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5th practice Medical Informatics Biomedical Signal Processing TAMUS, Zoltán Ádám

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Presentation on theme: "5th practice Medical Informatics Biomedical Signal Processing TAMUS, Zoltán Ádám"— Presentation transcript:

1 5th practice Medical Informatics Biomedical Signal Processing TAMUS, Zoltán Ádám

2 The electrical manifestation of the contractile activity of the heart The ECG can be easily recorded with surface electrodes on the limbs or chest (Einthovens triangle) The waveshape is altered by cardiovascular diseases

3 Einthovens triangle

4 The ECG is an electrical signal (function of time)

5 The SA node fires

6 Slow-moving depolarization (contraction) of the atria The P wave in ECG mV ms

7 Propagation delay at atrio- venricular (AV) node Normally iso- electric segment PQ segment ms

8 His bundle, the bundle branches, and the Purkinje system of specialized conduction fibers propagate the stimulus to the ventricles at high rate

9 The wave of stimulus spreads rapidly from the apex of the heart upwards Rapid depolarization (contraction) of ventricles QRS wave 1 mV 80 ms

10 The ventricular muscle cells possess a relatively long action potential ms Result: iso- electric segment ST segment ms

11 Repolarization (relaxation) of ventricles causes slow T wave mV ms

12 Physiological interference Respiration, squirms, coughs etc. Mothers ECG appearing with the ECG of the fetus Electromagnetic interference TV and radiostations, CRTs, computers, fluorescent lamps Result: noise in the ECG signal

13 Signal Deterministic signal: the value at a given instance of time may be computed using a closed-form mathematical function of time or Predicted from a knowledge of a few past values of the signal Nondeterministic signal (random signal): That does not meet the conditions of the deterministic signal The noise may be random, structured (deterministic) and physiological

14 Random noise ensemble average: 0 Reduction: Moving Average (MA) filter general form: b k :filter coefficients

15 Examples of MA filters von Hann or Hanning filter: 8-point average:

16 Rangaraj M. Rangayyan: Biomedical Signal Analysis, IEEE Press/Wiley, New York, NY, 2002.

17 1. Observation of noisy ECG signal 2. Filtering the noisy ECG signal by MA filter von Hann or Hanning filter 8-point MA filter sample files: software: MS Excel


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