The reliability of spirometry is dependent on strict quality control. We examined whether quality control criteria recommended for adults could be applied to children aged 2-5 years. Forty-two children with cystic fibrosis and 37 healthy children attempted spirometry during their first visit to our laboratory. Whereas 59 children (75%) were able to produce a technically satisfactory forced expiration lasting 0.5 second, only 46 (58%) could produce an expiration lasting 1 second, with the youngest children having the most difficulty. Start of test criteria for adults were inappropriate for this age group, with only 16 of 59 children producing a volume of back extrapolation as a proportion of forced vital capacity of less than 5%, whereas all but 4 could produce a volume of back extrapolation of 80 ml or less. More than 90% of children were able to produce a second forced vital capacity and a second forced expired volume in 0.75 second within 10% of their highest. Errors in the spirometry software resulted in inaccurate reporting of expiratory duration and inappropriate timed expired volumes in some children. We describe recommendations for modified start of test and repeatability criteria for this age group, and for improvements in software to facilitate better quality control.

Background: Lung clearance index (LCI), a measure of ventilation inhomogeneity derived from the multiplebreath inert gas washout (MBW) technique, has been shown to detect abnormal lung function more readily than spirometry in preschool children with cystic fibrosis, but whether this holds true during infancy is unknown. Objectives: To compare the extent to which parameters derived from the MBW and the raised lung volume rapid thoraco-abdominal compression (RVRTC) techniques identify diminished airway function in infants with cystic fibrosis when compared with healthy controls. Methods: Measurements were performed during quiet sleep, with the tidal breathing MBW technique being performed before the forced expiratory manoeuvres. Results: Measurements were obtained in 39 infants with cystic fibrosis (mean (SD) age 41.4 (22.0) weeks) and 21 controls (37.0 (15.1) weeks). Infants with cystic fibrosis had a significantly higher respiratory rate (38 (10) vs 32 (5) bpm) and LCI (8.4 (1.5) vs 7.2 (0.3)), and significantly lower values for all forced expiratory flow-volume parameters compared with controls. Girls with cystic fibrosis had significantly lower forced expiratory volume ) than boys (mean (95% CI girls-boys): -1.2 (-2.1 to 20.3) for FEV 0.5 Z score; FEF 25-75 : -1.2 (-2.2 to 20.15)). When using both the MBW and RVRTC techniques, abnormalities were detected in 72% of the infants with cystic fibrosis, with abnormalities detected in 41% using both techniques and a further 15% by each of the two tests performed. Conclusions: These findings support the view that inflammatory and/or structural changes in the airways of children with cystic fibrosis start early in life, and have important implications regarding early detection and interventions. Monitoring of early lung disease and functional status in infants and young children with cystic fibrosis may be enhanced by using both MBW and the RVRTC.

This study aimed to investigate the evolution of airway function in infants newly diagnosed with cystic fibrosis (CF). FEV(0.5) was measured soon after diagnosis (median age of 28 weeks) and 6 months later in subjects with CF and on two occasions 6 months apart (median ages of 7.4 and 33.7 weeks) in healthy infants, using the raised-volume technique. Repeated measurements were successful in 34 CF and 32 healthy subjects. After adjustment for age, length, sex, and exposure to maternal smoking, mean FEV(0.5) was significantly lower in infants with CF both shortly after diagnosis and at the second test, with no significant difference in rate of increase in FEV(0.5) with growth between the two groups. When compared with published reference data, FEV(0.5) was reduced by an average of two z scores on both test occasions in those with CF, with 72% of individuals having an FEV(0.5) of less than 1.64 z-scores (i.e., less than the fifth percentile) on one or both test occasions. On longitudinal analysis, subjects with CF experienced a mean (95% confidence interval) reduction in FEV(0.5) of 20% (11, 28). Airway function is diminished soon after diagnosis in infants with CF and does not catch up during infancy and early childhood. These findings have important implications for early interventions in CF.