Thirty seven healthy infants (18 born at full term and 19 preterm) were studied serially with cross sectional and Doppler echocardiography to compare their postnatal circulatory adaptation. Pulmonary artery pressure was assessed by its inverse relationship with the ratio of pulmonary artery time to peak velocity and right ventricular ejection time measured from Doppler waveform. Patency of the ductus arteriosus and interatrial shunting were assessed by imaging and Doppler ultrasound. The ratio rose after birth in all infants; it rose more slowly in the preterm infants. After 6 hours of age the mean was significantly less in the preterm group, the greatest difference being between 25 and 36 hours. By 73 to 96 hours the difference was no longer significant. There was a trend towards later ductal closure in the preterm infants but this was not significant. Atrial shunting level varied, but some left to right shunting was seen in all infants satisfactorily studied. Pulmonary artery pressure seems to fall more slowly after preterm birth even in the absence of respiratory problems, but ductal shunting persisting for more than three days is unusual in healthy preterm infants.
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