Page 105 - Computational Modeling in Biomedical Engineering and Medical Physics

94 Computational Modeling in Biomedical Engineering and Medical Physics

myocardial tissue are responsible for the heart’s fascinating automatism, which keeps
the myocardium contracting as long as the nodal cells are still alive, despite the lack of
any physical links with the nervous system (Royston Maloeuf, 1935; Valenzuela and
Kabela, 1984). Several aspects of the nonlinear dynamics of the heart excitable tissue
are touched in Section 4.3.
While the cardiovascular system is responsible for pumping blood through arteries and
veins, ensuring proper oxygenation of the whole body, proper functioning of the heart,
responsible for this vital function, is strongly related to the electric activity of the myocar-
dium. Cardiac electric signal properties spark off the mechanical activity (myocardium
contraction and relaxation) that produces the pressure gradients responsible for the blood
flow. Showing the complex link between the electric and mechanical activities of the
heartiscrucial fordeeplyunderstanding itsfunction(Capasso et al., 1983; Tournoux
et al., 2007). Pathological variations of hemodynamic parameters are usually correlated
with myocardial tissue dysfunctions that alter normal, physiological pathways of the electric
signal propagation. Their values are a consequence of the electric activity of the heart that
triggered them. Thus the noninvasive investigation of the coupled electric (ECG) and
mechanical (ICG, ECM, TEB, Chapter 5: Bioimpedance Methods) activities of the heart
is a way of good practice when evaluating a patient. Applanation tonometry (AT), dis-
cussed later in this chapter (Sections 4.5 and 4.6), may provide valuable information and
insights concerning the pressure pulse wave, its direct and reverse components.
Physical modeling of the heart for numerical simulation still represents a great chal-
lenge due to the complex phenomena underlying the myocardial tissue electrophysiol-
ogy. The heart muscle contractions are generated through a complex succession of
sequences, originating with the SA electric pulses generated spontaneously. The nodal
cells that comprise the myocardial tissue are responsible for the heart’s impressive
automatism, which keeps the myocardium contracting as long as the nodal cells are
still alive (Royston Maloeuf, 1935; Valenzuela and Kabela, 1984), while the rhythm
itself is under nervous control. SA autorhythmic cells depolarize spontaneously and
generate peaks of their transmembrane voltage, called low action potentials (low AP).
The numerical models based on anatomically accurate computational domains, gen-
erated using medical image construction, combined with the appropriate mathematical
models can become essential tools for the analysis, understanding and improvement of
the cardiovascular system and its functionality. The advantage package that they carry
through numerical simulation and image based construction will always include the lack
of bioethical problems and restrictions, the safe, unharmful, clean, simple, usually cheap,
mode of experimenting, testing, and optimization. And this concurs with European
Union Directive 86/609/EEC Art. 7, Section 2 of November 24, 1986, concerning the
usage of animals in experiments or other scientific purposes: “an experiment shall not be
performed if another scientifically satisfactory method of obtaining the result sought, not
entailing the use of an animal, is reasonably and practicably available.”