Risk factors for bronchiectasis in children with cystic fibrosis.

BACKGROUND: Bronchiectasis develops early in the course of cystic fibrosis, being detectable in infants as young as 10 weeks of age, and is persistent and progressive. We sought to determine risk factors for the onset of bronchiectasis, using data collected by the Australian Respiratory Early Surveillance Team for Cystic Fibrosis (AREST CF) intensive surveillance program. METHODS: We examined data from 127 consecutive infants who received a diagnosis of cystic fibrosis after newborn screening. Chest computed tomography (CT) and bronchoalveolar lavage (BAL) were performed, while the children were in stable clinical condition, at 3 months and 1, 2, and 3 years of age. Longitudinal data were used to determine risk factors associated with the detection of bronchiectasis from 3 months to 3 years of age. RESULTS: The point prevalence of bronchiectasis at each visit increased from 29.3% at 3 months of age to 61.5% at 3 years of age. In multivariate analyses, risk factors for bronchiectasis were presentation with meconium ileus (odds ratio, 3.17; 95% confidence interval [CI], 1.51 to 6.66; P=0.002), respiratory symptoms at the time of CT and BAL (odds ratio, 2.27; 95% CI, 1.24 to 4.14; P=0.008), free neutrophil elastase activity in BAL fluid (odds ratio, 3.02; 95% CI, 1.70 to 5.35; P<0.001), and gas trapping on expiratory CT (odds ratio, 2.05; 95% CI, 1.17 to 3.59; P=0.01). Free neutrophil elastase activity in BAL fluid at 3 months of age was associated with persistent bronchiectasis (present on two or more sequential scans), with the odds seven times as high at 12 months of age and four times as high at 3 years of age. CONCLUSIONS: Neutrophil elastase activity in BAL fluid in early life was associated with early bronchiectasis in children with cystic fibrosis. (Funded by the National Health and Medical Research Council of Australia and Cystic Fibrosis Foundation Therapeutics.)

Impact of lung disease on respiratory impedance in young children with cystic fibrosis.

This study aimed to evaluate the ability of the forced oscillation technique (FOT) to detect underlying lung disease in preschool children with cystic fibrosis (CF) diagnosed following newborn screening.184 children (aged 3-6 years) with CF underwent lung function testing on 422 occasions using the FOT to assess respiratory resistance and reactance at the time of their annual bronchoalveolar lavage collection and chest computed tomography scan. We examined associations between FOT outcomes and the presence and progression of respiratory inflammation, infection and structural lung disease.Children with CF who had pronounced respiratory disease, including free neutrophil elastase activity, infection with pro-inflammatory pathogens and structural lung abnormalities had similar FOT outcomes to those children without detectable lung disease. In addition, the progression of lung disease over 1 year was not associated with worsening FOT outcomes.We conclude that the forced oscillation technique is relatively insensitive to detect underlying lung disease in preschool children with CF. However, FOT may still be of value in improving our understanding of the physiological changes associated with early CF lung disease.

Oxidation contributes to low glutathione in the airways of children with cystic fibrosis.

Glutathione is an important antioxidant in the lungs but its concentration is low in the airways of patients with cystic fibrosis. Whether this deficit occurs from an early age or how oxidative stress contributes to lowering glutathione is unknown. We measured glutathione, its oxidation products, myeloperoxidase, and biomarkers of hypochlorous acid in bronchoalveolar lavage from children with cystic fibrosis and disease controls using mass spectrometry and immunological techniques. The concentration of glutathione was lower in bronchoalveolar lavage from children with cystic fibrosis, whereas glutathione sulfonamide, a specific oxidation product of hypochlorous acid, was higher. Oxidised glutathione and glutathione sulfonamide correlated with myeloperoxidase and a biomarker of hypochlorous acid. The percentage of glutathione attached to proteins was higher in children with cystic fibrosis than controls. Pulmonary infections in cystic fibrosis resulted in lower levels of glutathione but higher levels of oxidised glutathione and glutathione sulfonamide in bronchoalveolar lavage. The concentration of glutathione is low in the airways of patients with cystic fibrosis from an early age. Increased oxidation of glutathione by hypochlorous acid and its attachment to proteins contribute to this deficiency. Therapies targeted against myeloperoxidase may boost antioxidant defence and slow the onset and progression of lung disease in cystic fibrosis.

Airway, but not serum or urinary, levels of YKL-40 reflect inflammation in early cystic fibrosis lung disease.

BACKGROUND: Cystic fibrosis (CF) lung disease begins in early life and is progressive with the major risk factor being an exaggerated inflammatory response. Currently, assessment of neutrophilic inflammation in early cystic fibrosis (CF) lung disease relies on bronchoalveolar lavage (BAL). The chitinase-like protein YKL-40 is raised in sputum and serum of adults with CF. We investigated YKL-40 in BAL, serum and urine to determine whether this reflected inflammation and infection in young children with CF. METHODS: YKL-40 was measured in matched samples of BAL, serum and urine obtained from 36 infants and young children with CF participating in an early surveillance program. Levels were compared to clinical data and markers of inflammation detected in the lung. RESULTS: YKL-40 in BAL correlated with pulmonary infection [ß=1.30 (SE 0.34), p < 0.001] and BAL markers of inflammation [macrophage number: r2 = 0.34, p < 0.001; neutrophil number: r2 = 0.74, p < 0.001; neutrophil elastase: r2 = 0.47, p < 0.001; CXCL8: r2 = 0.45, p < 0.001; IL-ß: r2 = 0.62, p < 0.001]. YKL-40 was detectable in serum but levels did not correlate with BAL levels in the same individuals (r2 = 0.04, p = 0.14) or with inflammatory markers. YKL-40 was below the limit of detection in urine (30 pg/ml). CONCLUSIONS: This study demonstrates that levels of the chitinase-like protein YKL-40 reflect airway inflammation and infection in early CF lung disease. The lack of increased YKL-40 in serum in the absence of systemic inflammation limits the benefit of this potential biomarker in early disease.

Distribution of early structural lung changes due to cystic fibrosis detected with chest computed tomography.

OBJECTIVE: To examine the distribution of early structural lung changes in clinically stable infants and young children with cystic fibrosis using chest computed tomography (CT). STUDY DESIGN: This cross-sectional study included 62 children aged 1-6 years with volume-controlled volumetric chest CT scans performed under general anesthesia as part of an early surveillance program. Each lobe was scored for presence and extent of bronchiectasis, mucus plugging, and air trapping using a semiquantitative score. The topographic distribution of structural abnormalities was evaluated by comparing the presence and extent of abnormalities in different lung regions and examining relationships between components. RESULTS: Although bronchiectasis was most common in the right upper lobe, overall changes in lung structure were not more common or more extensive in the upper lobes. Rather, bronchiectasis was more common in the right lung (right lung 0.95, left lung 0.68, P = .003), and mucus plugging (upper 0.41, middle 0.41, lower 0.72, P = .028) and air trapping (upper 0.79, middle 0.48, lower 0.96, P < .001) were more common in the lower lobes. The extents of bronchiectasis (P < .001) and air trapping (P = .011) were greater in the right lung. Scans with bronchiectasis were also more likely to have coexisting mucus plugging (P = .008) and air trapping (P < .001). CONCLUSION: Early structural lung disease is heterogeneously distributed in the lung. Quantitative scoring tools for studies using chest CT as an end point, and mechanistic studies that seek to better understand the pathogenesis of early cystic fibrosis lung disease, should take account of this differential topographic expression of disease early in life.

Progression of early structural lung disease in young children with cystic fibrosis assessed using CT.

BACKGROUND: Cross-sectional studies implicate neutrophilic inflammation and pulmonary infection as risk factors for early structural lung disease in infants and young children with cystic fibrosis (CF). However, the longitudinal progression in a newborn screened population has not been investigated. AIM: To determine whether early CF structural lung disease persists and progresses over 1 year and to identify factors associated with radiological persistence and progression. METHODS: 143 children aged 0.2-6.5 years with CF from a newborn screened population contributed 444 limited slice annual chest CT scans for analysis that were scored for bronchiectasis and air trapping and analysed as paired scans 1 year apart. Logistic and linear regression models, using generalised estimating equations to account for multiple measures, determined associations between persistence and progression over 1 year and age, sex, severe cystic fibrosis transmembrane regulator (CFTR) genotype, pancreatic sufficiency, current respiratory symptoms, and neutrophilic inflammation and infection measured by bronchoalveolar lavage. RESULTS: Once detected, bronchiectasis persisted in 98/133 paired scans (74%) and air trapping in 178/220 (81%). The extent of bronchiectasis increased in 139/227 (63%) of paired scans and air trapping in 121/264 (47%). Radiological progression of bronchiectasis and air trapping was associated with severe CFTR genotype, worsening neutrophilic inflammation and pulmonary infection. DISCUSSION: CT-detected structural lung disease identified in infants and young children with CF persists and progresses over 1 year in most cases, with deteriorating structural lung disease associated with worsening inflammation and pulmonary infection. Early intervention is required to prevent or arrest the progression of structural lung disease in young children with CF.

Inflammatory responses to individual microorganisms in the lungs of children with cystic fibrosis.

BACKGROUND: We hypothesized that the inflammatory response in the lungs of children with cystic fibrosis (CF) would vary with the type of infecting organism, being greatest with Pseudomonas aeruginosa and Staphylococcus aureus. METHODS: A microbiological surveillance program based on annual bronchoalveolar lavage (BAL) collected fluid for culture and assessment of inflammation was conducted. Primary analyses compared inflammation in samples that grew a single organism with uninfected samples in cross-sectional and longitudinal analyses. RESULTS: Results were available for 653 samples from 215 children with CF aged 24 days to 7 years. A single agent was associated with pulmonary infection (≥10(5) cfu/mL) in 67 BAL samples, with P. aeruginosa (n = 25), S. aureus (n = 17), and Aspergillus species (n = 19) being the most common. These microorganisms were associated with increased levels of inflammation, with P. aeruginosa being the most proinflammatory. Mixed oral flora (MOF) alone was isolated from 165 BAL samples from 112 patients, with 97 of these samples having a bacterial density ≥10(5) cfu/mL, and was associated with increased pulmonary inflammation (P < .001). For patients with current, but not past, infections there was an association with a greater inflammatory response, compared with those who were never infected (P < .05). However, previous infection with S. aureus was associated with a greater inflammatory response in subsequent BAL. CONCLUSIONS: Pulmonary infection with P. aeruginosa, S. aureus, or Aspergillus species and growth of MOF was associated with significant inflammatory responses in young children with CF. Our data support the use of specific surveillance and eradication programs for these organisms. The inflammatory response to MOF requires additional investigation.

Evolution of pulmonary inflammation and nutritional status in infants and young children with cystic fibrosis.

INTRODUCTION: Improved nutrition is the major proven benefit of newborn screening programmes for cystic fibrosis (CF) and is associated with better clinical outcomes. It was hypothesised that early pulmonary inflammation and infection in infants with CF is associated with worse nutrition. METHODS: Weight, height and pulmonary inflammation and infection in bronchoalveolar lavage (BAL) were assessed shortly after diagnosis in infants with CF and again at 1, 2 and 3 years of age. Body mass index (BMI) was expressed as z-scores. Inflammatory cells and cytokines (interleukin 1ß (IL-1ß), IL-6, IL-8 and tumour necrosis factor α (TNFα)), free neutrophil elastase activity and myeloperoxidase were measured in BAL. Mixed effects modelling was used to assess longitudinal associations between pulmonary inflammation, pulmonary infection (Staphylococcus aureus and Pseudomonas aeruginosa) and BMI z-score after adjusting for potential confounding factors. RESULTS: Forty-two infants were studied (16 (38%) male; 39 (93%) pancreatic insufficient); 36 were diagnosed by newborn screening (at median age 4 weeks) and six by early clinical diagnosis (meconium ileus). Thirty-one (74%) received antistaphylococcal antibiotics. More than two-thirds were asymptomatic at each assessment. Mean BMI z-scores were -1.5 at diagnosis and 0.5, -0.2 and -0.1 at 1, 2 and 3 years, respectively. Neutrophil elastase and infection with S aureus were associated with lower BMI, whereas age (p=0.01) and antistaphylococcal antibiotics (p=0.013) were associated with increased BMI. On average, each log(10) increase in free neutrophil elastase activity was associated with a 0.43 (95% CI 0.06 to 0.79) reduction in BMI z-score. DISCUSSION: Early nutritional status is associated with the underlying pulmonary pathophysiology in CF, and better understanding of these relationships is required. Studies are required to assess whether interventions can decrease pulmonary inflammation and improve nutrition. Early surveillance will enable such targeted interventions with the aim of improving these important clinical outcomes.

Lung disease at diagnosis in infants with cystic fibrosis detected by newborn screening.

RATIONALE: The promise of newborn screening (NBS) for cystic fibrosis (CF) has not been fully realized, and the extent of improvement in respiratory outcomes is unclear. We hypothesized that significant lung disease was present at diagnosis. OBJECTIVES: To determine the extent of lung disease in a geographically defined population of infants with CF diagnosed after detection by NBS. METHODS: Fifty-seven infants (median age, 3.6 mo) with CF underwent bronchoalveolar lavage and chest computed tomography (CT) using a three-slice inspiratory and expiratory protocol. MEASUREMENTS AND MAIN RESULTS: Despite the absence of respiratory symptoms in 48 (84.2%) of infants, a substantial proportion had lung disease with bacterial infection detected in 12 (21.1%), including Staphylococcus aureus (n = 4) and Pseudomonas aeruginosa (n = 3); neutrophilic inflammation (41. 4 x 10(3) cells/ml representing 18.7% of total cell count); proinflammatory cytokines, with 44 (77.2%) having detectable IL-8; and 17 (29.8%) having detectable free neutrophil elastase activity. Inflammation was increased in those with infection and respiratory symptoms; however, the majority of those infected were asymptomatic. Radiologic evidence of structural lung disease was common, with 46 (80.7%) having an abnormal CT; 11 (18.6%) had bronchial dilatation, 27 (45.0%) had bronchial wall thickening, and 40 (66.7%) had gas trapping. On multivariate analysis, free neutrophil elastase activity was associated with structural lung disease. Most children with structural lung disease had no clinically apparent lung disease. CONCLUSIONS: These data support the need for full evaluation in infancy and argue for new treatment strategies, especially those targeting neutrophilic inflammation, if the promise of NBS for CF is to be realized.

Bronchiectasis in infants and preschool children diagnosed with cystic fibrosis after newborn screening.

OBJECTIVES: To determine the prevalence of bronchiectasis in young children with cystic fibrosis (CF) diagnosed after newborn screening (NBS) and the relationship of bronchiectasis to pulmonary inflammation and infection. STUDY DESIGN: Children were diagnosed with CF after NBS. Computed tomography and bronchoalveolar lavage were performed with anesthesia (n = 96). Scans were analyzed for the presence and extent of abnormalities. RESULTS: The prevalence of bronchiectasis was 22% and increased with age (P = .001). Factors associated with bronchiectasis included absolute neutrophil count (P = .03), neutrophil elastase concentration (P = .001), and Pseudomonas aeruginosa infection (P = .03). CONCLUSIONS: Pulmonary abnormalities are common in infants and young children with CF and relate to neutrophilic inflammation and infection with P. aeruginosa. Current models of care for infants with CF fail to prevent respiratory sequelae. Bronchiectasis is a clinically relevant endpoint that could be used for intervention trials that commence soon after CF is diagnosed after NBS.

Disease surveillance using bronchoalveolar lavage.

The role of pulmonary infection and inflammation in the pathogenesis of destructive lung disease in cystic fibrosis (CF) is undisputed. The use of bronchoscopy and bronchoalveolar lavage (BAL) has demonstrated that these processes may begin early in life and be present in the absence of overt clinical symptoms. Some children diagnosed following newborn screening can be infected with Pseudomonas aeruginosa in infancy. Studies using BAL have demonstrated a relationship between lower airway inflammation and bacterial load in the lungs; however, inflammation may occur in the absence of obvious current infection. BAL has the potential to provide a greater understanding of the pathogenesis of CF lung disease and microbiological surveillance provides the opportunity for early detection and eradication of P. aeruginosa. Lack of standardization inhibits the ability to compare data from different centres and to optimize treatment strategies. This review discusses the recommendations from a workshop held in early 2007 aimed at achieving a standardized approach to BAL in infants and young children with CF.

Early detection of lung disease in children with cystic fibrosis using lung function.

Measurement of lung function is routine in older children and adults with cystic fibrosis (CF) but not in infants and preschool children. Pulmonary infection, neutrophil-dominated inflammation and clinical exacerbations in young children similar to those seen in older subjects have been identified and highlight the urgent need to evaluate lung function in early life. Mounting evidence suggests lung function techniques sensitive to changes in peripheral lung function may be required to detect the early functional abnormalities in infants and preschool children with CF. In addition, the majority of studies in young children with CF have not reported longitudinal data and therefore the prognostic potential of existing lung function methods to track disease progression is poorly understood. This review aims to describe recent research findings in infants and preschool children and to outline currently available lung function techniques, issues around their standardization and their relative advantages and disadvantages in young children with CF.

Brief exposure to cigarette smoke impairs airway epithelial cell innate anti-viral defence.

BACKGROUND: Human rhinovirus (hRV) infections commonly cause acute upper respiratory infections and asthma exacerbations. Environmental cigarette smoke exposure is associated with a significant increase in the risk for these infections in children. OBJECTIVE: To determine the impact of short-term exposure to cigarette smoke on innate immune responses of airway epithelial cells infected with hRV. METHODS: A human bronchial epithelial cell line (HBEC-3KT) was exposed to cigarette smoke extract (CSE) for 30 min and subsequently infected with hRV serotype 1B. Viral-induced cytokine release was measured with AlphaLISA and viral replication quantified by shed viral titer and intracellular viral copy number 24h post-infection. RESULTS: CSE induced a concentration-dependent decrease in CXCL10 (p<0.001) and IFN-ß (p<0.001), with a 79% reduction at the highest dose with an associated 3-fold increase in shed virus. These effects were maintained when infection was delayed up to 24h post CSE exposure. Exogenous IFN-ß treatment at t=0 after infection blunts the effects of CSE on viral replication (p<0.05). CONCLUSION: A single exposure of 30 min to cigarette smoke has a lasting impact on epithelial innate defence providing a plausible mechanism for the increase in respiratory infections seen in children exposed to second-hand tobacco smoke.

Reference ranges for Mexican preschool-aged children using the forced oscillation technique.

INTRODUCTION: Recently, multi-ethnic reference ranges for spirometry have been created for use worldwide. In comparison, forced oscillation technique (FOT) reference values are limited to specific equipment and study populations, with current FOT reference ranges created in a Caucasian population. We aimed to develop FOT reference ranges for preschool-aged Mexican children and to compare these with current FOT reference ranges. PATIENTS AND METHODS: Respiratory resistance (Rrs) and reactance (Xrs) was measured in healthy Mexican children three to five years of age using commercial FOT equipment. The relationship between height and Rrs and Xrs was determined using regression analyses, taking into account age, weight, sex, and exposure to tobacco smoke. Reference equations were calculated for the Mexican children and Z-scores determined for Rrs and Xrs at 6 and 8Hz. A paired t-test assessed the difference in Z-scores between the Australian reference values and those created for the Mexican cohort. RESULTS: FOT was successfully measured in 584 children. Height was a significant predictor of Rrs and Xrs at 6 and 8Hz (P<.05). Z-scores calculated using the Australian reference equations overestimated lung function in Mexican children for both Rrs and Xrs at 6 and 8Hz (P<.001). CONCLUSION: The development of FOT reference ranges specific to Mexican preschool-aged children will allow for the correct interpretation of FOT measurements. This study also showed that current FOT reference ranges overestimate lung function in Mexican children. Highlighting, the importance of using ethnic appropriate reference ranges for interpreting lung function.

Lung function testing in preschool-aged children with cystic fibrosis in the clinical setting.

In cystic fibrosis (CF) lung function testing is a means of monitoring progression of lung disease. The preschool years have often been referred to as the "silent years" due to the previous lack suitable measures of lung function testing in this age group. This review outlines the various techniques of lung function testing in preschool children with CF in the clinical setting. This includes measures requiring tidal breathing including the forced oscillation technique, the interrupter technique, plethysmography, and multiple breath washout, as well as spirometry that requires respiratory maneuvers. We describe the feasibility and variability of different lung function methods used in preschoolers and report measurements made during tidal breathing have greater feasibility, although greater variability compared to spirometry. We also report associations with lung function and markers of CF lung disease. In the preschool age group measurements made during tidal breathing may be more appropriate in the clinic setting than those that require a higher degree of cooperation and specific respiratory maneuvers.maneuvers.

Identifying peroxidases and their oxidants in the early pathology of cystic fibrosis.

We aimed to determine whether myeloperoxidase (MPO) is the main peroxidase present in the airways of children with cystic fibrosis (CF) and to assess which oxidants it produces and whether they are associated with clinical features of CF. Children with CF (n=54) and without CF (n=16) underwent bronchoscopy and bronchoalveolar lavage (BAL) for assessment of pulmonary infection and inflammation. BAL fluid was analyzed for MPO, halogenated tyrosines as markers of hypohalous acids, thiocyanate, and protein carbonyls. MPO was the only peroxidase detected in BAL samples from children with CF and its concentration was markedly higher than in controls. Levels of 3-chlorotyrosine and 3-bromotyrosine in proteins were higher in the CF group. They correlated with neutrophils and MPO. The concentration of thiocyanate in BAL samples was below 1µM. Protein carbonyl levels correlated with MPO and halogenated tyrosines in patients with CF. Levels of MPO and halogenated tyrosines were higher in children with infections, especially Pseudomonas aeruginosa, and in the presence of respiratory symptoms. They also correlated with the Kanga clinical score. Our findings suggest that MPO produces hypobromous acid as well as hypochlorous acid in the airways of children with CF and that these oxidants are involved in the early pathogenesis of CF.

Bronchiectasis in an asymptomatic infant with cystic fibrosis diagnosed following newborn screening.

Many countries have introduced newborn screening for cystic fibrosis to facilitate diagnosis prior to the development of lung disease. Although most infants with cystic fibrosis are asymptomatic from a respiratory point of view at diagnosis, structural lung disease has been detected by computed tomography. We present a case of an asymptomatic infant with cystic fibrosis diagnosed following newborn screening who had endobronchial infection with Pseudomonas aeruginosa and radiological evidence of bronchiectasis at 3 months of age.

Application of a shortened inhaled adenosine-5'-monophosphate challenge in young children using the forced oscillation technique.

BACKGROUND: Adenosine-5'-monophosphate (AMP) is an indirect challenge agent thought to reflect allergic airway inflammation. The forced oscillation technique (FOT) is ideal for use in young children and is suitable for inhaled challenge studies in patients who are in this age group. We assessed the agreement between a shortened and a standard AMP challenge and the repeatability of the shortened AMP challenge using FOT as a primary outcome variable. METHODS: Eighteen children completed a shortened and a standard AMP challenge, and 20 children completed repeated shortened AMP challenges. The children inhaled nebulized AMP tidally for 2 min, following which the presence of wheeze and pulse oximetric saturation (Spo(2)) was recorded prior to FOT measurement. Testing continued until the maximum dose was reached or until wheeze, a decrease in Spo(2) to < 90%, or an increase in respiratory resistance at 8 Hz of 2.0 hPa/s/L or 30% was noted. Concordance was assessed as a binary response, and agreement in provocation concentrations (PCs) causing a response was assessed with intraclass correlations. RESULTS: There was a high degree of concordance between the shortened and standard AMP protocols (94%) and repeated shortened AMP protocols (100%). The mean log(10) PCs displayed a high degree of agreement for both AMP protocols, with intraclass correlation coefficients of 0.94 (95% confidence interval, 0.85 to 0.98) and 0.94 (95% confidence interval, 0.82 to 0.98), respectively. CONCLUSIONS: We demonstrated that a shortened AMP challenge that can be applied to young children is comparable to the standard AMP challenge and is highly repeatable. Further studies in young children to assess the clinical role of a shortened AMP challenge using FOT are required.

Respiratory function in healthy young children using forced oscillations.

BACKGROUND: Monitoring of respiratory function is important in the diagnosis and management of respiratory disease. The forced oscillation technique requires minimal patient cooperation and is ideal for the determination of respiratory function in young children. This study aimed to develop reference ranges and to document the repeatability in healthy young children using commercially available forced oscillation equipment. METHODS: The forced oscillation technique, which uses a pseudo-random noise forcing signal between 4 and 48 Hz, was used to measure respiratory function in healthy young children. Repeatability over a 15 min period was also assessed. Regression equations and standardised Z scores were determined for respiratory resistance (Rrs) and reactance (Xrs) at 6, 8 and 10 Hz. RESULTS: Respiratory function was obtained in 158 healthy children aged two to seven years and between 92 and 127 cm in height. Oscillatory respiratory mechanics exhibited linear relationships with height. Within-test variability for resistance ranged between 6% and 9% and between 17% and 20% for reactance. Resistance and reactance did not change significantly over a 15 min period. CONCLUSIONS: Reference ranges for respiratory impedance variables in healthy children aged two to seven years are presented. The short-term repeatability of forced oscillatory variables in this age group is reported, allowing appropriate cut-off values for therapeutic interventions to be defined.