Pulsatile diameter and elastic modulus of the aortic arch in essential hypertension: a noninvasive study

Age and vascular aging: an unexplored frontier

Vascular age is an emerging field in cardiovascular risk assessment. This concept includes multifactorial changes in the arterial wall, with arterial stiffness as its most relevant manifestation, leading to increased arterial pressure and pulsatile flow in the organs. Today, the approved test for measuring vascular age is pulse wave velocity, which has been proven to predict cardiovascular events. Furthermore, vascular phenotypes, such as early vascular aging and "SUPERNOVA," representing phenotypic extremes of vascular aging, have been found. The identification of these phenotypes opens a new field of study in cardiovascular physiology. Lifestyle interventions and pharmacological therapy have positively affected vascular health, reducing arterial stiffness. This review aims to define the concepts related to vascular age, pathophysiology, measurement methods, clinical signs and symptoms, and treatment.

The Relation Between Viscous Energy Dissipation and Pulsation for Aortic Hemodynamics Driven by a Left Ventricular Assist Device

Left ventricular assist device (LVAD) provides mechanical circulatory support for patients with advanced heart failure. Treatment using LVAD is commonly associated with complications such as stroke and gastro-intestinal bleeding. These complications are intimately related to the state of hemodynamics in the aorta, driven by a jet flow from the LVAD outflow graft that impinges into the aorta wall. Here we conduct a systematic analyses of hemodynamics driven by an LVAD with a specific focus on viscous energy transport and dissipation. We conduct a complementary set of analysis using idealized cylindrical tubes with diameter equivalent to common carotid artery and aorta, and a patient-specific model of 27 different LVAD configurations. Results from our analysis demonstrate how energy dissipation is governed by key parameters such as frequency and pulsation, wall elasticity, and LVAD outflow graft surgical anastomosis. We find that frequency, pulsation, and surgical angles have a dominant effect, while wall elasticity has a weaker effect, in determining the state of energy dissipation. For the patient-specific scenario, we also find that energy dissipation is higher in the aortic arch and lower in the abdominal aorta, when compared to the baseline flow without an LVAD. This further illustrates the key hemodynamic role played by the LVAD outflow jet impingement, and subsequent aortic hemodynamics during LVAD operation.

Soft Biomimetic 3D Free-Form Artificial Vascular Graft Using a Highly Uniform Microspherical Porous Structure

This study presents a biomimetic 3D customizable artificial vascular graft with a highly porous and uniform microscale structure. The structural features were obtained by dip coating of a highly close-packed microsphere suspension on a 3D printed sacrificial template. Considering the structured arrangement of microspherical porogens in the coating layer, the microsphere-leached constructs showed higher uniformity and porosity than the conventionally particulate-leached structures, leading to ultrasoft mechanical compliance. Considering biomechanical compatibility, the resulting elastic moduli were at the sub-MPa level, comparable with those of native vascular tissues. In addition, the developed porous graft was reinforced selectively at the edge regions using a nonporous coating to secure its practical sutureability for clinical use. The sufficiently low cytotoxicity was clinically confirmed to alleviate the stiffness mismatch issues at the anastomotic interface between the native tissue and the artificial graft, thus overcoming the relevant clinical complications. Furthermore, the overall superior properties could be implemented on the 3D printed template for patient-specific medicare, thus implying the manufacturability of patient-specific vascular grafts.

Comparative Effect of Antihypertensive Drugs in Improving Arterial Stiffness in Hypertensive Adults (RIGIPREV Study). A Protocol for Network Meta-Analysis

(1) Background: Arterial stiffness is closely and bi-directionally related to hypertension and is understood as both a cause and a consequence of hypertension. Several studies suggest that antihypertensive drugs may reduce arterial stiffness. Therefore, effective prescription of antihypertensive drugs should consider both blood pressure and arterial stiffness. The aim of this protocol is to provide a review comparing the effects of different types of antihypertensive drug interventions on the reduction of arterial stiffness in hypertensive subjects. (2) Methods: The literature search will be performed through the MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials, Cochrane Database of Systematic Reviews, and Web of Science databases. Randomised clinical trials assessing the effect of antihypertensive drug interventions on arterial stiffness measured in subjects with hypertension will be included. A frequentist network meta-analysis will be performed to determine the comparative effects of different antihypertensive drugs. (3) Results: The findings of this study will be published in a peer-reviewed journal. (4) Conclusions: This study will provide evidence for health care professionals on the efficacy of different antihypertensive drugs in decreasing arterial stiffness; in addition, it will analyse the efficacy of the drugs not only in terms of arterial stiffness but also in terms of blood pressure treatment.

The aortic-femoral arterial stiffness gradient is blood pressure independent in older adults: the atherosclerosis risk in communities (ARIC) study

BACKGROUND

Aortic arterial stiffness is a strong independent predictor of cardiovascular disease (CVD); however, its dependence on mean arterial pressure (MAP) limits its clinical utility. The aortic-femoral arterial stiffness gradient (af-SG), a novel marker of CVD risk, may be a promising alternative, but its dependence on MAP is not known. The aim of this study was to determine the relationship between MAP and the af-SG in healthy older adults and those with established disease, including hypertension and diabetes.

METHOD

We evaluated the dependency of the af-SG on MAP in healthy older adults (n = 694, aged 74 ± 5 years), and adults with hypertension (n = 2040, aged 76 ± 5 years), and diabetes (n = 1405, aged 75 ± 5 years) as part of the community-based Atherosclerosis Risk in Communities (ARIC) Study. Carotid-femoral pulse-wave velocity (cfPWV), femoral-ankle PWV (faPWV) and blood pressure were measured using standardized protocols. The af-SG was calculated as faPWV divided by cfPWV. Multivariable regression analysis was performed to test the independent association of MAP with af-SG, with adjustments for known confounders, including age, sex, BMI, blood glucose and heart rate.

RESULTS

There was no significant relationship between the af-SG and MAP in healthy (β = 0.002, P = 0.301), hypertension (β = -0.001, P = 0.298) or diabetes (β = -0.001, P = 0.063) population groups, with MAP explaining less than 0.1, less than 0.1 and 0.2% of the variance in the af-SG, respectively.

CONCLUSION

These findings suggest that the af-SG may be regarded as a MAP independent index of arterial health and CVD risk in older adults.

The Phenotypic Responses of Vascular Smooth Muscle Cells Exposed to Mechanical Cues

During the development of atherosclerosis and other vascular diseases, vascular smooth muscle cells (SMCs) located in the intima and media of blood vessels shift from a contractile state towards other phenotypes that differ substantially from differentiated SMCs. In addition, these cells acquire new functions, such as the production of alternative extracellular matrix (ECM) proteins and signal molecules. A similar shift in cell phenotype is observed when SMCs are removed from their native environment and placed in a culture, presumably due to the absence of the physiological signals that maintain and regulate the SMC phenotype in the vasculature. The far majority of studies describing SMC functions have been performed under standard culture conditions in which cells adhere to a rigid and static plastic plate. While these studies have contributed to discovering key molecular pathways regulating SMCs, they have a significant limitation: the ECM microenvironment and the mechanical forces transmitted through the matrix to SMCs are generally not considered. Here, we review and discuss the recent literature on how the mechanical forces and derived biochemical signals have been shown to modulate the vascular SMC phenotype and provide new perspectives about their importance.

Towards a Clinical Implementation of Measuring the Elastic Modulus of the Aorta from Cardiac Computed Tomography Images

OBJECTIVE

The elasticity of the aortic wall varies depending on age, vessel location, and the presence of aortic diseases. Noninvasive measurement will be a powerful tool to understand the mechanical state of the aorta in a living human body. This study aimed to determine the elastic modulus of the aorta using computed tomography images.

METHODS

We constructed our original formulae based on mechanics of materials. Then, we performed computed tomography scans of a silicon rubber tube by applying four pressure conditions to the lumen. The segment elastic modulus was calculated from the scanned images using our formulae. The actual modulus was measured using a tensile loading test for comparison.

RESULTS

The segment moduli of elasticity from the images were 0.525 [0.524, 0.527], 0.524 [0.520, 0.524], 0.520 [0.515, 0.523], and 0.522 [0.516, 0.532] (unit: MPa, median [25%, 75% quantiles]) for the four pressure conditions, respectively. The corresponding measurements in the tensile test were 0.548 [0.539, 0.566], 0.535 [0.528, 0.553], 0.526 [0.513, 0.543], and 0.523 [0.508, 0.530], respectively. These results indicated errors of 4.2%, 2.1%, 1.1%, and 0.2%, respectively.

CONCLUSION

Our formulae provided good estimations of the segment elastic moduli of a silicon rubber tube under physiological pressure conditions using the computed tomography images.

SIGNIFICANCE

In addition to the elasticity, the formulae provide the strain energy as well. These properties can be better predictors of aortic diseases. The formulae consist of clinical parameters commonly used in medical settings (pressure, diameter, and wall thickness).

Development of an FEA framework for analysis of subject-specific aortic compliance based on 4D flow MRI

This paper presents a subject-specific in-silico framework in which we uncover the relationship between the spatially varying constituents of the aorta and the non-linear compliance of the vessel during the cardiac cycle uncovered through our MRI investigations. A microstructurally motivated constitutive model is developed, and simulations reveal that internal vessel contractility, due to pre-stretched elastin and actively generated smooth muscle cell stress, must be incorporated, along with collagen strain stiffening, in order to accurately predict the non-linear pressure-area relationship observed in-vivo. Modelling of elastin and smooth muscle cell contractility allows for the identification of the reference vessel configuration at zero-lumen pressure, in addition to accurately predicting high- and low-compliance regimes under a physiological range of pressures. This modelling approach is also shown to capture the key features of elastin digestion and SMC activation experiments. The volume fractions of the constituent components of the aortic material model were computed so that the in-silico pressure-area curves accurately predict the corresponding MRI data at each location. Simulations reveal that collagen and smooth muscle volume fractions increase distally, while elastin volume fraction decreases distally, consistent with reported histological data. Furthermore, the strain at which collagen transitions from low to high stiffness is lower in the abdominal aorta, again supporting the histological finding that collagen waviness is lower distally. The analyses presented in this paper provide new insights into the heterogeneous structure-function relationship that underlies aortic biomechanics. Furthermore, this subject-specific MRI/FEA methodology provides a foundation for personalised in-silico clinical analysis and tailored aortic device development. STATEMENT OF SIGNIFICANCE: This study provides a significant advance in in-silico medicine by capturing the structure/function relationship of the subject-specific human aorta presented in our previous MRI analyses. A physiologically based aortic constitutive model is developed, and simulations reveal that internal vessel contractility must be incorporated, along with collagen strain stiffening, to accurately predict the in-vivo non-linear pressure-area relationship. Furthermore, this is the first subject-specific model to predict spatial variation in the volume fractions of aortic wall constituents. Previous studies perform phenomenological hyperelastic curve fits to medical imaging data and ignore the prestress contribution of elastin, collagen, and SMCs and the associated zero-pressure reference state of the vessel. This novel MRI/FEA framework can be used as an in-silico diagnostic tool for the early stage detection of aortic pathologies.

Arterial Stiffness and Hypertension in the Elderly

Hypertension prevalence increases with age. Age and high blood pressure are the two main determinants of arterial stiffness. In elderly hypertensives, large arteries stiffen and systolic and pulse pressures increase, due to wave reflections. A major reason for measuring arterial stiffness in clinical practice in elderly hypertensive patients comes from the repeated demonstration that arterial stiffness and wave reflections have a predictive value for CV events. A large body of evidence has been published during the last two decades, concerning the epidemiology, pathophysiology, and pharmacology of large arteries in hypertension in various settings of age. Particularly, two expert consensus documents have reviewed the methodological agreements for measuring arterial stiffness. The concepts of Early Vascular Aging (EVA) and Supernormal Vascular Aging (SUPERNOVA) help to better understand on which determinants of arterial stiffness it is possible to act, in order to limit target organ damage and cardiovascular complications. This review will address the issues of the cellular and molecular mechanisms of arterial stiffening in elderly hypertensives, the consequences of arterial stiffening on central systolic and pulse (systolic minus diastolic, PP) pressures and target organs, the methodology for measuring arterial stiffness, central pulse pressure and wave reflection, the epidemiological determinants of arterial stiffening in elderly hypertensives, the pharmacology of arterial destiffening, and how the concepts of EVA and SUPERNOVA apply to the detection of organ damage and prevention of CV complications.

Carotid arterial stiffness is increased and related to left ventricular function in patients with hypertrophic cardiomyopathy

Aims

To assess the carotid mechanical properties in patients with hypertrophic cardiomyopathy and the relation between arterial stiffness and left ventricular function in this setting.

Methods and results

We have prospectively enrolled 71 patients (52 ± 16 years, 34 men) with hypertrophic cardiomyopathy, divided into two groups depending on the presence (46 patients) or absence (25 patients) of cardiovascular risk factors associated with increased arterial stiffness. Twenty-five normal subjects similar by age and gender with hypertrophic cardiomyopathy patients without risk factors formed the control group. A comprehensive echocardiography was performed in all subjects. Carotid arterial stiffness index (β index), pressure–strain elastic modulus, arterial compliance, and pulse wave velocity were also obtained using an echo-tracking system. β index, pulse wave velocity, and pressure–strain elastic modulus were significantly higher in hypertrophic cardiomyopathy patients without risk factors compared to controls. After linear regression analysis, the increase in carotid β index was independently correlated with the presence of hypertrophic cardiomyopathy [beta = 0.49, 95% confidence interval (CI) = 1.04–3.02; P < 0.001]. In the entire hypertrophic cardiomyopathy population arterial stiffness parameters correlated with age, gender, hypertension degree, presence of hypercholesterolaemia, and the E/e′ ratio. In multivariable analysis, β index (beta = 0.36, 95% CI = 0.32–1.25; P = 0.001), global left ventricular longitudinal strain, and the presence of left ventricular outflow tract obstruction were independently correlated with the E/e′ ratio.

Conclusion

In patients with hypertrophic cardiomyopathy arterial stiffness is increased independently of age or presence of cardiovascular risk factors. Carotid artery stiffness is independently related to left ventricular filling pressure, increased arterial stiffness representing a possible marker of a more severe phenotype.

Arterial Stiffness and Coronary Ischemia: New Aspects and Paradigms

PURPOSE OF REVIEW

Aortic stiffness (AS) is widely associated with hypertension and considered as a major predictor of coronary heart disease (CHD). AS is measured using carotid-femoral pulse wave velocity (PWV), particularly when this parameter is associated with an index involving age, gender, heart rate, and mean blood pressure. The present review focuses on the interest of measurement of PWV and the calculation of individual PWV index for the prediction of CHD, in addition with the use of new statistical nonlinear models enabling results with very high levels of accuracy.

RECENT FINDINGS

PWV index may so constitute a substantial marker of large arteries prediction and damage in CHD and may be also used in cerebrovascular and renal circulations models. PWV index determinations are particularly relevant to consider in angiographic CHD decisions and in the presence of vulnerable plaques with high cardiovascular risk. Due to the variability in symptoms and clinical characteristics of patients, together with some imperfections in results, there is no very simple adequate diagnosis approach enabling to improve the so defined CHD prediction in usual clinical practice. In recent works in relation to "artificial intelligence" and involving "decision tree" models and "artificial neural networks," it has been possible to determine consistent pathways introducing predictive medicine and enabling to obtain efficient algorithm classification models of coronary prediction.

Elastin-like recombinamers in collagen-based tubular gels improve cell-mediated remodeling and viscoelastic properties

The partial substitution of collagen with elastin-like recombinamers in tubular gels improves cell-mediated remodeling, elastic moduli and strength during maturation.

Comparative study of variations in mechanical stress and strain of human blood vessels: mechanical reference for vascular cell mechano-biology

The diseases of human blood vessels are closely associated with local mechanical variations. A better understanding of the quantitative correlation in mechanical environment between the current mechano-biological studies and vascular physiological or pathological conditions in vivo is crucial for evaluating numerous existing results and exploring new factors for disease discovery. In this study, six representative human blood vessels with known experimental measurements were selected, and their stress and strain variations in vessel walls under different blood pressures were analyzed based on nonlinear elastic theory. The results suggest that conventional mechano-biological experiments seeking the different biological expressions of cells at high/low mechanical loadings are ambiguous as references for studying vascular diseases, because distinct "site-specific" characteristics appear in different vessels. The present results demonstrate that the inner surface of the vessel wall does not always suffer the most severe stretch under high blood pressures comparing to the outer surface. Higher tension on the outer surface of aortas supports the hypothesis of the outside-in inflammation dominated by aortic adventitial fibroblasts. These results indicate that cellular studies at different mechanical niches should be "disease-specific" as well. The present results demonstrate considerable stress gradients across the wall thickness, which indicate micro-scale mechanical variations existing around the vascular cells, and imply that the physiological or pathological changes are not static processes confined within isolated regions, but are coupled with dynamic cell behaviors such as migration. The results suggest that the stress gradients, as well as the mechanical stresses and strains, are key factors constituting the mechanical niches, which may shed new light on "factor-specific" experiments of vascular cell mechano-biology.

Differential impact of local and regional aortic stiffness on left ventricular remodeling: a cardiovascular magnetic resonance study

BACKGROUND

Left ventricular (LV) remodeling and aortic stiffness have independent predictive value for all causes and cardiovascular mortality. Because elastic properties of the arterial wall vary along the aortic pathway, we hypothesized that local and regional aortic stiffness could differently impact on LV remodeling.

METHODS AND RESULTS

Regional aortic stiffness was determined from carotid-femoral pulse wave velocity (cfPWV) measured by aplanation tonometry. Aortic arch pulse wave velocity was measured by phase contrast cardiovascular magnetic resonance (CMR). Local stiffness was calculated in the ascending aorta pulse wave velocity (aaPWV) and descending aorta pulse wave velocity using central pulse pressure measurement, cine CMR acquisition, and surface change estimation. CMR LV remodeling was expressed as LV mass to end-diastolic volume ratio.We evaluated 146 study participants (41 ± 15 years) free of overt cardiovascular disease. In stepwise multivariate regression analysis, cfPWV and aaPWV were significantly and independently correlated to mass to end-diastolic volume ratio (partial R = 0.07 and R = 0.10, respectively, all P < 0.005) after adjustment for age, sex, BMI, brachial mean blood pressure, and central pulse pressure. Descending aorta pulse wave velocity was correlated with mass to end-diastolic volume ratio to a lower extent (R = 0.04, P = 0.0115) and aortic arch pulse wave velocity was not independently associated with mass to end-diastolic volume ratio. CfPWV and aaPWV were both independently associated with mass to end-diastolic volume ratio, explaining 5 and 8% of mass to end-diastolic volume ratio variance, respectively.

CONCLUSION

In study participants free of overt cardiovascular disease, stiffness of the ascending aorta representing the local proximal aortic function face to the LV and of the downstream aortic pathway assessed by cfPWV reflecting more advanced alterations of material properties involving the entire aorta, are independent determinants of LV remodeling after adjustment to age, BMI, mean blood pressure, and sex.

[Essential hypertension: Definitions, hemodynamic, clinical and therapeutic review]

Arterial hypertension is à chronic disease that affects more than 25 % of the French adult population. Increased peripheral resistance combined with normal cardiac output is a special feature of arterial hypertension. The increase in the resistance of arterioles remains an important feature of arterial hypertension while the study of the rigidity of large arterials trunks remains poorly explored. Pulse wave velocity (PWV) measurement has been established as one of the major independent predictors of cardiovascular events in arterial hypertension.

Aortic-to-brachial artery stiffness gradient is not blood pressure independent

Aortic stiffness predicts cardiovascular mortality but is limited as a risk marker because it is dependent on blood pressure (BP). A potential solution is provided from the ratio of aortic-to-brachial artery stiffness (ab-ratio), which has been shown to be a BP-independent risk marker among patients with renal dysfunction (RD). We sought to determine the BP independence of the ab-ratio in patients with disease, including RD, and healthy populations. The ab-ratio (aortic/brachial pulse wave velocity) and mean arterial pressure (MAP) were recorded in patients with RD (n = 119, aged 65 ± 7 years), hypertension (n = 140, aged 62 ± 9 years), type 2 diabetes mellitus (n = 77, aged 60 ± 9 years) and healthy subjects (n = 99, aged 51 ± 8 years). Multiple-regression analysis was performed to test the independent association of MAP with the ab-ratio adjusted for age, sex, body mass index, glucose and heart rate. There was no significant relationship between the ab-ratio and MAP in patients with RD (β = 0.08, p = 0.34), hypertension (β = 0.04, p = 0.62) or diabetes (β = 0.22, p = 0.11). However, among healthy subjects the ab-ratio was significantly and independently associated with MAP (β = 0.31, p = 0.003). There was a significant difference in the strength of association between the ab-ratio and MAP between patients with disease and healthy subjects (z > 2.2, p < 0.05 all). Although ab-ratio is purported to be a risk marker that is independent of BP, this was observed only among patient populations, and not among healthy subjects. As a result, the ab-ratio has limited potential as a screening tool for the clinical assessment of arterial stiffness in otherwise healthy individuals.

Vascular Endothelial Cell Behavior in Complex Mechanical Microenvironments

The vascular mechanical microenvironment consists of a mixture of spatially and temporally changing mechanical forces. This exposes vascular endothelial cells to both hemodynamic forces (fluid flow, cyclic stretching, lateral pressure) and vessel forces (basement membrane mechanical and topographical properties). The vascular mechanical microenvironment is "complex" because these forces are dynamic and interrelated. Endothelial cells sense these forces through mechanosensory structures and transduce them into functional responses via mechanotransduction pathways, culminating in behavior directly affecting vascular health. Recent in vitro studies have shown that endothelial cells respond in nuanced and unique ways to combinations of hemodynamic and vessel forces as compared to any single mechanical force. Understanding the interactive effects of the complex mechanical microenvironment on vascular endothelial behavior offers the opportunity to design future biomaterials and biomedical devices from the bottom-up by engineering for the cellular response. This review describes and defines (1) the blood vessel structure, (2) the complex mechanical microenvironment of the vascular endothelium, (3) the process in which vascular endothelial cells sense mechanical forces, and (4) the effect of mechanical forces on vascular endothelial cells with specific attention to recent works investigating the influence of combinations of mechanical forces. We conclude this review by providing our perspective on how the field can move forward to elucidate the effects of the complex mechanical microenvironment on vascular endothelial cell behavior.

Vascular Smooth Muscle Cells and Arterial Stiffening: Relevance in Development, Aging, and Disease

The cushioning function of large arteries encompasses distension during systole and recoil during diastole which transforms pulsatile flow into a steady flow in the microcirculation. Arterial stiffness, the inverse of distensibility, has been implicated in various etiologies of chronic common and monogenic cardiovascular diseases and is a major cause of morbidity and mortality globally. The first components that contribute to arterial stiffening are extracellular matrix (ECM) proteins that support the mechanical load, while the second important components are vascular smooth muscle cells (VSMCs), which not only regulate actomyosin interactions for contraction but mediate also mechanotransduction in cell-ECM homeostasis. Eventually, VSMC plasticity and signaling in both conductance and resistance arteries are highly relevant to the physiology of normal and early vascular aging. This review summarizes current concepts of central pressure and tensile pulsatile circumferential stress as key mechanical determinants of arterial wall remodeling, cell-ECM interactions depending mainly on the architecture of cytoskeletal proteins and focal adhesion, the large/small arteries cross-talk that gives rise to target organ damage, and inflammatory pathways leading to calcification or atherosclerosis. We further speculate on the contribution of cellular stiffness along the arterial tree to vascular wall stiffness. In addition, this review provides the latest advances in the identification of gene variants affecting arterial stiffening. Now that important hemodynamic and molecular mechanisms of arterial stiffness have been elucidated, and the complex interplay between ECM, cells, and sensors identified, further research should study their potential to halt or to reverse the development of arterial stiffness.

Integrated strategy for in vitro characterization of a bileaflet mechanical aortic valve

Background

Haemodynamic performance of heart valve prosthesis can be defined as its ability to fully open and completely close during the cardiac cycle, neither overloading heart work nor damaging blood particles when passing through the valve. In this perspective, global and local flow parameters, valve dynamics and blood damage safety of the prosthesis, as well as their mutual interactions, have all to be accounted for when assessing the device functionality. Even though all these issues have been and continue to be widely investigated, they are not usually studied through an integrated approach yet, i.e. by analyzing them simultaneously and highlighting their connections.

Results

An in vitro test campaign of flow through a bileaflet mechanical heart valve (Sorin Slimline 25 mm) was performed in a suitably arranged pulsatile mock loop able to reproduce human systemic pressure and flow curves. The valve was placed in an elastic, transparent, and anatomically accurate model of healthy aorta, and tested under several pulsatile flow conditions. Global and local hydrodynamics measurements and leaflet dynamics were analysed focusing on correlations between flow characteristics and valve motion. The haemolysis index due to the valve was estimated according to a literature power law model and related to hydrodynamic conditions, and a correlation between the spatial distribution of experimental shear stress and pannus/thrombotic deposits on mechanical valves was suggested. As main and general result, this study validates the potential of the integrated strategy for performance assessment of any prosthetic valve thanks to its capability of highlighting the complex interaction between the different physical mechanisms that govern transvalvular haemodynamics.

Conclusions

We have defined an in vitro procedure for a comprehensive analysis of aortic valve prosthesis performance; the rationale for this study was the belief that a proper and overall characterization of the device should be based on the simultaneous measurement of all different quantities of interest for haemodynamic performance and the analysis of their mutual interactions.

Electronic supplementary material

The online version of this article (doi:10.1186/s12938-017-0314-2) contains supplementary material, which is available to authorized users.

Interplay of Aging and Hypertension in Cardiac Remodeling: A Mathematical Geometric Model

Hypertensive disorder can cause cardiac deformities. Elastic characteristic parameters, like Young’s modulus of elasticity (E) derived from a traditional cylindrical model, increase significantly with aging. However, the geometric and component changes of aging hearts because of chronic hypertension remain unknown. To better describe the effects, we propose an elliptical elastic and mathematical model to evaluate myocardial stiffness. Ninety-six hypertensive patients (HTN^Pos) (men: 59.3%; age ≥ 65 years: 20.8%) were enrolled and compared with normotensive controls (HTN^Neg) (n = 47, 48.9%). HTN^Pos patients had a thicker interventricular septum in diastole (IVSd) (HTN^Pos: 0.96 ± 0.21 cm vs. HTN^Neg: 0.77 ± 0.15; p = 0.005) and higher intracardiac pressure (e/e′: 9.06 ± 4.85 cm vs. 7.76 ± 3.41; p = 0.01), especially the elderly (> 65 years) (IVSd: 1.03 ± 0.19 cm, e/e′: 11.39 ± 1.99; p = 0.006 and 0.01, respectively). Nevertheless, the internal dimension decreased more significantly in the HTN^Pos rather than in the HTN^Neg elderly (5.23 ± 0.46 vs. 4.74 ± 0.69 cm; p = 0.02). We found different directions of cardiac remodeling with normotensive and hypertensive loads. Different from the longitudinal and circumferential strain, E and Poisson’s ratio (υ) are values that directly present the rigidity of myocardium. E was significantly higher in the elderly (8011.92 ± 2431.85 vs. 6052.43 ± 3121.50; p = 0.02), whereas υ was significantly higher in all HTN^Pos patients (0.73 ± 0.12 vs. 0.61 ± 0.07; p < 0.001). Because E and υ reflected the material changes of myocardium in the HTN^Pos elderly, the proposed elliptical mathematical heart model better describes the geometric deformity induced by aging and hypertension.

Arterial Stiffness: Going a Step Beyond

Interest in arterial stiffness has been fueled by the scientific and clinical implications of its "vicious cycle" relationship with aging and systolic blood pressure. In physical terms, stiffness is the slope of the relationship between an artery's distending pressure and its cross-sectional area or volume. Pulse wave velocity (PWV, in m/s), the most common arterial stiffness indicator, is usually measured by the foot-to-foot time and distance method and is proportional to [stiffness × area (or volume)]1/2 at a given pressure. Its intrinsic pressure dependency and other flaws in current PWV methods limit its utility. In contrast, the arterial stiffness-arterial pressure relationship is near-linear, with a slope β, the exponent of the curvilinear arterial pressure-arterial volume relationship. The concept of arterial stiffening is related to β and describes a more functionally relevant aspect of arterial behavior: the change in stiffness for a given change in pressure. Arterial stiffening can be estimated from the variability of within-individual BP measurements (24-h ambulatory, home BP, or BP measured at different arm heights) and can be expressed as the pulse stiffening ratio (PSR) = [systolic stiffness]/[diastolic stiffness] or the ambulatory arterial stiffness index (AASI or its symmetric form, sAASI). High arterial stiffness (PWV) and stiffening (β, stiffness index, cardio-ankle vascular index, AASI, and PSR) are associated with increased cardiovascular disease risk, but it remains unclear whether these indicators are useful in improving medical care quality; the standard of care remains stringent BP control.

VALIDATION OF LOSS-COEFFICIENT-BASED OUTLET BOUNDARY CONDITIONS FOR SIMULATING AORTIC FLOW

Flow in a polyurethane model of a human aorta, driven by a heart-lung machine, is analyzed experimentally and computationally for antegrade and retrograde perfusion. The purpose of the analysis is the validation of the previously proposed loss-coefficient-based outlet boundary condition for aortic branches. This model is claimed to be commonly applicable to different perfusion modes of the aorta, unlike the alternative straightforward constant-pressure outlet boundary condition. First, the antegrade perfusion is analyzed computationally and experimentally. This step delivers the loss-coefficients that are to be used in any other perfusion mode of the aorta. Subsequently, a retrograde perfusion is applied to the same aorta, where the flow rates at the outlets of the aortic branches are measured and predicted by applying the loss-coefficient-based outlet boundary conditions. A very good agreement of the predictions with the measurements is observed. The predictions delivered by the standard constant-pressure outlet boundary condition are observed, on the contrary, to be highly in error. Thus, the advocated loss-coefficient-based outlet boundary condition is experimentally validated. It is shown that it is applicable to different perfusion modes with a quite good accuracy, which is much higher compared to the straightforward constant-pressure outlet boundary condition.

MRI-based aortic blood flow model in 3D ballistocardiography

Ballistocardiography (BCG) is a non-invasive technique which measures the acceleration of a body induced by cardiovascular activity, namely the force exerted by the beating heart. A one dimensional aortic flow model based on the transmission lines theory is developped and applied to the simulation of three dimensional BCG. A four-element Windkessel model is used to generate the pressure-wave. Using transverse MRI slices of a human subject, a reconstruction of the aorta allows the extraction of parameters used to relate the local change in mass of the 1D flow model to 3D acceleration BCG. Simulated BCG curves are then compared qualitatively with the ensemble average curves of the same subject recorded in sustained microgravity. Confirming previous studies, the main features of the y-axis are well simulated. The simulated z-axis, never attempted before, shows important similarities. The simulated x-axis is less faithful and suggests the presence of reflections.

Measurement of Arterial Stiffness: A Novel Tool of Risk Stratification in Hypertension

Cardiovascular diseases are the leading causes of morbidity and mortality in industrialized countries worldwide, despite highly effective preventive treatments available. As a difference continues to exist between the estimated and true number of events, further improvement of risk stratification is an essential part of cardiovascular research.Among hypertensive patients measurement of arterial stiffness parameters, like carotid-femoral pulse wave velocity (cfPWV) or brachial-ankle pulse wave velocity (baPWV) can contribute to the identification of high-risk subpopulation of patients. This is a hot topic of vascular research including the possibility of the non-invasive measurement of central hemodynamics, wave reflections and recently, 24-h arterial stiffness monitoring as well. This chapter discusses the past and the present of this area including the scientific achievements with cfPWV, baPWV and other measures, provides a short overview of methodologies and the representation of arterial stiffness parameters in guidelines.

Novel Methods for Pulse Wave Velocity Measurement

The great incidence of cardiovascular (CV) diseases in the world spurs the search for new solutions to enable an early detection of pathological processes and provides more precise diagnosis based in multi-parameters assessment. The pulse wave velocity (PWV) is considered one of the most important clinical parameters for evaluate the CV risk, vascular adaptation, and therapeutic efficacy. Several studies were dedicated to find the relationship between PWV measurement and pathological status in different diseases, and proved the relevance of this parameter. The commercial devices dedicate to PWV estimation make a regional assessment (measured between two vessels), however a local measurement is more precise evaluation of artery condition, taking into account the differences in the structure of arteries. Moreover, the current devices present some limitations due to the contact nature. Emerging trends in CV monitoring are moving away from more invasive technologies to non-invasive and non-contact solutions. The great challenge is to explore the new instrumental solutions that allow the PWV assessment with fewer approximations for an accurately evaluation and relatively inexpensive techniques in order to be used in the clinical routine.

The structural factor of hypertension: large and small artery alterations

Pathophysiological studies have extensively investigated the structural factor in hypertension, including large and small artery remodeling and functional changes. Here, we review the recent literature on the alterations in small and large arteries in hypertension. We discuss the possible mechanisms underlying these abnormalities and we explain how they accompany and often precede hypertension. Finally, we propose an integrated pathophysiological approach to better understand how the cross-talk between large and small artery changes interacts in pressure wave transmission, exaggerates cardiac, brain and kidney damage, and lead to cardiovascular and renal complications. We focus on patients with essential hypertension because this is the most prevalent form of hypertension, and describe other forms of hypertension only for contrasting their characteristics with those of uncomplicated essential hypertension.

Can we predict the presence of coronary lesions from blood pressure measurement? A new clinical method

The roles of arterial function and structure in cardiovascular physiology have expanded with the development of a variety of parameters that evaluate arterial stiffness. Markers of arterial stiffness have been correlated with cardiovascular outcomes. We aimed to find a simple, clinical, noninvasive method to predict atherosclerosis that leads to the development of coronary artery disease (CAD). We aimed to find a simple, clinical, noninvasive method to predict atherosclerosis that leads to the development of CAD. We included 100 cases that underwent coronary angiography in our center owing to different indications. The blood pressure in all cases was measured by two different observers. The oscillatory systolic blood pressure (OSBP) was defined as the point at which the mercury began to oscillate to a minimum level of 1 mm Hg. The auscultatory systolic blood pressure (AUSBP) was defined as the first Korotkoff sound. The difference between OSBP and AUSBP was calculated and called the oscillatory gap (OG). The correlation between the OG and the presence of coronary lesion in coronary angiography was statistically calculated. The study populations had a mean age of 57.3±9 years. The mean±s.d. OG was 14.44±10.44. There was a highly significantly positive correlation between the OG and the presence of coronary artery lesions (r=0.399 and P-value <0.000). There was also a significantly positive correlation between the presence of hypertension and the OG (r=0.376 and P-value <0.000). The difference between OSBP and AUSBP could be used as a simple method to detect atherosclerotic arterial changes. This method could indicate the degree of arterial stiffness. There was a significantly positive correlation between this new indicator of arterial stiffness and the presence of CAD. Any patient with a wide gap between OSBP and AUSBP should be treated early with antihypertensive drugs and statins before the development of CAD.

Pyridoxamine protects against mechanical defects in cardiac ageing in rats: studies on load dependence of myocardial relaxation

New Findings

Our team demonstrated in the past that pyridoxamine attenuated arterial stiffening by targeting the pathogenic formation of glycated collagen cross-links in aged rats. Herein, we examined whether pyridoxamine therapy can protect against mechanical defects in myocardial relaxation by improving arterial wave properties and cardiac contractile performance in senescent animals. Fifteen-month-old male Fisher 344 rats were treated daily with pyridoxamine (1 g l⁻¹ in drinking water) for 5 months and compared with age-matched untreated control animals (20 months old). Arterial wave properties were characterized by wave transit time (τ_w) and wave reflection factor (R_f). We measured the contractile status of the myocardium in an intact heart as the left ventricular (LV) end-systolic elastance (E_es). Myocardial relaxation was described according to the time constant of the LV isovolumic pressure decay (τ_e). Pyridoxamine therapy prevented the age-associated prolongation in LV τ_e and the diminished E_es in senescent rats. The drug also attenuated the age-related augmentation in afterload imposed on the heart, as evidenced by the increased τ_w and decreased R_f. We found that the LV τ_e was significantly influenced by both the arterial τ_w and R_f (τ_e = 16.3902 + 8.3123 × R_f − 0.4739 × τ_w; r = 0.7048, P < 0.005). In the meantime, the LV τ_e and the LV E_es showed a significant inverse linear correlation (τ_e = 13.9807 − 0.0068 × E_es; r = 0.6451, P < 0.0005). All these findings suggested that long-term treatment with pyridoxamine might ameliorate myocardial relaxation rate, at least partly through its ability to enhance myocardial contractile performance, increase wave transit time and decrease wave reflection factor in aged rats.

Vascular elastography: a validation study

Vascular elastography techniques are promising tools for mechanical characterization of diseased arteries. These techniques are usually validated with simulations or phantoms or by comparing results with histology or other imaging modalities. In the study described here, vascular elastography was applied to porcine aortas in vitro during inflation testing (n = 10) and results were compared with those of standard bi-axial tensile testing, a technique that directly measures the force applied to the tissue. A neo-Hookean model was fit to the stress-strain data, valid for large deformations. Results indicated good correspondence between the two techniques, with GUS = 110 ± 11 kPa and GTT = 108 ± 10 kPa for ultrasound and tensile testing, respectively. Bland-Altman analysis revealed little bias (GUS-GTT = 2 ± 20 kPa). The next step will be the application of a non-linear material model that is also adaptable for in vivo measurements.

To compare the effect of Telmisartan with Metoprolol on arterial stiffness in hypertension: prospective randomized parallel group trial

BACKGROUND

Hypertension is often complicated by increased arterial stiffness and is an independent predictor of adverse cardiovascular (CV) outcome. Beta blockers and angiotensin receptor blockers (ARBs) are commonly used antihypertensive agents. The effect of beta blockers and ARBs on arterial stiffness has not been compared adequately. The aim of the present study is to compare the effect of telmisartan with metoprolol on arterial stiffness in hypertensive patients in prospective open label randomized parallel group intervention study.

METHODS

100 patients of hypertension, not on any antihypertensive agents, were enrolled after obtaining informed consent. Baseline recording of data related to demographics, CV risk factors, anthropometry and BP were made. Arterial stiffness was measured noninvasively by recording pulse wave velocity (PWV) using periscope (Genesis medical system). Left ventricular (LV) mass was measured using 2D guided M-mode echocardiography. Blood sugar, renal function, lipids and uric acid estimations were done in fasting state. Patients were randomized to receive metoprolol and telmisartan using stratified randomization technique. Dose of the study drugs were titrated to achieve target BP of <140/90 mmHg. Data related to PWV, BP, anthropometry and blood biochemistry was repeated after 6 months of treatment with study drugs.

RESULTS

Telmisartan resulted in significantly greater reduction in arterial stiffness index (ASI) in left and right lower limb arterial bed (39.9 ± 11.7 vs. 46.8 ± 17.0 m/s, p < 0.02) and (36.4 ± 9.6 vs. 44.86 ± 15.1 m/s, p < 0.002) respectively and systolic blood pressure (SBP) (-4.9 mmHg with 95% C.I. of -8.0-1.7 mmHg, p < 0.003) compared to metoprolol. Reduction in diastolic blood pressure (DBP) in telmisartan and metoprolol groups was not different statistically (-1.0 mmHg with 95% C.I. of -3.3-1.2 mmHg, p < 0.3). The change in LV mass was not significantly different between the study groups (135.5 ± 37.6 vs. 143.2 ± 41.5, p < 0.3).

Characterization of aging-associated cardiac diastolic dysfunction

AIMS

Diastolic dysfunction is common in geriatric heart failure. A reliable parameter to predict myocardium stiffness and relaxation under similar end-diastolic pressure is being developed. We propose a material and mathematical model for calculating myocardium stiffness based on the concept of linear correlation between [Formula: see text] and wedge pressure.

METHODS AND RESULTS

We enrolled 919 patients (male: [Formula: see text][Formula: see text]). Compared with the younger population of controls (mean age: [Formula: see text] years; [Formula: see text]; male: [Formula: see text] [Formula: see text]), the elderly (mean age: [Formula: see text]; [Formula: see text]; male: [Formula: see text] [Formula: see text]) had a greater prevalence of hypertension, diabetes mellitus, and coronary artery disease (all [Formula: see text]). We collected their M-mode and 2-D echocardiographic volumetric parameters, intraventricular filling pressure, and speckle tracking images to establish a mathematical model. The feasibility of this model was validated. The average early diastolic velocity of the mitral annulus assessed using tissue Doppler imaging was significantly attenuated in the elderly ([Formula: see text]: [Formula: see text] vs. [Formula: see text]; [Formula: see text]) and corresponded to the higher estimated wedge ([Formula: see text]) pressure ([Formula: see text] vs. [Formula: see text]; [Formula: see text]) in that cohort. E (Young's modulus) was calculated to describe the tensile elasticity of the myocardium. With the same intraventricular filling pressure, E was significantly higher in the elderly, especially those with [Formula: see text] values [Formula: see text]. Compared with diastolic dysfunction parameters, E also presented sentinel characteristics more sensitive for detecting early myocardial relaxation impairment, which indicates stiffer myocardium in aging hearts.

CONCLUSION

Our material and geometric mathematical model successfully described the stiffer myocardium in aging hearts with higher intraventricular pressure. Additional studies that compare individual differences, especially in health status, are needed to validate its application for detecting diastolic heart failure.

Fibulin-5 null mice with decreased arterial compliance maintain normal systolic left ventricular function, but not diastolic function during maturation

The large arteries serve as compliant vessels that store energy during systole and return it during diastole. This function is made possible by the elastic fibers in the arterial wall that are assembled during late embryonic and early postnatal development from various proteins, including fibulin‐5. Mice and humans with insufficient amounts of fibulin‐5 have reduced arterial compliance as adults. Reduced compliance of the large arteries is correlated with hypertension, reduced cardiac function, and an increased risk of death from cardiac and cardiovascular disease. The goal of this study was to quantify arterial compliance, blood pressure, and left ventricular (LV) function from early postnatal development to young adulthood in fibulin‐5 null (Fbln5−/−) mice to determine the effects of reduced arterial compliance during this critical period of elastic fiber assembly. We find that ascending aorta compliance is reduced as early as postnatal day (P) 7 and carotid artery compliance is reduced by P21 in Fbln5−/− mice. We did not find significant increases in systolic blood pressure by P60, but pulse pressures are increased by P21 in Fbln5−/− mice. LV systolic function, as measured by ejection fraction and fractional shortening, is unaffected in Fbln5−/− mice. However, LV diastolic function, as measured by tissue Doppler imaging, is compromised at all ages in Fbln5−/− mice. We propose that Fbln5−/− mice represent a suitable model for further studies to determine mechanistic relationships between arterial compliance and LV diastolic function.

Carotid intima media thickness, oxidative stress, and inflammation in children with chronic kidney disease

OBJECTIVE

We evaluated the association between inflammation and oxidative stress with carotid intima media thickness (cIMT) and elasticity increment module (E(inc)) in pediatric patients with chronic kidney disease (CKD).

METHODS

This analytical, cross-sectional study assessed 134 children aged 6-17 years with CKD. Anthropometric measurements and biochemistry of intact parathyroid hormone (iPTH), high-sensitivity C-reactive protein (CRP), interleukin (IL)-6, IL-1β, reduced glutathione (GSH), malondialdehyde, nitric oxide, and homocysteine were recorded. Bilateral carotid ultrasound (US) was taken. Patients were compared with controls for cIMT and E(inc) using ≥ 75 percentile (PC).

RESULTS

Mean cIMT was 0.528 ± 0.089 mm; E(inc) was 0.174 ± 0.121 kPa × 10(3); cIMT negatively correlated with phosphorus (r -0.19, p =0.028) and the calcium × phosphorus (Ca × P) product (r -0.26, p =0.002), and positively with iPTH (r 0.19,p =0.024). After adjusting for potential confounders, hemodialysis (HD) (β=0.111, p =<0.001), automated peritoneal dialysis (APD) (β=0.064, p =0.026), and Ca x P product(β=-0.002, p =0.015) predicted cIMT (R(2)=0.296). In patients on dialysis, HD (β=0.068, p =0.010), low-density lipoprotein cholesterol (LDL-C) (β=0.001, p =0.048), and GSH(β=-0.0001, p=0.041) independently predicted cIMT (R(2)=0.204); HD, hypoalbuminemia, and high iPTH increased the risk of increased cIMT. In dialysis, E(inc) was inversely associated with GSH, and in predialysis, Ca × P correlated with/predicted E(inc) (β=0.001, p =0.009).

CONCLUSIONS

cIMT and E(inc) strongly associate with several biochemical parameters and GSH but not with other oxidative stress or inflammation markers.

Quantification of regional differences in aortic stiffness in the aging human

There has been a growing awareness over the past decade that stiffening of the aorta, and its attendant effects on hemodynamics, is both an indicator and initiator of diverse cardiovascular, neurovascular, and renovascular diseases. Although different clinical metrics of arterial stiffness have been proposed and found useful in particular situations, there remains a need to understand better the complex interactions between evolving aortic stiffness and the hemodynamics. Computational fluid-solid-interaction (FSI) models are amongst the most promising means to understand such interactions for one can parametrically examine effects of regional variations in material properties and arterial geometry on local and systemic blood pressure and flow. Such models will not only increase our understanding, they will also serve as important steps towards the development of fluid-solid-growth (FSG) models that can further examine interactions between the evolving wall mechanics and hemodynamics that lead to arterial adaptations or disease progression over long periods. In this paper, we present a consistent quantification and comparison of regional nonlinear biaxial mechanical properties of the human aorta based on 19 data sets available in the literature and we calculate associated values of linearized stiffness over the cardiac cycle that are useful for initial large-scale FSI and FSG simulations. It is shown, however, that there is considerable variability amongst the available data and consequently that there is a pressing need for more standardized biaxial testing of the human aorta to collect data as a function of both location and age, particularly for young healthy individuals who serve as essential controls.

Mechanosensing in developing lymphatic vessels

The lymphatic vasculature is responsible for fluid homeostasis, transport of immune cells, inflammatory molecules, and dietary lipids. It is composed of a network of lymphatic capillaries that drain into collecting lymphatic vessels and ultimately bring fluid back to the blood circulation. Lymphatic endothelial cells (LECs) that line lymphatic capillaries present loose overlapping intercellular junctions and anchoring filaments that support fluid drainage. When interstitial fluid accumulates within tissues, the extracellular matrix (ECM) swells and pulls the anchoring filaments. This results in opening of the LEC junctions and permits interstitial fluid uptake. The absorbed fluid is then transported within collecting lymphatic vessels, which exhibit intraluminal valves that prevent lymph backflow and smooth muscle cells that sequentially contract to propel lymph.Mechanotransduction involves translation of mechanical stimuli into biological responses. LECs have been shown to sense and respond to changes in ECM stiffness, fluid pressure-induced cell stretch, and fluid flow-induced shear stress. How these signals influence LEC function and lymphatic vessel growth can be investigated by using different mechanotransduction assays in vitro and to some extent in vivo.In this chapter, we will focus on the mechanical forces that regulate lymphatic vessel expansion during embryonic development and possibly secondary lymphedema. In mouse embryos, it has been recently shown that the amount of interstitial fluid determines the extent of lymphatic vessel expansion via a mechanosensory complex formed by β1 integrin and vascular endothelial growth factor receptor-3 (VEGFR3). This model might as well apply to secondary lymphedema.

Validity of the Water Hammer Formula for Determining Regional Aortic Pulse Wave Velocity: Comparison of One-Point and Two-Point (Foot-to-Foot) Measurements Using a Multisensor Catheter in Human

BACKGROUND

Lack of high-fidelity simultaneous measurements of pressure and flow velocity in the aorta has impeded the direct validation of the water-hammer formula for estimating regional aortic pulse wave velocity (AO-PWV1) and has restricted the study of the change of beat-to-beat AO-PWV1 under varying physiological conditions in man.

METHODS

Aortic pulse wave velocity was derived using two methods in 15 normotensive subjects: 1) the conventional two-point (foot-to-foot) method (AO-PWV2) and 2) a one-point method (AO-PWV1) in which the pressure velocity-loop (PV-loop) was analyzed based on the water hammer formula using simultaneous measurements of flow velocity (Vm) and pressure (Pm) at the same site in the proximal aorta using a multisensor catheter. AO-PWV1 was calculated from the slope of the linear regression line between Pm and Vm where wave reflection (Pb) was at a minimum in early systole in the PV-loop using the water hammer formula, PWV1 = (Pm/Vm)/ρ, where ρ is the blood density. AO-PWV2 was calculated using the conventional two-point measurement method as the distance/traveling time of the wave between 2 sites for measuring P in the proximal aorta. Beat-to-beat alterations of AO-PWV1 in relationship to aortic pressure and linearity of the initial part of the PV-loop during a Valsalva maneuver were also assessed in one subject.

RESULTS

The initial part of the loop became steeper in association with the beat-to-beat increase in diastolic pressure in phase 4 during the Valsalva maneuver. The linearity of the initial part of the PV-loop was maintained consistently during the maneuver. Flow velocity vs. pressure in the proximal aorta was highly linear during early systole, with Pearson's coefficients ranging from 0.9954 to 0.9998. The average values of AO-PWV1 and AO-PWV2 were 6.3 ± 1.2 and 6.7 ± 1.3 m/s, respectively. The regression line of AO-PWV1 on AO-PWV2 was y = 0.95x + 0.68 (r = 0.93, p <0.001).

CONCLUSION

This study concluded that the water-hammer formula (one-point method) provides a reliable and conventional estimate of beat-to-beat aortic regional pulse wave velocity consistently regardless of the changes in physiological states in human clinically. (English Translation of J Jpn Coll Angiol 2011; 51: 215-221).

Pseudostatic and dynamic nanomechanics of the tunica adventitia in elastic arteries using atomic force microscopy

Tunica adventitia, the outer layer of blood vessels, is an important structural feature, predominantly consisting of collagen fibrils. This study uses pseudostatic atomic force microscopy (AFM) nanoindentation at physiological conditions to show that the distribution of indentation modulus and viscous creep for the tunica adventitia of porcine aorta and pulmonary artery are distinct. Dynamic nanoindentation demonstrates that the viscous dissipation of the tunica adventitia of the aorta is greater than the pulmonary artery. We suggest that this mechanical property of the aortic adventitia is functionally advantageous due to the higher blood pressure within this vessel during the cardiac cycle. The effects on pulsatile deformation and dissipative energy losses are discussed.