Page 95 - Computational Modeling in Biomedical Engineering and Medical Physics

Computational domains 83

The 3D arteries reconstructed in this chapter are used as computational domains in the
numerical models developed for the study of pulsatile blood flow patterns and impact in
both rigid (pathological) and elastic (physiologically normal and aneurysm affected) arterial
networks. These morphologies are next FEM discretized and linked to different physical
and mathematical models that, once solved, will outline the hemodynamic specificities.
The heart

The cardiovascular system (Mohrman and Heller, 2013) is responsible for the blood
oxygenation and pumping in the arterial venous network. The mechanical (pump-
ing) function of the heart is strongly related to the cardiac electrical activity. The elec-
trical pulses parameters trigger the heart contraction and relaxation that generates the
systemic pressure gradients, which makes the blood flow. The understanding and anal-
ysis of the mechanisms governing the complex electrical activity of the heart makes
the subject of a very important topic. When the hemodynamic parameters begin to
rise or fall outside of physiologically normal variation intervals, dysfunctions of the
myocardial tissue that generates and diffuses the electrical signals are, usually, present.
The mathematical modeling and numerical simulation of the nonlinear activity of the
heart is still a great challenge due to the complex phenomena and the internal structure of
the cardiac tissue. The heart contraction is triggered by the electrical pulses generated in
the sinoatrial node, which is the most important component of the heart, belonging to
the intrinsic electrical conduction system. The cardiac tissue cells, called nodal cells,are
responsible for the specific automatism of the heart. These make the heart muscle contract
even when there are no links to the nervous system, as long as the nodal cells are viable.
The hemodynamic parameters mirror the electrical activity of the heart that generates
them. Thus noninvasive investigation and correlation between the electrical and mechani-
cal functions of the heart could be a good practice when setting diagnostics. Over time
different methods were developed and optimized, such as the electrocardiography (ECG)
(Vijay Raghawa Rao, 2017), which maps the electrical activity of the heart using various
electrode configurations placed on the subject’sthorax.
Recently the focus is on methods based on the evaluation of passive electrical parameters
such as the electrical impedance of the thoracic region, influenced by the electrical conduc-
tivity of blood flowing within the aorta (Kubicek et al., 1970; Sherwood et al., 1990;
Bernstein and Osypka, 2003; Song et al., 2014). These new noninvasive investigation tech-
niques, based on the analysis of thoracic electrical impedance dynamics, along with the classi-
cal methods, such as ECG, provide an in-depth clear picture of the patient’s condition.
The development of numerical models that use image-based reconstructed realistic
morphologies as computational domains and adequate physical and mathematical models,
could represent valuable tools for the analysis, understanding, and improvement of the
noninvasive (bio)impedance techniques applied for the assessment of the electrical and
mechanical functions of the heart. Furthermore the numerical models are not limited by