Real-time simulation and control of spatio-temporal cardiac excitation using an analog-digital hybrid circuit model
Action potential of a cardiac cell membrane and its conduction in the cardiac tissue provide a basis of the electrophysiological function of the heart through the cardiac excitation-contraction coupling mechanism. Towards a better and a quantitative understanding of electrophysiological mechanism...
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| Format: | Thesis |
| Language: | English |
| Published: |
2011
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| Subjects: | |
| Online Access: | http://eprints.uthm.edu.my/2996/1/24p%20FARHANAHANI%20MAHMUD.pdf |
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| Summary: | Action potential of a cardiac cell membrane and its conduction in the cardiac tissue
provide a basis of the electrophysiological function of the heart through the cardiac
excitation-contraction coupling mechanism. Towards a better and a quantitative understanding
of electrophysiological mechanisms of the reentrant cardiac arrhythmias at cellular,
tissue, and organ levels, mathematical models of cardiac cells, tissues, and the heart
have been developed and analyzed by simulating conduction of action potentials in a va-
riety of conditions. However it is inevitable for those models to become large scale in the
number of dynamical variables, requiring immense amount of computational time for their
dynamic simulations. In this study, an analog-digital hybrid circuit model of electrical excitation
of a cardiac cell based on Luo-Rudy phase I (LR-I) model, a typical mathematical
model of a cardiac cell was developed. Through its hardware implementation, real-time
simulations of the cellular excitations as well as their propagation in a cardiac tissue model
have been performed with the hybrid circuit model.
This thesis is organized as follows. It is started with a general introduction in Chapter
1. The research background is discussed in Chapter 2, where physiology of the heart
and the mechanism of electrical system which controls the cardiac contraction are elaborated.
These are then followed by explaining the basis of knowledge on electrical potentials
that exist across cell membranes and describing how they are modeled. Computational
techniques of mathematical modeling and hardware-implemented circuits that have been
developed over past few decades in understanding the dynamics of cells and excitationconduction
are also reviewed especially in cardiac cell modeling.
Chapter 3 is focusing on the work presented in a single cell model, where a design
method of the analog-digital hybrid circuit cell is overviewed, followed by details of the
analog-digital hybrid active circuit. The design method of current-voltage (I-V ) relationships
between ion currents and the membrane potential reproduced by analog and digital
circuits is also explained. Furthermore, action potential of the hybrid circuit model is initiated
by an external stimulus and the result is compared to the result of the LR-I model.
Action potential generation of the hybrid circuit model in response to periodic current
impulse trains with different interval (period) T are carried out and comparisons to the
result from the LR-I model are presented. Classification of excitation response patterns
on the parameter plane spanned by the period T and the intensity A of the impulse trains in the hybrid model and LR-I model are analyzed, and the results between the two models
are also compared. According to the simulations results, the action potential characteristics
of the hybrid cell model and the LR-I cell model are comparable as the hybrid cell
model generally well reproduces the I-V relationships of ion currents described in the LR-I
model, as well as the action potential waveform, and the excitation dynamics in response
to periodic current impulse trains with various intervals and intensity levels.
In Chapter 4, the work on investigating the spatio-temporal dynamics and control of
reentrant action potential conduction in active cable models is being reviewed. Manner
and underlying mechanisms in the initiation of the reentrant action potential conduction
in a one dimensional ring-topology-network of the hybrid active circuit cable model are
constructed as a model of anatomical reentrant tachycardia. Dynamics of the hybrid
active circuit cable model are then compared with those in the numerical simulation of
the LR-I cable model. Resetting and annihilation of the reentrant wave under the influence
of single and sequence of stimulations are investigated by using the hybrid cable model
and comparisons to the result from the LR-I cable model are carried out. Resetting and
annihilation of the reentrant wave are of crucial importance in clinical situations where the
reentrant cardiac arrhythmias are often controlled and terminated by delivering electrical
stimulations to the heart through catheters. Phase resetting curves (PRCs) of both models
are presented to show the relationship between the phase reset of the reentry and the
phase of single stimulation. According to the PRCs, sequential phase resetting by periodic
stimulation that leads to annihilations of the reentry are predicted and illustrated with onedimensional
discrete Poincare mappings. As the results in the simulations of the reentrant
action potential conduction, quantitative correspondence between the hybrid cable model
and the LR-I cable model was demonstrated using a one dimensional active cable as
a model of the anatomical reentry in a cardiac tissue with various conditions. Those
include (1) unidirectional block to initiate reentry, (2) phase resetting by single impulsive
stimulations, (3) annihilations of the reentry by appropriately timed single stimulations,
(4) phase resetting curves (PRCs) that can characterize the reentry dynamics in response
to single stimulations at various timings, and (5) sequential phase resetting that leads to
annihilation of the reentry as predicted by the one dimensional discrete Poincare mappings.
Finally, general discussion and conclusions are being reviewed in Chapter 5. The overall
results of the hybrid circuit model are satisfied with those of the LR-I model, corresponding
to the subjects examined in the study. Therefore, by taking into account the satisfactory
results and the real-time simulation capability of the hybrid model, these can be concluded
that the hybrid model might be a useful tool for large scale simulations of cardiac tissue
dynamics, as an alternative to numerical simulations, toward further understanding of the
reentrant mechanisms. As a matter of fact, minimizing power consumption and physical
size of the circuits need to put into consideration regarding to large-scale development of
the hybrid model. |
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