ABSTRACT
Focusing on the heart rate control mode of acceleration sensor based rate responsive pacemakers, this paper implemented the design of activity--heart rate prediction system. Bluetooth module was used as communication means in activity--heart rate prediction system, and the slave computer was used to complete the acceleration signal acquisition and processing, map from acceleration signal to the pacing rate signal, and achieve real-time transmission of acceleration signal and heart rate signal. The master computer fulfilled real-time display and recording of acceleration signal and heart rate signal, moreover, it achieved control function to the slave computer algorithm through classification of 6 parameters. The results of verification experiment showed that there was a significant relation between mapping heart rate and actual heart rate using linear mapping algorithm (R2 = 0.787, P < 0.001).
Subject(s)
Humans , Algorithms , Cardiac Pacing, Artificial , Methods , Heart Rate , Physiology , Motor Activity , Pacemaker, Artificial , Signal Processing, Computer-AssistedABSTRACT
Torsades de Pointes is a kind of severe ventricular arrhythmia. Myocardial ischaemia is one of the major causes leading to TdP. In this paper the mechanisms of the TdP were quantitatively studied under the condition of ischaemia based on the Noble98 dynamic model of the ventricular action potential. The study was conducted on one-dimensional homogeneous myocardium with the method of computer simulation. The models were firstly developed to simulate the lower excitability, extracellular accumulation of the K+ concentration or the decreased gap junctions in ischaemic myocardium. By separately reducing the Na+ conductance, increasing the extracellular K+ concentration or decreasing the conductance of the gap junctions enabled us to study the effect of each change in isolation. Then different degrees of ischaemic models were established to study their physiological features. The study showed that the conduction velocity became slower with the ischaemia aggravation, the action potential duration became shorter and the width of the vulnerable window obviously became larger than the normal conditions. The results illustrated that ischaemia was easily leading to unidirectional conduction block and resulted in re-entry and arrhythmias.
Subject(s)
Computer Simulation , Models, Cardiovascular , Myocardial IschemiaABSTRACT
On the basis of mammalian ventricular action potential model Noble98, and with the use of Runge-Kutta for solution, the Wenckebach periodicity phenomenon, the transmural heterogeneity of the ventricular myocardium and its rate dependence are studied. The results indicate that these inherent properties may, lead to temporal-space disorganized in the normal heart,and may become the underlying factors for arrhythmias. At the same time, in this study are established the basic methods for quantitative cellular electrophysiology which is essential for future studies on the mechanism of arrhythmia.
Subject(s)
Humans , Action Potentials , Physiology , Arrhythmias, Cardiac , Computer Simulation , Electrophysiology , Heart Conduction System , Physiology , Heart Ventricles , Ion Channels , Metabolism , Models, Cardiovascular , Myocytes, Cardiac , PhysiologyABSTRACT
Optical mapping of the membrane potential with voltage-sensitive dyes is an advanced approach that involves in many theories such as molecular photonica, physiology and computer science. Compared with the conventional techniques of membrane patch-clamp and microelectrode, the optical mapping system can measure not only the changes of a single membrane potential from multiple sites simultaneously but also the conduction properties of the cell populations. So this technique provides an important method for studying the electrophysiology of the small cell, the tiny neurite and the cardiac arrhythmia, etc. Because this technique can also avoid the electromagnetic interferences, it uniquely provides an ideal means for studying the mechanisms such as cardiac defibrillation. In this paper the principles and the system structure of the optical mapping are introduced, its applications and future developments are also presented at the same time.
Subject(s)
Animals , Humans , Brain , Physiology , Electrodes , Electrophysiology , Methods , Fluorescent Dyes , Membrane Potentials , Physiology , Myocytes, Cardiac , Physiology , Optics and PhotonicsABSTRACT
Malignant arrhythmias and ventricular fibrillation are generally accepted as one of the major causes of death in cardiovascular diseases. Based on the H-H equations, the mathematical model of the cardiac cell action potential consists of the ion channels, pumps, exchangers and transporters that are closely connected with intra- and extra-cellular ion concentrations, the channel's conditions, nerve transductors and drugs. It can build the link between cell electrophysiology and clinical pathophysiology. By altering the cellular environments the computer simulating study on this kind of model can help us look into the electrophysiological changes of the cardiac tissue and even the whole heart and investigate the mechanisms of the cardiac arrhythmias as well. The components of the model and its computer simulating study are introduced in the paper.
Subject(s)
Humans , Action Potentials , Arrhythmias, Cardiac , Computer Simulation , Heart , Models, Cardiovascular , Ventricular FibrillationABSTRACT
Objective To study ischemic effects on reentrant activities and cardiac arrhythmias using a computational approach. Method The Noble 98 mathematical model of ventricular cell was used in the study. The operator splitting and adaptive time step methods were utilized to integrate the partial differential equations in cardiac conduction models. The ischemic cells were simulated by decreasing the intracellular ATP concentration, reducing the Na+ conductance, and increasing the extracellular K+ concentration in a two-dimensional tissue. Spiral waves were initiated by the cross field technique. Result The results showed that spiral waves in local severe ischemia displayed three different morphologies,whereas in moderate ischemia only two kinds of wave forms exhibited. When the degree of ischemia reached a critical value, the reentrant wave could break. But for larger areas of ischemia spiral wave formed a typical functional reentry around the obstacle. Conclusion The study demonstrates that size and level of ischemia have effects on VTs and VFs. Large ischemic area is beneficial for maintenance of spiral wave and can provide a high probability in the genesis of VTs. Spiral waves can easily break up and degenerate into VFs under critical area or level of ischemia.