17%) and sensitisation to perennial allergens (41% vs 14%) were present at age 18 in the RSV cohort compared with controls. Persistent/relapsing wheeze associated with early allergic sensitisation predominated in the RSV cohort compared with controls (30% vs 1%). Spirometric function was reduced in subjects with RSV with or without current asthma, but not in asthmatic controls. LCI was linked only to current asthma, airway hyperresponsiveness and FeNO. CONCLUSIONS: Severe early RSV bronchiolitis is associated with an increased prevalence of allergic asthma persisting into early adulthood. Small airway dysfunction (LCI) is related to current asthma and airway inflammation but not to RSV bronchiolitis. Reduced spirometry after RSV may reflect airway remodelling.

End-expiratory lung volume remains stable during N2 MBW in healthy sleeping infants.

We have previously shown that functional residual capacity (FRC) and lung clearance index were significantly greater in sleeping healthy infants when measured by N2 (nitrogen) washout using 100% O2 (oxygen) versus 4% SF6 (sulfur hexafluoride) washout using air. Following 100% O2 exposure, tidal volumes decreased by over 30%, while end-expiratory lung volume (EELV, i.e., FRC) rose markedly based on ultrasonic flow meter assessments. In the present study to investigate the mechanism behind the observed changes, N2 MBW was performed in 10 separate healthy full-term spontaneously sleeping infants, mean (range) 26 (18-31) weeks, with simultaneous EELV monitoring (respiratory inductance plethysmography, RIP) and oxygen uptake (V´O2 ) assessment during prephase air breathing, during N2 washout by exposure to 100% O2 , and subsequently during air breathing. While flow meter signals suggested a rise in ELLV by mean (SD) 26 (9) ml over the washout period, RIP signals demonstrated no EELV change. V'O2 /FRC ratio during air breathing was mean (SD) 0.43 (0.08)/min, approximately seven times higher than that calculated from adult data. We propose that our previously reported flow meter-based overestimation of EELV was in fact a physiological artifact caused by rapid and marked movement of O2 across the alveolar capillary membrane into the blood and tissue during 100% O2 exposure, without concomitant transfer of N2 to the same degree in the opposite direction. This may be driven by the high observed O2 consumption and resulting cardiac output encountered in infancy. Furthermore, the low resting lung volume in infancy may make this error in lung volume determination by N2 washout relatively large.

Inert gas washout: theoretical background and clinical utility in respiratory disease.

Inert gas washout was first described more than 60 years ago and 2 principal tests have been developed from it: the single breath and multiple breath washout (MBW) techniques. The invention of fast responding gas analysers almost 60 years ago and small computers 30 years later have facilitated breath-by-breath analysis and the development of sophisticated analysis techniques. It is now possible to detect not only the degree of pulmonary ventilation inhomogeneity, but also to gain important insight into the location of the underlying disease process. While single breath washout requires a full vital capacity effort, tidal breathing during the multiple breath test requires minimal co-operation and co-ordination, and is feasible in subjects of all ages. Available MBW normative data from parameters, such as the lung clearance index, appears to vary minimally with age, making MBW particularly useful to follow children longitudinally. Multiple breath inert gas washout has demonstrated improved sensitivity, in comparison to spirometry, in the early detection of a number of important disease processes, including cystic fibrosis. Despite this, these important techniques remain under-utilised in the clinical setting and there is a lack of commercially available devices currently available. The recent resurgence of research in this area has produced a large number of important studies and a pronounced international interest has developed in these techniques. This review article will provide an overview of the theoretical background of inert gas washout and analysis indices, review important physiological and clinical insights gained from research to date (as well as from our own experience) to illustrate its utility, and outline the challenges that lie ahead in incorporating these techniques into the mainstream clinical setting.

Exercise performance after surgery for pulmonary atresia and intact ventricular septum.

The objective of this study was to assess exercise performance in subjects born in Sweden between 1980 and 1995 and undergoing surgery for pulmonary atresia and intact ventricular septum and to identify determinants of exercise performance. Twenty-seven subjects, 16 with biventricular repair and 11 with univentricular palliation, and 28 age- and sex-matched controls completed cardiopulmonary exercise and lung function testing. Peak oxygen uptake was determined using a symptom-limited ramp bicycle exercise protocol. Regression analysis was performed to identify predictors of peak oxygen uptake (V'O(2)), The index group had lower peak V'O(2) (1.4 [median 0.8; range 2.5] l/min) than controls (1.9 [0.7; 3.1]; p < 0.05). Subjects without ventriculocoronary arterial communications (VCAC), corrected to biventricular circulation, had higher peak V'O(2), than the remaining index subjects. Decreased total lung capacity, low minute ventilation, and high physiologic dead space measured at peak exercise were all independent determinants of low peak V'O(2) Exercise capacity is generally decreased in subjects with pulmonary atresia and intact ventricular septum, although there are marked interindividual differences. Good exercise capacity was found in subjects without VCAC who had undergone biventricular repair. Decreased lung function was an unfavourable predictor of exercise capacity.

One-year evolution and variability in multiple-breath washout indices in children and young adults with primary ciliary dyskinesia.

Background and objective: Cross-sectional and longer-term studies have demonstrated abnormal yet stable multiple-breath inert gas washout (MBW) indices in patients with primary ciliary dyskinesia (PCD). This study aimed to assess the intermediate term evolution and the between-occasion variability of MBW indices in PCD over 1 year. Methods: Children and young adults with a confirmed diagnosis of PCD were included in this single-centre, prospective, observational, longitudinal study. Over 1 year, nitrogen (N2) MBW and spirometry were performed at three occasions during ordinary scheduled outpatient visits. Trends and variability in lung clearance index (LCI), moment ratios, normalized N2 concentration at six lung volume turnovers, and regional ventilation inhomogeneity indices of the conducting and intra-acinar airways (Scond*VT and Sacin*VT) were analysed using linear mixed models. Results: Forty-two patients, aged 6-29 years (median: 15.4), performed 116 N2 MBW test occasions and 96.6% were technically acceptable. A minimal, although significant, increase in LCI over 1 year (mean: 0.51 units, 95% CI: 0.12-0.91, p = 0.01) was found; while, all other N2 MBW indices and FEV1 remained unchanged. A moderate correlation was observed between LCI and FEV1 (r = -0.47, p = 0.0001). The limits of agreement between tests 1 year apart were for LCI: -1.96 to 2.98; Scond*VT: ± 0.039; Sacin*VT: -0.108 to 0.128. Conclusions: Children and young adults with PCD managed at a specialist centre showed slightly, but significant, increasing LCI and otherwise unchanged ventilation inhomogeneity indices and dynamic volumes over the intermediate term of 1 year. Estimates of the variability of N2 MBW indices may inform sample size calculations of future randomized controlled trials.

Association between Gm allotypes and asthma severity from childhood to young middle age.

Immunoglobulin constant heavy G chain (IGHG) gene polymorphisms are associated with atopy and can be determined by the serum Gm allotypes. We studied whether certain polymorphisms are related to asthma severity and to the extent or intensity of allergic sensitization in asthmatic subjects followed from childhood to young middle age. Fifty-five subjects (28 males) with childhood asthma were all followed-up prospectively on six occasions from a mean age of 9 to 35 years in a study including asthma severity scoring, spirometry, skin prick, and specific serum IgE antibody testing. At the last visit, extended lung function tests and a cold air challenge were performed, and IGHG gene polymorphisms were identified by the alternative serum IgG subclass allotypes, employing ELISA and double immunodiffusion. The 19 subjects with the homozygous IGHG*bf/*bf genotype (originating from the IGHG3*b and the IGHG1*f alleles, which are in strong linkage disequilibrium), showed significantly higher asthma scores, lower airway function, and greater bronchodilator responses from childhood to adulthood, and in middle age greater airway hyperresponsiveness, compared to the subjects with the IGHG*bf/*ga or IGHG*ga/*ga genotypes. Among the subjects sensitized to animal danders, those with the IGHG*bf/*bf genotype showed the highest specific IgE levels. In conclusion, IGHG gene polymorphisms were associated with the severity and outcome of childhood asthma, and with the intensity of allergic sensitization.

Effects of cystic fibrosis lung disease on gas mixing indices derived from alveolar slope analysis.

S(cond) and S(acin) are derived from analysis of concentration-normalized phase III slopes (Sn(III)) of a multiple breath inert gas washout. Studies in healthy and COPD subjects suggest these reflect ventilation heterogeneity in conducting and acinar airway zones respectively, but similar studies in cystic fibrosis (CF) are lacking. S(cond), S(acin) and lung clearance index (LCI, a measure of overall gas mixing efficiency) were measured in 22 adults and 18 children with CF and 17 adult and 29 child controls. Plethysmography and gas transfer measurements were performed in adults, and spirometry in all subjects. S(cond) was elevated in almost all CF patients, including children with mild disease and normal LCI. However, S(cond) did not correlate with other measurements and appeared to reach a maximum; further increase in ventilation heterogeneity being restricted to S(acin). The nature and/or severity of CF lung disease may invalidate assumptions underlying the ability to separate phase III slope analysis of ventilation heterogeneity into proximal and peripheral components, and LCI may be a better indicator of gas mixing in this population.