Cardiac output and central distribution of blood flow in the human fetus

Comparison of Left Ventricular Stroke Volume in 2nd- and 3rd-Trimester Fetuses Measured by the Product of VTI and Aortic Annular Area With That Assessed by Simpson's Single-Plane Rule Using the STE Technique

OBJECTIVES

The aim of the study was to compare left ventricle stroke volume in healthy, eutrophic fetuses in the 2nd and 3rd trimesters evaluated using the velocity time integral and aortic annulus area with left ventricular stroke volume measured using Simpson's single-plane rule and to determine the discrepancy equation.

METHODS

The study included 354 fetuses. In each fetus, during the same examination, simultaneous assessment of stroke volume was performed by pulsed-wave Doppler using the product of the velocity time integral and aortic annulus area and by the fetalHQ® software using Simpson's single-plane rule. The Mann-Whitney U test was used to compare the "product-derived" stroke volume and stroke volume using fetalHQ® software values in the 2nd and 3rd trimesters separately. The agreement between the two methods were verified using Bland-Altman analysis. A linear regression model was used to obtain the discrepancy equation.

RESULTS

In the 2nd trimester, the mean percentage difference between both the techniques showed that the stroke volume values determined using pulsed-wave Doppler were, on average, 88% higher than the stroke volume values determined using fetalHQ®. The upper limit of agreement between the compared techniques was approximately 146% and the lower limit of agreement was equal to 29.6%. In the 3rd trimester, the results indicated that the stroke volume values determined using pulsed-wave Doppler were, on average, 76% higher than the stroke volume values determined using fetalHQ®. The upper limit of agreement between the compared techniques was approximately 129% and the lower limit of agreement was 23%. Based on the results of the linear regression models, discrepancy formulas of the stroke volume values were obtained. The equations to calculate the predicted mean and standard deviations were used to compute the reference intervals for the mean, 5th and 95th centiles.

CONCLUSION

The calculation of left ventricular stroke volume using pulsed Doppler has higher result in relation to stroke volume determined using Simpson's rule significantly. The aortic annulus area showed a higher correlation regarding stroke volume than the velocity time integral in both the 2nd and 3rd trimesters. Stroke volume increased with the increase in aortic annulus area, whereas the velocity time integral remained relatively constant. The retrospective analysis of the collected material enabled the determination of the discrepancy equation.

Cardiac Development and Related Clinical Considerations

The anatomy, physiology, and hemodynamics of the premature heart vary along the range of gestational ages cared for in neonatal intensive care units, from 22 weeks to term gestation. Clinical management of the preterm neonate should account for this heterogenous development. This requires an understanding of the impact of ex utero stressors on immature and disorganized cardiac tissue, the different state of hemodynamics across intracardiac shunts impacting the natural transition from fetal to neonatal life, and the effects of intensive pharmacologic and non-pharmacologic interventions that have systemic consequences influencing cardiac function. This article provides a review of the increasing but still limited body of literature on the anatomy, hemodynamics, and electrophysiology of the preterm heart with relevant clinical considerations.

Association between patent ductus arteriosus flow and home oxygen therapy in extremely preterm infants

BACKGROUND

Central blood flow measurements include the estimation of right and left ventricular output (RVO, LVO), superior vena cava (SVC) flow, and calculated patent ductus arteriosus (PDA) flow. We aimed to provide an overview of the maturation patterns of these values and the relationship between PDA flow and the need for home oxygen therapy.

METHODS

This prospective single-center study was conducted in infants born at <26 weeks of gestation. We performed echocardiographic measurements five times during their life (from the 4th post-natal day to the 36th postmenstrual week).

RESULTS

Sixty patients with a mean birth weight of 680 (590, 760) g were included. Postnatal development of LVO and PDA flow peaked at the end of the second postnatal week (427 and 66 mL/kg/min, respectively). The RVO increased between days 4 and 7-8. The SVCF was most stable. The development curves of PDA flow differed between the groups with (n = 28; 47%) and without home oxygen therapy.

CONCLUSION

We present the central blood flow values and their postnatal development in infants <26 weeks of gestation. This study demonstrates the association between PDA flow and the future need for home oxygen therapy.

IMPACT

This study enriches our knowledge of the long-term development of central blood flow parameters and derived patent ductus arteriosus (PDA) flow in extremely preterm infants (<26 weeks). While pulmonary resistance decreased, PDA flow continued to increase from day 4 to the end of the second week of life. Similarly, left ventricular output increased as a marker of preload. The superior vena cava flow remained stable. The observed association between PDA flow and an unfavorable respiratory outcome is important for future studies focusing on the prevention of chronic lung disease.

Prioritization of Kidney Cell Types Highlights Myofibroblast Cells in Regulating Human Blood Pressure

Introduction

Blood pressure (BP) is a highly heritable trait with over 2000 underlying genomic loci identified to date. Although the kidney plays a key role, little is known about specific cell types involved in the genetic regulation of BP.

Methods

Here, we applied stratified linkage disequilibrium score (LDSC) regression to connect BP genome-wide association studies (GWAS) results to specific cell types of the mature human kidney. We used the largest single-stage BP genome-wide analysis to date, including up to 1,028,980 adults of European ancestry, and single-cell transcriptomic data from 14 mature human kidneys, with mean age of 41 years.

Results

Our analyses prioritized myofibroblasts and endothelial cells, among the total of 33 annotated cell type, as specifically involved in BP regulation (P < 0.05/33, i.e., 0.001515). Enrichment of heritability for systolic BP (SBP) was observed in myofibroblast cells in mature human kidney cortex, and enrichment of heritability for diastolic BP (DBP) was observed in descending vasa recta and peritubular capillary endothelial cells as well as stromal myofibroblast cells. The new finding of myofibroblast, the significant cell type for both BP traits, was consistent in 8 replication efforts using 7 sets of independent data, including in human fetal kidney, in East-Asian (EAS) ancestry, using mouse single-cell RNA sequencing (scRNA-seq) data, and when using another prioritization method.

Conclusion

Our findings provide a solid basis for follow-up studies to further identify genes and mechanisms in myofibroblast cells that underlie the regulation of BP.

Quantifying fetal heart health in gestational diabetes: a new approach with fetal heart quantification technology

Objective

This study aimed to assess the impact of gestational diabetes mellitus (GDM) on fetal heart structure and function using a technique called fetal heart quantification (Fetal HQ), with a focus on mitochondrial dynamics, which employs advanced imaging technology for comprehensive analysis.

Methods

A total of 180 fetuses with normal heart structures, aged 24-40 weeks of gestation, were examined. A 2-3 s cine loop in the standard four-chamber oblique view was captured and analyzed using the speckle-tracking technique with Fetal HQ. Various echocardiographic parameters were evaluated, including four-chamber view (4CV), global spherical index (GSI), global longitudinal strain (GLS), 24-segment spherical index (SI), ventricular fractional area change (FAC), cardiac output (CO), and stroke volume (SV). These parameters were compared between the GDM group and the control group during two gestational periods: 24+0 to 28+0 weeks and 28+1 to 40+1 weeks. Statistical analysis was performed using independent samples t-tests and Mann-Whitney U tests to identify significant differences.

Results

Twenty fetuses from mothers with GDM and 40 from the control group were recruited at 24+0 to 28+0 weeks. At 28+1 to 40+1 weeks, 40 fetuses from mothers with GDM and 80 from the control group were recruited. The fetal left ventricular global longitudinal function was similar between the GDM and control groups. However, compared to the controls, right ventricular function in the GDM group was lower only at 28+1 to 40+1 weeks. In the GDM group, the global spherical index (GSI) was lower than in the control group at 28+1 to 40+1 weeks (1.175 vs. 1.22; p = 0.001). There were significant decreases in ventricular FAC (38.74% vs. 42.83%; p < 0.0001) and 4CV GLS for the right ventricle (-22.27% vs. -26.31%; p = 0.005) at 28+1 to 40+1 weeks.

Conclusion

Our findings suggest that GDM is associated with decreased right ventricular function in the fetal heart, particularly during the later stages of pregnancy (28+1 to 40+1 weeks), compared to fetuses from healthy pregnancies. The Fetal HQ technique represents a valuable tool for evaluating the structure and function of fetal hearts affected by GDM during the advanced stages of pregnancy.

Impact of cord clamping on haemodynamic transition in term newborn infants

OBJECTIVE

To assess the haemodynamic consequences of cord clamping (CC) in healthy term infants.

DESIGN

Cohort study.

SETTING

Tertiary maternity hospital.

PATIENTS

46 full-term vigorous infants born by caesarean section.

INTERVENTIONS

Echocardiography was performed before CC, immediately after CC and at 5 min after birth.

MAIN OUTCOME MEASURES

Pulsed wave Doppler-derived cardiac output and the pulmonary artery acceleration time indexed to the right ventricle ejection time were obtained. As markers of loading fluctuations, the myocardial performance indexes and the velocities of the tricuspid and mitral valve annuli were determined with tissue Doppler imaging. Heart rate was derived from Doppler imaging throughout the assessments.

RESULTS

Left ventricular output increased throughout the first minutes after birth (mean (SD) 222.4 (32.5) mL/kg/min before CC vs 239.7 (33.6) mL/kg/min at 5 min, p=0.01), while right ventricular output decreased (306.5 (48.2) mL/kg/min before vs 272.8 (55.5) mL/kg/min immediately after CC, p=0.001). The loading conditions of both ventricles were transiently impaired by CC, recovering at 5 min. Heart rate progressively decreased after birth, following a linear trend temporarily increased by CC. The variation in left ventricular output across the CC was directly correlated to the fluctuation of left ventricular preload over the same period (p=0.03).

CONCLUSIONS

This study illustrates the cardiovascular consequences of CC in term vigorous infants and offers insight into the haemodynamic transition from fetal to neonatal circulation in spontaneously breathing newborns. Strategies that aim to enhance left ventricular preload before CC may prevent complications of perinatal cardiovascular imbalance.

Cardiovascular Effects of a Thoracoamniotic Shunt in a Fetus Affected by Isolated Right Congenital Diaphragmatic Hernia and Hydrops

A thoracoamniotic shunt was placed in a fetus affected by a right congenital diaphragmatic hernia (RCDH) complicated by voluminous nonimmune hydrops (NIH) at 30 weeks of gestation. The fetus showed congestive cardiac failure with a combined cardiac output (CCO) of 460.7 ml/min (Z-score: -1.2). After seven days, no edema, ascites, or pleural effusion was present. CCO increased significantly, reaching a Z-score of -0.2, as well as right and left cardiac output (Z-scores: -0.3 and -0.8, respectively). Two weeks later, the cardiac function and the ascites got worse despite the correct shunt placement, suggesting a possible occlusion. At 33 weeks, a C-section was performed due to labor in breech presentation. Despite the intensive care provided, the newborn died due to pulmonary hypertension and respiratory insufficiency. The thoracoamniotic shunt's effect on fetal circulation and the mechanisms of NIH in the event of RCDH are still unclear. Due to the high mortality rate of this condition and its poorer outcomes compared to left-sided defects, shunting cannot be considered an efficient attempt to improve fetal and neonatal survival rates to date. A close relationship between the amount of lymphatic effacement and cardiac function is clear, but further studies are needed to provide more information about this severe condition and its treatment.

Visualizable intracardiac flow pattern in fetuses with congenital heart defect: pilot study of blood speckle-tracking echocardiography

OBJECTIVES

Blood-flow pattern is an essential factor in cardiovascular development. Recently, blood speckle-tracking echocardiography (BST) based on high-frame-rate ultrasound has emerged as a promising technique for the assessment of blood-flow patterns and properties. The objectives of this study were to determine the feasibility of BST in the fetus and to assess intracardiac blood-flow patterns of fetuses with a congenital heart defect (CHD) using this technique.

METHODS

This was a prospective study consisting of 35 normal fetuses, 35 fetuses with left-sided obstructive lesion (LSOL) and 35 fetuses with right-sided obstructive lesion (RSOL). BST images of fetal intracardiac regions of interest (ROIs), including the left ventricle (LV), right ventricle (RV), ascending aorta (AAo), aortic arch (AA), descending aorta (DAo) and pulmonary artery (PA), were obtained and analyzed. The feasibility of BST was assessed, and blood-flow pattern and number of vortices in the ROIs were recorded.

RESULTS

The median gestational age of the fetuses was 24.7 weeks (range, 19.6-34.3 weeks). BST was feasible in 81.6% of cases, and the cut-off value of depth for an adequate BST image was ≤ 7.9 cm. There were no differences in the presence of vortex/turbulent blood flow in the LV or RV among the three groups. Vortex/turbulent blood flow in the AAo was detected in 0% (0/35), 14.3% (5/35) and 57.1% (20/35) of cases in the control, LSOL and RSOL groups, respectively. The respective values were 5.7% (2/35), 14.3% (5/35) and 51.4% (18/35) for the AA; 0% (0/35), 48.6% (17/35) and 0% (0/35) for the DAo; and 0% (0/35), 40.0% (14/35) and 51.4% (18/35) for the PA. With the exception of the DAo in the RSOL group, vortex/turbulent flow in the great artery ROIs was significantly more common in the LSOL and RSOL groups than in controls (P < 0.01). In the LSOL group, the number of vortices in the AAo, AA, DAo and PA was significantly greater compared with that in controls (P < 0.01). In the RSOL group, the number of vortices in the LV, AAo, AA and PA was significantly greater compared with that in controls (P < 0.01).

CONCLUSIONS

Fetuses with CHD were more likely to exhibit vortex/turbulent blood flow and increased number of vortices in the great arteries compared with healthy controls. Further research is needed to determine the biomechanical effect of blood-flow patterns, especially vortex flow, on fetal cardiovascular structure and function. © 2023 International Society of Ultrasound in Obstetrics and Gynecology.

Intrahepatic cholestasis of pregnancy and fetal cardiac dysfunction: a systematic review and meta-analysis

OBJECTIVE

Intrahepatic cholestasis of pregnancy is associated with adverse perinatal outcomes. Fetal cardiac dysfunction may be 1 part of the pathophysiology of pregnancies complicated by intrahepatic cholestasis of pregnancy. This systematic review and meta-analysis aimed to evaluate the association between intrahepatic cholestasis of pregnancy and fetal cardiac dysfunction.

DATA SOURCES

Systematic searches were performed on the databases of Medline, Embase, and Cochrane Library (up to March 2, 2023) for studies evaluating fetal cardiac function in pregnancies complicated by intrahepatic cholestasis of pregnancy in addition to the reference lists of included studies.

STUDY ELIGIBILITY CRITERIA

Studies were eligible for inclusion if they assessed the fetal cardiac function by fetal echocardiography in women with intrahepatic cholestasis of pregnancy (mild or severe) and compared with fetuses of healthy pregnant women. The studies published in English were included.

METHODS

The quality of the retrieved studies was assessed using the Newcastle-Ottawa Scale. Data on fetal myocardial performance index, E wave/A wave peak velocities ratio, and PR interval were pooled for the meta-analysis using random-effects models. The results were presented as weighted mean differences and 95% confidence intervals. This meta-analysis was registered with the International Prospective Register of Systematic Reviews (registration number: CRD42022334801).

RESULTS

A total of 14 studies were included in this qualitative analysis. Of note, 10 studies that reported data on fetal myocardial performance index, E wave/A wave peak velocities ratio, and PR interval were included in the quantitative analysis and showed a significant association between intrahepatic cholestasis of pregnancy and fetal cardiac dysfunction. Significantly higher fetal left ventricular myocardial performance index values (weighted mean difference, 0.10; 95% confidence interval, 0.04-0.16) and longer fetal PR intervals (weighted mean difference, 10.10 ms; 95% confidence interval, 7.34-12.86) were revealed in pregnancies complicated by intrahepatic cholestasis of pregnancy. Compared with the situation in pregnancies complicated by mild intrahepatic cholestasis of pregnancy, PR intervals were even longer in pregnancies complicated by severe intrahepatic cholestasis of pregnancy (weighted mean difference, 5.98 ms; 95% confidence interval, 0.20-11.77). There was no significant difference in fetal E wave/A wave peak velocities ratio between the group with intrahepatic cholestasis of pregnancy and the healthy pregnant group (weighted mean difference, 0.01; 95% confidence interval, -0.03 to 0.05).

CONCLUSION

Our findings supported the idea that intrahepatic cholestasis of pregnancy is associated with overall impaired fetal myocardial performance and impaired fetal cardiac conduction system. However, current evidence about the association between fetal cardiac dysfunction and intrahepatic cholestasis of pregnancy-induced stillbirth is lacking. Further studies are needed to reveal the relationship between fetal cardiac dysfunction and adverse perinatal outcomes in pregnancies complicated by intrahepatic cholestasis of pregnancy.

Anatomy of the Ductus Arteriosus in Fetal Autopsies: Correlations With Placental Pathology and Cause of Death

BACKGROUND

Differences in the shape of the ductus arteriosus (DA), an important vascular shunt between the pulmonary artery and aorta, may reflect fetoplacental blood flow. Our aim was to examine tapering of the DA in a fetal autopsy population and correlate it with placental pathology and cause of death (COD).

METHODS

This autopsy case control study of stillborn fetuses selected cases (tapered DA) and consecutive age-matched controls (no DA tapering) between January 2017 and January 2022. We abstracted demographic and clinical data from pathology reports. Autopsy data included COD and histologic evidence of fetal hypoxia. Placental pathology included umbilical cord abnormalities, acute and chronic inflammation, fetal vascular malperfusion (FVM), and maternal vascular malperfusion (MVM).

RESULTS

We identified 50 cases and 50 controls. Gestational age ranged from 18 to 38 weeks. Maternal and fetal demographic characteristics did not differ significantly between cases and controls. COD related to an umbilical cord accident/FVM was significantly more prevalent in cases vs controls (46% vs 26%, P = .037), and FVM in the placenta, regardless of COD, trended higher in cases than controls.

CONCLUSION

Tapering of the DA is present in stillborn fetuses and associated with COD related to fetal vascular blood flow obstruction.

Adapting to a new environment: postnatal maturation of the human cardiomyocyte

The postnatal mammalian heart undergoes remarkable developmental changes, which are stimulated by the transition from the intrauterine to extrauterine environment. With birth, increased oxygen levels promote metabolic, structural and biophysical maturation of cardiomyocytes, resulting in mature muscle with increased efficiency, contractility and electrical conduction. In this Topical Review article, we highlight key studies that inform our current understanding of human cardiomyocyte maturation. Collectively, these studies suggest that human atrial and ventricular myocytes evolve quickly within the first year but might not reach a fully mature adult phenotype until nearly the first decade of life. However, it is important to note that fetal, neonatal and paediatric cardiac physiology studies are hindered by a number of limitations, including the scarcity of human tissue, small sample size and a heavy reliance on diseased tissue samples, often without age-matched healthy controls. Future developmental studies are warranted to expand our understanding of normal cardiac physiology/pathophysiology and inform age-appropriate treatment strategies for cardiac disease.

Acute resveratrol exposure does not impact hemodynamics of the fetal sheep

Babies born growth restricted are at an increased risk of both poor short-and long-term outcomes. Current interventions to improve fetal growth are ineffective and do not lower the lifetime risk of poor health status. Maternal resveratrol (RSV) treatment increases uterine artery blood flow, fetal oxygenation, and fetal weight. However, studies suggest that diets high in polyphenols such as RSV may impair fetal hemodynamics. We aimed to characterize the effect of RSV on fetal hemodynamics to further assess its safety as an intervention strategy. Pregnant ewes underwent magnetic resonance imaging (MRI) scans to measure blood flow and oxygenation within the fetal circulation using phase contrast-MRI and T2 oximetry. Blood flow and oxygenation measures were performed in a basal state and then repeated while the fetus was exposed to RSV. Fetal blood pressure and heart rate were not different between states. RSV did not impact fetal oxygen delivery (DO2 ) or consumption (VO2 ). Blood flow and oxygen delivery throughout the major vessels of the fetal circulation were not different between basal and RSV states. As such, acute exposure of the fetus to RSV does not directly impact fetal hemodynamics. This strengthens the rationale for the use of RSV as an intervention strategy against fetal growth restriction.

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.

Normative change with gestation in fetal intraventricular pressure difference with color M-mode Doppler echocardiography

AIM

The intraventricular pressure difference (IVPD) is the pressure difference in early diastole from the base to the apex of the ventricle. It is a useful marker for evaluating diastolic function because of its role as a suction force. This study investigated the changes in total and segmental IVPDs in normal fetuses throughout gestation to obtain normative data equations.

METHODS

One hundred thirty-seven healthy pregnant women at 12-40 weeks of gestation were prospectively enrolled to evaluate IVPD. The color M mode was performed, and the image was evaluated using our own code to calculate the IVPD. Segmental IVPD was divided into mid to apex and base. Pearson's correlation coefficient was used to evaluate this relationship.

RESULTS

There was a significant, positive relationship between IVPD and gestational age in both ventricles (right ventricle [RV]: r = 0.800, left ventricle [LV]: r = 0.818). As for segmental IVPD, basal and mid-apical IVPD also increased with gestation in both ventricles (RV: basal, r = 0.627; mid-apical, r = 0.705; LV: basal r = 0.758; mid-apical, r = 0.756). IVPG, which was calculated as IVPD/ventricular length, also showed a weak, positive relationship with gestation in both ventricles (RV r = 0.351, p < 0.001; LV r = 0.373, p < 0.001).

CONCLUSION

The total and segmental IVPDs significantly increased linearly through time.

Poor Correlation between Fetal Tissue Doppler Imaging and Pulsed Wave Myocardial Performance Indices

INTRODUCTION

Both tissue Doppler imaging (TDI) and pulsed wave Doppler (PWD) Myocardial Performance Indices (MPIs) have been proposed as tools for functional fetal cardiology. We wished to determine if there was any correlation between TDI-MPI and PWD-MPI.

METHODS

A cohort of uncomplicated women with morphologically normal singleton fetuses between 22 and 39 weeks of gestation was recruited. A single sonologist acquired Doppler waveforms for evaluation of both left and right TDI-MPI and PWD-MPI. The PWD-MPI values were calculated using a previously published algorithm and the TDI-MPI time intervals were measured manually by a single operator.

RESULTS

Achievability and repeatability were high for both modalities. TDI produced significantly lower right MPI values yet significantly higher left MPI values, potentially reflecting their evaluation of physiologically different events, blood flow versus myocardial contraction.

CONCLUSION

This study demonstrates that MPIs measured from PWD and TDI have a weak correlation and cannot be used interchangeably, even with the exclusion of suboptimal TDI-MPI scans from the analysis. Given the lack of correlation between the two methods, the high variation in TDI waveform, and the lack of unified approach to TDI analysis, we feel further research is needed before adoption of this technique.

Minute Stroke Distance Is a More Reproducible Measurement Than Cardiac Output in the Assessment of Fetal Ventricular Systolic Function

BACKGROUND

Echocardiographic quantification of fetal cardiac output (CO) aids clinical decision-making in the management of various cardiac and extracardiac diseases. Small variability in measuring semilunar valve dimension significantly reduces the reproducibility of the calculated CO. The authors propose minute stroke distance or velocity-time integral (VTI) as a more reproducible measure reflecting fetal ventricular systolic function. The aim of this study was to test the hypothesis that right and left ventricular minute VTI increase predictably with estimated fetal weight and are more reproducible than CO.

METHODS

Five hundred seventy-one singleton fetuses without cardiovascular pathology between 16 and 36 weeks' gestation were reviewed retrospectively. Twenty-two fetuses with pathology resulting in low- or high-CO states were also assessed for comparison. VTI was measured in both ventricular outflow tracts at the level of the semilunar valve, excluding a Doppler insonation angle of >30°. Heart rate, semilunar valve dimension, and VTI determined minute VTI and CO. Inter- and intrarater variability were evaluated in a random 10% subset.

RESULTS

Minute VTI and CO measurements were feasible in 67% to 89% of fetuses in this retrospective study. Minute VTI and CO increased with estimated fetal weight nonlinearly (R = 0.61-0.94). The mean inter- and intrarater variability for VTI, 6% and 5.7%, were significantly less than for CO, 25% and 23.7% (P < .001 for all).

CONCLUSIONS

Minute VTI is an easily measured, highly reproducible method of quantifying fetal ventricular systolic function. Variability in calculated CO from valve measurement differences is minimized by solely using VTI. Nomograms of minute VTI provide an efficient and precise assessment of fetal systolic function and may be used to track fetuses in disease states with low or high CO.

Modified myocardial performance index for evaluation of fetal heart function and perinatal outcomes in intrahepatic pregnancy cholestasis

This study aims to evaluate cardiac function in cases of intrahepatic cholestasis of pregnancy (ICP) and compare results with those from healthy controls using the fetal left ventricular modified myocardial performance index (LMPI) and E-wave/A-wave peak velocities (E/A ratio). Moreover, the association between LMPI values, total bile acid (TBA) levels, fetal Doppler measurements, and adverse neonatal outcomes was evaluated. A prospective cross-sectional study of 120 pregnant women was conducted, with 60 having ICP and the other 60 serving as controls. Doppler ultrasound and two-dimensional gray-scale fetal echocardiography were used to calculate the LMPI values and E/A ratios, respectively. The association between LMPI values and TBA levels, fetal Doppler measurements, and adverse neonatal outcomes was evaluated. Fetal LMPI values were significantly higher in the ICP group than in the control group (0.54 ± 0.54 vs. 0.44 ± 0.03; p < 0.001), but the E/A ratio was similar in both groups (0.69 ± 0.10 vs. 0.66 ± 0.14; p = 0.203). TBA levels were positively and significantly correlated with LMPI values (r = 0.546, p < 0.01); however, no significant correlation was found between umbilical arterial pulsatility index values and LMPI values (r = 0.071, p > 0.01). LMPI values were not associated with adverse neonatal outcomes in ICP cases. Fetal cardiac function (LMPI) is associated with increased bile acid levels in ICP. However, because it was not associated with adverse neonatal outcomes in ICP cases, the clinical significance of this finding is unclear. Further studies are required to evaluate the implications of increased LMPI.

Pulmonary vasodilator strategies in neonates with acute hypoxemic respiratory failure and pulmonary hypertension

The management of acute hypoxemic respiratory failure (AHRF) in newborns continues to be a clinical challenge with elevated risk for significant morbidities and mortality, especially when accompanied with persistent pulmonary hypertension of the newborn (PPHN). PPHN is a syndrome characterized by marked hypoxemia secondary to extrapulmonary right-to-left shunting across the ductus arteriosus and/or foramen ovale with high pulmonary artery pressure and increased pulmonary vascular resistance (PVR). After optimizing respiratory support, cardiac performance and systemic hemodynamics, targeting persistent elevations in PVR with inhaled nitric oxide (iNO) therapy has improved outcomes of neonates with PPHN physiology. Despite aggressive cardiopulmonary management, a significant proportion of patients have an inadequate response to iNO therapy, prompting consideration for additional pulmonary vasodilator therapy. This article reviews the pathophysiology and management of PPHN in term newborns with AHRF while highlighting both animal and human data to inform a physiologic approach to the use of PH-targeted therapies.

Cardiac Function Assessment in Fetuses With Ductus Arteriosus Constriction: A Two-Dimensional Echocardiography and FetalHQ Study

Background

Fetal ductal constriction (DC) is associated with excessive polyphenol-rich food (PRF) consumption during pregnancy. However, the effect of this hemodynamic change on fetal cardiac function still needs to be elucidated. Therefore, this study aimed to evaluate the cardiac function of fetuses with PRF-related DC and to describe serial observations of cardiac function changes.

Methods

We compared the traditional echocardiographic indices, including morphological, hemodynamic, and functional parameters, between study fetuses and controls. For global and segmental deformation analysis of the left and right ventricles, fetalHQ with the speckle-tracking technique was used to calculate sphericity index (SI), global longitudinal strain (GLS), fractional shortening (FS), fractional area change (FAC), etc. In addition, follow-up data were compared with the generalized linear model.

Results

A total of 60 DC fetuses and 60 gestational-matched controls were enrolled in our study, with 20 DC fetuses undertaking a follow-up echocardiogram after 2–3 weeks. Compared with controls, there was a distinct decrease in right ventricular GLS (RVGLS) (−13.39 ± 3.77 vs. −21.59 ± 2.51, p &lt; 0.001), RVFAC (22.20 ± 9.56 vs. 36.01 ± 4.84, p &lt; 0.001), left ventricular GLS (LVGLS) (−19.52 ± 3.24 vs. −23.81 ± 2.01 p &lt; 0.001), and LVFAC (39.64 ± 7.32 vs. 44.89 ± 4.91, p = 0.004). For 24-segment FS analysis, DC fetuses showed lower FS in left ventricular (LV) segments 18–24, with no difference in LV segments 1–17. Right ventricular (RV) FS in segments 4–23 was also reduced in the DC group. The 24-segment SI analysis indicated significantly lower SI in DC than those in controls for LV segments 1–14 and RV segments 19–24. We found that the pulsatility index (PI) of ductus arteriosus (DA) was an independent variable for RVGLS (β = −0.29, p = 0.04). In 20 DC fetuses with follow-up echocardiograms, no obvious difference in myocardial deformation was found between the initial examination and follow-up data.

Conclusion

Left and right ventricular performances were both impaired in DC fetuses, along with a series of morphological and hemodynamic changes. Although the state of DA constriction improved on second examinations, cardiac function was not completely restored.

Alterations in Cardiac Output in Fetuses with Congenital Heart Disease

OBJECTIVE

Fetuses with severe congenital heart disease (CHD) have altered blood flow patterns. Prior work to assess fetal combined cardiac output (CCO) is limited by sample size and lack of longitudinal gestational data. Our aim was to evaluate CCO in CHD fetuses to determine whether the presence of single ventricle (SV) physiology or aortic obstruction impacts fetal blood flow and cardiovascular hemodynamics.

METHOD

Prospective study including singleton fetuses with CHD (n=141) and controls (n=118) who underwent a mid and late gestation fetal echocardiogram. Ventricular cardiac output was calculated using the standard computation. CCO was derived as the sum of the right and left cardiac outputs and indexed to estimated fetal weight.

RESULTS

Fetuses with two ventricle (2V) CHD had significantly higher CCO compared to controls and SV-CHD fetuses. Fetuses with SV-CHD had similar CCO compared to controls. Fetuses with 2V-CHD and aortic obstruction had significantly higher CCO than fetuses with SV-CHD and aortic obstruction.

CONCLUSION

Our findings suggest that the SV can compensate and increase CCO despite the lack of a second functioning ventricle however, the degree of compensation may be insufficient to support the increased blood flow needed to overcome the hemodynamic and physiologic alternations seen with severe CHD. This article is protected by copyright. All rights reserved.

Aortic Elasticity and Cardiac Function in Fetuses With Aortic Coarctation

Objective

The purpose of the study was to observe the elasticity of the ascending aorta (AAo) in normal fetuses and fetuses with coarctation of the aorta (CoA) by M-mode echocardiography.

Methods

This was a prospective clinical study performed on 16 fetuses with CoA and 48 gestational-age matched normal fetuses. The minimum internal diameter in the diastolic phase (Dmin) and the maximum internal diameter in the systolic phase (Dmax) of the AAo were measured by M-mode echocardiography. The aortic strain was calculated using the formula 100 × (Dmax−Dmin)/Dmin). Doppler echocardiography was performed to measure the cardiac function parameters. Correlations between aortic strain and cardiac function were assessed in fetuses with CoA.

Results

The aortic strain of the ascending aorta in the fetuses with CoA was significantly lower than that in normal fetuses (18.12 ± 4.88% vs. 25.22 ± 4.92%, p < 0.01). The fetuses with CoA showed significantly higher combined cardiac output than the controls (471.89 ± 93.98 vs. 411.57 ± 46.35 ml/min/kg, p < 0.05). Compared with the normal group, the early diastolic velocities (E') and peak systolic velocities (S') of the left side were obviously decreased in the CoA group (p < 0.05), while the left early diastolic velocity ratio (E/E') was significantly increased in the fetuses with CoA (p < 0.01). For the fetuses with CoA, the aortic strain of the AAo was correlated with the left E/E' and S' (r = −0.522 and 0.504, respectively, P < 0.05).

Conclusions

The aortic strain of the ascending aorta was significantly decreased in fetuses with CoA in middle-late gestation. The impaired strain of the ascending aorta was correlated with the left ventricle function in the fetuses with CoA. These findings imply that the abnormalities of the intrinsic aortic wall of CoA might develop early in utero.

Fetal myocardial deformation measured with two-dimensional speckle-tracking echocardiography: longitudinal prospective cohort study of 124 healthy fetuses

OBJECTIVES

Two-dimensional speckle-tracking echocardiography (2D-STE) is a promising technique which allows assessment of fetal cardiac function, and can be used in the evaluation of cardiac and non-cardiac diseases in pregnancy. However, reliable fetal reference values for deformation parameters measured using 2D-STE are needed before it can be introduced into clinical practice. This study aimed to obtain reference values for fetal global longitudinal strain (GLS) and GLS rate (GLSR) measured using 2D-STE and compare right and left ventricular values.

METHODS

This was a prospective longitudinal cohort study of uncomplicated pregnancies that underwent echocardiography every 4 weeks from inclusion at 18-21 weeks until delivery to obtain four-chamber loops of the fetal heart. Left and right ventricular GLS and GLSR were measured using 2D-STE at each examination. Using Bayesian mixed-effects models, reference values with lower and upper 5% prediction limits were calculated according to gestational age. Right and left ventricular GLS values according to gestational age were compared using the Wilcoxon signed-rank test.

RESULTS

A total of 592 left ventricular and 566 right ventricular GLS and GLSR measurements were obtained from 124 women with uncomplicated pregnancy and non-anomalous, appropriately grown fetuses. Reference values were obtained for both fetal ventricles according to gestational week. GLS and GLSR values of both ventricles increased (i.e. became less negative) significantly during pregnancy. Right ventricular GLS values were significantly higher (i.e. less negative) than the respective left ventricular values at every gestational week.

CONCLUSIONS

Reference values were obtained for fetal GLS and GLSR measured using 2D-STE. GLS and GLSR values increased significantly for both ventricles from the second trimester until delivery. GLS values were significantly higher for the right ventricle compared with the left ventricle. Future studies are needed to assess whether the obtained reference values are helpful in clinical practice in the assessment of pregnancy complications, such as fetal growth restriction or cardiac anomaly. © 2022 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Cardiovascular fetal-to-neonatal transition: an in silico model

BACKGROUND

Previous models describing the fetal-to-neonatal transition often lack oxygen saturation levels, homeostatic control mechanisms, phasic hemodynamic signals, or describe the heart with a time-varying elastance model.

METHODS

We incorporated these elements in the adapted CircAdapt model with the one-fiber model for myocardial contraction, to simulate the hemodynamics of the healthy term human fetal circulation and its transition during the first 24 h after birth. The fetal-to-neonatal model was controlled by a time- and event-based script of changes occurring at birth, such as lung aeration and umbilical cord clamping. Model parameters were based on and validated with human and animal data.

RESULTS

The fetal circulation showed low pulmonary blood flow, right ventricular dominance, and inverted mitral and tricuspid flow velocity patterns, as well as high mean ductus venosus flow velocity. The neonatal circulation showed oxygen saturation levels to gradually increase to 98% in the first 15 min after birth as well as temporary left ventricular volume overload.

CONCLUSIONS

Hemodynamics of the term fetus and 24-h-old neonate, as well as the events occurring directly after birth and the transition during the first 24 h after birth, were realistically represented, allowing the model to be used for educational purposes and future research.

IMPACT

With the addition of oxygen saturation levels, homeostatic pressure-flow control mechanisms, and the one-fiber model for myocardial contraction, a new closed-loop cardiovascular model was constructed to give more insight into the healthy term human fetal circulation and its cardiovascular transition during the first 24 h after birth. Extensive validation confirmed that the hemodynamics of the term fetus and the fetal-to-neonatal transition were realistically represented with the model. This well-validated and versatile model can serve as an education as well as a research platform for in silico investigation of fetal-to-neonatal hemodynamic changes under a wide range of physiological and pathophysiological conditions.

Impact of ductus arteriosus constriction and restrictive foramen ovale on global hemodynamics for term fetuses with d-TGA

The ductus arteriosus (DA) constriction and restrictive foramen ovale (FO) are known as the leading cause of compromise and death of fetuses with dextro-transposition of the great arteries (d-TGA). Although the d-TGA fetal hemodynamics is of great importance in making diagnosis and management of the congenital heart defect, it remains poorly understood, particularly in terms of abnormal DA and FO. In this study, we developed a closed-loop 0-1D multiscale model of the fetal cardiovascular system (CVS) specified for the d-TGA circulation and conducted a systematic study of the impact of the DA constriction and restrictive FO on fetal hemodynamics. We found that the DA constriction led to a pronounced increase in the pulmonary artery pressure, pulmonary and mitral valve (PV and MV) regurgitation as well as left heart volume; the restrictive FO was responsible for reducing MV E/A ratio, ie, the ratio of peak early filling and late diastolic filling velocities, and PV peak systolic flow (PSV) but could increase both aortic valve (AV) PSV and aortic isthmus systolic index (ISI). Moreover, the amount of blood flowing through the DA was observed equivalent to that through the FO; the influence of DA constriction on the cerebral and placental perfusions are larger than that of the FO. Our results demonstrate that the proposed fetal cardiovascular model may be a useful tool for studying the underlying mechanisms associated with d-TGA fetal circulation and providing insights into its complex physiology and pathology.

Perinatal Cardiovascular Physiology and Recognition of Critical Congenital Heart Defects

Understanding the perinatal cardiovascular physiology is essential for timely diagnosis and management of congenital heart defects (CHDs) in neonatal period. The incidence of CHDs is reported in 7 to 9 out of 1000 live births, with around 25% of them being critical congenital heart disease, defined as a congenital heart condition needing surgery/intervention or leading to death within 1 month after birth. Around 50% to 60% of the critical CHDs are detected on fetal anomaly screening. The signs and symptoms of critical congenital heart defects are often nonspecific during early neonatal period. The routine newborn physical examination often fails to detect many of these critical CHDs during the transitional circulation because of lack of signs soon after birth. While routine pulse oximetry screening typically performed at 24 to 48 hours after birth may help in detecting cyanotic heart conditions, noncyanotic CHDs such as coarctation of aorta may go undetected on pulse oximetry screening in asymptomatic infants. Some infants may deteriorate early while waiting for pulse oximetry screening, and this risk is much higher if the pulse oximetry screening is not performed to detect congenital heart conditions. There should be high degree of suspicion of critical CHDs in infants presenting with shock or hypoxia. Delay in diagnosis of CHDs has been reported to be associated with poor outcomes, and hence, it is extremely important to detect them in asymptomatic well-infants. Timely recognition and therapy with prostaglandin E1 infusion can be lifesaving in neonatal cardiac emergencies, and they should be urgently discussed with a pediatric cardiologist. This article reviews diagnosis and management of CHD in the delivery room and before surgery in the NICU.

High Output Cardiovascular Physiology and Outcomes in Fetal Diagnosis of Vein of Galen Malformation

Vein of Galen aneurysmal malformation (VGAM) is a rare anomaly associated with poor outcomes from high output cardiac failure and neurologic complications. Studies addressing fetal cardiovascular status and outcomes in this population are limited. A single-center retrospective review was conducted on patients with a prenatal diagnosis of VGAM who underwent a fetal echocardiogram between January 2015 and July 2019. Fetal echocardiographic data, brain magnetic resonance imaging (MRI) findings and outcomes were collected. Nine fetuses [median gestational age at echocardiogram 34 (1.1) weeks] were included. All patients had superior vena cava dilation and reversal of diastolic flow in the transverse aortic arch. Median cardiothoracic (CT) ratio was 0.39 (0.09). Right ventricular (RV) and left ventricular (LV) dysfunction was present in 66% and 11% fetuses, respectively. Four out of five patients that underwent postnatal endovascular neurosurgical interventions at our center were alive at follow-up (mean 2.7 years). Of the non-survivors (n = 5), 3 received comfort care because of severe brain damage and died in the neonatal period. Non-survivors more commonly had > mild tricuspid regurgitation (TR) (40% vs. 25%) and > mild RV dilation (60% vs. 25%). Combined cardiac index (CCI) was higher in non-survivors when compared to survivors (672.7 vs. 530.2 ml/kg/min, p = 0.016). Fetuses with significant parenchymal damage on brain MRI tended to have a higher CCI than those without (979.8 vs. 605.0 ml/kg/min, p = 0.047). RV dysfunction, TR and elevated CCI are more commonly seen in non-survivors with VGAM. A higher CCI is seen in those deemed untreatable due to significant parenchymal volume loss. Future multicenter studies are needed to assess for prenatal prediction of outcomes in this high-risk population.

Fetal Superior Vena Cava Blood Flow and Its Fraction of Cardiac Output: A Longitudinal Ultrasound Study in the Second Half of Pregnancy

Introduction: In the fetus, a large proportion of the superior vena cava blood flow (QSVC) comes from the brain. To provide the possibility of using this blood flow as a representation of fetal brain circulation, we aimed to determine the fetal QSVC and its fraction of cardiac output during the second half of physiological pregnancies. Materials and Methods: This was a prospective longitudinal study specifically designed for studying fetal hemodynamic development. Healthy women with singleton low-risk pregnancies were included. Ultrasonography was performed at 4-weekly intervals from 20+0 gestational weeks to term. Doppler velocity recordings of the superior vena cava (SVC) and cardiac ventricular outflow tracts were used to obtain the time-averaged maximum velocities (TAMxV). Vessel diameters were measured to calculate their cross-sectional areas (CSA): π(diameter/2)2. Blood flow (Q) was computed as: h *TAMxV*CSA, h being the spatial blood velocity profile, to obtain QSVC and cardiac outputs. The sum of left and right ventricular cardiac outputs constituted the combined cardiac output (CCO). Ultrasound biometry based estimated fetal weight and brain weight were used to normalize the flow. QSVC was also expressed as the fraction (%) of CCO. Gestational age specific percentiles were established for each blood flow parameter using multilevel modeling. Results: Totally, 134 of the 142 included women were eligible for the study with 575 sets of observations. The SVC mean diameter (19-52 mm), mean TAMxV (8.83-16.14 cm/s), and QSVC (15.4-192.0 ml/min) increased significantly during the second half of pregnancy (p < 0.001) while the mean QSVC normalized by estimated fetal weight (49 ml/min/kg) and by estimated brain weight (50 ml/min/100 g) were relatively stable. Similarly, the mean CCO increased (156-1,776 ml/min; p < 0.001) while the normalized CCO (509 ± 13 ml/min/kg) and QSVC as a fraction of CCO (10 ± 0.92%) did not change significantly with gestational age. Conclusion: We provide reference values for fetal QSVC which increases significantly with gestation, and constitutes roughly 10% of the fetal CCO at any time during the second half of pregnancy.

Prescriptive standards of echocardiographic morphometric and functional parameters in uncomplicated monochorionic diamniotic fetuses

OBJECTIVE

To create prescriptive standards of cardiac morphometric and functional parameters in a cohort of uncomplicated monochorionic diamniotic (MCDA) twins.

METHOD

Fetal echocardiography was performed in a cohort of uncomplicated monochorionic twin fetuses scanned longitudinally, including comprehensive morphometric and functional parameters, using 2-D imaging, M-mode and conventional Doppler. A multilevel polynomial hierarchical model adjusted by gestational age and estimated fetal weight was used to fit each cardiac parameter.

RESULTS

The global heart dimensions including the atrial and ventricular areas, the ventricles dimensions and myocardial wall thicknesses and most of the functional parameters, such as the longitudinal myocardial motion and the biventricular cardiac output showed a positive quadratic increment throughout pregnancy. On the other hand, the left ejection fraction, shortening fraction and right fractional area change decreased with gestational age. Scatterplots for the main structural and functional parameters and ratios by gestational age, with mean, 5th, 10th, 90th, and 95th percentiles are provided. Regression equations by estimated fetal weight are also created.

CONCLUSION

We provide specific comprehensive echocardiographic prescriptive standards for uncomplicated MCDA twin fetuses following current standardized methodology. The implementation of these charts will potentially help to better identify abnormal cardiovascular parameters associated to monochorionic complications.

Maternal diabetes and fetal cardiac output

BACKGROUND

The intrauterine environment is a key determinant for long-term health outcomes. Adverse fetal environments, such as maternal diabetes, obesity and placental insufficiency are strongly associated with long-term health risks in children. Little is known about differences in fetal cardiac output hemodynamics of diabetic mothers (DM) vs. non-diabetic mothers (NDM). Our study aims to investigate the left-sided, right-sided, and combined cardiac output (CCO) in fetuses of DM vs. NDM.

METHODS

Retrospective data were collected in fetuses of DM (N = 532) and NDM (103) at mean gestational age 24 weeks. Examination included 2D echo and pulse wave Doppler. Wilcoxon rank sum tests and Chi-square tests were used to test for distribution difference of maternal and fetal continuous and categorical measures respectively between DM and NDM. Intraclass correlation coefficients were calculated to assess intra-observer reliability of fetal cardiac measurements.

RESULTS

DM mothers had higher mean weight (89.7±22.2 kg) than NDM (76.8±19.8 kg), p <  0.0001 and higher mean BMI (33.4±7.5) than NDM (28.3±5.8), p <  0.0001. C-section delivery occurred in 66% of DM vs. 35% of NDM fetuses. Fetuses of DM mothers had significantly larger semilunar valve diameter, higher left ventricular (LV) output, higher combined cardiac output and lower right ventricle /left ventricle ratio compared to NDM.

CONCLUSION

The greater CCO (adjusted for fetal weight), left sided cardiac output in the fetuses of DM, compared to NDM, represent differences in cardiac adaptation to the diabetic environment.

Influences of adversity across the lifespan on respiratory sinus arrhythmia during pregnancy

There is limited understanding of factors across the lifespan that influence pregnant women's respiratory sinus arrhythmia (RSA), which could have implications for their health and offspring development. We examined associations among 162 English- and Spanish-speaking pregnant women's childhood maltreatment history, emotion dysregulation, recent life stress, and resting RSA during the third trimester. Moderated mediation analyses indicated that more severe childhood maltreatment history (95% confidence interval (CI) [0.26, 0.63]) and higher emotion dysregulation (95% CI [0.001, 0.006]) predicted more stress during pregnancy, and childhood maltreatment history interacted with emotion dysregulation to predict resting RSA (95% CI [-0.04, -0.0003]). Exploratory analyses revealed that women's health-related stress during pregnancy mediated the relation between emotion dysregulation and RSA regardless of childhood maltreatment severity (95% CI [-0.007, -0.002]). These findings suggest that women's resting RSA during pregnancy may reflect physical and emotional stress accumulation across the lifespan and that relations between early life adversity and prenatal psychophysiology may be buffered by protective factors, such as emotion regulation. In addition, these findings underscore the importance of distinguishing between types of prenatal stress. Given the implications for women's health and offspring development, we urge researchers to continue exploring factors associated with pregnant women's psychophysiology.

Evaluation of fetal foramen ovale blood flow by pulsed Doppler ultrasonography combined with spatiotemporal image correlation : To define the normal reference range of fetal foramen ovale blood volume for each gestational age: a cross-sectional study

Objective

The objective of this study was to determine fetal foramen ovale blood flow utilizing pulsed Doppler combined with spatiotemporal image correlation.

Methods

A cross-sectional study was performed in 440 normal fetuses between 20 and 40 weeks of gestation. In order to calculate foramen ovale blood flow, the foramen ovale flow velocity–time integral was obtained by pulsed Doppler ultrasonography, and the foramen ovale area was measured by using spatiotemporal image correlation rendering mode. Foramen ovale blood flow was calculated as the product of the foramen ovale area and the velocity–time integral.

Results

Gestational age-specific reference ranges are given for the absolute blood flow (ml/min) of foramen ovale, showing an exponential increase from 20 to 30 weeks of gestation, and a flat growth trend during the last trimester, while the weight-indexed flow (ml/min/kg) of foramen ovale decreased significantly. The median weight-indexed foramen ovale blood flow was 320.82 ml/min/kg (mean 319.1 ml/min/kg; SD 106.33 ml/min/kg).

Conclusions

The reference range for fetal foramen ovale blood flow was determined from 20 to 40 weeks of gestation. The present data show that the volume of foramen ovale blood flow might have a limited capacity to increase during the last trimester.

Spectral Doppler, tissue Doppler, and speckle-tracking echocardiography for the evaluation of fetal cardiac function: an update

The functional assessment of the fetal heart has been incorporated into cardiac ultrasound screening as a routine procedure, encompassing fetuses with and without structural heart diseases. It has long been known that various cardiac and extracardiac conditions, such as fetal growth restriction, fetal tumors, twin-to-twin transfusion syndrome, fetal anemia, diaphragmatic hernia, arteriovenous fistula with high cardiac output, and congenital heart diseases (valvular regurgitation and primary myocardial disease), can alter hemodynamic status and fetal cardiac function. Several ultrasound and Doppler echocardiographic parameters of fetal cardiovascular disease have been shown to correlate with perinatal mortality. However, it is still difficult to identify the signs of fetal heart failure and to determine their relationship with prognosis. The aim of this study was to review the main two-dimensional Doppler ultrasound parameters that can be used in the evaluation of fetal cardiac function, with a focus on how to perform that evaluation and on its clinical applicability.

T2* placental MRI in pregnancies complicated with fetal congenital heart disease

BACKGROUND

Congenital heart disease (CHD) is one of the most important and common group of congenital malformations in humans. Concurrent development and close functional links between the fetal heart and placenta emphasise the importance of understanding placental function and its influence in pregnancy outcomes. The aim of this study was to evaluate placental oxygenation by relaxometry (T2*) to assess differences in placental phenotype and function in CHD.

METHODS

In this prospective cross-sectional observational study, 69 women with a fetus affected with CHD and 37 controls, whole placental T2* was acquired using a 1.5-Tesla MRI scanner. Gaussian Process Regression was used to assess differences in placental phenotype in CHD cohorts compared to our controls.

RESULTS

Placental T2* maps demonstrated significant differences in CHD compared to controls at equivalent gestational age. Mean T2* values over the entire placental volume were lowest compared to predicted normal in right sided obstructive lesions (RSOL) (Z-Score 2.30). This cohort also showed highest lacunarity indices (Z-score -1.7), as a marker of lobule size. Distribution patterns of T2* values over the entire placental volume were positively skewed in RSOL (Z-score -4.69) and suspected, not confirmed coarctation of the aorta (CoA-) (Z-score -3.83). Deviations were also reflected in positive kurtosis in RSOL (Z-score -3.47) and CoA- (Z-score -2.86).

CONCLUSION

Placental structure and function appear to deviate from normal development in pregnancies with fetal CHD. Specific patterns of altered placental function assessed by T2* deliver crucial complementary information to antenatal assessments in the presence of fetal CHD.

Pulmonary Hypoplasia Resulting from Pulmonary Artery Banding in Infancy: A Neonatal Rat Model Study

The aim of this study was to establish a neonatal rat model of decreased pulmonary blood flow (PBF) for studying pulmonary pathophysiological changes in newborn lung development with reduced PBF. Horizontal thoracotomy surgery with banding of the main pulmonary artery (PA) was performed on 30 rats in the PA banding (PAB) group and without banding on another 30 rats in the sham group within 6 h after birth. The body growth and mortality were recorded. Constriction of PA was checked by echocardiography on postnatal day 7 (P7). Lung morphology was assessed with computed tomography scanning and three-dimensional reconstruction. Histological differences of two groups were evaluated using hematoxylin and eosin (H&E) staining, Masson's trichrome staining, TdT-mediated dUTP nick-end labeling assay, and CD31 labeling with microscopic examination. PA ultrasound confirmed the establishment of constriction on P7. Relative to the sham group, the neonates' physical growth, survival fraction, and lung geometry volume were decreased in the PAB group over time (p < 0.05). Histologic appearance with reduced PBF characterized a markedly simplified alveolarization with noted lower radial alveolar count and alveolar septal thickness in the PAB group (p < 0.0001), pulmonary arteries with thinner/uneven membranous layers and smaller lumina. The deficient alveolar capillary bed, enhanced pulmonary collagen deposition, and increased apoptotic alveolar epithelium were significant in the PAB group compared to the sham group (p < 0.0001). A neonatal rat PAB model demonstrated that PBF reduction during early infancy impairs alveolarization and pulmonary microvasculature.

Fetal Physiologically Based Pharmacokinetic Models: Systems Information on Fetal Cardiac Output and Its Distribution to Different Organs during Development

BACKGROUND AND OBJECTIVE

Fetal circulation is unique and the parameters describing hemodynamic status during development are critical for constructing a fetal physiologically based pharmacokinetic model. To date, a comprehensive review of circulatory changes during fetal development, with a specific focus on developing these models, has not been reported. The objective of this work was to collate, analyze, and mathematically describe physiological information on fetal cardiac output and tissue blood flows during development.

METHODS

A comprehensive literature search was carried out to collate and evaluate the changes to fetal cardiac output and fetal tissue blood flows during growth. The collated data were assessed, integrated, and analyzed to establish continuous mathematical functions describing the average parameter changes and variability during development.

RESULTS

Data were available for fetal cardiac output (14 Doppler studies), blood flow through the fetal umbilical vein (15 studies), ductus venosus (6 studies), liver veins (5 studies), brain (4 studies), lungs (5 studies), and kidneys (2 studies). Fetal cardiac output is described as either an age- or weight-dependent function. The latter is preferred as it generates an individualized cardiac output that is correlated to the fetal body weight. Blood flow as a proportion of fetal cardiac output to the liver, placenta, brain, kidneys, and lungs was age varying, whilst for the adipose, bone, heart, muscle, and skin the blood flow proportions were fixed. The pattern of change (with respect to direction and pace) for each of these parameters was different.

CONCLUSIONS

Despite limitations in the availability of some values, the collected data provide a useful resource for fetal physiologically based pharmacokinetic modeling. Potential applications of these data include predicting xenobiotic exposure and risk assessment in the fetus following the administration of maternally dosed drugs or unintended exposure to environmental toxicants.

Neonatal blood pressure before and after delayed umbilical cord clamping

OBJECTIVE

To describe values of blood pressure (BP) before and after delayed cord clamping (DCC) in healthy term neonates born to low risk pregnancies, examine differences in the temporal patterns of BP during this transition, and assess potential correlation of these parameters with maternal and perinatal clinical and demographic variables.

METHODS

Prospective observational study of term infants eligible for DCC born vaginally from uncomplicated pregnancies. Neonatal BP was estimated noninvasively before DCC, at 30 min and 24 h of life. Median, minimum, maximum, mean and standard deviation, as well as percentiles for BP values were calculated. Pearson correlation assessed the correlation between demographic and clinical variables and BP measurements. Spearman correlation studied the association between BP parameters prior to DCC and Apgar scores. Repeated measures ANOVA and Tukey post hoc analyses were used to compare BP measurements over time. A p-value of <.05 was considered significant.

RESULTS

A total of 54 patients were included. Mean neonatal birthweight was 3185 g and gestational age 39/3 weeks. The mean values for the systolic, diastolic, and mean BP prior to DCC were 97 ± 24.9 mmHg, 58 ± 21.9 mmHg and 67 ± 27.7 mmHg respectively. A statistically significant difference was detected when comparing BP values obtained before DCC with those measured afterwards (Figure 1). A positive correlation was found between SBP and MAP prior to DCC and Apgar scores at 1 min. [Figure: see text].

CONCLUSION

We describe novel values of BP before DCC in healthy term infants following vaginal delivery. Data suggest that neonates whose cord is clamped in a delayed fashion experience an increase blood pressures immediately after birth, followed by a significant drop within 30 min to levels that remain unchanged at 24 h of life. BP values obtained after DCC in our study are similar to those found by previous authors. Further studies are needed to determine the clinical significance of these findings and assess the potential of BP prior to DCC to evaluate immediate postnatal adaptation.

LIMITATIONS

Results generalizability may have been limited by varying degrees of neonatal resuscitation, inability to perform more than one measurement before cord clamping ensued, as well as an unequal distribution of self-reported race in our cohort. Also, noninvasive BP estimates have proven less accurate that invasive methods. Finally, our cohort was comprised by a relatively small sample and larger studies will be required to corroborate our findings.

Ultrasound measurement of fetal arterial pulse pressure using phased-tracking methods: A phantom study and clinical experience with antenatal corticosteroid therapy

AIM

This study aimed to compare the accuracy of fetal pulse pressure estimated with a vascular simulator with that obtained by a manometer (reference) and evaluate the pulse pressure in normal human fetuses and fetuses whose mothers received corticosteroids.

METHODS

Fetal pulse pressure was estimated as the product of blood flow velocity and pulse wave velocity, based on the water hammer equation. Ultrasonic raw radiofrequency signals for blood flow velocity were captured from the fetal descending aortas at the diaphragm level, and pulse wave velocity was simultaneously measured from different directions using the phased-tracking method. First, the precision and accuracy of pulse pressure in the estimated method were verified by a circulatory phantom simulator, which reproduced fetal blood flow using a pulsating pump. Then, the pulse pressure of 98 normal human fetuses after 17 weeks of gestation and the fetal pulse pressure in 21 mothers who received antenatal corticosteroids for fetal maturation were measured.

RESULTS

A significant correlation between the estimated pulse pressure values and the actual values was found in the phantom simulation (r = 0.99, P < 0.01). The estimated pulse pressure was significantly correlated with gestational age in normal fetuses (r = 0.74, P < 0.01). In steroid-treated pregnant women, fetal pulse pressure was observed to increase significantly on the second day of administration (P < 0.01).

CONCLUSION

A noninvasive and accurate estimation model of fetal pulse pressure could be established using phased-tracking method, and this method has the potential to improve the assessment of human fetal hemodynamics.

Myocardial peak systolic velocity-a tool for cardiac screening of HIV-exposed uninfected children

HIV-uninfected children exposed prenatally to the virus and to prophylactic antiretroviral therapy are at an uncertain risk of long-term myocardial dysfunction. This study aimed to analyse the structure and function of their ventricles and to identify potential screening tools for this at-risk population. One hundred and fifteen children (77 exposed vs 38 controls) aged between 2.7 and 16.2 years were included. An echocardiographic study was performed where both ventricles' dimensions and systolic functions were evaluated. In the left ventricle, parameters related to diastolic function were also analysed. Tissue Doppler values were determined in the basal state and after passive leg raising. Serologic analysis of amino-terminal pro-B-type natriuretic peptide (NT-proBNP) was carried out. The two groups had identical ventricular sizes and left ventricular diastolic functions. However, contractility assessed by myocardial peak systolic velocity was significantly inferior in the exposed group. These systolic echocardiographic differences were present despite similar values of NT-proBNP in both groups.Conclusion: HIV-exposed uninfected children may be vulnerable to ventricular systolic dysfunction at long term. Cardiovascular surveillance and periodic monitoring of biventricular function are therefore recommended. Myocardial peak systolic velocity may be a useful screening tool for this purpose.What is Known:• Previous studies on HIV-exposed uninfected children subjected prenatally to antiretroviral therapy have alerted to potential long-term cardiovascular toxicity effects on the left ventricle.What is New:• The study gives new insights on ventricular function and morphology in HIV-exposed uninfected children.• Myocardial peak systolic velocities are significantly inferior in this paediatric sub-group, therefore long-term cardiac surveillance is recommended.

Z Score Reference Ranges of Fetal Cardiac Output From 12 to 40 Weeks of Pregnancy

OBJECTIVES

To develop the Z score reference ranges of fetal cardiac output (CO) in healthy fetuses from 12 to 40 weeks of pregnancy.

METHODS

A cross-sectional descriptive study was undertaken among low-risk singleton pregnancies with healthy fetuses between 12 and 40 weeks. The right ventricular cardiac output (RCO), left ventricular cardiac output (LCO), and combined cardiac output (CCO) were measured by 2-dimensional ultrasound with the Doppler velocity of the aorta and pulmonary arteries. The pregnancies were followed until delivery RESULTS: The RCO, LCO, and CCO were determined in 700 fetuses. The predictive models of the CO as a function of gestational age (GA) and biparietal diameter were identified, and the Z score reference ranges were constructed. The means and standard deviations of CO on both sides were increased with GA and biparietal diameter as power models. Nomograms for the LCO, RCO, and CCO were established (ie, RCO = 0.000148 × GA^4.283034 ; SD = 0.000131 × GA^4.026209 ; LCO = 0.000514 × GA^3.790944 ; SD = 0.000169 × GA^3.815546 ). The RCO was much more increased than the LCO with advancing GA.

CONCLUSIONS

The Z score reference ranges and percentile charts of fetal CO were constructed throughout gestation with a large sample size. This may be helpful in detection of cardiac disorders, especially cardiomyopathy, cardiac anomalies, fetal anemia, and fetal growth restriction.

Fetal echocardiographic prediction score for perinatal mortality in tricuspid valve dysplasia and Ebstein's anomaly

OBJECTIVES

Tricuspid valve dysplasia (TVD) and Ebstein's anomaly (EA) diagnosed by fetal echocardiography vary greatly in terms of clinical severity and prognosis. The Celermajer index and Simpson-Andrews-Sharland (SAS) score have been reported previously for the prediction of prognosis in cases of TVD/EA; however, they do not take into account the hemodynamic impact of left ventricular (LV) function, which has recently been implicated as being important in the pathophysiology of TVD/EA. The aim of this study was to develop a novel scoring system that includes LV function for the prediction of perinatal death in fetuses diagnosed with TVD/EA.

METHODS

The clinical records of 36 fetuses diagnosed prenatally with TVD/EA between 2000 and 2015 in our hospital were reviewed. Univariate analysis was used to assess the association between perinatal death (defined as death between 22 weeks' gestation and 4 weeks after delivery) and gestational age at diagnosis, cardiothoracic area ratio (CTAR), degree of pulmonary artery flow, direction of ductal flow, right-to-left ventricular diameter ratio, tricuspid regurgitation (TR) maximum velocity, Celermajer index, SAS score and LV-Tei index. A new prognostic score, the TRIPP score (TRIcuspid malformation Prognosis Prediction score), was developed using the parameters found to be associated significantly with perinatal death. The predictive value of this score was assessed in an additional nine fetuses diagnosed with TVD/EA.

RESULTS

Thirty-six fetuses were diagnosed prenatally with TVD/EA, two of which were terminated, one was lost to follow-up and two died before 22 weeks' gestation. Of the 31 included fetuses, 10 (32%) died in the perinatal period. Univariate analysis demonstrated that TR maximum velocity was significantly lower (2.22 ± 0.17 m/s vs 3.26 ± 0.12 m/s; P < 0.001) and SAS score was significantly higher (5.7 ± 0.6 points vs 2.8 ± 0.4 points; P = 0.0014) in cases of perinatal death than in surviving fetuses. The degree of pulmonary artery flow and the direction of ductal flow were also associated significantly with perinatal death (P < 0.01 for both). Notably, LV-Tei index was significantly higher in cases of perinatal death than in surviving fetuses (0.81 ± 0.08 vs 0.50 ± 0.05; P < 0.001). In contrast, there was no significant difference in Celermajer index, CTAR or right-to-left ventricular diameter ratio. Finally, we established a novel combinatorial scoring system, the TRIPP score, including the four significant factors: TR maximum velocity, pulmonary artery flow, direction of ductal flow and LV-Tei index. The TRIPP score was found to predict efficiently perinatal mortality in fetuses with TVD/EA.

CONCLUSIONS

Our novel combinatorial score of echocardiographic parameters, the TRIPP score, including LV-Tei index, is easy to measure and provides a good tool for the prediction of perinatal mortality in fetuses diagnosed prenatally with TVD/EA. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.

Differential gene responses 3 days following infarction in the fetal and adolescent sheep heart

There are critical molecular mechanisms that can be activated to induce myocardial repair, and in humans this is most efficient during fetal development. The timing of heart development in relation to birth and the size/electrophysiology of the heart are similar in humans and sheep, providing a model to investigate the repair capacity of the mammalian heart and how this can be applied to adult heart repair. Myocardial infarction was induced by ligation of the left anterior descending coronary artery in fetal (105 days gestation when cardiomyocytes are proliferative) and adolescent sheep (6 mo of age when all cardiomyocytes have switched to an adult phenotype). An ovine gene microarray was used to compare gene expression in sham and infarcted (remote, border and infarct areas) cardiac tissue from fetal and adolescent hearts. The gene response to myocardial infarction was less pronounced in fetal compared with adolescent sheep hearts and there were unique gene responses at each age. There were also region-specific changes in gene expression between each age, in the infarct tissue, tissue bordering the infarct, and tissue remote from the infarction. In total, there were 880 genes that responded to MI uniquely in the adolescent samples compared with 170 genes in the fetal response, as well as 742 overlap genes that showed concordant direction of change responses to infarction at both ages. In response to myocardial infarction, there were specific changes in genes within pathways of mitochondrial oxidation, muscle contraction, and hematopoietic cell lineages, suggesting that the control of energy utilization and immune function are critical for effective heart repair. The more restricted gene response in the fetus may be an important factor in its enhanced capacity for cardiac repair.

Pressure and Flow Relations in the Systemic Arterial Tree Throughout Development From Newborn to Adult

Objective: Distributed models of the arterial tree allow studying the effect of physiological and pathophysiological changes in the vasculature on hemodynamics. For the adult, several models exist; however, a model encompassing the full age range from newborn to adult was until now lacking. Our goal is to describe a complete distributed hemodynamic model for normal development from newborn to adult. Methods: The arterial system was modeled by 121 segments characterized by length, radius, wall thickness, wall stiffness, and wall viscosity. The final segments ended in three-element Windkessels. All parameters were adapted based on body height and weight as a function of age as described in the literature. Results: Pressures and flows are calculated as a function of age at sites along the arterial tree. Central to peripheral transfer functions are given. Our results indicate that peripheral pressure in younger children resembles central pressure. Furthermore, total arterial compliance, inertance and impedance are calculated. Findings indicate that the arterial tree can be simulated by using a three-element Windkessel system. Pulse wave velocity in the aorta was found to increase during development. Conclusions: The arterial system, modeled from newborn to adult bears clinical significance, both for the interpretation of peripheral measured pressure in younger and older children, and for using a Windkessel model to determine flow from pressure measurements.

Fetal cardiac function by three-dimensional ultrasound using 4D-STIC and VOCAL - an update

Three- and four-dimensional (3D/4D) ultrasonography with spatio-temporal image correlation (4D-STIC) allows obtaining fetal cardiac volumes and their static and real-time analysis in multiplanar and rendering modes. Cardiac biometrics and Doppler-echocardiographic parameters for evaluation of fetal heart function, including cardiac output and stroke volume, can be analyzed using M-mode, two-dimensional (2D), and 3D/4D cardiac ultrasound. In recent years, functional echocardiography has been used to study fetuses without a structurally cardiac defect but who are at risk of heart failure due to the presence of extra-cardiac conditions, such as, fetal growth restriction, tumors/masses, twin-to-twin transfusion syndrome, fetal anemia (Rh alloimmunization), congenital infections, or maternal diabetes mellitus. The assessment of cardiac function provides important information on hemodynamic status and can help optimize the best time for delivery and reduce perinatal morbidity and mortality. Since 2003, with the advent of the 4D-STIC software, it is possible to evaluate the fetal heart in multiplanar, and rendering modes. This technology associated with virtual organ computer-aided analysis (VOCAL) enables determining the ventricular volume (end-diastole, end-systole), the stroke-volume, the ejection fraction, and the cardiac output of each ventricle. Since 2004, several studies demonstrated that the 4D-STIC and VOCAL had good reproducibility to measure cardiac volumes This study reviews published studies that evaluated the fetal cardiac function by 3D ultrasound using 4D-STIC and VOCAL software.

Nomograms of Fetal Right Ventricular Fractional Area Change by 2D Echocardiography

OBJECTIVES

Fetal right ventricular (RV) function assessment is challenging due to the RV geometry and limitations of in utero assessment. Postnatally, 2D echocardiographic RV fractional area change (FAC) is used to assess RV global systolic function by calculating the percentage of change in RV area from systole to diastole. Reports on FAC are scarce in prenatal life, and nomograms throughout pregnancy are not available. Our aims were (1) to study prenatal RV FAC feasibility and reproducibility and (2) to construct nomograms for RV FAC and end-diastolic (ED) and end-systolic (ES) RV areas from 18 to 41 weeks of gestation.

METHODS

Prospective cohort study including 602 low-risk singleton pregnancies undergoing a fetal echocardiography from 18 to 41 weeks of gestation. RV ED and ES areas were measured following standard recommendations for ventricular dimensions and establishing strict landmarks to identify the different phases of the cardiac cycle. RV FAC was calculated as: ([ED area - ES area]/ED area) × 100. RV FAC intra- and inter-observer reproducibility was evaluated in 45 fetuses by calculating the intraclass correlation coefficient (ICC). Parametric regressions were tested to model each parameter against gestational age (GA) and estimated fetal weight (EFW).

RESULTS

RV areas and FAC were successfully obtained in ∼99% of fetuses with acceptable reproducibility throughout gestation (RV ED area inter-observer ICC [95% CI] 0.96 [0.93-0.98], RV ES area 0.97 [0.94-0.98], and FAC 0.69 [0.44-0.83]). Nomograms were constructed for RV ED and ES areas and FAC. RV areas showed a quadratic and logarithmic increase with GA and EFW, respectively. In contrast, RV FAC showed a slight quadratic decrease throughout gestation (mean RV FAC ranged from 36% at 18 weeks of gestation [10-90th centiles: 25-47%, respectively] to 29% at 41 weeks [10-90th centiles: 18-40%, respectively]). The best models for RV areas and FAC were a second-degree polynomial.

CONCLUSIONS

RV FAC is a feasible and reproducible parameter to assess RV global systolic function in fetal life. We provide reference ranges adjusted by GA and EFW that can be used as normal references for the assessment of RV function in prenatal conditions.

Quantitative Assessment of Left Ventricular Dysfunction in Fetal Ebstein's Anomaly and Tricuspid Valve Dysplasia

BACKGROUND

Fetal Ebstein's anomaly and tricuspid valve dysplasia (EA/TVD) are associated with high perinatal mortality relative to pulmonary atresia with intact ventricular septum (PAIVS), despite both requiring redistribution of the cardiac output (CO) to the left ventricle (LV). LV dysfunction is suspected to contribute to adverse outcomes in EA/TVD.

OBJECTIVE

We sought to examine global and segmental LV function in fetal EA/TVD with comparison to normal controls and PAIVS. We hypothesized that LV dysfunction in EA/TVD is associated with abnormal LV remodeling and interventricular mechanics.

METHODS

We retrospectively identified 63 cases of fetal EA/TVD (40 with retrograde ductal flow) and 22 cases of PAIVS encountered from 2004 to 2015 and compared findings to 77 controls of comparable gestational age. We measured the combined CO and global LV function using two-dimensional, Doppler-derived, deformational (six-segmental vector velocity imaging) and dyssynchrony indices (DIs; SD of time to peak), and a novel global DI.

RESULTS

EA/TVD fetuses demonstrated abnormal LV global systolic function with reduced ejection fraction, fractional area change, and CO, while in PAIVS we observed a normal ejection fraction, fractional area change, and CO. PAIVS, but not EA/TVD, demonstrated increased LV sphericity, suggestive of remodeling, and associated enhanced radial function in the third trimester. In contrast, while EA/TVD fetuses had normal LV segmental longitudinal strain, there was abnormal radial segmental deformation and LV dyssynchrony with increased SD of time to peak and DI.

CONCLUSIONS

Fetal EA/TVD is associated with a lack of spherical remodeling and presence of mechanical dyssynchrony, which likely contribute to reduced CO and ejection fraction. Clinical monitoring of LV function is warranted in fetal EA/TVD. Further studies incorporating quantification of LV function into prediction models for adverse outcomes are required.

The Transitional Heart: From Early Embryonic and Fetal Development to Neonatal Life

Formation of the human heart involves complex biological signals, interactions, specification of myocardial progenitor cells, and heart tube looping. To facilitate survival in the hypoxemic intrauterine environment, the fetus possesses structural, physiological, and functional cardiovascular adaptations that are fundamentally different from the neonate. At birth, upon separation from the placental circulation, the neonatal cardiovascular system takes over responsibility of vital processes for survival. The transition from the fetal to neonatal circulation is considered to be a period of intricate physiological, anatomical, and biochemical changes in the cardiovascular system. With a successful cardiopulmonary transition to the extrauterine environment, the fetal shunts are functionally modified or eliminated, enabling independent life. Investigations using medical imaging tools such as ultrasound and magnetic resonance imaging have helped to define normal and abnormal patterns of cardiac remodeling both in utero and ex utero. This has not only allowed for a better understanding of how congenital cardiac malformations alter the hemodynamic transition to the extrauterine environment but also how other more common complications during pregnancy including intrauterine growth restriction, preeclampsia, and preterm delivery adversely affect offspring cardiac remodeling during this early transitional period. This review article describes key cardiac progenitors involved in embryonic heart development; the cellular, physiological, and anatomical changes during the transition from fetal to neonatal circulation; as well as the unique impact that different pregnancy complications have on cardiac remodeling.

Empirical models for anatomical and physiological changes in a human mother and fetus during pregnancy and gestation

Many parameters treated as constants in traditional physiologically based pharmacokinetic models must be formulated as time-varying quantities when modeling pregnancy and gestation due to the dramatic physiological and anatomical changes that occur during this period. While several collections of empirical models for such parameters have been published, each has shortcomings. We sought to create a repository of empirical models for tissue volumes, blood flow rates, and other quantities that undergo substantial changes in a human mother and her fetus during the time between conception and birth, and to address deficiencies with similar, previously published repositories. We used maximum likelihood estimation to calibrate various models for the time-varying quantities of interest, and then used the Akaike information criterion to select an optimal model for each quantity. For quantities of interest for which time-course data were not available, we constructed composite models using percentages and/or models describing related quantities. In this way, we developed a comprehensive collection of formulae describing parameters essential for constructing a PBPK model of a human mother and her fetus throughout the approximately 40 weeks of pregnancy and gestation. We included models describing blood flow rates through various fetal blood routes that have no counterparts in adults. Our repository of mathematical models for anatomical and physiological quantities of interest provides a basis for PBPK models of human pregnancy and gestation, and as such, it can ultimately be used to support decision-making with respect to optimal pharmacological dosing and risk assessment for pregnant women and their developing fetuses. The views expressed in this article are those of the authors and do not necessarily represent the views or policies of the U.S. Environmental Protection Agency.