The changes in pulmonary artery pressure during recovery from hyaline membrane disease were studied by serial Doppler echocardiography on 37 preterm infants. Pulmonary artery pressure was assessed noninvasively by its inverse relationship with the ratio of pulmonary artery Doppler time to peak velocity and right ventricular ejection time. The pattern of rise in ratio after the acute phase of hyaline membrane disease divided into three types. In 25 infants the ratio returned to the normal range: in 12 (group 1) at the same time as the fractional inspired oxygen fell below 0.5 and in 13 (group 2) after a delay of at least 24 hours. In 12 infants (group 3) the ratio remained below the normal range during their hospital stay, suggesting pulmonary artery pressure remained high. Infants in group 3 were of significantly lower gestation and required oxygen treatment for significantly longer than infants in groups 1 and 2. Persistently raised pulmonary pressures in group 3 may reflect lung damage either directly affecting pulmonary vasculature or exerting a secondary effect on pulmonary vascular resistance through hypoxaemia.
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