Aortic Isthmus and Cardiac Monitoring of the Growth-Restricted Fetus

Understanding the Aortic Isthmus Doppler Profile and Its Changes with Gestational Age Using a Lumped Model of the Fetal Circulation

“…In addition, the flow difference between the pulmonary artery and the aorta during the deceleration of ejection was highly correlated with the magnitude of the end-systolic notch of the AoI flow. Our data confirm the previously formulated hypothesis by Acharya et al [5,10] that any difference in ejection force duration or volume between both ventricles affects the shape of the AoI velocity waveform during systole. Our data are also in agreement with the previously reported correlation between the right ventricular output and the magnitude of the notch by Chabaneix et al [7] .…”

“…The estimated time difference in the onset of ejection between aorta and pulmonary artery flows was much bigger for the fetus showing reversal of flow in the AoI as compared to the fetus without peak. This result fits well with the experimental data of De Muylder et al [6] showing a delay in the onset of right ventricular ejection, and suggest that this delay could explain the reversal of AoI flow at late systole [5,10] . The striking finding of the present study is the in silico demonstration that the timing differences between pulmonary and aortic blood flows are the main determinants for the appearance of the end-systolic reversal flow in the AoI.…”

“…A small notch could be seen at the end of systole in the model-based flow pattern of AoI corresponding to week 25 that progressively became more pronounced as gestation progressed into a short peak of reversal flow from week 34-35 onwards. These results are consistent with human data such as those of Acharya et al [5,10] describing a small AoI notch from 25 weeks that becomes more pronounced as gestation advances (with a clear AoI reversal peak in almost all fetuses around 31 weeks of gestation). Our data also showed that increased CO or changes in size and properties of the vasculature are not main determinants for the appearance of AoI reversal end-systolic peak.…”

“…Del Río et al [3] considered this brief reversal of flow as artifactual. Conversely, some authors hypothesized that this peak occurs as a result of delayed onset and longer acceleration time of the flow coming from the ductus arteriosus [4][5][6] . Also, a recent study found that the magnitude of the peak correlates with the right ventricular output [7] .…”

“…It is well known that prenatally the right ventricle ejects more blood than the left ventricle, and this dominance of the right ventricle increases with advancing gestation [8,9] . In addition, several clinical studies have reported a delay in the onset of right ventricular ejection [5,10] , differences in the duration of the ejection of both ventricles [11] and time-to-peak velocity (TPV) or acceleration time [12,13] . Finally, changes in the elastic properties of the pulmonary vasculature could also have an effect in the appearance of the notch [7] .…”