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

Objective To establish the nature and gestational age dependency of the pul monary venous flow velocity pattern into the left atrium relative to systol ic and diastolic phases of the cardiac cycle. Design This was a cross-sectional study of Doppler measurements of fetal pu lmonary venous inflow velocities, which were correlated with simultaneous r ecordings of transmitral and aortic flow velocity waveforms based on an equ al cardiac cycle length (+/- 5%). Results Successful recordings were obtained in 28 out of 60 (47%) normal si ngleton pregnancies at 20-36 weeks of gestation. Reproducibility of wavefor m analysis of the various phases of the cardiac cycle was satisfactory with in-patient variance ranging between 1.7% and 6.5%. A statistically signific ant increase (p < 0.05) in pulmonary venous time average velocity and veloc ity integral with advancing gestational age was established. A statisticall y significant increase (p < 0.05) of the pulmonary flow velocity integral w as also found when related to each of the systolic and diastolic segments o f the cardiac cycle, with the exception of isovolemic relaxation time. The duration of each of the diastolic and systolic segments of the cardiac cycl e, as well as the pulmonary venous velocity integral expressed as a percent age of the cardiac cycle, remained constant with advancing gestational age. Conclusions The second half of pregnancy is characterized by pulmonary veno us inflow into the left atrium throughout the cardiac cycle. Pulmonary veno us inflow into the left atrium occurs predominantly during the filling and election phases of the cardiac cycle. Absolute cardiac diastolic and systol ic time intervals as well as the percentage distribution of pulmonary venou s flow velocity integrals between these cardiac time intervals remain uncha nged with advancing gestational age.