Lung function abnormalities at 6 months of age after neonatal intensive care

Respiratory function was studied in 46 preterm infants (median gestational age 28 weeks) at 6 months of age. Respiratory function was assessed by measurement of thoracic gas volume, airways resistance (from which specific conductance was calculated), and functional residual capacity. To determine the effect of the duration of neonatal intermittent positive pressure ventilation (IPPV) on respiratory function, the infants' results were divided into three groups: group A, no IPPV; group B, IPPV for less than seven days; and group C, IPPV for more than seven days. Measurements of thoracic gas volume and functional residual capacity were similar to published reference ranges and there were no significant differences between the three groups. Measurements of airways resistance and specific conductance were higher than published reference ranges (mean airways resistance of group A, 34 cm H2O/l/sec; B, 34.1 cm H2O/l/sec, and C, 30.4 cm H2O/l/sec) but there was no significant difference between the three groups. The 95% confidence intervals of the difference of the means between groups A and B were -6.94 to 6.73 cm H2O/l/sec and between groups A and C -3.8 to 11.0 cm H2O/l/sec. Our results suggest that factors other than neonatal ventilation may be more important in the pathogenesis of chronic lung function abnormalities in preterm infants.