We have previously shown that preterm infants at discharge have increased lung resistance(R1) and decreased lung compliance(C1) compared to normal fullterm infants. These changes were not related to use of oxygen, days on mechanical ventilation or other respiratory problems during the nursery stay. One of the possible explanations is that lung growth is different in the extra-uterine environment. This study was designed to further investigate this hypothesis. We studied two groups of infants, respectively, with less than 34 weeks gestation and more than 38 weeks gestation. None of the premature infants had ben on mechanical ventilation or more than 24hs on oxygen, and were on room air at the time of the study. Pulmonary function tests were performed in the first week of life for both groups and repeated after 4 weeks for the prematures. We measured lung compliance, resistance and functional residual capacity(FRC) during quiet sleep, with the infants in an incubator and no sedation. Air flow was measured with a face mask and a pneumotach and esophageal pressure with a water filled catheter. All signals were digitized in a computer and stored for further analysis. C1 and R1 were calculates by the regression analysis technique and FRC was measured by the nitrogen washout in an open circuit.
We observed that right after birth, values for C1,R1 and FRC were not different between term and preterm infants. After 4 weeks, we observed that absolute values for FRC increased and FRC corrected by weight, was not different between term and preterm infants. C1 did not change and R1(reported as cmH20/ml/sec) was significantly increased(p<0.02) in the preterm from 34 to 38 weeks. Our data suggests that lung parenchyma as reflected by compliance and airways reflected by resistance may be growing at different rates. Our data is shown in the table below:
