Lung function and energy expenditure in infants with cystic fibrosis

Lung disease is thought to occur early in children with cystic fibrosis (CF) and it is recognised that nutritional status relates to prognosis, however the natural history of lung disease and how it might relate to nutritional measures and particularly energy expenditure require further evaluation. Methods to objectively evaluate lung disease are required so that interventions may be planned and assessed. Intervention studies in infancy will also require assessment in the toddler years through to school age when spirometry may be more reliable. Therefore methods of measuring lung function, particularly non-invasive methods, need to be developed. Seventeen infants with CF diagnosed through neonatal screening and 9 healthy control infants were enrolled in a prospective, cohort study and lung function and energy expenditure were measured from shortly after birth every three months until aged two years. Lung function was measured using the SensorMedics pulmonary function cart. Respiratory system resistance was higher and specific respiratory system conductance was lower in CF infants than control infants from three months of age until 18 months and there was a trend for this to continue to two years of age. There was no difference in FRCN2 between the groups. Resting energy expenditure expressed per gram of total body potassium (REE/TBK) was higher in CF infants than controls and was highest in infants who were homozygous for F508 mutation. There was no detectable relationship between measurements of lung function and REE/TBK. Young children with CF aged between 6 months and 5 years of age had lung function measured using the same technique to assess the suitability of the methods for toddlers. The method was not found to be suitable in children over the age of two years. Tidal breathing flow-volume curves (TBFV) are non invasive and the shape of the expiratory TBFV may change with obstructive airways disease. Thirty nine subjects took part in a study to examine the stability of a new index based on the shape of the expiratory flow- volume curve called Ai compared with the widely used index of shape tPTEF/tE with change in respiratory rate (RR). Eight tidal breathing flow volume loops were stored at resting RR and then RR was increased by 10 breaths per minute and 8 loops stored at each rate until a rate of 60 breaths per minute was reached. Subjects also performed spirometry and lung volumes were measured by whole body plethysmography. Neither of the indices varied much with RR, but Ai had less than one third of the variability seen in tPTEF/tE. The correlation between FEV1 and both indices was very similar