Effect of surrounding tissue on propagation of axisymmetric waves in arteries.
A model of an artery consisting of a thin-walled flexible tube filled with a Newtonian incompressible liquid and surrounded by an external viscoelastic tissue is studied. The dispersion relations and attenuation lengths are determined for the lowest axially symmetric propagation modes: the Young, Lamb, and torsional modes. The numerical calculations confirm a low attenuation of the Young mode and a relatively weak dependence of its phase velocity on the elastic parameters of the surrounding medium. The Lamb and torsional modes show a nonzero frequency (a gap) at zero wave vector except for the limiting case of the absence of surroundings. The attenuation of the Lamb mode at zero frequency and the gap frequency turns out to be particularly sensitive to the elastic parameters of the surroundings. However, the spatial attenuation of the Lamb mode extends over a length of the order of 10cm at the viscoelastic parameters corresponding to human tissues. Such lengths are comparable to the size of human organs. Three kinds of local axially symmetric perturbations have been studied, and the corresponding amplitude ratios of the Lamb to the Young mode calculated. The amplitude of the Lamb mode turns out to exceed that of the Young mode by a factor of ten at some frequencies with perturbations involving axial motions. Physiological consequences of this effect are discussed.
Jagielska
K
K
The H. Niewodniczański Institute of Nuclear Physics PAN, ulica Radzikowskiego 152, 31-342 Kraków, Poland. Katarzyna.Jagielska@ifj.edu.pl
Trzupek
D
D
Lepers
M
M
Pelc
A
A
Zieliński
P
P