Estimation of arterial stiffness, compliance, and distensibility from M-mode ultrasound measurements of the common carotid artery

Elastomers in vascular tissue engineering

Elastomers are popular in vascular engineering applications, as they offer the ability to design implants that match the compliance of native tissue. By mimicking the natural tissue environment, elastic materials are able to integrate within the body to promote repair and avoid the adverse physiological responses seen in rigid alternatives that often disrupt tissue function. The design of elastomers has continued to evolve, moving from a focus on long term implants to temporary resorbable implants that support tissue regeneration. This has been achieved through designing chemistries and processing methodologies that control material behavior and bioactivity, while maintaining biocompatibility in vivo. Here we review the latest developments in synthetic and natural elastomers and their application in cardiovascular treatments.

Mechanisms of Vascular Smooth Muscle Contraction and the Basis for Pharmacologic Treatment of Smooth Muscle Disorders

The smooth muscle cell directly drives the contraction of the vascular wall and hence regulates the size of the blood vessel lumen. We review here the current understanding of the molecular mechanisms by which agonists, therapeutics, and diseases regulate contractility of the vascular smooth muscle cell and we place this within the context of whole body function. We also discuss the implications for personalized medicine and highlight specific potential target molecules that may provide opportunities for the future development of new therapeutics to regulate vascular function.

Investigation of peripheral photoplethysmographic morphology changes induced during a hand-elevation study

A hand-elevation study was carried out in the laboratory in order to alter peripheral blood flow with the aim of increasing understanding of factors affecting the morphology of peripheral photoplethysmographic signals. Photoplethysmographic (PPG) signals were recorded from twenty healthy volunteer subjects during a hand-elevation study in which the right hand was raised and lowered relative to heart level, while the left hand remained static. Red and infrared (IR) PPG signals were obtained from the right and left index fingers using a custom-made PPG processing system. PPG features were identified using a feature-detection algorithm based on the first derivative of the PPG signal. The systolic PPG amplitude, the reflection index, crest time, pulse width at half height, and delta T were calculated from 20 s IR PPG signals from three positions of the right hand with respect to heart level (-50, 0, +50 cm) in 19 volunteers. PPG features were found to change with hand elevation. On lowering the hand to 50 cm below heart level, ac systolic PPG amplitudes from the finger decreased by 68.32 %, while raising the arm increased the systolic amplitude by 69.99 %. These changes in amplitude were attributed to changes in hydrostatic pressure and the veno-arterial reflex. Other morphological variables, such as crest time, were found to be statistically significantly different across hand positions, indicating increased vascular resistance on arm elevation than on dependency. It was hypothesized that these morphological PPG changes were influenced by changes in downstream venous resistance, rather than arterial, or arteriolar, resistance. Changes in hand position relative to heart level can significantly affect the morphology of the peripheral ac PPG waveform. These alterations are due to a combination of physical effects and physiological responses to changes in hand position, which alter vascular resistance. Care should be taken when interpreting morphological data derived from PPG signals and methods should be standardized to take these effects into account.

A new production method of elastic silicone carotid phantom based on MRI acquisition using rapid prototyping technique

In vitro experimental simulations of blood fluid in carotid artery require ideal phantoms that are as precise as possible. The purpose of this work is to demonstrate a method for carotid phantom fabrication by rapid prototyping technique (RP). By using 3D reconstructed projection of the 3D time-of-flight (TOF) Magnetic Resonance Imaging (MRI) sequence, a 12.5 cm multi-dimensional spatial structure of a carotid artery has been set up. Y-shaped and patient specific models have been generated respectively using silicone elastomer, which has a high resilience and a good tensile strength. The final patient specific model has internal carotid artery (ICA) with a highly spiraling siphon and an external carotid artery (ECA). Elastic properties of carotid walls have also been evaluated by Young's elastic modulus test and dynamic behaviors in optical and echography simulation experiments.

Stress-Strain Measurements in Vitrified Arteries Permeated With Synthetic Ice Modulators

This study measures the Young's modulus in vitrified blood vessels below the glass transition temperature in conditions relevant to cryogenic storage and focuses on the cryoprotective agents (CPAs) cocktail DP6 mixed with synthetic ice modulators (SIMs). Small steplike strain changes were observed during the loading without affecting the bulk behavior, suggesting microfracture occurrences resembling previous observation on microfracture formation under compression in crystallized blood vessels. Young's modulus was measured to be 0.92-3.01 GPa, with no clear indication of SIM dependency on the Young's modulus. Instead, the range of values is attributed to variations between specimens of the same species.

Technical Validation of ARTSENS-An Image Free Device for Evaluation of Vascular Stiffness

Vascular stiffness is an indicator of cardiovascular health, with carotid artery stiffness having established correlation to coronary heart disease and utility in cardiovascular diagnosis and screening. State of art equipment for stiffness evaluation are expensive, require expertise to operate and not amenable for field deployment. In this context, we developed ARTerial Stiffness Evaluation for Noninvasive Screening (ARTSENS), a device for image free, noninvasive, automated evaluation of vascular stiffness amenable for field use. ARTSENS has a frugal hardware design, utilizing a single ultrasound transducer to interrogate the carotid artery, integrated with robust algorithms that extract arterial dimensions and compute clinically accepted measures of arterial stiffness. The ability of ARTSENS to measure vascular stiffness in vivo was validated by performing measurements on 125 subjects. The accuracy of results was verified with the state-of-the-art ultrasound imaging-based echo-tracking system. The relation between arterial stiffness measurements performed in sitting posture for ARTSENS measurement and sitting/supine postures for imaging system was also investigated to examine feasibility of performing ARTSENS measurements in the sitting posture for field deployment. This paper verified the feasibility of the novel ARTSENS device in performing accurate in vivo measurements of arterial stiffness. As a portable device that performs automated measurement of carotid artery stiffness with minimal operator input, ARTSENS has strong potential for use in large-scale screening.

Age-related vascular stiffening: causes and consequences

Arterial stiffening occurs with age and is closely associated with the progression of cardiovascular disease. Stiffening is most often studied at the level of the whole vessel because increased stiffness of the large arteries can impose increased strain on the heart leading to heart failure. Interestingly, however, recent evidence suggests that the impact of increased vessel stiffening extends beyond the tissue scale and can also have deleterious microscale effects on cellular function. Altered extracellular matrix (ECM) architecture has been recognized as a key component of the pre-atherogenic state. Here, the underlying causes of age-related vessel stiffening are discussed, focusing on age-related crosslinking of the ECM proteins as well as through increased matrix deposition. Methods to measure vessel stiffening at both the macro- and microscale are described, spanning from the pulse wave velocity measurements performed clinically to microscale measurements performed largely in research laboratories. Additionally, recent work investigating how arterial stiffness and the changes in the ECM associated with stiffening contributed to endothelial dysfunction will be reviewed. We will highlight how changes in ECM protein composition contribute to atherosclerosis in the vessel wall. Lastly, we will discuss very recent work that demonstrates endothelial cells (ECs) are mechano-sensitive to arterial stiffening, where changes in stiffness can directly impact EC health. Overall, recent studies suggest that stiffening is an important clinical target not only because of potential deleterious effects on the heart but also because it promotes cellular level dysfunction in the vessel wall, contributing to a pathological atherosclerotic state.

Peripheral vascular stiffness, assessed with two-dimensional speckle tracking versus the degree of coronary artery calcification, evaluated by tomographic coronary artery calcification index

INTRODUCTION

Even in asymptomatic patients, the result of atherosclerosis progression is deterioration of the function and morphology of the artery wall. Two-dimensional speckle-tracking (2DST) is a sonographic technique that allows for precise evaluation of arterial wall compliance. Together with measurement of intima-media thickness (IMT), it can be applied for quick and non-invasive assessment of the progression of peripheral artery atherosclerosis.

MATERIAL AND METHODS

Fifty-eight patients of mean age 61 years (SD 10.6) underwent cardiac computed tomography (CT) and subsequent ultrasonographic evaluation of the left common carotid artery. The calcium score was calculated according to the Agatston method and compared with IMT, circumferential strain variables assessed by 2DST, conventional arterial stiffness parameters (β-stiffness index and elastic modulus) and clinical data. Intra-observer and inter-observer agreement was evaluated.

RESULTS

Strain variables and IMT differed significantly in patients with calcium score (CS) > 0 and CS = 0. Moreover, they correlated with CS, systolic blood pressure and age of patients. Conventional stiffness parameters were not able to identify the group of patients with calcifications present in the coronary arteries. For the 2DST technique, interclass and intraclass agreements were 84.83% and 94.42% respectively.

CONCLUSIONS

Circumferential strain variables assessed by 2DST and measurement of IMT can be used for evaluation of peripheral artery deterioration in patients until the 6(th) decade of life. These parameters reflect the development of calcifications in coronary arteries and, more importantly, can be used for a more detailed estimation of the atherosclerosis risk in patients with CS = 0.

Image-free evaluation of carotid artery stiffness using ARTSENS: a repeatability study

Evaluation of arterial stiffness is significant in early detection and vascular diagnosis. We have developed and validated an image free system called ARTSENS for evaluation of carotid artery stiffness. In this paper, we present a detailed study on the repeatability of arterial stiffness measurements performed using ARTSENS. The study protocol was designed to emulate typical constraints encountered in field usage of ARTSENS as a screening tool. The intra operator variability (repeatability) of ARTSENS was verified by in-vivo measurements on 18 subjects. Inter operator variability (reproducibility) was also studied. The ability of the instrument to give reliable measurements in both sitting and supine posture of the subject was verified. Further, the variation of arterial stiffness measurements over different times of the day was investigated to verify the ability of the instrument to give a practically usable stable measure of stiffness. The repeatability and reproducibility of ARTSENS measurements was found to be comparable to those provided by state of art image-based systems. Stiffness measurements provided by ARTSENS were found to be stable over a day indicating utility of the instrument in providing a quick and reliable measure of carotid artery stiffness.

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.

A clinically applicable stochastic approach for noninvasive estimation of aortic stiffness using computed tomography data

The degeneration of the vascular wall tissue induces a change of the arterial stiffness, i.e., the capability of the vessel to distend under the pulsatile hemodynamic load. In the literature, the aortic stiffness is usually computed following a simple deterministic approach, in which only the maximum and the minimum values of arterial diameter and blood pressure over the cardiac cycle are considered. In this paper, we propose a stochastic approach to assess the stiffness, and its spatial variation, of a given aortic region exploiting patient-specific geometrical data derived from computed tomography angiography (CTA). In particular, the arterial stiffness is computed linking the aortic kinematic information derived from CTA with pressure waveforms, generated using a lumped parameter model of the arterial circulation. The proposed method is able to include the uncertainty of the input variables as well as to use the entire diameter and blood pressure waveforms over the cardiac cycle rather than only their maximum and minimum values. Although the efficiency and accuracy of the proposed method are tested on a single patient-specific case, the proposed approach is powerful and already possesses the ability to evaluate regional changes of stiffness in human aorta using noninvasive data. The final objective of our paper is to support the adoption of techniques such as CTA as a standard tool for diagnosis and treatment planning of aortic diseases.

Cervical stiffness evaluated in vivo by endoflip in pregnant women

Objective

To determine the stiffness of the pregnant uterine cervix in vivo.

Method

Five women in early pregnancy and six women in late pregnancy were included. The EndoFlip is a 1-m-long probe with a 12-cm-long bag mounted on the tip. The tip of the probe was inserted into the cervical canal. Sensors spaced at 0.5-cm intervals along the probe were used to determine 16 serial cross-sectional areas of the bag. The diameter of the cervical canal could thereby be determined during inflation with up to 50 ml saline solution. Tissue stiffness was calculated from the geometric profiles and the pressure-strain elastic modulus (EP) at each sensor site. Three parts of the cervix were defined: the uterus-near part, the middle and the vaginal part. The EP_max was defined as the highest EP detected along the cervical canal.

Results

The EP_max was always found in the middle part of the cervix. The median EP_max was 243 kPa (IQR, 67–422 kPa) for the early pregnant women and 5 kPa (IQR, 4–15 kPa) for those at term. In the early pregnant women the stiffness differed along the cervical length (p<0.05) whereas difference along the cervix was not found for late pregnant women. A positive correlation coefficient (Spearman’s rho) was established between the EPs of the uterus-near and the middle part (0.84), between the vaginal and the middle part (0.81), and between the uterus-near and the vaginal part (0.85).

Conclusion

This new method can estimate the stiffness along the cervical canal in vivo. This method may be useful in the clinical examination of the biomechanical properties of the uterine cervix.

Feasibility of Crosslinked Acrylic Shape Memory Polymer for a Thrombectomy Device

Purpose

To evaluate the feasibility of utilizing a system of SMP acrylates for a thrombectomy device by determining an optimal crosslink density that provides both adequate recovery stress for blood clot removal and sufficient strain capacity to enable catheter delivery.

Methods

Four thermoset acrylic copolymers containing benzylmethacrylate (BzMA) and bisphenol A ethoxylate diacrylate (Mn~512, BPA) were designed with differing thermomechanical properties. Finite element analysis (FEA) was performed to ensure that the materials were able to undergo the strains imposed by crimping, and fabricated devices were subjected to force-monitored crimping, constrained recovery, and bench-top thrombectomy.

Results

Devices with 25 and 35 mole% BPA exhibited the highest recovery stress and the highest brittle response as they broke upon constrained recovery. On the contrary, the 15 mole % BPA devices endured all testing and their recovery stress (5 kPa) enabled successful bench-top thrombectomy in 2/3 times, compared to 0/3 for the devices with the lowest BPA content.

Conclusion

While the 15 mole% BPA devices provided the best trade-off between device integrity and performance, other SMP systems that offer recovery stresses above 5 kPa without increasing brittleness to the point of causing device failure would be more suitable for this application.

Arterial compliance across the spectrum of ankle-brachial index: the Multiethnic Study of Atherosclerosis

OBJECTIVE

A low ankle-brachial index is associated with cardiovascular disease and reduced arterial compliance. A high ankle-brachial index is also associated with an increased risk of cardiovascular events. We tested the hypothesis that subjects with a high ankle-brachial index demonstrate a lower arterial compliance. In addition, we assessed whether pulse pressure amplification is increased among subjects with a high ankle-brachial index.

METHODS

We studied 6814 adults enrolled in the Multiethnic Study of Atherosclerosis who were, by definition, free of clinical cardiovascular disease at baseline. Differences in total arterial compliance (ratio of stroke volume to pulse pressure), aortic and carotid distensibility (measured with magnetic resonance imaging and duplex ultrasound, respectively) were compared across ankle-brachial index subclasses (≤0.90, 0.91-1.29; ≥1.30) with analyses adjusted for cardiovascular risk factors and subclinical atherosclerosis.

RESULTS

Peripheral arterial disease was detected in 230 (3.4%) and high ABI in 648 (9.6%) of subjects. Those with high ankle-brachial index demonstrated greater aortic/radial pulse pressure amplification than those with a normal ankle-brachial index. In adjusted models aortic and carotid distensibility as well as total arterial compliance, were lowest among those with ankle-brachial index≤0.9 (p<0.01 vs. all), but were not reduced in subjects with an ankle-brachial index≥1.3.

CONCLUSION

Lower aortic, carotid and total arterial compliance is not present in subjects free of overt cardiovascular disease and with a high ankle-brachial index. However, increased pulse pressure amplification contributes to a greater ankle-brachial index in the general population and may allow better characterization of individuals with this phenotype.

Distensibility of the anal canal in patients with idiopathic fecal incontinence: a study with the Functional Lumen Imaging Probe

BACKGROUND

Anatomical structures and their distensibility vary along the length of the anal canal. The anal sphincter muscles have dynamic properties that are not well-reflected by standard manometry. Abnormal distensibility of the anal canal may be of importance in idiopathic fecal incontinence (IFI). The functional lumen imaging probe (FLIP) allows detailed studies of the distensibility and axial variation of sphincters. We aimed at comparing segmental distensibility of the anal canal in patients with IFI and healthy subjects.

METHODS

The FLIP was used for distension of the anal canal in 22 patients with IFI (17 female, age 27-82 years) and 21 healthy volunteers (18 female, age 32-73 years). The distensibility was determined from changes in luminal diameter. Closure of the anal canal during voluntary squeeze was computed as the combined length of closed anal canal and time. Pressure-strain elastic modulus was computed at rest.

KEY RESULTS

In all subjects, the proximal anal canal was the most distensible segment. During distension at rest and during squeeze the middle and distal anal canal became significantly larger in IFI than in healthy (F < 22.4, p < 0.05). The closure of the anal canal during voluntary squeeze did not differ between healthy (75.9 ± 92.9 mm s) and IFI patients (90.4 ± 105 mm s; p = 0.6). Compared with healthy, IFI patients had lower pressure-strain elastic modulus of the middle and distal (q > 4.5, p < 0.05) but not the proximal anal canal (q < 0.7, p > 0.05).

CONCLUSIONS & INFERENCES

Patients with IFI have increased distensibility of the middle and distal parts of the anal canal.

Asymmetric radial expansion and contraction of rat carotid artery observed using a high-resolution ultrasound imaging system

The geometry of carotid artery bifurcation is of high clinical interest because it determines the characteristics of blood flow that is closely related to the formation and development of atherosclerotic plaque. However, information on the dynamic changes in the vessel wall of carotid artery bifurcation during a pulsatile cycle is limited. This pilot study investigated the cyclic changes in carotid artery geometry caused by blood flow pulsation in rats. A high-resolution ultrasound imaging system with a broadband scanhead centered at 40 MHz was used to obtain longitudinal images of the rat carotid artery. A high frame rate retrospective B-scan imaging technique based on the use of electrocardiogram to trigger signal acquisition was used to examine precisely the fast arterial wall motion. Two-dimensional geometry data obtained from nine rats showed that the rat carotid artery asymmetrically contracts and dilates during each cardiac cycle. Systolic/diastolic vessel diameters near the upstream and downstream regions from the bifurcation were 0.976 ± 0.011/0.825 ± 0.015 mm and 0.766 ± 0.015/0.650 ± 0.016 mm, respectively. Their posterior/anterior wall displacement ratios in the radial direction were 41.0 ± 14.9% and 2.9 ± 1.6%, respectively. These results indicate that in the vicinity of bifurcation, the carotid artery favorably expands to the anterior side during the systolic phase. This phenomenon was observed to be more prominent in the downstream region near the bifurcation. The cyclic variation pattern in wall movement varies depending on the measurement site, which shows different patterns at far upstream and downstream of the bifurcation. The asymmetric radial expansion and contraction of the rat carotid artery observed in this study may be useful in studying the hemodynamic etiology of cardiovascular diseases because the pulsatile changes in vessel geometry may affect the local hemodynamics that determines the spatial distribution of wall shear stress, one of important cardiovascular risk factors. Further systematic study is needed to clarify the effects of wall elasticity, branch angle and vessel diameter ratio on the asymmetric wall motion of carotid artery bifurcation.

Association of resting heart rate with carotid and aortic arterial stiffness: multi-ethnic study of atherosclerosis

Resting heart rate is an easily measured, noninvasive vital sign that is associated with cardiovascular disease events. The pathophysiology of this association is not known. We investigated the relationship between resting heart rate and stiffness of the carotid (a peripheral artery) and the aorta (a central artery) in an asymptomatic multi-ethnic population. Resting heart rate was recorded at baseline in the Multi-Ethnic Study of Atherosclerosis (MESA). Distensibility was used as a measure of arterial elasticity, with a lower distensibility indicating an increase in arterial stiffness. Carotid distensibility was measured in 6484 participants (98% of participants) using B-mode ultrasound, and aortic distensibility was measured in 3512 participants (53% of participants) using cardiac MRI. Heart rate was divided into quintiles and we used progressively adjusted models that included terms for physical activity and atrioventricular nodal blocking agents. Mean resting heart rate of participants (mean age, 62 years; 47% men) was 63 bpm (SD, 9.6 bpm). In unadjusted and fully adjusted models, carotid distensibility and aortic distensibility decreased monotonically with increasing resting heart rate (P for trend <0.001 and 0.009, respectively). The relationship was stronger for carotid versus aortic distensibility. Similar results were seen using the resting heart rate taken at the time of MRI scanning. Our results suggest that a higher resting heart rate is associated with an increased arterial stiffness independent of atrioventricular nodal blocker use and physical activity level, with a stronger association for a peripheral (carotid) compared with a central (aorta) artery.

Progression of arterial stiffness and coronary atherosclerosis: longitudinal evaluation by cardiac CT

OBJECTIVE

We sought to use cardiac CT angiography (CTA) to longitudinally examine the relationship between changes in aortic stiffness and of the atherosclerotic burden over time.

MATERIALS AND METHODS

One hundred sixty-four patients with suspected coronary artery disease underwent two retrospectively ECG-gated cardiac CTA studies an average of 12 ± 10 months apart. Arterial stiffness was represented by the aortic distensibility index (ADI) and atherosclerosis by segment involvement score (SIS) (defined as the number of coronary artery segments per patient displaying atherosclerotic plaque). Changes in ADI and SIS between the studies were compared using linear and logistic regression accounting for differences in clinical and demographic baseline characteristics.

RESULTS

Age (p = 0.004), time between studies (p = 0.02), and increase in SIS (p < 0.001) were associated with a decrease in ADI on univariate analysis. Increase in SIS remained a significant independent predictor of decreased ADI on both multivariate logistic regression (with change in ADI represented categorically) and multivariate linear regression (both p < 0.001).

CONCLUSION

On longitudinal evaluation with cardiac CTA, the progression of aortic stiffness is associated with the progression of coronary atherosclerosis. Although outcome studies are needed, a comprehensive assessment of vascular health with cardiac CTA, including both indexes of arterial stiffness and atherosclerotic burden, may improve risk stratification and therapy monitoring.

Effect of velocity profile skewing on blood velocity and volume flow waveforms derived from maximum Doppler spectral velocity

Given evidence that fully developed axisymmetric flow may be the exception rather than the rule, even in nominally straight arteries, maximum velocity (V(max)) can lie outside the Doppler sample volume (SV). The link between V(max) and derived quantities, such as volume flow (Q), may therefore be more complex than commonly thought. We performed idealized virtual Doppler ultrasound on data from image-based computational fluid dynamics (CFD) models of the normal human carotid artery and investigated how velocity profile skewing and choice of sample volume affected V(max) waveforms and derived Q variables, considering common assumptions about velocity profile shape (i.e., Poiseuille or Womersley). Severe velocity profile skewing caused substantial errors in V(max) waveforms when using a small, centered SV, although peak V(max) was reliably detected; errors with a long SV covering the vessel diameter were orientation dependent but lower overall. Cycle-averaged Q calculated from V(max) was typically within ±15%, although substantial skewing and use of a small SV caused 10%-25% underestimation. Peak Q derived from Womersley's theory was generally accurate to within ±10%. V(max) pulsatility and resistance indexes differed from Q-based values, although the Q-based resistance index could be predicted reliably. Skewing introduced significant error into V(max)-derived Q waveforms, particularly during mid-to-late systole. Our findings suggest that errors in the V(max) and Q waveforms related to velocity profile skewing and use of a small SV, or orientation-dependent errors for a long SV, could limit their use in wave analysis or for constructing characteristic or patient-specific flow boundary conditions for model studies.

Hyperglycemia and arterial stiffness: the Atherosclerosis Risk in the Communities study

OBJECTIVES

Hyperglycemia has been associated with an increased risk of cardiovascular morbidity and mortality. Although numerous studies have demonstrated that hyperglycemia is associated with the atherosis component of atherosclerosis, limited studies have addressed the independent role of hyperglycemia in the pathophysiology of sclerotic vascular disease. We hypothesized that hyperglycemia, as assessed by hemoglobin A1c (HbA1c), would be independently associated two common indices of arterial stiffness (pressure-strain elastic modulus (Ep) and Young's elastic modulus (YEM)).

METHODS

We examined the cross-sectional association between HbA1c and arterial stiffness using B-mode ultrasound examination of the carotid artery in 9050 participants from the community-based Atherosclerosis Risk in Communities (ARIC) study. We used multivariable linear and logistic regression models to characterize the association between HbA1c and increased Ep and YEM.

RESULTS

Higher values of HbA1c were associated in a graded fashion with increased arterial stiffness (P-trend < 0.001 for both EP and YEM). After adjusting for traditional risk factors, increasing HbA1c deciles were significantly associated with elevated EP (OR for the highest decile of HbA1c compared to the lowest, 2.01, 95% CI: 1.30, 3.11) and YEM (OR = 1.71, 95% CI: 1.15, 2.55).

CONCLUSION

Elevated HbA1c is associated with measures of increased arterial stiffness, even after accounting for arterial wall thickness. This is consistent with the hypothesis that hyperglycemia contributes to arterial stiffness beyond its effects on atherosis and suggests that hyperglycemia is associated with altered material within the arterial wall.

Longitudinal displacement of the carotid wall and cardiovascular risk factors: associations with aging, adiposity, blood pressure and periodontal disease independent of cross-sectional distensibility and intima-media thickness

The recently discovered longitudinal displacement of the common carotid arterial wall (i.e., the motion along the same plane as the blood flow), may be associated with incident cardiovascular events and represents a novel and relevant clinical information. At present, there have only been a few studies that have been conducted to investigate this longitudinal movement. We propose here a method to assess noninvasively the wall bi-dimensional (two-dimensional [2-D], cross-sectional and longitudinal) motion and present an original approach that combines a robust speckle tracking scheme to guidance by minimal path contours segmentation. Our method is well suited to large clinical population studies as it does not necessitate strong imaging prerequisites. The aim of this study is to describe the association between the longitudinal displacement of the carotid arterial wall and cardiovascular risk factors, among which periodontal disease. Some 126 Indigenous Australians with periodontal disease, an emerging risk factor, and 27 healthy age- and sex-matched non-indigenous control subjects had high-resolution ultrasound scans of the common carotid artery. Carotid intima-media thickness and arterial wall 2-D motion were then assessed using our method in ultrasound B-mode sequences. Carotid longitudinal displacement was markedly lower in the periodontal disease group than the control group (geometric mean (IQR): 0.15 mm (0.13) vs. 0.42 mm (0.30), respectively; p < 0.0001), independent of cardiovascular risk factors, cross-sectional distensibility and carotid intima-media thickness (p < 0.0001). A multivariable model indicated that the strongest correlates of carotid longitudinal displacement in adults with periodontal disease were age (β-coefficient = -.235, p = .03), waist (β-coefficient = -.357, p = 0.001), and pulse pressure (β-coefficient = .175, p = 0.07), independent of other cardiovascular risk factors, cross-sectional distensibility and pulse wave velocity. Carotid longitudinal displacement, estimated with our approach, is impaired in the periodontal disease group, independent of established cardiovascular risk factors and other noninvasive measures of arterial stiffness, and may represent an important marker of cardiovascular risk.

A knowledge-based approach to arterial stiffness estimation using the digital volume pulse

We have developed a knowledge based approach for arterial stiffness estimation. The proposed new approach reliably estimates arterial stiffness based on the analysis of age and heart rate normalized reflected wave arrival time. The proposed new approach reduces cost, space, technical expertise, specialized equipment, complexity, and increases the usability compared to recently researched noninvasive arterial stiffness estimators. The proposed method consists of two main stages: pulse feature extraction and linear regression analysis. The new approach extracts the pulse features and establishes a linear prediction equation. On evaluating proposed methodology with pulse wave velocity (PWV) based arterial stiffness estimators, the proposed methodology offered the error rate of 8.36% for men and 9.52% for women, respectively. With such low error rates and increased benefits, the proposed approach could be usefully applied as low cost and effective solution for ubiquitous and home healthcare environments.

Arterial function of carotid and brachial arteries in postmenopausal vegetarians

Background:

Vegetarianism is associated with a lower risk of cardiovascular disease. However, studies of arterial function in vegetarians are limited.

Methods:

This study investigated arterial function in vegetarianism by comparing 49 healthy postmenopausal vegetarians with 41 age-matched omnivores. The arterial function of the common carotid artery was assessed by carotid duplex, while the pulse dynamics method was used to measure brachial artery distensibility (BAD), compliance (BAC), and resistance (BAR). Fasting blood levels of glucose, lipids, lipoprotein (a), high-sensitivity C-reactive protein, homocysteine, and vitamin B12 were also measured.

Results:

Vegetarians had significantly lower serum cholesterol, high-density and low-density lipoprotein, and glucose compared with omnivores. They also had lower vitamin B12 but higher homocysteine levels. Serum levels of lipoprotein (a) and high-sensitivity C-reactive protein were no different between the two groups. There were no significant differences in carotid beta stiffness index, BAC, and BAD between the two groups even after adjustment for associated covariates. However, BAR was significantly lower in vegetarians than in omnivores. Multiple linear regression analysis revealed that age and pulse pressure were two important determinants of carotid beta stiffness index and BAD. Vegetarianism is not associated with better arterial elasticity.

Conclusion:

Apparently healthy postmenopausal vegetarians are not significantly better in terms of carotid beta stiffness index, BAC, and BAD, but have significantly decreased BAR than omnivores. Prevention of vitamin B12 deficiency might be beneficial for cardiovascular health in vegetarians.

Long-term exposure to airborne particles and arterial stiffness: the Multi-Ethnic Study of Atherosclerosis (MESA)

BACKGROUND

Increased arterial stiffness could represent an intermediate subclinical outcome in the mechanistic pathway underlying associations between average long-term pollution exposure and cardiovascular events.

OBJECTIVE

We hypothesized that 20 years of exposure to particulate matter (PM) ≤ 2.5 and 10 μm in aerodynamic diameter (PM2.5 and PM10, respectively) would be positively associated with arterial stiffness in 3,996 participants from the Multi-Ethnic Study of Atherosclerosis (MESA) who were seen at six U.S. study sites.

METHODS

We assigned pollution exposure during two decades preceding a clinical exam (2000-2002) using observed PM10 from monitors nearest participants' residences and PM10 and PM2.5 imputed from a space-time model. We examined three log-transformed arterial stiffness outcome measures: Young's modulus (YM) from carotid artery ultrasound and large (C1) and small (C2) artery vessel compliance from the radial artery pulse wave. All associations are expressed per 10 μg/m3 increment in PM and were adjusted for weather, age, sex, race, glucose, triglycerides, diabetes, waist:hip ratio, seated mean arterial pressure, smoking status, pack-years, cigarettes per day, environmental tobacco smoke, and physical activity. C1 and C2 models were further adjusted for heart rate, weight, and height.

RESULTS

Long-term average particle exposure was not associated with greater arterial stiffness measured by YM, C1, or C2, and the few associations observed were not robust across metrics and adjustment schemes.

CONCLUSIONS

Long-term particle mass exposure did not appear to be associated with greater arterial stiffness in this study sample.

Pericardial fat is associated with carotid stiffness in the Multi-Ethnic Study of Atherosclerosis

BACKGROUND AND AIMS

Arterial stiffness is a prominent feature of vascular aging and a risk factor for cardiovascular disease (CVD). Fat around the heart and blood vessels (i.e. pericardial fat, Pfat) may contribute to arterial stiffness via a local paracrine effect of adipose tissue on the surrounding vasculature. Thus, we determined the association between Pfat and carotid stiffness in 5770 participants (mean age 62 years, 53% female, 25% African American, 24% Hispanic, and 13% Chinese) from the Multi-Ethnic Study of Atherosclerosis.

METHODS AND RESULTS

Pfat was measured by computed tomography, and ultrasonography of the common carotid artery was used to calculate the distensibility coefficient (DC) and Young's modulus (YM). Lower DC and higher YM values indicate stiffer arteries. Pfat quartile was highly associated with demographic, behavioral, anthropometric, hemodynamic, metabolic, and disease variables in both men and women. After adjusting for height, clinical site, CVD risk factors, and medications, a 1 standard deviation (41.91 cm(3)) increment in Pfat was associated with a 0.00007±0.00002 1/mm Hg lower DC (p=0.0002) in men and a 48.1±15.1 mm Hg/mm higher YM in women (p=0.002). Additional adjustment for C-reactive protein, coronary artery calcification, and carotid intima-media thickness had only modest effects. More importantly, adjusting for body mass index and waist circumference did not significantly change the overall results.

CONCLUSION

Higher Pfat is associated with higher carotid stiffness, independent of traditional CVD risk factors and obesity.

A method for arterial diameter change measurements using ultrasonic B-mode data

Arterial diameter change is related to distending blood pressure and is used in estimation of arterial stiffness parameters. A common technique to track the arterial walls is by integration of wall velocities estimated by different methods using cross correlation or tissue Doppler. However, because of the high pulse repetition frequency and the need for separate pulsing sequences, the B-mode image quality is affected. We have previously developed a fast algorithm for direct measurement of lumen diameter using B-mode images. In this study we have improved the technique to be more robust and also implemented measurements of diameter change, maximum differential wall velocity and relative diameter change of the common carotid artery noninvasively in vivo. The influence of the lateral width of the region of interest (ROI; 1 pixel, 0.1 mm, 0.5 mm, 1 mm, 2.5 mm and 5 mm) was evaluated. Using the optimal lateral width (2.5 mm), the systematic and random differences between two consecutive measurements were 21 microm and 105 microm, respectively, for lumen diameter measurement; -7 microm and 39 microm, respectively, for lumen diameter change measurements; -0.2 mm/s and 0.9 mm/s, respectively, for maximum relative wall velocity; and -0.2 % and 0.8 %, respectively, for measurements of the relative diameter change. The coefficient of variation (CV) was 1.9%, 5.2%, 7.9% and 6.0%, respectively. The study indicates that the reproducibility is sufficient for in vivo studies when the width of the ROI is 1.0 mm or wider.

Thoracic aortic distensibility and thoracic aortic calcium (from the Multi-Ethnic Study of Atherosclerosis [MESA])

Decreased arterial distensibility is an early manifestation of adverse structural and functional changes within the vessel wall. Its correlation with thoracic aortic calcium (TAC), a marker of atherosclerosis, has not been well demonstrated. We tested the hypothesis that decreasing aortic compliance and increasing arterial stiffness would be independently associated with increased TAC. We included 3,540 subjects (61 +/- 10 years, 46% men) from the Multi-ethnic Study of Atherosclerosis who had undergone an aortic distensibility (AD) assessment using magnetic resonance imaging. TAC was calculated using a modified Agatston algorithm on noncontrast cardiac computed tomographic scans. Multivariate regression models were calculated for the presence of TAC. Overall, 861 subjects (24%) had detectable TAC. Lower AD was observed among those with versus without TAC (2.02 +/- 1.34 vs 1.28 +/- 0.74, p <0.0001). The prevalence of TAC increased significantly across decreasing quartiles of AD (7%, 17%, 31%, and 42%, p <0.0001). Using multivariate analysis, TAC was independently associated with AD after adjusting for age, gender, ethnicity, and other covariates. In conclusion, our analysis has demonstrated that increased arterial stiffness is associated with increased TAC, independent of ethnicity and other atherosclerotic risk factors.

Noninvasive measures of vascular health are reliable in preschool-aged children

Measures of vascular health are known to be important predictors of cardiovascular disease in adulthood. The reliability of commonly used measures of vascular health has been demonstrated in school-aged children, adolescents, and adults; however, their reliability in preschool-aged children remains to be determined. Twenty 2- to 6-year-old children participated in 2 identical testing sessions on different days. Following 10 min of supine rest, carotid artery blood pressures and common carotid artery images were assessed simultaneously for 10 heart cycles, using applanation tonometry and B-mode ultrasound, respectively, while electrocardiogram (ECG) and infrared measures of arterial pressure waves at the dorsalis pedis were recorded continuously. Brachial artery blood pressures were determined using an automated oscillometric device. Carotid artery diameters and intima-media thickness (IMT) were analyzed using a semiautomated detection software program. Carotid compliance, distensibility, and stiffness index were calculated from carotid diameters and carotid blood pressures. Whole-body pulse-wave velocity (PWV) was determined from the time delay between the R spike of the ECG and the foot of the dorsalis pedis arterial pressure wave. Reliability of all measures was assessed using the coefficient of variation (CV) and the intraclass correlation coefficient (ICC). The most reliable measures were carotid artery IMT and PWV with CVs of 2.6% and 3.5% and ICCs of 0.86 and 0.76, respectively. The lower reliability of carotid compliance and distensibility (ICC ≤ 0.63) is likely attributable to the variability of blood pressure measurements. This study confirms that vascular measurements demonstrate substantial reliability in preschool-aged children as young as 2 years.

Ultrasonographic strain imaging is superior to conventional non-invasive measures of vascular stiffness in the detection of age-dependent differences in the mechanical properties of the common carotid artery

AIMS

Elastic properties of large arteries have been shown to deteriorate with age and in the presence of atherosclerotic vascular disease. In this study, the performance of ultrasonographic strain measurements was compared with conventional measures of vascular stiffness in the detection of age-dependent differences in the elastic properties of the common carotid artery (CCA).

METHODS AND RESULTS

In 10 younger (25-28 years, four women) and 10 older (50-59 years, four women) healthy individuals, global and regional circumferential, and radial strain variables were measured in the short-axis view of the right CCA using ultrasonographic two-dimensional (2D) strain imaging with recently introduced speckle tracking technique. Conventional elasticity variables, elastic modulus (E(p)), and beta stiffness index, were calculated using M-mode sonography and non-invasive blood pressure measurements. Global and regional circumferential systolic strain and strain rate values were significantly higher (P < 0.01 for regional late systolic strain rate, P < 0.001 otherwise) in the younger individuals, whereas the values of conventional stiffness variables in the same group were lower (P < 0.05). Among all strain and conventional stiffness variables, principal component analysis and its regression extension identified only circumferential systolic strain variables as contributing significantly to the observed discrimination between the younger and older age groups.

CONCLUSION

Ultrasonographic 2D-strain imaging is a sensitive method for the assessment of elastic properties in the CCA, being in this respect superior to the conventional measures of vascular stiffness. The method has potential to become a valuable non-invasive tool in the detection of early atherosclerotic vascular changes.

Increased arterial stiffness in children and adolescents with type 1 diabetes: no association between arterial stiffness and serum levels of adiponectin

OBJECTIVE

Type 1 diabetes is associated with an increased risk of atherosclerosis. Adiponectin serum levels correlate inversely with cardiovascular disease in adults. The aim of this study was to examine associations between arterial stiffness indices and serum adiponectin concentrations in children and adolescents with type 1 diabetes and to study the impact of metabolic control.

SUBJECTS AND METHODS

We evaluated arterial stiffness, distensibility, and compliance in 93 children and adolescents with type 1 diabetes and correlated the data with clinical parameters and HbA1c levels. The control group comprised 85 matched healthy children. Serum levels of adiponectin in children with diabetes were measured by enzyme-linked immunoassay and correlated with arterial stiffness indices.

RESULTS

Arterial stiffness was significantly increased in children and adolescents with type 1 diabetes (aged 13.0 +/- 3.8 yr) compared with matched healthy children (p = 0.03). Arterial stiffness was elevated in males with type 1 diabetes compared with females (p = 0.023). Arterial distensibility was significantly lower in children with diabetes compared with healthy controls (p = 0.025). Arterial stiffness, distensibility, and compliance did not correlate with diabetes duration, level of HbA1c, or serum cholesterol. Adiponectin concentrations in children and adolescents with diabetes were significantly elevated compared with normal values based on gender, age, and body mass index. We found no significant associations between arterial stiffness indices and adiponectin levels in children with type 1 diabetes.

CONCLUSIONS

Children and adolescents with type 1 diabetes had increased arterial stiffness and reduced arterial distensibility and arterial compliance. However, no associations between arterial functional alterations and adiponectin concentrations were seen.

Optimization of MR phase-contrast-based flow velocimetry and shear stress measurements

This study was designed to measure the pixel-by-pixel flow velocity and shear stress from phase-contrast MR images. An optimized method was suggested and the use of the method was confirmed. A self-developed, straight steady flow model system was scanned by MRI with a velocity-encoded phase-contrast sequence. In-house developed software was used for the pixel-by-pixel flow velocity and shear stress measurements and the measurements were compared with physically measured mean velocity and shear stress. A comparison between the use of the in-house velocimetry software and a commercial velocimetry system was also performed. Curved steady flow models were scanned by phase-contrast MRI. Subsequently, velocity and shear stress were measured to confirm the shifted peak flow velocity and shear stress toward the outer side of the lumen. Peak velocity and shear stress were calculated for both the inner and outer half of the lumen and were statistically compared. The mean velocity measured with the use of in-house software had a significant correlation with the physical measurements of mean velocity; in addition, the measurement was more precise compared to the commercial system (R(2) = 0.85 vs. 0.75, respectively). The calculated mean shear stress had a significant correlation with the physical measurements of mean shear stress (R(2) = 0.95). The curved flow model showed a significantly shifted peak velocity and shear stress zones toward the outside of the flow (P < 0.0001). The technique to measure pixel-by-pixel velocity and shear stress of steady flow from velocity-encoded phase-contrast MRI was optimized. This technique had a good correlation with physical measurements and was superior to a commercially available system.

Relationship of carotid distensibility and thoracic aorta calcification: multi-ethnic study of atherosclerosis

Stiffening of the central elastic arteries is one of the earliest detectable manifestations of adverse change within the vessel wall. Although an association between carotid artery stiffness and adverse events has been demonstrated, little is known about the relationship between stiffness and atherosclerosis. Even less is known about the impact of age, sex, and race on this association. To elucidate this question, we used baseline data from the Multi-Ethnic Study of Atherosclerosis (2000-2002). Carotid artery distensibility coefficient was calculated after visualization of the instantaneous waveform of the common carotid diameter using a high-resolution B-mode ultrasound. Thoracic aorta calcification was identified using noncontrast cardiac computed tomography. We found a strong association between decreasing distensibility coefficient (increasing carotid stiffness) and increasing thoracic aorta calcification, as well as a graded increase in the thoracic aorta calcification score (P<0.001). After controlling for age, sex, race, and traditional and emerging cardiovascular risk factors, individuals in the stiffest quartile had a prevalence ratio of 1.52 (95% CI: 1.15 to 2.00) for thoracic aorta calcification compared with the least stiff quartile. In exploratory analysis, carotid stiffness was more highly correlated with calcification of the aorta than calcification of the coronary arteries (rho=0.32 versus 0.22; P<0.001 for comparison). In conclusion, there is a strong independent association between carotid stiffness and thoracic aorta calcification. Carotid stiffness is more highly correlated with calcification of the aorta, a central elastic artery, than calcification of the coronary arteries. The prognostic significance of these findings requires longitudinal follow-up of the Multi-Ethnic Study of Atherosclerosis cohort.

Measurement of common carotid artery lumen dynamics during the cardiac cycle using magnetic resonance TrueFISP cine imaging

PURPOSE

To demonstrate magnetic resonance (MR) measurements of vascular lumen dynamics in common carotid arteries by using true fast imaging with steady-state precession (TrueFISP) cine imaging with an aim to provide additional physiologic information on the vessels.

MATERIALS AND METHODS

The left and right common carotid arteries were studied in normal young men (N = 6; age = 21-24 years; body weight = 130-175 lbs) using electrocardiogram (ECG)-triggered TrueFISP cine imaging at 20 frames per cardiac cycle. Lumen area waveforms were characterized with specific time and amplitude ratios. Distension values were quantified.

RESULTS

Distension values were measured at 25.92 +/- 2.58% and 27.58 +/- 4.44% for the left and right common carotid arteries, respectively. These findings are consistent with those previously documented using ultrasound imaging in a similar age group. Consistent lumen area waveform characteristics were found among the subjects studied.

CONCLUSION

These findings demonstrate for the first time that the use of TrueFISP cine imaging is a robust, rapid technique for quantifying carotid lumen area dynamics and distension, which may be valuable in characterizing and diagnosing cardiovascular diseases.

Abdominal aortic wall motion of healthy and hypertensive subjects: evaluation of tissue Doppler velocity imaging

PURPOSE

To investigate the potential clinical application of tissue Doppler imaging (TDI) for motion measurement of the aortic wall in healthy and hypertensive adults.

METHOD

We used TDI to examine 53 hypertensive and 29 sex-matched healthy adults. Maximum velocity of the first and second systolic wall expansion peaks (S1, S2), maximum velocity of early (D) and end (E) diastolic retraction velocity peaks, pulse wave transmit time (PWTT), and stiffness index (beta) of the abdominal aorta were measured and compared as for factors influencing vascular compliance, including age, sex, and blood pressure.

RESULTS

Compared with the healthy subjects, the wall motion waveform of hypertensive patients showed absent E, mixed S1 and S2 peaks, and blunted S1. S1 and D were lower in hypertensive than in healthy subjects. Shortened PWTT and increased indicated increased aortic stiffness in both male and female hypertensive subects when compared with controls. Age, diastolic blood pressure (DBP) and sex were the significant independent factors modulating S1, while DBP and age were the significant independent factors modulating D. PWTT was independently influenced by age and systolic blood pressure.

CONCLUSION

This study provides evidence that abdominal aortic wall motion measurement with TDI could demonstrate qualitative and quantitative wall motion features differentiating hypertensive from healthy adults. Wall motion velocity and PWTT could reflect abdominal aortic compliance changes related to age, sex, and blood pressure.

Derivation of the distensibility coefficient using tissue Doppler as a marker of arterial function

To date, the main cardiovascular application of TDI (tissue Doppler imaging) has been in myocardial evaluation. In the present study, we investigated the feasibility and reproducibility of assessing arterial elasticity using the DC (distensibility coefficient) measured by TDI, the correlation of this with the DC obtained by other methods and the DC in patients with various degrees of cardiovascular risk. We studied 450 subjects (256 men; age, 51±10 years) with and without risk factors of cardiovascular disease. Arterial displacement was measured from TDI, and B-mode and M-mode images of the common carotid artery in the longitudinal plane, and the DC with each method was compared. Linear regression showed a good correlation between all three methods. The results for TDI and B-mode were comparable [(21±10) compared with (21±10)×10−3/kPa respectively; P=not significant], but there were significant differences between TDI and M-mode [(21±10) compared with (31±13)×10−3/kPa respectively; P<0.0001] and between B-mode and M-mode [(21±10) compared with (31±13)×10−3/kPa respectively; P<0.0001]. Similarly, Bland–Altman analysis showed the least variability in the DC between TDI and B-mode, and there were no significant differences between the average measurements. The TDI DC also had the lowest paired difference for inter-observer variability [(−0.1±1.1)×10−3/kPa; P=not significant]. In conclusion, the results of the present study suggest that TDI of the carotid arteries is feasible, comparable with B-mode measurements, more robust than M-mode and less variable than the other methods.

A reproducibility study of a TDI-based method to calculate indices of arterial stiffness

The aim of the study was to investigate the reproducibility of estimation of Young's modulus E and pressure strain elastic modulus Ep, derived from a tissue Doppler imaging (TDI) wall motion technique. Healthy subjects had their arteries insonated at the same sitting by two different observers and at two different sittings by the same observer. From 32 subjects in the reproducibility study, within-scan coefficient of variation (CV) was 4.5%. Intraobserver between-scan CV for E was 12.7% and for Ep 11.0%. Interobserver CVs were 8.3% and 9.3%, respectively. TDI is a reproducible, valid and highly sensitive direct assessment of arterial wall parameters. It is at least as reproducible as other ultrasound based methods for assessing arterial stiffness and also provides increased information about the arterial distension waveform.

Large-vessel distensibility measurement with electrocardiographically gated multidetector CT: phantom study and initial experience

The purpose of this study was to prospectively examine vessel distensibility measurements by using electrocardiographically gated multidetector computed tomography (CT) in a phantom compared with measurements by using a digital camera and to examine feasibility in humans. Large-vessel phantoms were constructed, using a pulsatile flow pump, and absolute diameter and percentage diameter changes during pulsation were measured. After institutional review board approval and patient consent were obtained, the abdominal aorta of four patients was scanned with an electrocardiographically gated CT protocol. The mean difference in percentage diameter change between CT and optical measurements for the phantom ranged from -0.47% to 0.14%. The range of area changes in five locations along the abdominal aorta in four patients was 2.97%-37.16%. Findings of this study indicate that electrocardiographically gated CT angiography data reconstructed across cardiac phases permit measurements of large-vessel distensibility in a phantom model and that vessel distensibility measurement in humans may be possible.

Physical properties of tissues relevant to arterial ultrasound imaging and blood velocity measurement

A review was undertaken of physical phenomena and the values of associated physical quantities relevant to arterial ultrasound imaging and measurement. Arteries are multilayered anisotropic structures. However, the requirement to obtain elasticity measurements from the data available using ultrasound imaging necessitates the use of highly simplified constitutive models involving Young's modulus, E. Values of E are reported for healthy arteries and for the constituents of diseased arteries. It is widely assumed that arterial blood flow is Newtonian. However, recent studies suggest that non-Newtonian behavior has a strong influence on arterial flow, and the balance of published evidence suggests that non-Newtonian behavior is associated primarily with red cell deformation rather than with aggregation. Hence, modeling studies should account for red cell deformation and the shear thinning effect that this produces. Published literature in healthy adults gives an average hematocrit and high-shear viscosity of 0.44 +/- 0.03 and 3.9 +/- 0.6 mPa.s, respectively. Published data on the acoustic properties of arteries and blood is sufficiently consistent between papers to allow compilation and derivation of best-fit equations summarizing the behavior across a wide frequency range, which then may be used in future modeling studies. Best-fit equations were derived for the attenuation coefficient vs. frequency in whole arteries (R(2) = 0.995), plasma (R(2) = 0.963) and blood with hematocrit near 45% (R(2) = 0.999), and for the backscatter coefficient vs. frequency from blood with hematocrit near 45% (R(2) = 0.958).

Insulin resistance, the metabolic syndrome, diabetes, and cardiovascular disease risk in women with PCOS

Polycystic ovary syndrome is the most common endocrinopathy of reproductive aged women affecting 6-10% of the population. Traditionally considered a reproductive disorder manifesting as chronic anovulation, infertility, and hyperandrogenism, management has primarily focused on short-term reproductive outcomes. Recently, however, significant metabolic aspects in conjunction with longer-term health sequealae of PCOS have been recognized. The metabolic features are primarily related to underlying insulin resistance (IR), which is now understood to play an important role in both the pathogenesis and long-term sequelae of PCOS.

Insulin resistance, the metabolic syndrome, diabetes, and cardiovascular disease risk in women with PCOS

Polycystic ovary syndrome is the most common endocrinopathy of reproductive aged women affecting 6-10% of the population. Traditionally considered a reproductive disorder manifesting as chronic anovulation, infertility, and hyperandrogenism, management has primarily focused on short-term reproductive outcomes. Recently, however, significant metabolic aspects in conjunction with longer-term health sequealae of PCOS have been recognized. The metabolic features are primarily related to underlying insulin resistance (IR), which is now understood to play an important role in both the pathogenesis and long-term sequelae of PCOS.

Common carotid arterial stiffness and the risk of ischaemic stroke

In the present case-control study we aimed to investigate the association of common carotid arterial (CCA) stiffness with ischaemic stroke (IS) and to determine whether this relationship was independent of conventional risk factors including CCA intima-media thickness (CCA-IMT). CCA distensibility, defined as the change of CCA-diameter during the cardiac cycle, and CCA-IMT were evaluated by means of high-resolution B-mode carotid ultrasound examination in consecutive, first-ever IS patients (n=193) and in age- and sex-matched control subjects (n=106). The CCA distensibility (inverse of CCA stiffness) was significantly (P=0.007) lower in IS (0.353 mm, 95% CI: 0.326-0.379) than in control subjects (0.415 mm, 95% CI: 0.378-0.451) even after adjusting for blood pressure values, diastolic CCA-diameter and height. The multivariate logistic regression procedure selected CCA-IMT and CCA distensibility as the only independent predictor variables of IS. Each 1 SD increase in the CCA-IMT and each 1 SD decrease in the CCA distensibility independently increased the likelihood of IS by 167.0% (OR: 2.67, 95% CI: 1.80-3.96, P<0.001) and 59.0% (OR: 1.59, 95% CI: 1.22-2.07, P=0.001) respectively. Increased CCA stiffness is associated with IS independent of conventional risk factors and CCA-IMT. The causal interrelationship between the elastic properties of the CCA and the risk of stroke deserves further investigation by longitudinal studies.