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RATIONALE: Advances in spirometry measurement techniques have made it possible to obtain measurements in children as young as 3 years of age; however, in practice, application remains limited by the lack of appropriate reference data for young children, which are often based on limited population-specific samples. OBJECTIVES: We aimed to build on previous models by collating existing reference data in young children (aged 3-7 years), to produce updated prediction equations that span the preschool years and that are also linked to established reference equations for older children and adults. METHODS: The Asthma UK Collaborative initiative was established to collate lung function data from healthy young children aged 3-7 years. Collaborators included researchers with access to pulmonary function test data in healthy preschool children. Spirometry centiles were created using the LMS (Lambda-Mu-Sigma) method and extend previously published equations down to 3 years of age. MAIN RESULTS: The Asthma UK centiles charts for spirometry are based on the largest sample of healthy young Caucasian children aged 3-7 years (n=3777) from 15 centers across 11 countries and provide a continuous reference with a smooth transition into adolescence and adulthood. These equations improve existing pediatric equations by considering the between-subject variability to define a more appropriate age-dependent lower limit of normal. The collated dataset reflects a variety of equipment, measurement protocols and population characteristics and may be generalizable across different populations. CONCLUSIONS: We present prediction equations for spirometry for preschool children and provide a foundation which will facilitate continued updating.

Rationale: It remains unclear whether premature birth, in the absence of neonatal respiratory disease, results in abnormal growth and development of the lung. We previously reported that a group of healthy infants born at 32–34 weeks' gestation and without respiratory complications had decreased forced expiratory flows and normal forced vital capacities at 2 months of age. Objectives: Our current study evaluated whether these healthy infants born prematurely exhibited improvement or “catch-up” in their lung function during the second year of life. Methods: Longitudinal measurements of forced expiratory flows by the raised volume rapid thoracic compression technique were obtained in the first and the second years of life for infants born prematurely at 32.7 (range, 30–34) weeks' gestation (n = 26) and infants born at full term (n = 24). Measurements and Main Results: Healthy infants born prematurely demonstrate decreased forced expiratory flows and normal forced vital capacities in the first and second years of life. In addition, the increases in lung function with growth were similar to full-term infants. Conclusions: Persistently reduced flows in the presence of normal forced vital capacity and the absence of catch-up growth in airway function suggest that premature birth is associated with altered lung development.

Preterm delivery has been associated with a higher incidence of respiratory morbidity even in infants that do not have significant respiratory disease during the neonatal period. Reduced flows have been reported in children and adolescents born prematurely.The aim of this study was to assess lung function in healthy preterm infants in the first months of life.Preterm infants with less than 48 h of supplemental oxygen were recruited. Lung function was assessed by the raised-volume rapid thoracic compression in the first months of life. The control group consisted of full-term infants without a history of respiratory diseases.Sixty-two preterm (29 male) and 27 full-term (10 male) infants were tested. Adjusting for length, age, and sex, we found a mean significant reduction of 92 ml/s (22%) in FEF(50), 73 ml/s (21%) in FEF(25-75), and 19 ml (28%) in FEV(0.5) in the preterm group. These differences in expiratory flows remained significant using another model that adjusts for lung volume (p0.01 for FEF(50), FEF(25-75), and FEV(0.5), and p0.05 for FEF(75)). In the preterm group, after adjusting for length, male sex, lower gestational age, and increased weight were significantly and independently associated with reduced flows.Our findings confirm that prematurity is independently associated with reduced lung function and that this is detectable in the first months of life. Male sex, lower gestational age, and weight are important predictors for reduced expiratory flows in this group.

Forced expiratory flows (FEF) can be measured in infants from lung volumes initiated near total lung capacity. In order to establish reference values and to evaluate lung growth, we obtained measurements in 155 healthy subjects between 3 and 149 wk of age. Forced vital capacity (FVC) was highly correlated with body length; however, after accounting for length, age was also significant. When subjects were divided at the median age (40 wk) younger compared with older subjects had a significantly larger slope for length (3.7 versus 2.8; p = 0.002). The flow parameters (FEF(50), FEF(75), FEF(85), and FEF(25-75)) were highly correlated with length, and those infants whose mothers smoked had lower flows. For FEF(75), male subjects had lower flows than female subjects. The relationship between FEF and volume was assessed using FEV(0.5)/FVC, which decreased with increasing length. Smaller subjects emptied their lung volume proportionately faster. We conclude that our study provides reference values for this age group and demonstrates that smoke-exposed infants and male subjects have decreased FEF. In addition, our findings indicate that lung volume increases most rapidly during the first year of life and that airways are large relative to lung volume very early in life.

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We evaluated the ability of forced expiratory flow volume curves from raised lung volumes to assess airway function among infants with differing severities of respiratory symptoms. Group 1 (n = 33) had previous respiratory symptoms but were currently asymptomatic; group 2 (n = 36) was symptomatic at the time of evaluation. As a control group, we used our previously published sample of 155 healthy infants. Flow volume curves were quantified by FVC, FEF50, FEF75, FEF25-75, FEV0.5, and FEV0.5/FVC, which were expressed as Z scores. All variables except FVC had Z scores that were significantly less than zero and distinguished groups 1 and 2 with progressively lower Z scores. The mean Z scores of the flow variables (FEF50%, FEF75%, and FEF25-75%) were more negative than the Z scores for the timed expired volumes (FEV0.5 or FEV0.5/FVC) for both groups. In general, measures of flow identified a greater number of infants with abnormal lung function than measures of timed volume; FEF50 had the highest performance in detecting abnormal lung function. In summary, forced expiratory maneuvers obtained by the raised volume rapid compression technique can discriminate among groups of infants with differing severity of respiratory symptoms, and measures of forced expiratory flows were better than timed expiratory volume in detecting abnormal airway function.

Forced expiratory flows by the rapid compression technique are often used to assess airway function in infants; however, it remains unclear as to whether flow limitation (FL) is achieved. Studies in adults have used negative expiratory pressure (NEP) at the airway opening as a noninvasive technique to assess whether FL is achieved. An increase in flow with NEP indicates that FL has not been achieved, whereas no increase in flow with NEP indicates FL has been achieved. In the adult studies, the change in flow was assessed by visual inspection of the flow-volume curve. We evaluated whether NEP could be used to assess FL during forced expiration in infants. In addition, we quantified the change in flow secondary to NEP. We applied -5 cm H(2)O NEP to four infants during forced expiratory maneuvers. The step increase in flow with NEP was always less than 5% at high jacket compression pressures and consistent with FL. For one subject, FL was also confirmed from isovolume pressure flow-curves measured with an esophageal catheter. We conclude that NEP can be used in infants to assess FL during forced expiratory maneuvers by the rapid compression technique.

Continuous positive airway pressure (CPAP) is used to minimize airway collapse in infants with tracheomalacia. Forced expiratory flows (FEFs) at functional residual capacity (FRC) increase with increasing CPAP in infants with tracheomalacia, and it has been suggested that CPAP prevents airway collapse by "stenting" the airway open. Since FEF is greater at higher than at lower lung volumes, we evaluated whether the increase in flow measured at FRC (V FRC) with CPAP could be explained by the increase in FRC with CPAP. We measured full FEF-volume curves at CPAP levels of 0, 4, and 8 cm H2O in six infants with tracheomalacia and five healthy control infants. In both groups of infants, FVC did not change with CPAP; however, inspiratory capacity (IC) decreased and thus FRC increased with increasing CPAP. FEFs at FRC increased with increasing levels of CPAP; however, the FEFs at 50% and 75% of expired volume were not different for the three levels of CPAP for both groups of infants. Our finding that FEFs measured at the same lung volumes did not differ for the different levels of CPAP indicates that CPAP affects forced flows primarily by increasing lung volume.