Pulmonary venous flow from fetal to neonatal period

There are few reports about the effect of fetal or transitional circulation on the pulmonary venous flow. The purposes of this study were to investigate flow patterns of the pulmonary vein serially from fetal to neonatal period and to determine the relationship between pulmonary venous flow and other parameters from aortic and mitral valve. Pulmonary venous flow velocity was analyzed in 21 normal term human fetuses. Postnatal follow-up studies were performed at 1, 6, 24 h, 3 days, 1 week and 1 month. In each time point, pulsed Doppler echocardiography was used to interrogate right upper pulmonary vein, mitral and aortic valve. The measured parameters of pulmonary vein were heart rate, velocity time integral (VTI), and velocities at systolic peak (S), at diastolic peak (D), at nadir between S and D (O), and at nadir between D and the next S (X). E/A ratio and VTI were measured for mitral valve and peak systolic velocity and VTI for aortic valve. Pulmonary venous flow in fetus was phasic and continuous with low velocity. One hour after birth, without a change of flow pattern, all velocities increased dramatically. These high velocities showed a significant decrease during 24 h after birth. Three days after birth, the velocity decreased slightly and flow pattern changed from continuous to interrupted pattern with or without atrial reversal. No Doppler parameters from aortic or mitral valve showed any correlation with parameters from pulmonary vein. In conclusion, the flow pattern of the pulmonary vein in fetus may result from low pulmonary flow and decreased capacitance of the pulmonary venous system. Sudden increase in the pulmonary flow after birth is likely to be responsible for the highest velocities recorded immediately after birth. Left to right shunt through the ductus arteriosus may also contribute to the flow pattern observed in the first several days, as do changes in reservoir function of the pulmonary vein.