1、MEDICAL INSTRUMENTATION: Application and Design2013.3School of Life Science and Technology4.3 EMG measurement and device4.3.1 What is EMG4.3.2 Electrode of EMG 4.3.3 EMG machineElectromyography 肌電描記法Electrooculogram 肌電圖motor unit 運(yùn)動(dòng)單元Indwelling 留置,內(nèi)置Rectification 整流Electrooculogram 眼電圖Cornea 角膜Retin

2、a 視網(wǎng)膜Electronystagmogram 眼震圖Electrogastrogram 胃電圖 Bradygastria 胃動(dòng)過緩Tachygastria 胃動(dòng)過速M(fèi)uscle Physiology4.3.1 What is Electromyography (EMG)motor units Motor units: the biological unit of muscle function A motor unit is a single motor neuron and all of the corresponding muscle fibers it innervates One

3、muscle may have many motor units of different fiber types (slow or fast twitch) One motor unit can have from 5 to few thousands muscle fibers.The relationship between nerve and muscleA mammalian motor end plate (MEP)How it works髓磷脂The EMG obtained with various electrode types.The signal is the recor

4、ding of the action potentials from an entire muscle (or at least significant portion of one). It is a compound action potentialWhat is EMG signal? Reflects electrical field generated by Muscle Action Potentials (MAPs)4.3.2 Electrodes of EMG2 Basic CategoriesIndwelling （內(nèi)置，留置）Study activation of a si

5、ngle motor unitNeedleFine WireSurfaceStudy composite action of multiple motor unitsHypodermic（皮下） needle with insulated wire in its barrel Picture Source: Fine WireIndwelling ElectrodesAdvantagesExtremely sensitiveRecord single muscle activityAccess to deep musculature（肌肉組織）Little cross-talk concern

6、DisadvantagesExtremely sensitiveRequires medical personnel, certificationRepositioning nearly impossibleDetection area may not be representative of entire muscleSurface ElectrodesSurface ElectrodesAdvantagesQuick, easy to applyNo medical supervision, required certification Minimal fortDisadvantagesG

7、enerally used only for superficial musclesCross-talk concernsNo standard electrode placementMay affect movement patterns of subjectLimitations with recording dynamic muscle activitySurface Electrode PlacementAmplitude range: 010 mV (+5 to -5) prior to amplificationUseable energy: Range of 0 - 500 Hz

8、 Dominant energy: 50 150 HzElectrode PlacementAway from motor pointMUAP traveling in opposite directionsSimultaneous (+) & (-) APs Resultant increased frequency componentsMore jagged signalMiddle of muscle belly is generally acceptedElectrode PlacementAway from tendonFewer, thinner muscle fibersClos

9、er to other muscle origins, insertionsMore susceptible to cross-talkAway from outer edge of muscleCloser to other musculatureOrientation（方向） parallel to muscle fibersMore accurate conduction velocityIncreased probability of detecting same signalReference Electrode Placement (Ground)As far away as po

10、ssible from recording electrodesElectrically neutral tissueBony prominenceGood electrical contactLarger sizeGood adhesive properties4.3.3 EMG DeviceAmplifier Gain and dynamic rangeEMG signals: ( desired output 05 V)Surface: 100V to 5 mVIndwelling: up to 10 mVNoise level: 2050 VRange of selectable ga

11、in: 100 to 10000System mendationsDetection Surfaces2 parallel bars, each 1.0 cm (L) x 1-2 mm (W)Spacing between bars is 1.0 cm apartFrequency Bandwidth of 20-500 HzCommon Mode Rejection Ratio 80 dBNoise 100 MPost Processing of EMG DataRectifyFilterLow pass linear envelop ( 3 Hz cutoff)Band pass filt

12、er (10 20 Hz, signal passes between)Integrated EMG (IEMG)NormalizeDetermining onset and offset of muscle activationRectifiers (整流器) One-op-amp full-wave rectifier. For vi 0, the op amp disconnects and the passive resistor chain yields a gain of +0.5.Full-wave precision rectifier. For vi0, D2, D3 con

13、duct, the noninverting amplifier at the top is active, making vo 0. For vi 0.Raw EMGFull Wave RectifiedREMG = |raw EMG|Linear EnvelopButterworth 2nd order, cutoff = 2 HzLinear EnvelopButterworth 2nd order, cutoff = 3 HzLinear EnvelopButterworth 2nd order, cutoff = 10 HzBandpass Filter Cutoffs 10 and

14、 20 HzKeeps EMG signal between 10 and 20 Hz (i.e., it passes through the filter unattenuated)IntegratedIEMG = EMG(t)dttTRoot Mean Square (RMS)RMS = (1/T EMG(t)2 dt) tTNormalized EMGNorm EMG = EMG / max(EMG during norm trial)Ultimately trying to find the greatest possible EMG and relate the EMG durin

15、g the trial to that max (% of max EMG possible). But this needs to be done consistently.Illustration of Temporal ValuesOnsetOffsetDurationSummary4.3.1 What is EMG4.3.2 Electrode of EMG 2 Basic Categories Electrode Placement4.3.3 EMG machine System diagram Rectify Filter4.4 Other bio-potential measur

16、ement and device 4.4.1 EOG (Electrooculogram)4.4.2 EGG (Electrogastrogram)4.4.1 EOG (Electrooculogram) A record of the difference in electrical charge between the front and back of the eye that is correlated with eyeball movement (as in REM sleep) and obtained by electrodes placed on the skin near t

17、he eye.What is EOG?photosensitive component: Retina optical energy electrical energyAnatomy and physiology of the eyeOrigin of EOGthe cornea of the eye is electrically positive relative to the back of the eye This source behaves as if it were a single dipole oriented from the retina to the cornea Ey

18、e movements thus produce a moving (rotating) dipole source Electrooculogram (EOG)Records the movements (and direction) of the eyes by electrodes placed over the muscles that move the eyeCan have binocular or monocular set-up (binocular more reliable)Head must be kept still so the center of the visua

19、l field is constantIdeal impedance of the electrodes is under 2,000 ohms (we have been dealing with impedances under 50 Kohms)Binocular Electrode PlacementElectrodes A & B are used to measure horizontal eye movementsElectrodes C & D measure vertical eye movementsElectrode E is the groundFigure 5.13E

20、OG Recording(1) one second timer; (2) horizontal unipolar reading;(3) horizontal bipolar reading; (4) marking channel with artifact noiseENG (electronystagmogram,眼震圖)An electronystagmogram (ENG) measures normal eye movement and involuntary rapid eye movements called nystagmus（眼球振顫） ENG checks how we

21、ll the eyes, inner ears, and brain help you keep your balance and position 4.4.2 EGG (Electrogastrogram)What is EGGMeasures muscle activity related to the stomach and abdominal region.Measured from a baseline reading containing a regular rhythm. In a normal subject a current increase is observed after a meal.Still an early experimental procedure because it has