Chpt 2-Lec 3 Bioelectric Signals Monitoring PDF

Chapter 2 Bioelectric Signals Monitoring Learning Objective I. ECG II. EMG III. EEG IV. Sleep Study Bioelectric Signals Monitoring OCTOBER SEMESTER Bioelectric Potentials – Lets Revise… What is the purpose of 3, 5, and 12 leads ECG? How many electrodes are required in 1...

Chapter 2 Bioelectric Signals Monitoring Learning Objective I. ECG II. EMG III. EEG IV. Sleep Study Bioelectric Signals Monitoring OCTOBER SEMESTER Bioelectric Potentials – Lets Revise… What is the purpose of 3, 5, and 12 leads ECG? How many electrodes are required in 12 leads ecg? What are the groups of leads in a 12 leads ecg? What is Einthoven Triangle? What is the equations for each leads? How is the common point established in augmented limb leads? What happen to the right leg in all the leads? Bioelectric Signals Monitoring OCTOBER SEMESTER Electro-Conduction System of the Heart Cardiac Axis and 12 Leads ECG V6 RA LA V2 V1 V6 V5 V3 V5 V4 V4 N LL V1 V3 V2 Bioelectric Signals Monitoring OCTOBER SEMESTER Presentation title Electro-Conduction System of the Heart Cardiac Axis and 12 Leads ECG 6 unipolar chest leads Close to heart Examine horizontal cross-section of the heart Designated lead V1 to V6 V1 – Fourth intercostal space, right sternal border; V2 – Fourth intercostal space, left sternal border; V3 – Midway between V2 and V4; V4 – Fifth intercostal space, left midclavicular line; V5 – Level with V4 , left anterior auxillary line; V6 – Level with V4 , left mid auxillary line Bioelectric Signals Monitoring OCTOBER SEMESTER Presentation title Electro-Conduction System of the Heart Cardiac Axis and 12 Leads ECG 6 unipolar chest leads Individual chest leads is connected to amplifier’s non-inverting input The 3 limbs are averaged by summing them through a resistor network and then connected to amplifier’s inverting input This averaged point (known as Wilson terminal) is use as reference to record the chest points Wilson terminal equation : VW = (VLA + VRA + VLL)/3 Also known as “indifferent electrode” as the sum of all limb leads should theoretically give output of zero RL(Right leg) is the ground reference, must be connected to the ground of the amplifier Bioelectric Signals Monitoring OCTOBER SEMESTER Presentation title Electro-Conduction System of the Heart Cardiac Axis and 12 Leads ECG 6 unipolar chest leads (Wilson terminal connected to inverting input for all chest leads) LEAD V1 – V1 connected to amplifier’s non-inverting input, – Lead V1 = VC1 - (VLA + VRA + VLL)/3 = VC1 – VW Wilson - Terminal + V1 V2 V6 V3 V4 V5 LEAD V2 – V2 connected to amplifier’s non-inverting input, – Lead V2 = VC2 - VW Bioelectric Signals Monitoring OCTOBER SEMESTER Presentation title Electro-Conduction System of the Heart Cardiac Axis and 12 Leads ECG 6 unipolar chest leads (Wilson terminal connected to inverting input for all chest leads) LEAD V3 – V3 connected to amplifier’s non-inverting input, – Lead V3 = VC3 - VW LEAD V4 – V4 connected to amplifier’s non-inverting input, – Lead V4 = VC4 - VW LEAD V5 – V5 connected to amplifier’s non-inverting input, – Lead V5 = VC5 - VW LEAD V6 – V6 connected to amplifier’s non-inverting input, – Lead V6 = VC6 - VW Bioelectric Signals Monitoring OCTOBER SEMESTER Presentation title  https://www.youtube.com/watch?v=kwLbSx9BNb U 12 Lead ECG Explained, Animation Bioelectric Signals Monitoring OCTOBER SEMESTER Electro-Conduction System of the Heart Rhythm Strip ECG is printed on standard thermal ECG graph strips Each small square is 1 mm x 1 mm, big square is 5 mm x 5 mm Horizontal axis measures time, vertical axis measures voltage level Standard setting: 25mm/s recording speed and x1 sensitivity Equals 0.04s/small square And 0.1mV/small square Alternative settings: 0.1mV 50mm/s & 12.5mm/s (0.02s & 0.08s) x0.5, x1.5 & x2 (0.2mV, etc) 0.04s 1mm Bioelectric Signals Monitoring OCTOBER SEMESTER Electro-Conduction System of the Heart Rhythm Strip – Lead II ECG Waveform x = ~ 20 squares Sinus Rhythm Calculating the heart rate (HR) from rhythm strip (Regular rhythm method) Number of squares per minute : 60s/0.04s = 1500 OR (25mm/s X 60s) Number of squares per R-R interval : x = 20 squares HR = 1500/x = 1500/20 = 75 bpm Bioelectric Signals Monitoring OCTOBER SEMESTER Electro-Conduction System of the Heart Rhythm Strip – Lead II ECG Waveform Sinus Arrhythmia y = number of R-R interval in this 6 sec period (150 small squares) 1 2 3 4 5 6 7 Calculating the heart rate (HR) from rhythm strip (Irregular rhythm method) Number of R-R interval in 6 sec period : y = 7 R-R interval HR = y * 10 = 7 * 10 = 70 bpm Bioelectric Signals Monitoring OCTOBER SEMESTER Electro-Conduction System of the Heart Rhythm Strip Cardiac Arrhythmias Slow or fast rhythm (Bradycardia & Tachycardia) Propagation slow down (eg. PR timing) Blockage along conduction path (eg. AV block) Cardiac arrest Fibrillation – asynchronous excitation of the heart muscles (atrial or ventricle) Asystole Bioelectric Signals Monitoring OCTOBER SEMESTER Presentation title Electro-Conduction System of the Heart Electrocardiograph (ECG Machine) Sensing Driven electrodes Right-leg circuit Lead-fail detector Protection Pre - Isolation Driver circuit Lead circuit amplifier Recorder amplifier selector printer Isolated Main Auto Baseline power Power calibration restoration supply supply ADC Operator Microcontroller/ display microcomputer Memory Keyboard Control program/ ECG analysis program Bioelectric Signals Monitoring OCTOBER SEMESTER  Electro-Conduction System of the Heart Electrocardiograph (ECG Machine) Bio-amplifier Detect unconnected for amplifying Common mode lead or dry electrodes ECG signal amplifier for Right leg drive Pick up ECG signals Isolate patient Protect preamplifier ECG from the from high voltage recorder circuit pulses Selecting of different leads Provide isolated Calibrate the preamplifier power supply for Provide base the Iso-amplifier and the recorder with a line stability known pulse Bioelectric Signals Monitoring OCTOBER SEMESTER  Electro-Conduction System of the Heart Electrocardiograph (ECG Machine) Print out the ECG signal Boost the power requirements of preamplifier to drive recorder Digitize analogue Main DC (ECG) signal power supply Display parameters Hold and status digitized signals for Enter data and recording to control the ECG machine Control the various functions Control the operations of the microcontroller of the machine and analyses the acquired ECG data Bioelectric Signals Monitoring OCTOBER SEMESTER Electro-Conduction System of the Heart Electrocardiograph (ECG Machine) Sensing Electrodes – pick up ECG signals from the body Protection Circuit – prevents high voltage at the sensing electrodes from damaging the unit Lead Selector – determines which pair of electrodes to configure to give the specific lead. In the auto mode, each lead is recorded for 10s. In the manual mode, the duration of recording for the selected number of leads (channels) is control by user. Lead-fail Detector – detect unconnected lead or dry electrodes Auto calibration – calibrate the preamplifier and the recorder with a known pulse. Bioelectric Signals Monitoring OCTOBER SEMESTER Electro-Conduction System of the Heart Electrocardiograph (ECG Machine) Preamplifier – usually a differential amplifier and provides the initial amplification of raw ECG signal. It has a very high input impedance and Common mode rejection ratio (CMRR). Typically, dry skin impedance is 500Ω, wet skin impedance is 20kΩ, disease skin impedance is 500kΩ. The differential stage of 3 operating amplifiers constitutes a biopotential amplifier whose input impedance is 10 times bigger than source impedance. Baseline Restoration – a circuit to provide base line stability so that recorded signal will not drift. Bioelectric Signals Monitoring OCTOBER SEMESTER Electro-Conduction System of the Heart Electrocardiograph (ECG Machine) Driven Right leg Circuit – Provide a reference point at ground potential. It is used to maintain the Electrocardiograph and patient at equipotential with each other, thus, minimise common mode interference. Isolation Circuit –isolate patient ECG from the recorder circuit. The isolation circuit blocks out ac line noise interference (50Hz AC current) and also prevent high surge current flow to the ground (earth line) of Electrocardiograph when patient touches live wire. Isolated power supply – provide isolated power supply for the Iso - amplifier and patient circuit Bioelectric Signals Monitoring OCTOBER SEMESTER Electro-Conduction System of the Heart Electrocardiograph (ECG Machine) Analogue to Digital Converter – to digitize analogue (ECG) signal. Each lead (channel) is sampled for 10sec. Driver amplifier – further amplifies the ECG recording before it is send to recorder printer to boost the power requirements from preamplifier to drive recorder. Memory – stores digitized patient ECG signals and information Recorder Printer – print out the ECG signal on a strip chart paper Microcomputer –control the various functions of the machine Control Program – control the operations of the micro-controller Bioelectric Signals Monitoring OCTOBER SEMESTER Electro-Conduction System of the Heart Electrocardiograph (ECG Machine) ECG analysis Program – analyse the recorded ECG, determines heart rate, detects and analyses a types of arrhythmias Operator Display – display parameters and status. Keyboard – to enter data and to control the ECG machine. Main power supply – provide DC power supply. Bioelectric Signals Monitoring OCTOBER SEMESTER  Summary Cardiac Axis and 12 Leads ECG – Wilson terminal equation : VW = (VLA + VRA + VLL)/3 – Lead Vn = VCn - (VLA + VRA + VLL)/3 = VCn – VW Rhythm Strip –HR calculation – Regular rhythm method – Irregular rhythm method Electrocardiograph (ECG Machine) – Block Diagram Bioelectric Signals Monitoring OCTOBER SEMESTER