The natural history of pulmonary artery pressure and extrapulmonary shunting in acute hyaline membrane disease was studied by serial Doppler echocardiography in 57 preterm infants, 38 with, and 19 without, hyaline membrane disease. Pulmonary artery pressure was assessed non-invasively by its inverse relationship with the ratio of pulmonary artery Doppler time to peak velocity: right ventricular ejection time. The mean ratio was significantly lower in the infants with hyaline membrane disease. The mean ratio for each infant with hyaline membrane disease varied widely and did not correlate with criteria of maturity or severity of disease. Individual ratios correlated with arterial pH. Between 60-80 hours after birth, 14 of 18 infants with hyaline membrane disease (78%) and one of 19 without (5%) had patent ductus arteriosus. Left to right and bidirectional shunting at ductal and atrial level were common; pure right to left shunting was uncommon. The mean ratio seen with bidirectional shunting was significantly lower than that seen with left to right shunting. Ratios and patterns of extra pulmonary shunting were similar when the fractional inspired oxygen (FIO2) was greater than 0.9 compared with when it was less than 0.9. Pulmonary artery pressure is high during the acute phase of hyaline membrane disease but varies widely among infants. A few infants have extrapulmonary right to left shunting, and these infants are difficult to detect clinically.
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