Effect of Constant External Force on Dynamics of Spiral Waves

In this paper, we investigate the effect of a constant external force on the dynamics of spiral waves in a excitable medium. The excitable medium is denoted by the FitzHugh Nagumo model. For a negative force, it firstly makes the exited domain reduced, then the new spiral wave with a different tip trajectory is created after a period of adjustment. The domain size of the new tip trajectory and core is an increasing function of the absolute value of the constant force. When the absolute is large enough, the original spiral wave is eliminated. For a positive force, it firstly makes the exited domain widened, and the size of the final tip attractors changes little with the force, but for different values of the force the locations of the attractors are very different. When the positive force is strong enough, the excited domain is widened to occupy the whole medium. In this case, if the external force is withdrawn, the whole medium can return consistently to the resting state. The causes of these phenomena are discussed.