Amplificador de Biopotencial

Transcription

1 Amplificador de Biopotencial Prof. Sérgio F. Pichorim Baseado no cap 6 do Webster e cap 17 do Kutz & Towe From J. G. Webster (ed.), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

2 Right leg electrode Sensing electrodes Lead-fail detect Driven right leg circuit ADC Memory Amplifier protection circuit Lead selector Amplifier Isolation circuit Driver amplifier Recorder printer Auto calibration Baseline restoration Isolated power supply Parallel circuits for simultaneous recordings from different leads Micro computer Control Figure 6.7 Block diagram of an electrocardiograph program Operator display Keyboard ECG analysis program From J. G. Webster (ed.), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

3 Figure 6.27 Block diagram of a system used with cardiac monitors to detect increased electrode impedance, lead wire failure, or From J. G. Webster (ed.), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, electrode fall-off.

4 Composição espectral dos sinais captados pelos eletrodos de ECG e composições espectrais de artefatos de movimento e ruído muscular From J. G. Webster (ed.), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, (EMG), sinais que interferem no registro do ECG.

5 Efeito de filtragem inadequada do sinal de ECG From J. G. Webster (ed.), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

6 Faixa dos Filtros: 0,5 a 40 Hz para Monitor de ECG 0,01 a 150 Hz para Eletrocardiógrafo Outros: Detector de onda R Rejeita 60 Hz (filtro notch) From J. G. Webster (ed.), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

7 Figure 6.8 Effect of a voltage transient on an ECG recorded on an electrocardiograph in which the transient causes the amplifier to saturate, and a finite period of time is required for the charge to bleed off enough to bring the ECG back into the amplifier s active region From J. G. Webster (ed.), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, of operation. This is followed by a first-order recovery of the system.

8 RESTAURAÇÃO RÁPIDA DA LINHA DE BASE From J. G. Webster (ed.), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

9 Figure 6.9 (a) 60 Hz power-line interference. Neste exemplo: ECG com 1mVpp e ruído com 200 µvpp (b) Electromyographic interference on the ECG. From J. G. Webster (ed.), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

10 From J. G. Webster (ed.), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, BIOELECTRICITY by TOWE in STANDARD HANDBOOK of BIOMEDICAL ENG. and DESIGN by KUTZ (2002) Cap 17

11 From J. G. Webster (ed.), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, BIOELECTRICITY by TOWE in STANDARD HANDBOOK of BIOMEDICAL ENG. and DESIGN by KUTZ (2002) Cap 17

12 From J. G. Webster (ed.), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, BIOELECTRICITY by TOWE in STANDARD HANDBOOK of BIOMEDICAL ENG. and DESIGN by KUTZ (2002) Cap 17

13 From J. G. Webster (ed.), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, BIOELECTRICITY by TOWE in STANDARD HANDBOOK of BIOMEDICAL ENG. and DESIGN by KUTZ (2002) Cap 17

14 Power line 120 V C 2 C 1 C 3 Z 1 I d1 A Z 2 I d2 B Electrocardiograph G Z G I d1+ I d2 Figure 6.10 A mechanism of electric-field pickup of an electrocardiograph resulting from the power line. Coupling capacitance between the hot side of the power line and lead wires causes current From J. G. Webster (ed.), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

15 Power line 120 V C b i db Electrocardiograph υ cm υ cm Z 1 A Z in Z 2 B Z in υ cm G Z G i db Figure 6.11 Current flows from the power line through the body and ground impedance, thus creating a common-mode voltage everywhere From J. G. on Webster the (ed.), body. Medical Zinstrumentation: is not application only resistive and design. 3 rd ed. but, New York: as John a result Wiley & Sons, of RF bypass capacitors at the amplifier input.

16 Figure 6.12 Magnetic-field pickup by the elctrocardiograph (a) Lead wires for lead I make a closed loop (shaded area) when patient and electrocardiograph are considered in the circuit. The change in magnetic From J. G. Webster field (ed.), passing Medical instrumentation: through application this and area design. induces 3 rd ed. New York: a current John Wiley & Sons, in the loop.

17 Figure 6.13 A voltage-protection scheme at the input of an electrocardiograph to protect the machine from high-voltage transients. Circuit elements connected across limb leads on lefthand From J. side G. Webster are (ed.), voltage-limiting Medical instrumentation: application devices. and design. 3 rd ed. New York: John Wiley & Sons, 1998.

18 Figure 6.14 Voltage-limiting devices (a) Current-voltage characteristics of a voltage-limiting device. (b) 0,7V Parallel silicondiode voltage-limiting circuit. (c) 2 to 20 V Back-to-back silicon Zener-diode voltage-limiting circuit. (d) 50 to 90 V Gas-discharge From J. G. Webster (ed.), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, tube (neon light) voltage-limiting circuit element.

19 i d υ 3 + R a R a υ cm + υ 4 R f RL Auxiliary op amp + R o R RL Figure 6.15 Driven-right-leg circuit for minimizing commonmode interference The circuit derives common-mode voltage from a pair From of J. G. averaging Webster (ed.), Medical resistors instrumentation: connected application and design. to v 3 and rd ed. New vyork: 4. The John Wiley right & Sons, leg is not grounded but is connected to output of the auxiliary op amp.

20 R a /2 R f i d 2υ cm /R a υ o /R f υ cm + R o υ o υ cm + R RL i d Figure E6.1 Equivalent circuit of driven-right-leg system. From J. G. Webster (ed.), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

21 Figure 6.16 Voltage and frequency ranges of some common biopotential signals; dc potentials include intracellular voltages as well as voltages measured from several points on the body (EOG, From J. G. Webster (ed.), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, EEG, ECG, EMG, and AAP is the axon action potential).

22 igure 6.18 This ECG amplifier has a gain of 25 in the dc-coupled stages. The highass filter feeds a noninverting-amplifier stage that has a gain of 32. The total gain is 5 32 = 800. When µa 776 op amps were used, the circuit was found to have a MRR From J. of G. 86 Webster db (ed.), at Medical 100 Hz instrumentation: and a noise application level and of design. 403 mv rd ed. New peak York: to John peak Wiley & at Sons, the output. he frequency response was Hz for ±3 db and was flat over 4-40 Hz.

23 From J. G. Webster (ed.), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, BIOELECTRICITY by TOWE in STANDARD HANDBOOK of BIOMEDICAL ENGINEERING and DESIGN by KUTZ (2002) Cap 17

24 From J. G. Webster (ed.), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

25 From J. G. Webster (ed.), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.

26 From J. G. Webster (ed.), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 1998.