ECE 501 Introduction to BME Dr. Hang

Part IV Bioinstrumentation Electrocardiogram ECE 501 Dr. Hang

Introduction Physiology Medicine Instrumentation ECE 501 Dr. Hang

Medicine The Electrical Cycle ECE 501 Dr. Hang

The Electrocardiogram Medicine The Electrocardiogram The electrocardiogram (ECG) is a standardized way to measure and display the electrical activity of the heart. • Physicians can diagnose problems with the heart by analyzing its ECG and comparing it to the ECG of a healthy heart. ECE 501 Dr. Hang

Medicine ECG Waves ECE 501 Dr. Hang

Medicine ECG Intervals ECE 501 Dr. Hang

Medicine A-V Blocks Complete Hear Block The cells in A-V node are dead and A-V node does not conduct action potential at all Atria and ventricles beat independently Ventricles are driven by abnormal pacemakers ECE 501 Dr. Hang

Medicine A-V Blocks First-degree Hear Block The A-V node is diseased The action potentials from atria can still reach ventricles It is greatly delayed ECE 501 Dr. Hang

Medicine Heart Flutter Paroxysmal Tachycardia An abnormal pacemaker in ventricle may discharge at a rapid rate Ventricles depolarize irregularly at a high rate ECE 501 Dr. Hang

Medicine Heart Flutter Atrial Flutter An abnormal pacemaker in atria may discharge at a rapid rate Atria depolarize irregularly at a high rate ECE 501 Dr. Hang

Premature V- Contraction Medicine Premature V- Contraction An accidental pacemaker within the ventricle causes an extra beat (extrasystole) ECE 501 Dr. Hang

Medicine Fibrillation Atrial Fibrillation Atria twitch irregularly ECE 501 Dr. Hang

Medicine Fibrillation Ventricular Fibrillation Ventricles twitch irregularly ECE 501 Dr. Hang

Medicine Ischemia Deficient in blood supply due to coronary occlusion Early stage: ST elevation Late stage: ST elevation + TQ depression ECE 501 Dr. Hang

Instrumentation The Dipole Model The electrical field generated by this dipole represents the electric activity of the heart at a specific instant Cardiac vector M: dipole moment, having a magnitude of proportional to the amount of charge multiplied by the separation of the two charges The magnitude and direction of M vary over time ECE 501 Dr. Hang

Instrumentation The Dipole Model a1,a2: Lead vectors va1= M.a1=|M|cosθ: ECG signal on lead a1 ECE 501 Dr. Hang

Instrumentation The ECG Model Electrodes are placed on points A and B RAB: Resistance between A and B RT1, RT2: Thoracic medium resistances ΦAB: ECG voltage signal on lead AB ECE 501 Dr. Hang

Instrumentation ECG leads –Limb leads ECE 501 Dr. Hang

ECG leads – Augmented Limb leads Instrumentation ECG leads – Augmented Limb leads a: aVR b: aVL c: aVF d: Lead vectors ECE 501 Dr. Hang

Instrumentation ECG leads – Chest leads Wilson’s Central Terminal ECE 501 Dr. Hang

Instrumentation ECG leads – Chest leads Lead vector: Between the electrode and Wilson’s Central Terminal Electrode positions Lead vectors ECE 501 Dr. Hang

Instrumentation 12 - lead ECG Simultaneous measurement from Three limb leads Three augmented limb leads Six chest leads Process all data from 12 leads to obtain ECG waveform ECE 501 Dr. Hang

Instrumentation Block Diagram of an Electrocardiograph Dr. Hang ECE 501 Dr. Hang

Instrumentation Protection Circuit Prevent high voltages from damage the electrocardiograph Voltage-limiting devices Current-voltage characteristics of Voltage-limiting devices ECE 501 Dr. Hang

Instrumentation Protection Circuit Parallel silicon-diode voltage limiting circuit Low voltage breakdown Vb: 600mV ECE 501 Dr. Hang

Instrumentation Protection Circuit Back-to-back silicon Zener-diode voltage limiting circuit Moderate voltage breakdown Vb: 2 to 20 V ECE 501 Dr. Hang

Instrumentation Protection Circuit Gas-discharge tube (neon light) voltage limiting circuit High voltage breakdown Vb: 50 to 90 V ECE 501 Dr. Hang

Instrumentation Lead Selector Determine which electrodes are necessary for a particular lead and to connect them to the remainder of the circuit Controlled by the operator or by the microcomputer of the electrocardiograph ECE 501 Dr. Hang

Instrumentation Calibration A 1-mV calibration signal is momentarily introduced into the electrocardiograph for each channel that is recorded ECE 501 Dr. Hang

Instrumentation Preamplifier Differential amplifier with high common-mode-rejection ratio (CMRR) Analog filters ECE 501 Dr. Hang

Instrumentation Preamplifier ECE 501 Dr. Hang

Instrumentation Isolation Circuit Contains a barrier to the passage of current from the power line Transformer isolation amplifier Optical isolator Capacitively coupled isolation ampifier ECE 501 Dr. Hang

Transformer isolation amplifier Instrumentation Isolation Circuit Transformer isolation amplifier ECE 501 Dr. Hang

Instrumentation Isolation Circuit Optical Isolator ECE 501 Dr. Hang

Instrumentation Isolation Circuit Capacitively coupled isolation amplifier ECE 501 Dr. Hang

Driven right leg circuit Instrumentation Driven right leg circuit Provides a reference point on the patient that normally is at ground potential The connection is made to an electrode on the patient’s right leg ECE 501 Dr. Hang

Driven right leg circuit Instrumentation Driven right leg circuit ECE 501 Dr. Hang

Instrumentation Driver amplifier Amplify the ECG to a level at which it can appropriately record the signal on the recorder Carry out the bandpass filtering ECE 501 Dr. Hang

Instrumentation Memory System Store digital electrocardiograms from different leads Store patient information ECE 501 Dr. Hang

Instrumentation Microcomputer Control the overall operation Perform a preliminary analysis to determine heart rate recognize some types of arrhythmia calculate intervals ECE 501 Dr. Hang

Instrumentation Recorder-printer Provide a hard copy of the recorded ECG signal Print out patient information, results of the automatic analysis Analog oscillograph-type recorder, thermal recorder, electrostatic recorder ECE 501 Dr. Hang

Instrumentation Inference in ECG Effect of voltage transient from other devices, such as cardiac defibrillation ECE 501 Dr. Hang

60 Hz power-line inference Instrumentation Inference in ECG 60 Hz power-line inference ECE 501 Dr. Hang

Electromyographic(EMG) inference Instrumentation Inference in ECG Electromyographic(EMG) inference ECE 501 Dr. Hang

Instrumentation Inference in ECG Electromagnetic inference Twisting wires to minimize inference ECE 501 Dr. Hang

A mechanism of electric-field pickup from the powerline Instrumentation Inference in ECG A mechanism of electric-field pickup from the powerline ECE 501 Dr. Hang

Another mechanism of electric-field pickup from the powerline Instrumentation Inference in ECG Another mechanism of electric-field pickup from the powerline ECE 501 Dr. Hang