LAB # 3
Abstract:
A major aim in systems biology is to build computational models of biological and physiological
systems for simulation and understanding of complex biological systems. Computational modeling
is systemic modeling of complicated processes using a mechanistic approach with the help of
computer programs, physics, and mathematics. Computational models of biological systems help
in understanding manner of development of complex diseases, promoting optimization of
treatment strategies and discoveries of new drugs. Computational modeling of engineering
complexities in medicine provides insights for the advancement of medical technology. Use of
computational modeling in biomedical engineering involves many engineering applications in
medical physics, diagnosis of diseases and techniques used for monitoring which include heart’s
electrical activity, monitoring hemodynamic activity, bioimpedance methods and magnetic drug
targeting. COMSOL Multiphysics is an interactive Multiphysics simulation software which
provides with graphical user interface along with Multiphysics and single physics modeling
capabilities. This software is used in all engineering fields for simulation of designs, devices, and
processes. In this research, computational model of Electrical Impedance Plethysmography (EIP)
system is designed using COMSOL Multiphysics software, and behavior of system with respect
to two physics i.e., electrical currents and heat transfer in solids is analyzed. The measurement
results include response of system at 1V, 5V and 9V electric potentials with respect to four
properties which include electric potential, electric field norm, temperature, and isothermal
contours.
1. Introduction
Modeling is creating visual representation of a real-world system. It is used to study the system
when system’s input and output is unpredictable. So, a modeling is done to test the predicted output
and for analyzing behavior of the system. A model is a small structure design or simplest
representation of a system having all same features, characteristics and parameters of that system
or structure. A model has a resemblance to real system as its prototype and anatomical structure is
designed same as real system. Real world processes replication is called simulation. Model
simulation is act of simulating a model by applying input stimulus and analyzing the output.
Biological or physiological systems and processes simulation is termed bio simulation. So
modeling is representation of simplified models of complex biological systems and bio simulation
is prediction of dynamics and behavior of system or process. Biological and physiological model
is a system representing a real human complex biological process. Studying real complicated
systems is one of the chief goals for which modeling, and simulation is done. Different types of
models include graphical model, qualitative model, hybrid model and multi-scale model.
Graphical model is pictural representation of a realistic system. Qualitative model is a real-valued
model proper abstraction and describes qualitative relationship between parameters. Hybrid model
the system is partitioned as inner part which consists of molecules of particular interest and outer
part which consists of remaining atoms in system. Multiscale model is studying biological system
at multiple level. In this research COMSOL Multiphysics is used to design and simulate the
graphical model of EIP system.
In EIP system current is injected into the system of interest using electrodes. Blood volume is
inversely proportional to the electrical impedance of the body segment. Pulsatile blood volume
increase in the body segment results in decrease in the electrical impedance. The electrical yield
great information about disorders related to blood volume.
2. Basic Idea:
The basic idea of research is to design and simulate the 2D model of EIP system. The system is
analyzed with respect to two physics including heat transfer in solids and electric currents. Change
in system behavior in response to electric stimulus and heat provided is observed.
Injecting Electrode
Ground Electrode
Copper block
Iron Block
Figure 1. Basic idea of research
3. Material and Method
 Model Design
From model wizard select space dimension as 2D , select physics > AC/DC > electric
currents > add. Select another physics > heat transfer in solids. Select stationary > study >
done. Geometry includes 3 rectangles of specified height and width with mm unit. Add
material. The electrodes are of copper material while the big base block is of iron material.
2mm
2mm
0.5mm
0.5mm
5mm
20 mm
Figure 2: 2d Model of the Block
 Material Design
Material design includes adding material and its properties in model geometry. Click on
material > add material from library > add iron material in big block > add copper material in
electrodes. One electrode is electric potential electrode which is boundary heat source and
user defined value is set to 0.1 while another electrode is ground electrode. Temperature is
provided at the base of big block and value is set to 310.15 k. The material properties added
are shown below
Property
Value
Electrical conductivity
(S/m)
Relative permittivity
Copper (7*10^6)
Iron (not set)
Copper (0.5)
Iron (5)
Table 1: Material properties added to model
 Physics Type:
Electric currents physics is added to analyze behavior of system in response to electrical
stimulus. The electric potential is varied from 1V to 10 V and system output is predicted.
Heat transfer in solids physics is also added and system response is observed by keeping
value of normal body temperature at base and providing heat source through potential
electrode.
4. RESULTS:
The electric potential electrode generates voltage and current which moves from higher potential
to lower potential i.e., towards ground electrode. After model designing model simulation is
done. Click on mesh > study >compute.
Figure 3. Geometry of model
Figure 4. Mesh of model geometry
Model is computed and electric potentials are shown by colors. The color near the electrode
indicates the electrode voltage and different colors indicate different voltages. Near the electric
potential electrode there is stronger electric field and mesh lines are closer.
(10,2) coordinate
Figure 5. Model Computation
Voltage is varied from 1 V to 10 V and simulation results of system for voltage 1V, 5V and 9V
are shown below.
(a) Electric potential
(b) Electric field norm
(c) Isothermal contours
Figure 6. Results for 1V
(a) Electric potential
(b) Electric field norm
(c) Isothermal contours
Figure 7. Results for 5V
(a) Electric potential
(b) Electric field norm
(d) Isothermal contours
Figure 8. Results for 9V
Different potential values and temperature values taken at coordinates (10,2) are shown below.
Voltage (V)
Temperature (K)
0.49823
310.15
0.99647
310.15
1.4947
310.15
1.9929
310.15
2.4912
310.15
2.9894
310.15
3.4876
310.15
3.9859
310.15
4.4841
310.15
4.9824
310.15
Table 1. Potential and temperature values
Graph is drawn showing voltage values at (10,2) coordinates. The graph shows the increase in
voltage with the increase in electric potential. Potential values are less for 1V and increase
drastically up to 10V.
Figure 9. Graph of potential values
Figure 10. Temperature
Graph is drawn showing temperature value at (10,2) coordinates. The graph shows there is no
drastic change in temperature and value remains constant for every change in voltage.
Figure 11. Graph of Temperature values
5. Discussion
Modeling is visual representation of real-world system. Modeling of real human system
physiological and biological processes is termed bio-simulation. Computed solution of
Multiphysics software is used for graphical modeling of biological system. The physics studied is
electric currents and thermal physics. Behavior of the system with respect to four properties i.e.,
electric potential, electric field norm, temperature, and isothermal contours is observed. Model
designing includes geometry, material type and physics addition. Visual representation is obtained
by meshing and computing the design and output is predicted. The output shows movement of
current from higher potential electrode to lower potential electrode i.e., ground electrode. High
voltage near electric potential electrode indicates stronger electric field whereas the temperature
value remains constant.
6. References
[1] Babu, J. P., et al. "Impedance plethysmography: basic principles." Journal of Postgraduate
Medicine 36.2 (1990): 57.
[2] Zi, Zhike. "Sensitivity analysis approaches applied to systems biology models." IET systems
biology 5, no. 6 (2011): 336-346.
[3] Kohl, Peter, et al. "Computational modelling of biological systems: tools and
visions." Philosophical Transactions of the Royal Society of London. Series A: Mathematical,
Physical and Engineering Sciences 358.1766 (2000): 579-610.
[4] Edwards, David. Introduction to graphical modelling. Springer Science & Business Media,
2012.
[5] Thomaseth, Karl. "Multidisciplinary modelling of biomedical systems." Computer methods
and programs in biomedicine 71.3 (2003): 189-2010