Biorheology - Volume 21, issue 5

Article Type: Editorial

DOI: 10.3233/BIR-1984-21506

Citation: Biorheology, vol. 21, no. 5, pp. I-III, 1984

Authors: Mahrenholtz, O.H. | Zimmermann, R.-U.

Article Type: Research Article

Abstract: The mechanical description of the behaviour of tissue started with the Hookean model, i.e. the tissue, in particular the vessel wall, was treated as linear elastic. Time dependent aspects have been included by an extension to the Kelvin-Voigt model and to the so-called 3-parameter model. The aim of this paper is to apply the concept of hereditary integrals to tissue deformability. This integral formulation has as its experimental background creep and relaxation.

Keywords: viscoelastic tissue, memory functions

DOI: 10.3233/BIR-1984-21501

Citation: Biorheology, vol. 21, no. 5, pp. 663-674, 1984

Authors: Koeller, W. | Funke, F. | Hartmann, F.

Article Type: Research Article

Abstract: 48 lumbar discs were tested; the creep tests lasted between 2 and 6 hours. All discs showed the known creep behavior, i.e. a decrease of height, rate of creep and axial deformability with time. In the first minutes of a test the viscoelastic behavior quickly alters so that the disc behaves more like an elastic body. Loss of mass normally observed after creep tests is due to loss of water. Creep behavior is reproducible if a disc has sufficiently recovered, i.e. if it has regained its initial height. Creep tests on “desiccated” discs revealed that creeping is possible without loss …of water and recovery is possible without absorption of water. The type of loading (static or dynamic) has hardly any influence on the biomechanical behavior. Our results indicate, that creep and recovery are chiefly due to extension and contraction of the anular fibers and not to fluid flow. Show more

Keywords: human intervertebral disc, creep, recovery, water flow

DOI: 10.3233/BIR-1984-21502

Citation: Biorheology, vol. 21, no. 5, pp. 675-686, 1984

Authors: Collins, Richard | Mouttahar, Abdelhak

Article Type: Research Article

Abstract: Early detection of cardiac disease is based on the quantitative interpretation of left ventricular wall motion throughout the cardiac pumping cycle. Wall deformations result from complex fluid-wall interactions wherein muscle fibre orientation, intraventricular pressure and regional variations of myocardial wall rheology play a crucial role. A reliable theoretical model would be of intrinsic value in aiding the cardiologist in his interpretation of clinical diagnostic results, particularly through the incorporation of microprocessor-based algorithms permitting automatic processing of clinical data within the framework of such a model. As a step in this direction, a theoretical analysis is formulated for a relatively simple …characterization of the left ventricle in terms of a truncated ellipsoidal shell. The myocardial wall contains contractile muscle fibres of known orientation. The stress tensor is derived on the basis of an inviscid fluid-fibre continuum. Principal stresses are calculated in terms of regional wall deformations and intraventricular pressure. These are determined from an inviscid fluid dynamic model for left ventricular contraction, subject to an appropriate Neumann condition on wall velocity as obtained from cineangiography. Local “defects” in wall velocity simulate the inhibition of wall contractility associated with the development of myocardial infarct. The theoretical model makes it possible to evaluate local variations in wall stress at those sites and to calculate both regional and overall changes in heart work as a noninvasive indicator of cardiomyopathies or valvular defects. Graphic results are presented depicting the role of myocardial tissue rheology on the dynamics of cardiac performance during the ejection phase, on the basis of the present theoretical model. Show more

Keywords: myocardial, rheology, theoretical model, hemodynamics, stresses

DOI: 10.3233/BIR-1984-21503

Citation: Biorheology, vol. 21, no. 5, pp. 687-708, 1984

Authors: Pelle, G. | Ohayon, J. | Oddou, C. | Brun, P.

Article Type: Research Article

Abstract: Different rheological concepts and theoretical studies have been recently presented. using models of myocardial mechanics. Complex analysis of the mechanical behavior of the left ventricular wall have been developed in order to estimate the local stresses and deformations that occur during the heart cycle as well as the ventricular stroke volume and pressure. Theoretical models have taken into account non-linear and viscoelastic passive properties of the myocardium tissue. when subjected to large deformations. through given strain energy functions or stress-strain relations. Different prolate spheroid geometries have been considered for such thick shell cardiac structure. During the active state of …the contraction. the rheological behavior of the fibers has been described using different muscle models and relationships between fiber tension and strain. and activation degree. A forthcoming approach for bridging the gap between the knowledge of the muscle fiber microrheological properties and the study of the mechanical behavior of the entire ventricle. consists in including anisotropic and inhomogeneous effects through fiber direction field. Show more

Keywords: Myocardium, Numerical Cylindrical Model, Mechanical Stress

DOI: 10.3233/BIR-1984-21504

Citation: Biorheology, vol. 21, no. 5, pp. 709-722, 1984

Authors: Richter, H.A. | Mittermayer, Ch.

Article Type: Research Article

Abstract: In order to measure the flow-dynamical effect of arteriosclerotic changes of the vessel wall we determined volume elasticity E′ and modulus of elasticity ϰ of 53 human aortae in a static p-V-test as other authors did, too. The p-V-curves are normalized to the aortic basic volume V0 , so that we could determine the haemodynamic effect of arteriosclerosis immediately from E′ and ϰ . Diameter, length, and, accordingly, the basic volume of the aorta without prestressing increase significantly in aortae with severe arteriosclerosis in comparison to those without sclerosis. The volume elasticity E′ as a function of the …static aortic pressure has a minimum within physiological pressure range and changes into a linear function when arteriosclerosis increases. The modulus of elasticity of a normal aorta remains constant within a pressure range of 20 to 100 mm Hg and it shows a linear increase at higher pressure. The differences between V0 , E′ and ϰ of aortae with and without severe arteriosclerosis, however, are highly significant. Show more

Keywords: Atherosclerosis, arterial elasticity, aorta properties, volume elasticity

DOI: 10.3233/BIR-1984-21505

Citation: Biorheology, vol. 21, no. 5, pp. 723-734, 1984