Biomedical Engineering Reference
In-Depth Information
less invasive techniques and through the design of less traumatic instruments (Gupta
et al.,
1997
). Obviously, the effectiveness of these new designs and techniques de-
pends on how well damage mechanisms are understood and how accurately thresh-
olds for safe tissue loading can be defined.
The implementation of safety thresholds during surgery obviously requires a con-
sensus as to what these thresholds are. In current surgical practice, the amount of
load that can safely be applied on a certain tissue is highly subjective, i.e. depending
on the surgeon's experience and judgement. Several steps are needed to make this
judgement more objective. This chapter describes an experimental and computa-
tional framework that allows a quantitative definition of damage to a certain tissue,
as well as a simulation tool to estimate the amount of damage to a tissue due to a
certain external load. Though generally applicable, we currently focus on the case
study of arterial clamping.
Four main steps can be defined in the framework. First, a quantitative method to
define damage for a certain tissue type is required. Next this quantitative damage
must be related to the amount of mechanical loading previously applied to the tis-
sue. This can be done experimentally for a specific loading situation, but to make
the relation generally applicable, a simulation of the damage process due to the
mechanical loading is needed. This requires a material model for cardiovascular
tissue, which is capable of capturing the typical damage processes to the different
constituents.
The first section of this chapter describes different damage quantification meth-
ods for arterial clamping. In the second section, one of these damage quantification
methods is combined with an
in vivo
arterial clamping experiment, resulting in an
experimental relation between damage and mechanical load. In the third section,
an extension of the Holzapfel-material model for arterial tissue (Holzapfel et al.,
2000
) is described, incorporating smooth muscle cell activation according to Mur-
tada et al. (
2010
) and damage according to Balzani et al. (
2006
). The model is suit-
able to simulate the damage process during the clamping of an artery. It captures
the decrease of active force generation in smooth muscle cells due to the sustained
damage. The fourth section shows how, embedded in a finite element environment,
this new model provides a useful tool to simulate the amount of damage induced
by a certain amount of mechanical load. Ultimately, the entire framework serves
to define safe loading regimes for arterial tissue, which could be used to inform
computer-enhanced surgical systems to minimize tissue damage in robotic surgery
and to optimize surgical instrument design towards minimal trauma.
10.2 Damage Quantification
Damage is defined as 'injury or harm that reduces value or usefulness'. A quantifi-
cation of damage can, therefore, be performed by assessing this reduction in value
or usefulness. First of all, biological tissue is an integral part of a larger mechanical
structure and, therefore, inherently has a (passive) mechanical function. Secondly,
