Morphometric study of the ductus arteriosus during human development

A Multiscale Mathematical Model for the Fetal Blood Circulation of the Second Half of Pregnancy

Doppler ultrasound is a commonly used method to assess hemodynamics of the fetal cardiovascular system and to monitor the well-being of the fetus. Indices based on the velocity profile are often used for diagnosis. However, precisely linking these indices to specific underlying physiology factors is challenging. Several influences, including wave reflections, fetal growth, vessel stiffness, and resistance distal to the vessel, contribute to these indices. Understanding these data is essential for making informed clinical decisions. Mathematical models can be used to investigate the relation between velocity profiles and physiological properties. This study presents a mathematical model designed to simulate velocity wave propagation throughout the fetal cardiovascular system, facilitating the assessment of factors influencing velocity-based indices. The model combines a one-fiber model of the heart with a 1D wave propagation model describing the larger vessels of the circulatory system and a lumped parameter model for the microcirculation. Fetal growth from 20 to 40 weeks of gestational age is incorporated by adjusting cardiac and circulatory parameter settings according to scaling laws. The model's results, including cardiac function, cardiac output distribution, and volume distribution, show a good agreement with literature studies for a growing healthy fetus from 20 to 40 weeks. In addition, Doppler indices are simulated in various vessels and agree with literature as well. In conclusion, this study introduces a novel closed-loop 0D-1D mathematical model that has been verified against literature studies. This model offers a valuable platform for analyzing factors influencing velocity-based indices in the fetal cardiovascular system.

Recasting Current Knowledge of Human Fetal Circulation: The Importance of Computational Models

Computational hemodynamic simulations are becoming increasingly important for cardiovascular research and clinical practice, yet incorporating numerical simulations of human fetal circulation is relatively underutilized and underdeveloped. The fetus possesses unique vascular shunts to appropriately distribute oxygen and nutrients acquired from the placenta, adding complexity and adaptability to blood flow patterns within the fetal vascular network. Perturbations to fetal circulation compromise fetal growth and trigger the abnormal cardiovascular remodeling that underlies congenital heart defects. Computational modeling can be used to elucidate complex blood flow patterns in the fetal circulatory system for normal versus abnormal development. We present an overview of fetal cardiovascular physiology and its evolution from being investigated with invasive experiments and primitive imaging techniques to advanced imaging (4D MRI and ultrasound) and computational modeling. We introduce the theoretical backgrounds of both lumped-parameter networks and three-dimensional computational fluid dynamic simulations of the cardiovascular system. We subsequently summarize existing modeling studies of human fetal circulation along with their limitations and challenges. Finally, we highlight opportunities for improved fetal circulation models.

Balancing Benefits and Risks of Indomethacin in the Management of Antenatal Bartter Syndrome: A Case Report

Background

Bartter syndrome, a very rare inherited renal tubular disorder, characterized by urinary salt wastage, hypokalemia, polyuria, and metabolic alkalosis, may manifest antenatally as severe isolated polyhydramnios. Indomethacin is known to reduce salt wastage and subsequent polyhydramnios during pregnancy; however, it reduces the Ductus Arteriosus diameter among other potential complications, such as inhibition of gastrointestinal perfusion and increasing the risk of renal toxicity.

Case

A 36-year-old multigravida presented with severe isolated polyhydramnios at 30 weeks of gestation. Based on a history of a previous pregnancy affected with Bartter syndrome, indomethacin was initiated. Amniotic fluid volume and Ductus Arteriosus diameter were monitored. As evidence lacks on optimal dose and duration of indomethacin, multiple-dose adjustments were made to reduce the amniotic fluid volume while maintaining normal Ductus Arteriosus diameter. Progressive polyhydramnios led to Cesarean section at 34+ weeks of gestation resulting in a healthy fetus diagnosed with Bartter syndrome in the early neonatal period.

Conclusion

We share our experience in the adjustment of the dose and duration of Indomethacin therapy in the treatment of severe polyhydramnios associated with antenatal Bartter syndrome. Amniotic fluid index, Ductus Arteriosus diameter, and umbilical artery doppler work together as key indicators to guide the success and safety of the therapy.

A computational model of the fetal circulation to quantify blood redistribution in intrauterine growth restriction

Intrauterine growth restriction (IUGR) due to placental insufficiency is associated with blood flow redistribution in order to maintain delivery of oxygenated blood to the brain. Given that, in the fetus the aortic isthmus (AoI) is a key arterial connection between the cerebral and placental circulations, quantifying AoI blood flow has been proposed to assess this brain sparing effect in clinical practice. While numerous clinical studies have studied this parameter, fundamental understanding of its determinant factors and its quantitative relation with other aspects of haemodynamic remodeling has been limited. Computational models of the cardiovascular circulation have been proposed for exactly this purpose since they allow both for studying the contributions from isolated parameters as well as estimating properties that cannot be directly assessed from clinical measurements. Therefore, a computational model of the fetal circulation was developed, including the key elements related to fetal blood redistribution and using measured cardiac outflow profiles to allow personalization. The model was first calibrated using patient-specific Doppler data from a healthy fetus. Next, in order to understand the contributions of the main parameters determining blood redistribution, AoI and middle cerebral artery (MCA) flow changes were studied by variation of cerebral and peripheral-placental resistances. Finally, to study how this affects an individual fetus, the model was fitted to three IUGR cases with different degrees of severity. In conclusion, the proposed computational model provides a good approximation to assess blood flow changes in the fetal circulation. The results support that while MCA flow is mainly determined by a fall in brain resistance, the AoI is influenced by a balance between increased peripheral-placental and decreased cerebral resistances. Personalizing the model allows for quantifying the balance between cerebral and peripheral-placental remodeling, thus providing potentially novel information to aid clinical follow up.

Intrauterine growth restriction (IUGR) is one of the leading causes of perinatal mortality and can be defined as a low birth weight together with signs of chronic hypoxia or malnutrition. It is mostly due to placental insufficiency resulting in a chronic restriction of oxygen and nutrients to the fetus. IUGR leads to cardiac dysfunction in utero which can persist postnatally. Under these altered conditions, IUGR fetuses redistribute their blood in order to maintain delivery of oxygenated blood to the brain, known as brain sparing. Given that, in the fetus the aortic isthmus (AoI) is a key arterial connection between the cerebral and placental circulations, quantifying AoI blood flow has been proposed to assess this brain sparing effect in clinical practice. However, which remodeling or redistribution processes in the cardiovascular systems induce the observed changes in AoI flow in IUGR fetuses is not fully understood. We developed a computational model of the fetal circulation, including the key elements related to fetal blood redistribution. Using measured cardiac outflow profiles to allow personalization, we can recreate and better understand the blood flow changes in individual IUGR fetuses.

Reference ranges of ductus arteriosus derived by cardio-spatiotemporal image correlation from 14 to 40 weeks of gestation

OBJECTIVE

To construct reference ranges of fetal ductus arteriosus (DA) derived by volume datasets of cardio-spatiotemporal image correlation (cardio-STIC).

METHODS

Cardio-STIC volume datasets were acquired from low-risk singleton pregnancies with a reliable gestational age from 14 to 40 weeks. In offline analysis with 4D View version 9, fetal DA was measured in the transverse ductal arch view with orthogonal control in the multiplanar view. The reference ranges of the DA and Z-score equation were constructed against gestational weeks and biparietal diameter (BPD) as independent variables.

RESULTS

A total of satisfactory 606 volumes were analyzed. The reference ranges for predicting means and SDs of fetal DA were constructed based on the best-fit regression model. Mean DA (mm) was best predicted by linear model as a function of GA (weeks) and BPD (cm) as follows: Predicted DA diameter (cm) = -0.051 + 0.014 × GA (weeks) (r = 0.84) and Predicted DA diameter (cm) = -0.015 + 0.053 × BPD (cm) (r = 0.83). Models for Z-score calculation and centile charts for predicting fetal DA were also provided.

CONCLUSION

Reference ranges of the fetal DA and Z-score model are provided. These may serve as a useful tool in the assessment of fetal DA, especially in fetal cardiac anomalies or in monitoring fetuses exposed to maternal indomethacin.

Quantitative anatomy of the growing abdominal aorta in human fetuses: an anatomical, digital and statistical study

Background

Advances in perinatal medicine have required an extensive knowledge of fetal aorto-iliac measurements. The present study was performed to compile reference data for dimensions of the abdominal aorta at varying gestational ages.

Material/Methods

Using the methods of anatomical dissection, digital-image analysis (Leica QWin Pro 16 system), and statistical analysis (Student’s t-test, one-way ANOVA, post-hoc RIR Tukey test, regression analysis, and Wilcoxon signed-rank test), the growth of length (mm), proximal and distal external diameters (mm), and volume (mm³) of the abdominal aorta in 124 (60 male, 64 female) spontaneously aborted human fetuses aged 15–34 weeks was examined.

Results

No significant male-female differences were found. The length ranged from 9.35±1.24 to 36.29±4.98 mm, according to the linear function y=−14.596+1.519 × Age ±2.639 (R²=0.92; p<0.0001). The proximal external diameter varied from 1.18±0.25 to 5.19±0.49 mm, according to the linear pattern y=−2.065+0.212 × Age ±0.348 (R²=0.92; p<0.0001). The distal external diameter increased from 1.03±0.23 to 4.92±0.46 mm, in accordance with the linear model y=−2.097+0.203 × Age ±0.351 (R²=0.92; p<0.0001). Both length and proximal external diameter of the abdominal aorta indicated a proportionate evolution, because the length-to-proximal external diameter ratio was stable, following the linear function y=7.724–0.017 × Age ±0.925. The abdominal aorta volume ranged from 9.6±4.5 to 740.5±201.8 mm³, given by the quadratic function y=911–101 × Age +2.838 × Age² ±78 (R²=0.89; p<0.0001).

Conclusions

There are no significant differences between males and females for morphometric parameters of the abdominal aorta. The abdominal aorta grows linearly in both length and diameters, and parabolically in volume. These detailed morphometric data of the abdominal aorta provide a database for intra-uterine echographic examinations in the early diagnosis, monitoring and management of aorto-iliac malformations.

The normal growth of the common iliac arteries in human fetuses - an anatomical, digital and statistical study

BACKGROUND

The present study was carried out to compile normative data for dimensions of the common iliac arteries at varying gestational ages.

MATERIAL/METHODS

We used anatomical dissection, digital-image analysis (system of Leica QWin Pro 16) and statistical analysis (Student T test, one-way ANOVA, post-hoc RIR Tukey test, and regression analysis) to examine the increase in length (mm), proximal external diameter (mm), and volume (mm³) of the common iliac arteries in 124 (60 males, 64 females) spontaneously aborted human fetuses aged 15-34 weeks.

RESULTS

Neither sex nor right-left significant differences were found (P>0.05). The length ranged from 4.76 ± 1.05 to 15.38 ± 1.60 mm on the right, and from 4.92 ± 1.33 to 14.91 ± 1.25 mm on the left, according to the linear functions y=-3.598+0.585 × Age ± 1.522 (R²=0.83) and y=-3.107+0.554 × Age ± 1.444 (R²=0.83). The proximal external diameter increased from 0.66 ± 0.19 to 2.30 ± 0.42 mm on the right, and from 0.66 ± 0.14 to 2.16 ± 0.42 mm on the left, according to the quadratic models y=1.392-0.110 × Age + 0.004 × Age² ± 0.285 (R²=0.77) and y=1.283-0.099 × Age + 0.004 × Age² ± 0.238 (R²=0.81). The volumes were increasing from 1.93 ± 1.74 to 66.95 ± 29.31 mm³ on the right, and from 1.91 ± 1.65 to 56.86 ± 25.17 mm³ on the left, given by the quadratic functions: y=99.69-10.60 × Age+0.28 7 × Age² ± 14.40 (R²=0.67) and y=82.62-8.86 × Age + 0.242 × Age² ± 11.60 (R²=0.71).

CONCLUSIONS

The common iliac arteries grow linearly in length, and parabolically in both diameter and volume. The right common iliac artery constitutes a predominant vessel in relation to its length, external diameter and volume. The morphometric data on the common iliac arteries may serve as a useful reference in the prenatal diagnosis and monitoring of congenital aorto-iliac abnormalities.

Microcirculation in preterm infants: profound effects of patent ductus arteriosus

OBJECTIVES

To assess potential effects of a hemodynamically significant persistent ductus arteriosus (sPDA) in the skin microcirculation in preterm neonates.

STUDY DESIGN

In 25 patients (<32 weeks of gestation; birth weight <1250 g) with sPDA (n = 13) or no significant PDA (non-sPDA; n = 12) functional vessel density and vessel diameters were investigated prospectively. Sidestream dark field imaging was performed in the skin of both arms from the third day of life until PDA closure or until day 7 or 8 for the non-sPDA group.

RESULTS

Before PDA treatment, functional vessel density was significantly lower in the sPDA group compared with the non-sPDA group. In the sPDA group, there were significantly fewer large vessels (diameter >20 microm) and significantly more small vessels (diameter <10 microm). After successful PDA treatment, these differences disappeared. In both groups, functional vessel density differed significantly between the left and right arm, persisting even after successful treatment. Regression analysis showed an inverse linear correlation between the hemodynamic echocardiographic findings and functional vessel density (P <.005).

CONCLUSION

sPDA causes major changes in the microcirculation of premature neonates; functional vessel density is reduced, with a shift in perfusion from larger toward smaller vessels. The redistribution of flow might be a compensatory mechanism to preserve physiologic metabolism.

Quantitative morphology of the left subclavian artery in human fetuses

PURPOSE

The present study was performed to compile normative data for dimensions of the left subclavian artery at varying gestational age.

MATERIAL AND METHODS

Using anatomical dissection, digital image analysis (Leica Q Win Pro 16 system) and statistical analysis (ANOVA, regression analysis) a range of measurements (length, original external diameter, volume) for the left subclavian artery in 128 spontaneously aborted human fetuses aged 15-34 weeks was examined.

RESULTS

No significant gender differences were found (P>0.05). The length ranged from 4.62 +/- 0.49 to 12.28 +/- 1.25 mm, according to the linear function y = -2.1482 + 0.4302 x +/- 0.9972 (r = 0.93 P<0.001). The original external diameter increased from 0.68 +/- 0.16 to 2.89 +/- 0.29 mm, according to the linear model y = -1.2169 + 0.1233 x +/- 0.2389 (r = 0.95 P<0.001). The left subclavian artery-to-aortic root diameter ratio increased from 0.337 +/- 0.064 to 0.423 +/- 0.103. Distance between the left common carotid and left subclavian arteries increased from 0.57 +/- 0.17 to 3.92 +/- 0.91 mm. Aortic arch diameter to distance between the left common carotid and left subclavian arteries decreased with advanced fetal age, from 2.82 +/- 0.51 to 1.56 +/- 0.27. The volume ranged from 1.77 +/- 0.89 to 80.60 +/-; 22.18 mm3, in accordance with the quadratic function y = 76.0 - 8.956 x + 0.031 x2 +/- 10.945 (R2 = 0.85).

CONCLUSIONS

The developmental dynamic of the length and diameter of the left subclavian artery follows a linear regression, whereas its volumetric dynamic follows a quadratic regression. The ratio of the aortic arch diameter to the distance between the left common carotid and left subclavian arteries has clinical application in the early recognition of aortic coarctation.

Morphometric study of the ascending aorta in human fetuses

The present study was performed on 128 spontaneously aborted human fetuses, aged 15-34 weeks, to compile normative data for ascending aorta dimensions at varying gestational age. Using anatomical dissection, digital-image analysis (system of Leica QWin Pro 16) and statistical analysis (ANOVA, regression analysis) a range of measurements (Length, original and terminal external diameters, volume) for the ascending aorta during gestation was examined. No significant gender differences were found (P > 0.05). The growth curves of the best fit for the plot for each morphometric feature against gestational age were generated. Both the Length and external diameters of the ascending aorta were found to increase in a linear fashion throughout gestation. The Length ranged from 2.63 +/- 0.42 to 10.80 +/- 1.49mm, according to the linear function y = -4.678 + 0.4647x +/- 0.8447 (r = 0.95). The original external diameter ranged from 2.02 +/- 0.26 to 6.84 +/- 0.63 mm, according to the linear model y = -2.103 + 0.2684x +/- 0.3958 (r = 0.97). The terminal external diameter ranged from 1.73 +/- 0.20 to 6.29 +/- 0.52 mm, with accordance to the linear function y = -2.354 + 0.2567x +/- 0.3826 (r = 0.97). The ascending aorta volume ranged from 7.56 +/- 2.65 to 370.99 +/- 105.42 mm3, according to the quadratic function y = 373.1 - 43.38x + 1.30x(2) +/- 24.51 (R2 = 0.89). The growth curves generated from my data might be useful as a reference for fetal echocardiographers in the detection of some congenital cardiovascular abnormalities.