A viscoelastic model of arterial wall motion in pulsatile flow: Implications for Doppler ultrasound clutter assessment
Institute of Biomaterials and Biomedical Engineering University of Toronto, 164 College St, Toronto, ON M5S 3G9, Canada. Physiological Measurement
(Impact Factor: 1.81).
03/2008; 29(2):157-79. DOI: 10.1088/0967-3334/29/2/001
The existing computational model studies of pulsatile blood flow in arteries have assumed either rigid wall characteristics or elastic arterial wall behavior with wall movement limited to the radial direction. Recent in vivo studies have identified significant viscoelastic wall properties and longitudinal wall displacements over the cardiac cycle. Determining the nature of these movements is important for predicting the effects of ultrasound clutter in Doppler ultrasound measurements. It is also important for developing an improved understanding of the physiology of vessel wall motion. We present an analytically-based computational model based on the Womersley equations for pulsatile blood flow within elastic and viscoelastic arteries. By comparison with published in vivo data of the human common carotid artery as well as uncertainty and sensitivity analyses, it is found that the predicted waveforms are in reasonable quantitative agreement. Either a pressure, pressure gradient or volumetric flow rate waveform over a single cardiac cycle is used as an input. Outputs include the pressure, pressure gradient, radial and longitudinal fluid velocities and arterial wall displacements, volumetric flow rate and average longitudinal velocity. It is concluded that longitudinal wall displacements comparable to the radial displacements can be present and should be considered when studying the effects of tissue movement on Doppler ultrasound clutter.
Available from: Jacopo Ferruzzi
- "Motivated by Ref. , the percent energy dissipation was calculated from the difference between the loading and unloading curves normalized by the energy associated with loading. Briefly, energies associated with loading (W L ) and unloading (W U ) were calculated as "
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ABSTRACT: The stiffness of central arteries, namely, the aorta and common carotids, is a fundamental determinant of cardiovascular function and disease risk. Loss of elastic fiber integrity is one of the primary contributors to increased arterial stiffening in hypertension, aging, and related conditions. Elastic fibers consist of an elastin core and associated glycoproteins, hence defects in any of these constituents can adversely affect wall mechanics. In this paper, we focused on the contributions to central arterial stiffness by fibulin-5, an elastin-associated glycoprotein involved in elastogenesis. Specifically, we compared, for the first time, the biaxial mechanical properties of four central arterial regions - the ascending aorta, descending thoracic aorta, infrarenal aorta, and common carotid artery - from male and female wild-type and fibulin-5 deficient mice. Results revealed that, independent of sex, all four regions in the mutant mice manifested a marked increase in structural stiffness, a marked decrease in elastic energy storage, and typically an increase in energy dissipation, with all differences being most dramatic in the ascending aorta. Given that the primary function of large arteries is to store elastic energy during systole and to return this energy during diastole to work on the blood, fibulin-5 deficiency results in a widespread diminishment of central artery function that can have significant effects on hemodynamics and cardiac function.
- "Introduction. Recent developments in ultrasound Contour and Speckle Tracking methods make it now possible to measure in vivo radial and longitudinal arterial wall displacements        . These measurements for the first time reveal that longitudinal displacement of the intima-media complex in healthy 2000 Mathematics Subject Classification. "
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ABSTRACT: Recent in vivo studies, utilizing ultrasound contour and speckle tracking methods, have identified significant longitudinal displacements of the intima-media complex, and viscoelastic arterial wall properties over a cardiac cycle. Existing computational models that use thin structure approximations of arterial walls have so far been limited to models that capture only radial wall displacements. The purpose of this work is to present a simple fluid-struture interaction (FSI) model and a stable, partitioned numerical scheme, which capture both longitudinal and radial displacements, as well as viscoelastic arterial wall properties. To test the computational model, longitudinal displacement of the common carotid artery and of the stenosed coronary arteries were compared with experimental data found in literature, showing excellent agreement. We found that, unlike radial displacement, longitudinal displacement in stenotic lesions is highly dependent on the stenotic geometry. We also showed that longitudinal displacement in atherosclerotic arteries is smaller than in healthy arteries, which is in line with the recent in vivo measurements that associate plaque burden with reduced total longitudinal wall displacement. This work presents a first step in understanding the role of longitudinal displacement in physiology and pathophysiology of arterial wall mechanics using computer simulations.
Available from: A. Ramos
- "There are some research works reporting laboratory ultrasonic experiments for estimation of wall thickness in blood vessels (for instance: carotid and femoral arteries), with the aim of obtaining an early diagnostic of relevant vascular problems [48–50]. They are related to diseases due to arterial hypertension and atherosclerosis, which often create modifications of the physical properties of the large vessels. "
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ABSTRACT: Achieving accurate measurements of inflammation levels in tissues or thickness changes in biological membranes (e.g., amniotic sac, parietal pleura) and thin biological walls (e.g., blood vessels) from outside the human body, is a promising research line in the medical area. It would provide a technical basis to study the options for early diagnosis of some serious diseases such as hypertension, atherosclerosis or tuberculosis. Nevertheless, achieving the aim of non-invasive measurement of those scarcely-accessible parameters on patient internal tissues, currently presents many difficulties. The use of high-frequency ultrasonic transducer systems appears to offer a possible solution. Previous studies using conventional ultrasonic imaging have shown this, but the spatial resolution was not sufficient so as to permit a thickness evaluation with clinical significance, which requires an accuracy of a few microns. In this paper a broadband ultrasonic technique, that was recently developed by the authors to address other non-invasive medical detection problems (by integrating a piezoelectric transducer into a spectral measuring system), is extended to our new objective; the aim is its application to the thickness measurement of sub-millimeter membranes or layers made of materials similar to some biological tissues (phantoms). The modeling and design rules of such a transducer system are described, and various methods of estimating overtones location in the power spectral density (PSD) are quantitatively assessed with transducer signals acquired using piezoelectric systems and also generated from a multi-echo model. Their effects on the potential resolution of the proposed thickness measuring tool, and their capability to provide accuracies around the micron are studied in detail. Comparisons are made with typical tools for extracting spatial parameters in laminar samples from echo-waveforms acquired with ultrasonic transducers. Results of this advanced measurement spectral tool are found to improve the performance of typical cross-correlation methods and provide reliable and high-resolution estimations.
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