Noninvasive measurement of regional pulse wave velocity in human ascending aorta with ultrasound imaging: an in-vivo feasibility study

Arterial Stiffness Assessment in Healthy Participants Using Shear Wave Elastography

BACKGROUND

Arterial stiffness is an important biomarker for cardiovascular disease. Shear wave elastography (SWE) provides quantitative estimates of tissue stiffness.

OBJECTIVE

This study aimed to provide reference values for arterial wall, assessing the suitability of SWE to quantify elasticity of the common carotid artery (CCA) and evaluating inter- and intra-observer reproducibility.

METHODS

A Supersonic Aixplorer ultrasound system with L15-4 probe was used to scan longitudinal sections of the CCA. Young's modulus (YM) was measured within 2-mm regions of interest. Reproducibility was assessed within a subgroup of 16 participants by two operators (one novice and one experienced) during two sessions >one week apart.

RESULTS

This study involves seventy-three participants with a mean age of 40±10 years and body mass index of 26 ±6 kg/m2. YM estimates were 59 kPa ±19 in men and 56 kPa ±12 in women. The average YM of the CCA walls was 58 kPa ±15 (57 ±15 kPa for the anterior wall and 58 ±20 kPa for the posterior wall, p=0.75). There was no significant difference in the mean of YM estimates of the CCA between the observers (observer: one 51 ±14 kPa and observer two: 55 ±17 kPa [p=0.46]). inter- and intra-observer reproducibility was fair to good (Intra-class correlations, ranging from 0.46 to 0.71). Inter-frame variability was 28%.

CONCLUSION

In healthy individuals, SWE provided an estimate of YM of the CCA (58 kPa) with fair to good reproducibility. This study demonstrated the potential of using SWE for assessing biomechanical properties of blood vessels.

Noninvasive Aortic Ultrafast Pulse Wave Velocity Associated With Framingham Risk Model: in vivo Feasibility Study

Background

Aortic pulse wave velocity (PWV) enables the direct assessment of aortic stiffness, which is an independent risk factor of cardiovascular (CV) events. The aim of this study is to evaluate the association between aortic PWV and CV risk model classified into three groups based on the Framingham risk score (FRS), i.e., low-risk (<10%), intermediate-risk (10~20%) and high-risk (>20%).

Methods

To noninvasively estimate local PWV in an abdominal aorta, a high-spatiotemporal resolution PWV measurement method (>1 kHz) based on wide field-of-view ultrafast curved array imaging (ufcPWV) is proposed. In the ufcPWV measurement, a new aortic wall motion tracking algorithm based on adaptive reference frame update is performed to compensate errors from temporally accumulated out-of-plane motion. In addition, an aortic pressure waveform is simultaneously measured by applanation tonometry, and a theoretical PWV based on the Bramwell-Hill model (bhPWV) is derived. A total of 69 subjects (aged 23–86 years) according to the CV risk model were enrolled and examined with abdominal ultrasound scan.

Results

The ufcPWV was significantly correlated with bhPWV (r = 0.847, p < 0.01), and it showed a statistically significant difference between low- and intermediate-risk groups (5.3 ± 1.1 vs. 8.3 ± 3.1 m/s, p < 0.01), and low- and high-risk groups (5.3 ± 1.1 vs. 10.8 ± 2.5 m/s, p < 0.01) while there is no significant difference between intermediate- and high-risk groups (8.3 ± 3.1 vs. 10.8 ± 2.5 m/s, p = 0.121). Moreover, it showed a significant difference between two evaluation groups [low- (<10%) vs. higher-risk group (≥10%)] (5.3 ± 1.1 vs. 9.4 ± 3.1 m/s, p < 0.01) when the intermediate- and high-risk groups were merged into a higher-risk group.

Conclusion

This feasibility study based on CV risk model demonstrated that the aortic ufcPWV measurement has the potential to be a new approach to overcome the limitations of conventional systemic measurement methods in the assessment of aortic stiffness.

Predictive value of novel inflammatory markers platelet-to-lymphocyte ratio, neutrophil-to-lymphocyte ratio, and monocyte-to-lymphocyte ratio in arterial stiffness in patients with diabetes: A propensity score-matched analysis

BACKGROUND

Increased arterial stiffness is common in patients with diabetes, and inflammation is one of the main causes of increased arterial stiffness. Platelet-to-lymphocyte ratio (PLR), neutrophil-to-lymphocyte ratio (NLR), and monocyte-to-lymphocyte ratio (MLR) are novel inflammatory markers that are reproducible, widely available, and easy to measure, and are associated with low costs. This study sought to investigate the predictive value of these novel inflammatory markers in patients with diabetes having arterial stiffness.

METHODS

We retrospectively included inpatients with diabetes mellitus from the Endocrinology Department of the Chengdu Fifth People's Hospital from June 2021 to May 2022 and collected data on their general information, biochemical indicators, and brachial-ankle pulse wave velocity (baPWV). After propensity matching, the risk relationship between PLR, NLR, and MLR and arterial stiffness was assessed in the recruited patients.

RESULTS

A total of 882 hospitalized patients with diabetes were included in this study and categorized into the low baPWV (507 cases) or high baPWV group (375 cases) based on the baPWV. After propensity matching, there were 180 patients in all in the high and low baPWV groups. Univariate and multivariate logistic regression analyses revealed that high PLR, NLR, and MLR were independently associated with an increased risk of arterial stiffness in patients with diabetes. In the receiver operating characteristic curve analysis, the NLR area under the curve (AUC) was 0.7194 (sensitivity = 84.4%, specificity = 51.1%) when distinguishing low baPWV and high baPWV in patients with diabetes, which was higher than that for PLR AUC (0.6477) and MLR AUC (0.6479), and the combined diagnosis for AUC.

CONCLUSIONS

NLR was superior to PLR, and MLR and combined diagnosis have certain predictive values that indicate the increase in arterial stiffness in patients with diabetes. These predictive values can help with the early identification of increased arterial stiffness in patients with diabetes.

Feasibility of Bilinear Mechanical Characterization of the Abdominal Aorta in a Hypertensive Mouse Model

A change in elastin and collagen content is indicative of damage caused by hypertension, which changes the non-linear behavior of the vessel wall. This study was aimed at investigating the feasibility of monitoring the non-linear material behavior in an angiotensin II hypertensive mice model. Aortas from 13 hypertensive mice were imaged with pulse wave imaging (PWI) over 4 wk using a 40-MHz linear array. The pulse wave velocity was estimated using two wave features: (i) the maximum axial acceleration of the foot (PWV_dia) and (ii) the maximum axial acceleration of the dicrotic notch (PWV_end-sys). The Bramwell-Hill equation was used to derive the compliance at diastolic and end-systolic pressure. This study determined the potential of PWI in a hypertensive mouse model to image and quantify the non-linear material behavior in vivo. End-systolic compliance could differentiate between the sham and angiotensin II groups, whereas diastolic compliance could not, indicating that PWI can detect early collagen-dominated remodeling.

Pressure-Corrected Carotid Stiffness and Young's Modulus: Evaluation in an Outpatient Clinic Setting

BACKGROUND

Conventional measures for assessing arterial stiffness are inherently pressure dependent. Whereas statistical pressure adjustment is feasible in (larger) populations, it is unsuited for the evaluation of an individual patient. Moreover, statistical "correction" for blood pressure may actually correct for: (i) the acute dependence of arterial stiffness on blood pressure at the time of measurement; and/or (ii) the remodeling effect that blood pressure (hypertension) may have on arterial stiffness, but it cannot distinguish between these processes.

METHODS

We derived-assuming a single-exponential pressure-diameter relationship-3 theoretically pressure-independent carotid stiffness measures suited for individual patient evaluation: (i) stiffness index β0, (ii) pressure-corrected carotid pulse wave velocity (cPWVcorr), and (iii) pressure-corrected Young's modulus (Ecorr). Using linear regression analysis, we evaluated in a sample of the CATOD study cohort changes in mean arterial pressure (ΔMAP) and comparatively the changes in the novel (Δβ0, ΔcPWVcorr, and ΔEcorr) as well as conventional (ΔcPWV and ΔE) stiffness measures after a 2.9 ± 1.0-year follow-up.

RESULTS

We found no association between ΔMAP and Δβ0, ΔcPWVcorr, or ΔEcorr. In contrast, we did find a significant association between ΔMAP and conventional measures ΔcPWV and ΔE. Additional adjustments for biomechanical confounders and traditional risk factors did neither materially change these associations nor the lack thereof.

CONCLUSIONS

Our newly proposed pressure-independent carotid stiffness measures avoid the need for statistical correction. Hence, these measures (β0, cPWVcorr, and Ecorr) can be used in a clinical setting for (i) patient-specific risk assessment and (ii) investigation of potential remodeling effects of (changes in) blood pressure on intrinsic arterial stiffness.

Association of incremental pulse wave velocity with cardiometabolic risk factors

We investigate the association of incremental pulse wave velocity (ΔC; the change in pulse wave velocity over a cardiac cycle) with cardiometabolic risk factors and report the first and (currently) the largest population-level data. In a cross-sectional study performed in a cohort of 1373 general population participants, ΔC was measured using clinically validated ARTSENS devices. There were 455 participants in the metabolic syndrome (MetS) group whose average ΔC was ~ 28.4% higher than that of the non-metabolic syndrome (Non-MetS) group. Females with MetS showed ~ 10.9% elevated average ΔC compared to males of the Non-MetS group. As the number of risk factors increased from 0 to 5, the average ΔC escalated by ~ 55% (1.50 ± 0.52 m/s to 2.33 ± 0.91 m/s). A gradual increase in average ΔC was observed across each decade from the younger (ΔC = 1.53 ± 0.54 m/s) to geriatric (ΔC = 2.34 ± 0.59 m/s) populations. There was also a significant difference in ΔC among the blood pressure categories. Most importantly, ΔC ≥ 1.81 m/s predicted a constellation of ≥ 3 risks with AUC = 0.615, OR = 2.309, and RR = 1.703. All statistical trends remained significant, even after adjusting for covariates. The study provides initial evidence for the potential use of ΔC as a tool for the early detection and screening of vascular dysfunction, which opens up avenues for active clinical and epidemiological studies. Further investigations are encouraged to confirm and establish the causative mechanism for the reported associations.

Reflected wave intensity increases based on aortic diameter after endovascular aortic therapy in a goat model

Reflected wave increases after endovascular aortic repair (EVAR) in patients with aortic aneurysm. This affects the left ventricular (LV) diastolic function and leads to a poor prognosis. This study aimed to evaluate the relationship between increased reflected wave amplitude and aortic diameter after EVAR. EVAR was performed in seven healthy goats. We assessed wave intensity (WI), aortic diameter, and stiffness parameter β. Moreover, we evaluated the relationship between negative reflected wave (NW, reflected waves toward the heart from the periphery by WI) and other parameters after EVAR. Results showed an increase in stiffness parameter β (3.5 ± 0.3 vs 15.9 ± 4.7, p = 0.018) and a decrease in the change of aortic diameter (6.9 ± 0.7 vs 2.7 ± 0.4%, p = 0.018) after EVAR. The NW was significantly amplified after EVAR from baseline (−589.8 ± 143.4 to  − 1192.3 ± 303.7 mmHg-m/sec³, p = 0.043). The NW showed a significant correlation with maximum aortic diameter (R = 0.707, p = 0.038) and minimum aortic diameter (R = 0.724, p = 0.033). The reflected wave was enhanced after EVAR and was correlated to the aortic diameter at the stent-graft site. It is important to consider that patients with smaller aortic diameters in landing zone who undergo EVAR may develop LV dysfunction.

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.

Constitutive interpretation of arterial stiffness in clinical studies: a methodological review

Clinical assessment of arterial stiffness relies on noninvasive measurements of regional pulse wave velocity or local distensibility. However, arterial stiffness measures do not discriminate underlying changes in arterial wall constituent properties (e.g., in collagen, elastin, or smooth muscle), which is highly relevant for development and monitoring of treatment. In arterial stiffness in recent clinical-epidemiological studies, we systematically review clinical-epidemiological studies (2012–) that interpreted arterial stiffness changes in terms of changes in arterial wall constituent properties (63 studies included of 514 studies found). Most studies that did so were association studies (52 of 63 studies) providing limited causal evidence. Intervention studies (11 of 63 studies) addressed changes in arterial stiffness through the modulation of extracellular matrix integrity (5 of 11 studies) or smooth muscle tone (6 of 11 studies). A handful of studies (3 of 63 studies) used mathematical modeling to discriminate between extracellular matrix components. Overall, there exists a notable gap in the mechanistic interpretation of stiffness findings. In constitutive model-based interpretation, we first introduce constitutive-based modeling and use it to illustrate the relationship between constituent properties and stiffness measurements (“forward” approach). We then review all literature on modeling approaches for the constitutive interpretation of clinical arterial stiffness data (“inverse” approach), which are aimed at estimation of constitutive properties from arterial stiffness measurements to benefit treatment development and monitoring. Importantly, any modeling approach requires a tradeoff between model complexity and measurable data. Therefore, the feasibility of changing in vivo the biaxial mechanics and/or vascular smooth muscle tone should be explored. The effectiveness of modeling approaches should be confirmed using uncertainty quantification and sensitivity analysis. Taken together, constitutive modeling can significantly improve clinical interpretation of arterial stiffness findings.

Demonstration of circumferential heterogeneity in displacement and strain in the abdominal aortic wall by spiral cine DENSE MRI

BACKGROUND

Knowledge of tissue properties of the abdominal aorta can improve understanding of vascular disease and guide interventional approaches. Existing MRI methods to quantify aortic wall displacement and strain are unable to discern circumferential heterogeneity.

PURPOSE

To assess regional variation in abdominal aortic wall displacement and strain as a function of circumferential position using spiral cine displacement encoding with stimulated echoes (DENSE).

STUDY TYPE

Prospective.

POPULATION

Cardiovascular disease-free men (n = 8) and women (n = 9) ages 30-42.

SEQUENCES

Prospective electrocardiogram (ECG)-gated and navigator echo-gated spiral, cine 2D DENSE and retrospective ECG-gated phase contrast MR (PCMR) sequences at 3T.

ASSESSMENT

In-plane displacement values of the aortic wall acquired with DENSE were used to determine radial and circumferential aortic wall motion. A quadrilateral-based 2D strain calculation method was implemented to determine strain from the displacement field. Peak displacement and its radial and circumferential contributions as well as peak circumferential strain were compared among eight circumferential wall segments. Distensibility was calculated using PCMR and compared with homogenized circumferential strain.

STATISTICAL TESTS

To account for repeated measurements in volunteers, linear mixed models for mean sector values were created for displacement magnitude, circumferential displacement, radial displacement, and circumferential strain. Comparisons were made between sectors. Calculated distensibility and homogenized circumferential strain were compared using Bland-Altman analysis. Statistical significance was defined as P < 0.05.

RESULTS

Displacement was highest in the anterior wall (1.5 ± 0.7 mm) and was primarily in the radial as compared with circumferential direction (1.04 ± 0.05 mm vs. 0.81 ± 0.42 mm). Circumferential strain was highest in the lateral walls (left 0.16 ± 0.05 and right 0.21 ± 0.12) with homogenized circumferential strain of 0.14 ± 0.05.

DATA CONCLUSION

DENSE imaging in the abdominal aortic wall demonstrated that the anterior aortic wall exhibits the greatest displacement, while the lateral wall experiences the largest circumferential strain.

LEVEL OF EVIDENCE

3 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;49:731-743.

An ultrasound elastography method to determine the local stiffness of arteries with guided circumferential waves

Arterial stiffness is highly correlated with the functions of the artery and may serve as an important diagnostic criterion for some cardiovascular diseases. To date, it remains a challenge to quantitatively assess local arterial stiffness in a non-invasive manner. To address this challenge, we investigated the possibility of determining arterial stiffness using the guided circumferential wave (GCW) induced in the arterial wall by a focused acoustic radiation force. The theoretical model for the dispersion analysis of the GCW is presented, and a finite element model has been established to calculate the dispersion curve. Our results show that under described conditions, the dispersion relations of the GCW are basically independent of the curvature of the arterial wall and can be well-described using the Lamb wave (LW) model. Based on this conclusion, an inverse method is proposed to characterize the elastic modulus of artery. Both numerical experiments and phantom experiments had been performed to validate the proposed method. We show that our method can be applied to the cases in which the artery has local stenosis and/or the geometry of the artery cross-section is irregular; therefore, this method holds great potential for clinical use.