1 ecg signal make-up. 2 biopotential requirements n high input impedance –minimum loading of the...

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ECG Signal Make-up

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Biopotential Requirements High Input Impedance

– Minimum loading of the signal being measured– Minimum 10M

Input circuit must have isolation and protection circuits to protect the patient

Output Impedance must be low compared to the load impedance

Proper bandwidth range. Not too narrow and not too wide

Gain at least 1000 times For bipolar electrodes, use differential amplifier

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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

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The Electrocardiogram

Outline The ECG Specific Requirements Functional Blocks Frequent Problems Some Solutions

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Heart Dipole

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Cardiac Vector

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Eindhoven’s Triangle

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Wilson’s Central Terminal Connection

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Augmented Leads

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Comparing Augmented leads to Standard Leads

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Precordial Leads

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

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Frequency Distortion

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Saturation - cutoff Distortion

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Ground Loops

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Ground Loops - 2

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Artifacts from large electric devices

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

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Mechanism of electric-field pickup from Power line

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Current flows from the power line into the body

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Magnetic-field Pickup by ECG

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Voltage protection scheme at input

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Voltage limiting device

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Electrostatic Shield - to eliminate electric-field interference

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Driven-Right-Leg System

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Equivalent Ct. of a driven right leg system

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Bio-Signals Charachteristics

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ECG Amplifier

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