Biomedical Engineering Reference
In-Depth Information
Fig. 20.1
(
a
) Congestion in the outflow disturbed territory (Dirsch et al.,
2008
); (
b
) animal model
with defined perfusion defect after PH-30 %; provided from U. Dahmen
canals. Distension of sinusoids into sinusoidal canals was accompanied by a shift in
gene and protein expression associated with a change in their wall structure, termed
vascularization of sinusoidal canals. Vascularization of sinusoidal canals led to a
thickening of the wall. Thickening of the sinusoidal wall is essential with respect
to the change of function of this distended sinusoid aimed at draining the outflow-
obstructed liver territory.
Changes in sinusoidal blood flow as well as the sinusoidal network were made
visible by using orthogonal polarization spectroscopy (OPS), a technique for intrav-
ital microscopy. Changes in vascular structure and protein expression were observed
using special histological and immunohistochemical staining methods.
The liver lobe is modeled as a sponge-like material with anisotropic perfusion
behavior resulting from the inhomogeneous distribution of the sinusoidal network.
This inner network structure of the liver admits such a high complexity that an ac-
curate geometrical description in a continuum mechanical manner is impractical.
Thus, a multiphase mixture theory based on the theory of porous media (TPM), see
de Boer (
1996
,
2000
) and Ehlers (
2002
), is used. Since the authors' past experience
with the theory of porous media is highly satisfactory, especially regarding accuracy
and thermodynamical consistency, we do not choose similar established multiphase
theories describing biological tissues such as the mixture theory, cf. Mow et al.
(
1989
)andLaietal.(
1991
) or Biot's theory, cf. Biot (
1935
,
1941
). The minor but
significant differences between the three theories is the introduction of the consti-
tutive framework; see de Boer (
1996
,
2000
)orLuandHanyga(
2005
). Thus, under
certain assumptions, the theories finally result in a set of field equations of similar
type, cf. Bluhm and de Boer (
1998
) and Schanz and Diebels (
2003
). The choice
of the theory of porous media should not be understood as a quantifying of these
theories but as a practical choice founded on previous results.
It is well known that living tissue has the capacity to grow and to adapt to environ-
mental changes by remodeling. In pathology, growth is understood as the increase
of volume whereas remodeling defines the change in tissue structures like vessels or
fibers, see, e.g., Majno and Joris (
1996
). In this paper we follow the definitions of
growth and remodeling given by Humphrey and Rajagopal (
2002
). Therein, growth
