1 ECG Signal Make-up

2 Biopotential Requirements n High Input Impedance –Minimum loading of the signal being measured –Minimum 10M  n Input circuit must have isolation and protection circuits to protect the patient n Output Impedance must be low compared to the load impedance n Proper bandwidth range. Not too narrow and not too wide n Gain at least 1000 times n For bipolar electrodes, use differential amplifier

3 ECG Functional Blocks 1. Protection circuit 2. Lead selector 3. Calibration signal 4. Preamplifier 5. Isolation circuit 6. Driven right leg system 7. Driver amplifier 8. Memory System 9. Microcomputer 10. Recorder - Printer

4 The Electrocardiogram n Outline n The ECG n Specific Requirements n Functional Blocks n Frequent Problems n Some Solutions

5 Heart Dipole

6 Cardiac Vector

7 Eindhoven’s Triangle

8 Wilson’s Central Terminal Connection

9 Augmented Leads

10 Comparing Augmented leads to Standard Leads

11 Precordial Leads

12 Problems Frequently Encountered n Frequency Distortion n Saturation or Cutoff Distortion n Ground Loops n Open Lead Wires n Artifacts from Large Electric Devices n Interference From Electric Devices n Electromagnetic Interference

13 Frequency Distortion

14 Saturation - cutoff Distortion

15 Ground Loops

16 Ground Loops - 2

17 Artifacts from large electric devices

18 (a) 60 Hz Line Interference (b) EMG interference

19 Mechanism of electric-field pickup from Power line

20 Current flows from the power line into the body

21 Magnetic-field Pickup by ECG

22 Voltage protection scheme at input

23 Voltage limiting device

24 Electrostatic Shield - to eliminate electric-field interference

25 Driven-Right-Leg System

26 Equivalent Ct. of a driven right leg system

27 Bio-Signals Charachteristics

28 ECG Amplifier

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