In recent years, great emphasis has been placed on the role of arterial stiffness in the development of cardiovascular diseases. Indeed, the assessment of arterial stiffness is increasingly used in the clinical assessment of patients. Although several papers have previously addressed the methodological issues concerning the various indices of arterial stiffness currently available, and their clinical applications, clinicians and researchers still report difficulties in selecting the most appropriate methodology for their specific use. This paper summarizes the proceedings of several meetings of the European Network for Non-invasive Investigation of Large Arteries and is aimed at providing an updated and practical overview of the most relevant methodological aspects and clinical applications in this area.

Expert consensus document on arterial stiffness: methodological issues and clinical applications

Expert consensus document on arterial stiffness : methodological issues and clinical applications. Commentary

The Rotterdam study

Background— Arterial stiffness has been associated with the risk of cardiovascular disease in selected groups of patients. We evaluated whether arterial stiffness is a predictor of coronary heart disease and stroke in a population-based study among apparently healthy subjects. Methods and Results— The present study included 2835 subjects participating in the third examination phase of the Rotterdam Study. Arterial stiffness was measured as aortic pulse wave velocity and carotid distensibility. Cox proportional hazards regression analysis was performed to compute hazard ratios. During follow-up, 101 subjects developed coronary heart disease (mean follow-up period, 4.1 years), and 63 subjects developed a stroke (mean follow-up period, 3.2 years). The risk of cardiovascular disease increased with increasing aortic pulse wave velocity index. Hazard ratios and corresponding 95% CIs of coronary heart disease for subjects in the second and third tertiles of the aortic pulse wave velocity index compared with subj...

Arterial Stiffness and Risk of Coronary Heart Disease and Stroke: The Rotterdam Study

The Society for Vascular Surgery practice guidelines on the care of patients with an abdominal aortic aneurysm

Doppler signal processing cannot only be employed to detect the local blood velocity as function of time, but also to assess transcutaneously the displacement of the arterial walls during the cardiac cycle (distension waveform) and, hence, the time-dependent changes in arterial diameter relative to its initial diameter at the start of a cardiac cycle. The distension waveform normalized with respect to the local pulse pressure provides useful information about the local elasticity of the arterial wall. The displacement of the arterial wall can be obtained by processing the RF-signals within a sample volume coinciding with the arterial wall. To evaluate this method a dedicated high-speed memory system has been developed storing the RF-signal, as obtained with a conventional echo-imager in M-mode, over a number of successive sweeps covering a selected depth range. The data are transferred line after line to a personal computer (PC) and processed on the fly, thereby relieving the memory requirements of the PC. It can be concluded that a RF-signal memory in combination with a PC provides a useful tool to extract detailed diameter waveforms from the RF-signals obtained. Although the system does not process the signals in real-time the process can be considered to be on-line since the results become available within one minute after the acquisition of the data is completed.

Assessment of the distensibility of superficial arteries.

The Young's modulus of an arterial segment, a measure of the elastic properties of the arterial wall, requires the simultaneous and local assessment of pulse pressure, wall thickness, diameter, and distensibility (relative increase in cross-sectional area per change in blood pressure). The diameter and relative increase in cross-sectional area can be obtained with a wall track system, processing the radiofrequency (r.f.) ultrasound signals received along a single line of observation (M-line processing). It will be demonstrated that it is feasible to combine, in a single measurement, the assessment of wall thickness and the (relative change in) diameter involving a minimum of user interaction. Phantom tests show a standard error of the estimate for intima-media thickness measurements of less than 20 μm; in vivo registrations exhibit a variation on the order of 45 μm. It is concluded that processing of the radiofrequency ultrasound signal, acquired along an M-line, provides an accurate and time-efficient alternative for videoprocessing of 2-dimensional B-mode ultrasound images to estimate artery wall thickness.

Automated detection of local artery wall thickness based on M-line signal processing.

An integrated system for the non-invasive assessment of vessel wall and hemodynamic properties of large arteries by means of ultrasound

Objectives: It has been postulated that in the arterial system mean wall shear stress is maintained at a constant value. The present study was performed to investigate the level of wall shear stress in the common carotid artery (CCA) as function of age and possible interactions between diameter and storage capacity, defined as the absolute area change per heart beat, with mean wall shear stress. Methods : Wall shear stress (wall shear rate multiplied by whole blood viscosity) was assessed in the right CCA of 111 presumed healthy male ( n =56) and female ( n =55) volunteers, varying in age between 10 and 60 years. Wall shear rate was measured with a high resolution ultrasound system. Simultaneously, arterial diameter and storage capacity were determined. Whole blood viscosity was calculated from haematocrit, plasma viscosity and shear rate. Results : From the second to the sixth age decade peak wall shear stress was significantly higher in males than in females and decreased from 4.3 Pa to 2.6 Pa ( r =−0.56, p <0.001) in males and from 3.3 Pa to 2.5 Pa ( r =−0.54, p <0.001) in females. Mean wall shear stress tended to decrease from 1.5 Pa to 1.2 Pa ( r =−0.26, p =0.057) in males and decreased significantly from 1.3 Pa to 1.1 Pa ( r =−0.30, p =0.021) in females. No significant difference in mean wall shear stress was found between males and females in any age decade. The diameter of the CCA increased significantly in both males ( r =0.26, p <0.05) and females ( r =0.40, p <0.003). Storage capacity decreased significantly in both sexes (males: r =−0.63, p <0.001; females: r =−0.68, p <0.001). Conclusions : These observations suggest that the reduction in mean wall shear stress with age results from the concomitant increase in diameter in an attempt of the arterial system to limit the reduction in storage capacity of the arterial system with increasing age.

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Wall shear stress in the human common carotid artery as function of age and gender

Wall shear stress (blood viscosity x wall shear rate), imposed by the flowing blood, and blood pressure are the main mechanical forces acting on a blood vessel wall. Accurate measurement of wall shear stress is important when investigating the development of vascular disease, since both high and low wall shear stresses have been cited as factors leading to vessel wall anomalies. Furthermore, in vitro studies have shown that endothelial cells, which play a key role in the function of the underlying arterial wall, undergo a variety of structural and functional changes in response to imposed shear stress. However, there is practically no knowledge about the influence of wall shear stress on the arterial wall in vivo because of the difficulty in measuring this stress in terms of magnitude and time variation. The method presented in this article to measure the time-dependent wall shear rate in the main arteries is based on the evaluation of velocity profiles determined by means of ultrasound, using off-line signal processing. Pulsed ultrasound is well suited for this application since it is noninvasive. The processing performed in the radio-frequency (RF) domain consists of a mean frequency estimator preceded by an adaptive vessel wall filter. In a pilot study (30 measurements in the carotid artery of five healthy volunteers) we investigated the reproducibility of our method to estimate wall shear rate as compared with the reproducibility of the measurement of blood flow velocity in the middle of the vessel. The coefficient of variation was on the order of 9% for blood flow velocity estimation, and for wall shear rate estimation on the order of 5%.

Peter J. Brands

Papers

Assessment of the distensibility of superficial arteries.

Automated detection of local artery wall thickness based on M-line signal processing.

An integrated system for the non-invasive assessment of vessel wall and hemodynamic properties of large arteries by means of ultrasound

Wall shear stress in the human common carotid artery as function of age and gender

A noninvasive method to estimate wall shear rate using ultrasound.