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ECG

ECG. Standard external ECG starts with three electrodes and four wires. . Right leg is typically connected to ground or a driven-right-leg circuit. Voltages from the other three electrodes are combined to create 6 leads. Standard ECG electrodes/leads. Right arm electrode. Left arm electrode.

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ECG

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  1. ECG 415-7

  2. Standard external ECG starts with three electrodes and four wires. Right leg is typically connected to ground or a driven-right-leg circuit. Voltages from the other three electrodes are combined to create 6 leads. 415-7

  3. Standard ECG electrodes/leads Right arm electrode Left arm electrode Left leg electrode 415-7

  4. Heart at equilibrium polarizationNo cardiac vector 415-7 From Bioelectromagnetism, http://www.bem.fi/book/index.htm

  5. Atria depolarizeCell exteriors become more negative as Na+ enters the cell 415-7 From Bioelectromagnetism, http://www.bem.fi/book/index.htm

  6. Pause at the AV node 415-7 From Bioelectromagnetism, http://www.bem.fi/book/index.htm

  7. Septal depolarization begins 415-7 From Bioelectromagnetism, http://www.bem.fi/book/index.htm

  8. Ventricular depolarization continues 415-7 From Bioelectromagnetism, http://www.bem.fi/book/index.htm

  9. Ventricular depolarization continues on left side (more muscle, must pump to entire body) Note that atria repolarized, but we didn’t even notice because ventricles are so much bigger and create a much bigger voltage. 415-7 From Bioelectromagnetism, http://www.bem.fi/book/index.htm

  10. 415-7 From Bioelectromagnetism, http://www.bem.fi/book/index.htm

  11. Complete ventricular depolarization 415-7 From Bioelectromagnetism, http://www.bem.fi/book/index.htm

  12. Ventricular repolarization begins 415-7 From Bioelectromagnetism, http://www.bem.fi/book/index.htm

  13. Heart is polarized, ready to beat again 415-7 From Bioelectromagnetism, http://www.bem.fi/book/index.htm

  14. Standard Lead II ECG with standard scaling P wave – atrial depolarization PR interval – pause at AV node QRS complex – ventricular depolarization (hiding atrialrepolarization) ST interval – plateau in action potential of ventricular cells T wave – ventricular repolarization U wave – often not seen; repolarization of muscles that aid in opening mitral and aortic valves? 415-7 From Bioelectromagnetism, http://www.bem.fi/book/index.htm

  15. Lead II showing characteristic features This chart does not show a strong Q (downward deflection just prior to R wave). 415-7

  16. Biopotential amplifier(saved from this week, but retest next) 415-7

  17. Next week we will be powering it with 9V batteries • Connected to circuit ground or reference, not earth ground • Test batteries for freshness - + - + 415-7

  18. ECG has additional filtering and gain 415-7

  19. What does this circuit do? • Analyze it in the frequency domain (i.e., with phasors) 415-7

  20. c = 22e-6; r = 100e3; rf = 150e3; cf = 0.01e-6; ri = 5e3; jw = tf('s'); Ghp = jw*r*c/(1 + jw*r*c); zcf= 1/(jw*cf); zf = rf*zcf/(rf + zcf); zi = ri; Goa = (1 + zf/zi); G = Ghp*Goa; [mag, phase, w] = bode(G); magdb = 20*log10(squeeze(mag)); f = w'/2/pi; semilogx(f, magdb); xlabel('frequency (Hz)');ylabel('magnitude (dB)'); • Define component values • Define Fourier or phasor variable (really LaPlace variable, but we just care about jw) • Define transfer function of high pass filter • Find impedances for op amp gain • Define transfer function of op amp circuit • Find overall gain • Calculate Bode plot data • Find magnitude in dB • Calculate frequency in Hz • Plot on log axis • Label axes 415-7

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  22. Add software filtering • Line noise • Additional high- and low-pass • Show both filtered and unfiltered for comparison 415-7

  23. Testing your ECG circuit • Test with a sawtooth waveform at 1-2 Hz, first with DC power supply, then with batteries. • Then test with the ECG simulator and batteries. We only have one so share! 415-7

  24. You can also test with the PC • Course website contains directions for downloading ECG data in an audio file (.wav) • Play the file with Windows Media Player • Volume controls amplitude (turn volume down) • Set to repeat • Cables with a headphone plug on one end and breadboard wires on the other will be provided 415-7

  25. Before attaching your circuit to your lab partner you must have your TA check it 415-7

  26. 415-7

  27. Three electrodes per team • Apply to upper arms and lower thigh • Wear shorts if possible • Use short black, green, and white wires with alligator clips to attach electrodes to circuit • Use alcohol to remove Floating disc Ag/AgCl electrodes Designed for short-term monitoring 415-7

  28. What should be attached to the three circuit inputs to measure Lead I? 415-7

  29. What should be attached to the three circuit inputs to measure Lead II? 415-7

  30. We don’t see anything! • Make sure your batteries aren’t dead • Adjust the gain • More or less? • Adjust the cutoff frequencies of your filters • Set up your DAQ to see a few heartbeats per acquisition 415-7

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