Fetal pulmonary venous flow into the left atrium relative to diastolic and systolic cardiac time intervals

Abstract

Objective. To establish the nature and gestational age dependency of the pulmonary venous flow velocity pattern into the left atrium relative to systolic and diastolic phases of the cardiac cycle. Design. This was a cross-sectional study of Doppler measurements of fetal pulmonary venous inflow velocities, which were correlated with simultaneous recording of transmitral and aortic flow velocity waveforms based on an equal cardiac cycle length (±5%). Results. Successful recordings were obtained in 28 out of 60 (47%) normal singleton pregnancies at 20-36 weeks of gestation. Reproducibility of waveform analysis of the various phases of the cardiac cycle was satisfactory, within-patient variance ranging between 1.7% and 6.5%. A statistically significant increase (p < 0.05) in pulmonary venous time average velocity and velocity integral with advancing gestational age was established. A statistically significant increase (p < 0.05) of the pulmonary flow velocity integral was also found when related to each of the systolic and diastolic segments of the cardiac cycle, with the exception of isovolemic relaxation time. The duration of each of the diastolic and systolic segments of the cardiac cycle, as well as the pulmonary venous velocity integral expressed as a percentage of the cardiac cycle, remained constant with advancing gestational age. Conclusions. The second half of pregnancy is characterized by pulmonary venous inflow into the left atrium throughout the cardiac cycle. Pulmonary venous inflow into the left atrium occurs predominantly during the filling and ejection phases of the cardiac cycle. Absolute cardiac diastolic and systolic time intervals as well as the percentage distribution of pulmonary venous time intervals remain unchanged with advancing gestational age.