Investigations on the intrinsic frequency of the cardiac cells in effecting synchronization

Biological rhythms, like the cardiac rhythm are often generated by large populations of mutually interacting cellular oscillators. The ability of such a population to generate a stable, regulated rhythm depends critically on the nature of interactions among the oscillators, as a network of nonlinear oscillators is intrinsically unstable. Although the entire cardiac system beats in perfect synchronization invivo, intrinsic frequencies of auto rhythmic cells have a significant dispersion. The sinoatrial node is a thin sheet of cardiac muscle fibers composed of several hundred thousand cells, each of which is an electrical oscillator. Studies of cells isolated enzymatically from the sino atrial node indicate that the intrinsic frequency of oscillation for each cell is different. Despite these differences, a coherent oscillatory electrical wave known as the pacemaker potential is generated within the node. This wave is conducted throughout the heart, determining its rate of beating. The pace making cells in the Rabbit heart beat at a wide range of frequencies (80-330 beats per minute) in culture, but within the heart they beat at a common frequency set by the normal sinus rhythm. As a result the synchronization within the heart becomes extremely difficult with such a wide range of intrinsic frequencies. The adjustment of rhythms due to an interaction is the essence of synchronization, the term originating from the Greek words chronos meaning time and syn meaning the same, common. This work attempts to explore the issues in the much desired synchronization within the rabbit heart with a valid electro physiological model of cardiac pacemaker cells in the cardiac system. For the species Rabbit, a matlab code for sinoatrial node cell was developed and the simulated results were validated against the prevailing experimental data. The existence of a free parameter that can influence the intrinsic frequency of the so generated action potential was investigated that resembled Gap Junction conductance in real electrophysiology. The functional role of the gap junctions in effecting the much desired synchronization issues with the aid of variations in the intrinsic frequency of the cell within the cardiac system was elucidated and the results indicated that the intrinsic frequency of the cells varied only for a limited range of adjustment. An external neural input was effected via integrate and fire neuron model that further coaxed the cells to oscillate at varied intrinsic frequencies that ascertained the fact that neural influence is much essential to enhance synchronization. This paper investigates with the aid of the simulation results, that the external neural input can also play a part in influencing the intrinsic frequency of the cardiac cells thereby effecting synchronization.