1. ECE 501 Introduction to BME
Dr. Hang

2. Part IV Bioinstrumentation Electrocardiogram
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Dr. Hang

3. Introduction
Physiology
Medicine
Instrumentation
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Dr. Hang

4. Medicine
The Electrical Cycle
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Dr. Hang

5. 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.
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6. Medicine
ECG Waves
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7. Medicine
ECG Intervals
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8. 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
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9. 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
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10. Medicine Heart Flutter Paroxysmal Tachycardia
An abnormal pacemaker in ventricle may discharge at a rapid rate
Ventricles depolarize irregularly at a high rate
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11. Medicine Heart Flutter Atrial Flutter
An abnormal pacemaker in atria may discharge at a rapid rate
Atria depolarize irregularly at a high rate
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12. Premature V- Contraction
Medicine
Premature V- Contraction
An accidental pacemaker within the ventricle causes an extra beat (extrasystole)
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Dr. Hang

13. Medicine Fibrillation Atrial Fibrillation Atria twitch irregularly
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14. Medicine Fibrillation Ventricular Fibrillation
Ventricles twitch irregularly
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15. Medicine Ischemia Deficient in blood supply due to coronary occlusion
Early stage: ST elevation
Late stage: ST elevation + TQ depression
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Dr. Hang

16. 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
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Dr. Hang

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

18. 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
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Dr. Hang

19. Instrumentation
ECG leads –Limb leads
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Dr. Hang

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

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

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

23. 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
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Dr. Hang

24. Instrumentation Block Diagram of an Electrocardiograph Dr. Hang
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Dr. Hang

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

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

27. Instrumentation Protection Circuit
Back-to-back silicon Zener-diode voltage limiting circuit
Moderate voltage breakdown
Vb: 2 to 20 V
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28. Instrumentation Protection Circuit
Gas-discharge tube (neon light) voltage limiting circuit
High voltage breakdown
Vb: 50 to 90 V
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Dr. Hang

29. 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
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Dr. Hang

30. Instrumentation Calibration
A 1-mV calibration signal is momentarily introduced into the electrocardiograph for each channel that is recorded
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31. Instrumentation Preamplifier
Differential amplifier with high common-mode-rejection ratio (CMRR)
Analog filters
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32. Instrumentation
Preamplifier
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33. Instrumentation Isolation Circuit
Contains a barrier to the passage of current from the power line
Transformer isolation amplifier
Optical isolator
Capacitively coupled isolation ampifier
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Dr. Hang

34. Transformer isolation amplifier
Instrumentation
Isolation Circuit
Transformer isolation amplifier
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Dr. Hang

35. Instrumentation
Isolation Circuit
Optical Isolator
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Dr. Hang

36. Instrumentation Isolation Circuit
Capacitively coupled isolation amplifier
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Dr. Hang

37. 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

38. Driven right leg circuit
Instrumentation
Driven right leg circuit
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Dr. Hang

39. 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
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40. Instrumentation Memory System
Store digital electrocardiograms from different leads
Store patient information
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41. Instrumentation Microcomputer Control the overall operation
Perform a preliminary analysis to
determine heart rate
recognize some types of arrhythmia
calculate intervals
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Dr. Hang

42. 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
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Dr. Hang

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

44. 60 Hz power-line inference
Instrumentation
Inference in ECG
60 Hz power-line inference
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Dr. Hang

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

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

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

48. 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