Clark, E.B.

Blood pressure estimation in the human fetal descending aorta (Article)

2008-10-01T00:00:00Z

Objectives: The objectives of this study were to estimate fetal blood pressure non-invasively from two-dimensional color Doppler-derived aortic blood flow and diameter waveforms, and to compare the results with invasively derived human fetal blood pressures available from the literature. Methods: Aortic pressures were calculated from digitally recorded color Doppler cineloops of the fetal descending aorta by applying the Womersley model in combination with the two-element Windkessel model, assuming constant pulse wave velocity during the second half of pregnancy. The results were compared with invasively derived human fetal blood pressures obtained from the literature. Results: In 21 normal pregnancies the estimated mean aortic pressure regression line increased linearly from 28 mmHg at 20 weeks of gestation to 45 mmHg at 40 weeks of gestation. The pulse pressure based on the regression line increased linearly from 21 mmHg at 20 weeks of gestation to 29 mmHg at 40 weeks of gestation. The aortic compliance exhibited a log linear relationship with the gestational age and a statistically significant eightfold increase was observed between 20 and 40 weeks. The aortic downstream peripheral resistance exhibited an exponentially decaying relationship across the same gestational age range. Non-invasively derived aortic systolic and diastolic aortic pressures were comparable with previously reported invasively derived systolic and diastolic umbilical arterial pressures; however, the mean pressures differed significantly from those reported in the umbilical artery in a separate study. The aortic systolic pressures calculated in this study were significantly higher than invasively derived left ventricular systolic pressures that have been previously reported in the literature. Conclusions: This study demonstrates the feasibility of estimating arterial blood pressure in the human fetus. The method described is of potential use in assessing fetal blood pressure non-invasively, particularly for studying relative changes with time. Copyright

Application of the Magnitude-Squared Coherence Function Between Uterine and Umbilical Flow Velocity Waveforms for Predicting Placental Dysfunction: A Preliminary Study (Article)

2007-07-01T00:00:00Z

To examine whether the magnitude-squared coherence between uterine and umbilical blood flow velocity waveforms can, in conjunction with estimated fetal weight, uterine and umbilical pulsatility indices, fetal and maternal heart rates, diastolic notching and the amniotic fluid index, create a sensitive and specific model for the prediction of placental dysfunction. Binary logistic prediction models are created for preeclampsia, pregnancy induced hypertension and intrauterine growth restriction in a study group of 284 unselected midtrimester pregnancies. In each study group, the median value of derived parameters were compared with the uncomplicated pregnancy control group. The magnitude-squared coherence function between the uterine and umbilical flow velocity waveforms was found to be a statistically significant predictor of preeclampsia during the midtrimester of pregnancy. The magnitude-squared coherence did not improve the prediction of intrauterine growth restriction or pregnancy induced hypertension. The inclusion of magnitude-squared coherence as one of the prediction parameters may improve the early identification of pregnancies subsequently complicated by preeclampsia. (E-mail: p.struijk@erasmusmc.nl).

Ventricular diastolic filling characteristics in stage-24 chick embryos after extra-embryonic venous obstruction (Article)

2004-01-01T00:00:00Z

Alteration of extra-embryonic venous blood flow in stage-17 chick embryos results in well-defined cardiovascular malformations. We hypothesize that the decreased dorsal aortic blood volume flow observed after venous obstruction results in altered ventricular diastolic function in stage-24 chick embryos. A microclip was placed at the right lateral vitelline vein in a stage-17 (52-64 h of incubation) chick embryo. At stage 24 (4.5 days of incubation), we measured simultaneously dorsal aortic and atrioventricular blood flow velocities with a 20-MHz pulsed-Doppler velocity meter. The fraction of passive and active filling was integrated and multiplied by dorsal aortic blood flow to obtain the relative passive and active ventricular filling volumes. Data were summarized as means +/- S.E.M. and analyzed by t-test. At similar cycle lengths ranging from 557 ms to 635 ms (P>0.60), dorsal aortic blood flow and stroke volume measured in the dorsal aorta were similar in stage-24 clipped and normal embryos. Passive filling volume (0.07+/-0.01 mm(3)) was decreased, and active filling volume (0.40+/-0.02 mm(3)) was increased in the clipped embryo when compared with the normal embryo (0.15+/-0.01 mm(3), 0.30+/-0.01 mm(3), respectively) (P<0.003). In the clipped embryos, the passive/active ratio was decreased compared with that in normal embryos (P<0.001). Ventricular filling components changed after partially obstructing the extra-embryonic venous circulation. These results suggest that material properties of the embryonic ventricle are modified after temporarily reduced hemodynamic load.