Research On Mechanism Of Spontaneous Generation And Control Of Spiral Wave In Biological System

Spiral waves are widely present in physical,chemical and biological systems.For example,spontaneous spiral waves have been observed in the cerebral cortex during epileptic seizures,as well as in cardiac tissues.In addition,it has also been found that some arrhythmias are related to the appearance of spiral waves and the breakup of spiral wave into spatiotemporal chaos in the heart.Therefore,it is of positive significance for the prevention and treatment of heart disease and nerve diseases to grasp the spontaneous generation mechanism of spiral wave in nervous system and cardiac tissues and to propose effective control methods of spiral wave.After decades of research,it has been found that noise,self-synapses,repulsive coupling,inhibitory coupling,cell heterogeneity factors can induce the generation of spiral waves in neuronal networks.It is observed that the special structure of the medium,the parameter heterogeneity of the system and the gradient distribution of the coupling strength can also induce the generation of spiral wave in some excitable media.Many control methods of spiral wave,such as periodic stimulation,optical control,rotating electric field control,active and passive control,and low-voltage defibrillation control,are proposed.Due to the complexity of the brain and heart systems,the spontaneous generation mechanism of spiral wave is far from being fully understood.The above-mentioned control methods of spiral wave are also difficult to implement in clinical practice.So it is necessary to continue to explore effective spiral wave control methods.In this paper,the Morris-Lecar neuron model is used to study the relationship between the synchronous discharge in the nervous system and the spontaneous generation of spiral waves in the neural network.The Luo-Rudy phase ?heart model is used to study the spontaneous generation and control of spiral waves in aging cardiac tissues.The content of the paper is arranged as follows:The first chapter is an overview of spiral wave dynamics in reaction-diffusion systems.We first briefly introduces the definition and classification of reaction diffusion system,typical reaction diffusion system and some models,and then introduces the characteristics and properties of neurons and various mechanisms of spontaneous generation of spiral wave in neuron networks,finally introduces the characteristics and properties of cardiomyocytes and the spontaneous generation mechanism and control methods of spiral waves in excitable media.The second chapter is our first research work.In this chapter,a two-dimensional neuronal network with the long-range coupling regions generated by adding long-range horizontal connections is constructed.The Morris-Lecar neuron model is used to study the propagation of waves in the two-dimensional neuronal network with the rectangular long-range coupling regions.Numerical simulation results show that the plan and target waves whose propagation direction is parallel to that of the long-range coupling can lead to synchronous excitation of neurons in the long-range coupling region.When the size of the rectangular region of the long-range coupling is properly selected,the synchronous excitation of neurons can cause network to appear the backfiring effect and to have the selectivity of wave propagation direction.Furthermore,the selectivity of wave propagation direction is very sensitive to whether the neuron is in the stationary state and the change of coupling strength.So we can control whether the wave can pass through the long-range coupling region of a certain width by giving the neurons in the long-range coupling region a tiny perturbation.For properly selected neural network structure,the self-sustaining plane wave,spiral wave and target wave can appear spontaneously in the network when the wave passes through the long-range coupling regions.The physical mechanism underlying those phenomena is heuristically analyzed.The third chapter is our second research work.In this chapter,the Luo-Rudy phase I model and the passive fibroblast model are applied to study the spontaneous formation of spiral waves in cardiac tissues.Three structures of composite myocardial tissues are constructed.It can be seen from the analysis of steady state solution that fibroblasts act as a current source in some cases,in which the myocyte-fibroblast coupling can lead to the self-excitation of cardiomyocytes.Fibroblasts act as a current sink in other cases,thus myocyte-fibroblast coupling can inhibit the excitation of cardiomyocytes.Numerical simulation results show that when the resting potential of fibroblasts or the strength of myocyte-fibroblast coupling is changed in a certain way,single spiral wave,double-spiral wave or counter rotating spiral wave pair can spontaneously appear in the composite myocardial tissues.The drift of spiral wave and disappearance of spiral wave by moving out boundary and the transition from spiral wave pair to target wave are observed.The forth chapter is our third research work.When spiral wave is generated by special structure,clinically using radiofrequency ablation to treat arrhythmia can obtain good therapeutic effects.However,this method is not suitable for the control of meandering spiral wave.Whether spiral wave and spatiotemporal chaos in the heart can be eliminated by the repolarization of the cell caused by local electric shock has not been studied yet.In this chapter,this problem is numerically studied by using the Luo-Rudy phase I heart model.A control method suppressing spiral wave and spatiotemporal chaos by using local electric shock produced by moving controller is proposed.The local electric shock is only applied to the myocardial cells around spiral wave tip to suppress the rotation of spiral wave tip,causing spiral wave tip to move out of the boundary.The numerical results show that as long as choosing an appropriate the number of grid points controlled by local electrical shock and the control thresholds of membrane potential,both spiral wave and spatiotemporal chaos can be suppressed.The minimum number of controlled grid points is 9.The shortest control times of spiral wave and spatiotemporal chaos are less than 150 ms and 500 ms,respectively.The fifth chapter is a summary and outlook.