Peripheral right pulmonary artery blood flow velocimetry: Doppler sonographic study of normal and abnormal fetuses.

Abstract

ecent advances in ultrasound equipment have facilitated exploration of small fetal blood vessels using noninvasive Doppler sonographic technology. Although much information has been accumulated regarding physiologic and pathologic fetal blood flow in the fetal aorta and the cerebral, renal, and splenic arteries, 1 limited knowledge exists on blood flow in the human fetal lung circulation. 2-3 Recently, investigators in two studies found that the PI in the pulmonary artery of normally growing fetuses decreased significantly during the second half of pregnancy. 4,5 These results contradict those of a previous study that showed a stable high-resistance value for the pulmonary circulation during gestation. 6 Laudy and coworkers 7 showed a significant decrease in the PI of the right pulmonary artery in an abnormal case of a fetus suspected of having lung hypoplasia. Since histologic studies in hypoplastic lungs have shown increased pulmonary arterial muscularization, 8,9 it was hypothesized that these changes may lead to alter- The knowledge of fetal lung circulation in normal and abnormal human fetuses is limited. Our objectives were to assess normal values for flow velocity waveforms in the fetal pulmonic circulation and to test the hypothesis that Doppler velocimetry can predict lung hypoplasia. In a cross-sectional study, peripheral right pulmonary artery flow velocimetry was investigated prospectively in 96 healthy fetuses between 14 and 37 weeks' gestation and four fetuses with abnormalities known to induce lung hypoplasia. The pulsatility index was used to quantify the velocity waveforms. In normal fetuses the mean pulsatility index in the peripheral right pulmonary artery was low, being equivalent to that corresponding to 14 to 17 weeks' gestation (2.89; confidence interval = 2.35 to 3.42), increasing at midgestation to 3.44, with a confidence interval of 3.04 to 3.83; P < 0.01. Thereafter, during the late second and third trimesters the mean pulsatility index did not change significantly with GA, being 3.66 (confidence interval = 3.04 to 4.04) at term. In fetuses with proven lung hypoplasia, the pulsatility index measurements were within the 95% confidence limits of those for normal fetuses. In a normal pregnancy, except for the early stages, a relatively stable high vascular resistance of the fetal pulmonary circulation was found. Our preliminary data suggest that the pulsatility index of the lung circulation cannot be used as an indicator of lung hypoplasia.

The fetal lung 2: pulmonary hypoplasia

“…Nevertheless, Rasanen 133 observed a decrease in pulsatility index until 31 weeks of gestation followed by a constant pattern thereafter, whereas Mitchell 138 and Rizzo 142 established a significant reduction in pulsatility index (or resistance index) throughout the second half of gestational age. Achiron et al 143 showed that the PI did not change with gestation, although there was a statistically significant increase when comparing the period of 14±17 weeks and the remainder of pregnancy. In the study of Laudy et al 144 , the pulsatility index from the middle arterial pulmonary branches showed a significant decrease from 20 to 29 weeks followed by a significant increase from 32 weeks to term and from the distal arterial pulmonary branches a significant decrease from 20 to 26 weeks and a rise from 31 weeks until term.…”

“…Rasanen et al 133 examined fetal distal branch pulmonary arterial vascular impedance and analyzed the relationships between proximal (after the bifurcation of the main pulmonary artery) and distal (beyond the first bifurcation of the branch pulmonary artery) pulmonary arterial blood velocity waveforms. Achiron et al 143 defined peripheral pulmonary artery blood flow as flow located 10±15 mm beyond the first bifurcation of the pulmonary artery branch. Data in the study by Mitchell et al 138 and Laudy et al 144 were obtained in the middle portion of the fetal lung and by Rizzo et al 142 and Laudy et al 144 in the most distal area of the fetal lung.…”

Effect of Betamethasone on Fetal Pulmonary and Umbilical Artery Doppler Velocimetry and Relationship With Respiratory Distress Syndrome Development

“…Corticosteroids administered antenatally may increase production of surfactant in the fetal lungs, and an increase in the fetal pulmonary blood flow may be another possible explanation for such reduced morbidity. [3][4][5][6][7] Also, Doppler velocimetry of the umbilical artery (UA) was found to be affected by corticosteroid administration. 8 On the other hand, repeated doses of steroids may especially have adverse effects on fetal growth or neuronal myelination.…”

Prenatal Prediction of Pulmonary Hypoplasia: Clinical, Biometric, and Doppler Velocity Correlates

“…So far, comparison with other studies is not possible because of differences in definition of Doppler sample site for distal pulmonary arteries. 28,29 Similar to the fetal biometric parameters, nearly all mean SDS of the proximal and middle arterial pulmonary flow velocity waveforms from the subset of combined nonlethal and absent LH were significantly different from the SDS of the mean of normal control subjects, independent of the addition of the 3 cases of nonlethal LH to the subset of absent LH. In the normally developing fetus, fluid leaves the pulmonary vasculature, passes through the interstitium of the lungs entering the potential air spaces, and flows out of the trachea.…”