Doppler velocimetry in branch pulmonary arteries of normal human fetuses during the second half of gestation

The objective of the present study was to determine the characteristics of Doppler flow velocity wave forms in branch pulmonary arteries in relation to gestational age. A total of 111 singleton normal pregnancies were studied during the second half of pregnancy using a combined color-coded Doppler and two-dimensional real-time ultrasound system. Pulsed Doppler measurements of the most proximal branch of the right or left pulmonary artery were attempted during fetal apnea from a transverse cross-section of the fetal chest at the level of the cardiac four-chamber view after visualization with color Doppler. The success rate in obtaining the pulmonary arterial wave form was 85%. The wave form displayed a rapid systolic velocity acceleration, followed by an initially rapid but then more gradual velocity deceleration which was interrupted in most cases by a short reversed flow interval at the beginning of the diastolic phase of the cardiac cycle. The diastolic phase was characterized by forward flow. Peak systolic, end-diastolic and time-averaged velocity, pulsatility index, and systolic integral remained constant during gestation. Changes in vessel diameter or compliance may play a role in this. A gestational age-dependent rise was established for peak diastolic velocity, diastolic integral, and early peak diastolic reverse flow, whereas a gestational age-determined decline was found for the peak systolic/peak diastolic ratio. Fetal heart rate demonstrated a statistically significant increase relative to gestational age. However, the observed relation between the flow velocity wave form parameters, pulsatility index calculations, and gestational age was independent of fetal heart rate. It is speculated that peak diastolic velocity, diastolic integral, and peak systolic/peak diastolic ratio rather than the pulsatility index are useful in detecting gestational age-related changes in human fetal pulmonary vascular resistance.