Measurement of internal diameter changes and pulse wave velocity in fetal descending aorta using the ultrasonic phased-tracking method in normal and growth-restricted fetuses

Z-score model of foetal ascending aorta diameter distensibility

Objective

The purpose of this study is to establish Z-scores models of normal fetal ascending aorta diameter and diameter distensibility.

Methods

The maximum systolic diameter (Dmax), minimum diastolic diameter (Dmin), and diameter distensibility of the sinotubular junction were measured and taken as dependent variables in 490 normal fetuses at 18–40 gestational weeks, and gestational age (GA), biparietal diameter (BPD), and femoral length (FL) were taken as independent variables. The data were subjected to regression analysis, and the best-fitting equations for the dependent variables based on the independent variables were determined. The fitting equations were then applied to construct the Z-scores models.

Results

The Dmax, Dmin and Diameter Distensibility in normal fetuses between 18 and 40 weeks of GA could be evaluated by utilizing the Z-scores models. Dmax and Dmin increased significantly with increasing GA, BPD, and FL. Diameter distensibility, assessed as (Dmax–Dmin)/Dmin, decreased significantly with increasing GA, BPD, and FL.

Conclusion

The Z-scores are valuable, and can be utilized as a potent supplement to the conventional approach as they can indirectly reflect the development of fetal ascending aortic elastic property.

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.

Maturation Fetus Ascending Aorta Elastic Properties: Circumferential Strain and Longitudinal Strain by Velocity Vector Imaging

Objective

This study aimed to assess the circumferential and longitudinal strain of the fetal ascending aortic (AA) wall and establish a gestational age-associated longitudinal reference for aortic wall strain during the second half of pregnancy.

Methods

Singleton fetuses with gestational age (GA) at 20 + 0 to 24 + 6 weeks were prospectively collected from a low-risk population. Global circumferential strain (GCS) and mean longitudinal strain (MLS) of the ascending aorta were measured serially at 4-week intervals using the velocity vector imaging (VVI) technique. Fractional polynomials were conducted to obtain the best-fitting curves between GA and AA strains. GA-specific reference percentiles of GCS and MLS were established by multilevel modeling.

Results

A total of 223 fetuses with a total of 1,127 serial observations were enrolled. GCS presented a second-degree fractional polynomial smoothing regression along GA (R2 = 0.635, P &lt; 0.05). Fetal aortic GCS remained unchanged at ~27.29% (20.36–35.6%) before 31 weeks and increased significantly from 31.36% (26.38–37.12%) at 31 weeks to 43.29% (30.5–56.78%) at term. MLS presented a third-degree fractional polynomial smoothing regression along GA (R2 = 0.465, P &lt; 0.05). MLS remained steady at ~10.03% (3.28–17.62%) between 20 and 31 weeks and then increased significantly from 12.68% (7.42–20.1%) at 32 weeks to 17.5% (9.67–25.34%) at term. The GCS was significantly higher than the MLS in the ascending aorta wall (p &lt; 0.001).

Conclusion

The fetal ascending aorta wall demonstrates obviously greater circumferential strain than longitudinal strain. Both strains remained steady before the late trimester and then gradually increased until delivery, suggesting progressive maturation of aortic elasticity mechanics.

Echocardiographic assessment of fetal cardiac function in the uterine artery ligation rat model of IUGR

BACKGROUND

Intrauterine growth restriction (IUGR) leads to cardiac dysfunction and adverse remodeling of the fetal heart, as well as a higher risk of postnatal cardiovascular diseases. The rat model of IUGR, via uterine artery ligation, is a popular model but its cardiac sequelae is not well investigated. Here, we performed an echocardiographic evaluation of its cardiac function to determine how well it can represent the disease in humans.

METHODS

Unilateral uterine artery ligation was performed at embryonic day 17 (E17) and echocardiography was performed at E19 and E20.

RESULTS

Growth-restricted fetuses were significantly smaller and lighter, and had an higher placenta-to-fetus weight ratio. Growth-restricted fetal hearts had reduced wall thickness-to-diameter ratio, indicating left ventricular (LV) dilatation, and they had elevated trans-mitral and trans-tricuspid E/A ratios and reduced left and right ventricular fractional shortening (FS), suggesting systolic and diastolic dysfunction. These were similar to human IUGR fetuses. However, growth-restricted rat fetuses did not demonstrate head-sparing effect, displayed a lower LV myocardial performance index, and ventricular outflow velocities were not significantly reduced, which were dissimilar to human IUGR fetuses.

CONCLUSIONS

Despite the differences, our results suggest that this IUGR model has significant cardiac dysfunction, and could be a suitable model for studying IUGR cardiovascular physiology.

IMPACT

Animal models of IUGR are useful, but their fetal cardiac function is not well studied, and it is unclear if they can represent human IUGR fetuses. We performed an echocardiographic assessment of the heart function of a fetal rat model of IUGR, created via maternal uterine artery ligation. Similar to humans, the model displayed LV dilatation, elevated E/A ratios, and reduced FS. Different from humans, the model displayed reduced MPI, and no significant outflow velocity reduction. Despite differences with humans, this rat model still displayed cardiac dysfunction and is suitable for studying IUGR cardiovascular physiology.

Feasibility of Non-invasive Pulse Pressure Measurement Using the Phased-Tracking Method

Phased tracking (PT) is a high-precision ultrasonic technology that enables measurements of pulse pressure (PP). The aim of this study was to verify the accuracy of estimated PP using PT. Estimated PPs were compared with measured PPs in three sheep fetuses that were connected to an artificial placenta system. Similarly, estimated and measured PPs of 30 human neonates were compared. PP was calculated using the Water-Hammer equation (PP = ρ × PWV (pulse wave velocity) × ΔU). PWV was estimated by measuring the transit times of pulse waves at two sites along the aorta using the PT method, and ΔU was obtained by subtracting end-diastolic velocity from peak systolic velocity. The correlation between the estimated and measured PPs of the sheep fetuses was strong (r = 0.95, p ˂ 0.01), as was the case with the human neonates (r = 0.88, p ˂ 0.05). It can be concluded from the results of this study that PT may be a non-invasive alternative method used to predict PP.

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.

Assessing vascular characteristics of the fetal descending aorta: A feasibility study

Research describing fetal arterial structure and function is lacking within the literature. This study's purpose was to measure intima-media thickness (IMT), compliance and distensibility of 24- to 25-week fetuses' abdominal aortas using conventional ultrasonography from 16 diabetic (DM) and 25 non-diabetic mothers (NDM). We found no significant differences in fetal abdominal aorta IMT (P = .68), diameter distensibility (P = .22), or cross-sectional distensibility (P = .23). However, both fetal abdominal aortic diameter compliance (P = .03) and cross-sectional compliance (P = .005) were greater in DM than in NDM (P = .005). This study demonstrates that it is possible and potentially useful to measure fetal abdominal aorta biometrics and biomechanical characteristics.

Wave intensity analysis of maternal arterial stiffness: augmentation index and pulse wave velocity in pregnancies complicated by diabetes or hypertension

PURPOSE

The aim of our study was to compare the maternal arterial stiffness in pregnant women with diabetic disease, hypertension and those with normal pregnancies.

METHODS

A cross-sectional study was performed involving 65 pregnant women with diabetic disease (DD group), 26 pregnant women with hypertension (RR group) and 448 women with normal pregnancies (control group). The augmentation index (AIx) and the pulse wave velocity (PWV) of the right carotid artery were assessed using non-invasive sonographic wave intensity analysis. Furthermore, the reliability of the measurements was evaluated in 21 healthy women.

RESULTS

Compared with the controls, the AIx and PWV were increased in the DD group [11.0 (interquartile range, IQR 7.3, 15.2) vs. 5.7 (IQR 2.4, 9.3), P < 0.001; 5.7 (IQR 5.1, 6.4) vs. 5.2 (IQR 4.6, 6.1), P = 0.001; respectively] and the RR group [9.3 (IQR 6.6, 11.5) vs. 5.7 (IQR 2.4, 9.3), P < 0.001; 7.1 (6.3, 7.9) vs. 5.2 (IQR 4.6, 6.1), P < 0.001; respectively]. The intraclass and interclass correlation coefficients were good to excellent for the AIx (ICC: 0.91, P < 0.001 and 0.74, P < 0.002; respectively) and PWV measurements (ICC: 0.71, P < 0.004 and 0.70, P < 0.005; respectively).

CONCLUSION

Pregnancies complicated by diabetic disease or hypertension are associated with increased maternal arterial stiffness. The importance of wave intensity analysis needs to be verified and larger studies are needed to establish both normal and cutoff values that may be relevant for clinical decisions.

Local Pulse Wave Velocity: Theory, Methods, Advancements, and Clinical Applications

Local pulse wave velocity (PWV) is evolving as one of the important determinants of arterial hemodynamics, localized vessel stiffening associated with several pathologies, and a host of other cardiovascular events. Although PWV was introduced over a century ago, only in recent decades, due to various technological advancements, has emphasis been directed toward its measurement from a single arterial section or from piecewise segments of a target arterial section. This emerging worldwide trend in the exploration of instrumental solutions for local PWV measurement has produced several invasive and noninvasive methods. As of yet, however, a univocal opinion on the ideal measurement method has not emerged. Neither have there been extensive comparative studies on the accuracy of the available methods. Recognizing this reality, makes apparent the need to establish guideline-recommended standards for the measurement methods and reference values, without which clinical application cannot be pursued. This paper enumerates all major local PWV measurement methods while pinpointing their salient methodological considerations and emphasizing the necessity of global standardization. Further, a summary of the advancements in measuring modalities and clinical applications is provided. Additionally, a detailed discussion on the minimally explored concept of incremental local PWV is presented along with suggestions of future research questions.

Altered Placental Chorionic Arterial Biomechanical Properties During Intrauterine Growth Restriction

Intrauterine growth restriction (IUGR) is a pregnancy complication due to placental dysfunction that prevents the fetus from obtaining enough oxygen and nutrients, leading to serious mortality and morbidity risks. There is no treatment for IUGR despite having a prevalence of 3% in developed countries, giving rise to an urgency to improve our understanding of the disease. Applying biomechanics investigation on IUGR placental tissues can give important new insights. We performed pressure-diameter mechanical testing of placental chorionic arteries and found that in severe IUGR cases (RI > 90th centile) but not in IUGR cases (RI < 90th centile), vascular distensibility was significantly increased from normal. Constitutive modeling demonstrated that a simplified Fung-type hyperelastic model was able to describe the mechanical properties well, and histology showed that severe IUGR had the lowest collagen to elastin ratio. To demonstrate that the increased distensibility in the severe IUGR group was related to their elevated umbilical resistance and pulsatility indices, we modelled the placental circulation using a Windkessel model, and demonstrated that vascular compliance (and not just vascular resistance) directly affected blood flow pulsatility, suggesting that it is an important parameter for the disease. Our study showed that biomechanics study on placenta could extend our understanding on placenta physiology.

A Novel Minimally Occlusive Cuff Method Utilizing Ultrasound Vascular Imaging for Stress-Free Blood Pressure Measurement: A-Proof-of-Concept Study

OBJECTIVE

Occlusive cuff inflation in ambulatory blood pressure (BP) monitoring disturbs the daily life of the user and affects efficacy of monitoring. To overcome this limitation, we have developed a novel minimally occlusive cuff method for stress-free measurement of BP. This study aimed to experimentally evaluate the reliability of this method.

METHODS

In this method, a thin plate-type ultrasound probe placed between the cuff and the skin is used to measure the ultrasonic dimension of the artery. Analyzing the arterial dimension and the cuff pressure measured during mild cuff inflation (cuff pressure <50 mmHg) allows estimation of systolic BP (SBP_e) and diastolic BP (DBP_e). We evaluated this method in six anesthetized dogs by attaching the cuff with the probe to the right thigh to get SBP_e and DBP_e. We measured reference SBP and DBP using an intra-arterial catheter and determined the pulse arrival time (PAT), commonly employed in cuffless BP monitoring. BP was perturbed by infusing noradrenaline or nitroprusside.

RESULTS

DBP_e correlated tightly with DBP with a coefficient of determination (R²) of 0.85 ± 0.08, and predicted DBP with a mean ± standard deviation of error of 3.9 ± 7.9 mmHg after one-time calibration. Reciprocal of PAT correlated poorly with DBP (R² = 0.49 ± 0.17), and predicted DBP less accurately than this method. SBP_e correlated well with SBP (R² = 0.78 ± 0.08).

CONCLUSION

This method reliably tracks BP changes without occlusive cuff inflation. Once calibrated, this method measures DBP accurately.

SIGNIFICANCE

This method has the potential for stress-free BP measurement in ambulatory BP monitoring.

Noninvasive early detection of anthracycline-induced cardiotoxicity in patients with hematologic malignancies using the phased tracking method

Anthracyclines are among the most effective and widely used anticancer drugs; however, their use is limited by serious cardiotoxicity. Early detection is necessary to prevent the high mortality rate associated with heart failure (HF). We evaluated cardiac function in 142 patients using conventional echocardiography and the phased tracking method (PTM), which was measured using the minute vibration and the rapid motion components, neither of which is recognized in standard M-mode nor in tissue Doppler imaging. For systolic function comparison, we compared left ventricular ejection fraction (LVEF) in conventional echocardiography with the average velocity of ventricular septum myocytes (Vave ) in the PTM. The Vave of 12 healthy volunteers was 1.5 (m/s)/m or more. At baseline of 99 patients, there was a positive correlation between LVEF and Vave in all patients. There were no significant differences in baseline cardiac function between patients with and without HF. There was a negative correlation between the cumulative anthracycline dose and LVEF or Vave among all patients. We determined that Vave 1.5 (m/s)/m was equivalent to LVEF 60%, 1.25 (m/s)/m to 55%, and 1.0 (m/s)/m to 50%. During the follow-up period, there was a pathological decrease in LVEF (<55%) and Vave (<1.25 m/s/m) in patients with HF; decreases in Vave were detected significantly earlier than those in LVEF (P < 0.001). When Vave declined to 1.5 (m/s)/m or less, careful continuous observation and cardiac examination was required. When Vave further declined to 1.0 (m/s)/m or lower, chemotherapy was postponed or discontinued; thus, serious drug-induced cardiomyopathy was avoided in patients who did not relapse. The PTM was superior to echocardiography for early, noninvasive detection and intermediate-term monitoring of left ventricle systolic function associated with anthracycline chemotherapy, among patients with hematologic malignancies. The PTM was an effective laboratory procedure to avoid the progression to serious cardiomyopathy.