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1 In The Name of Allah The Most Beneficent The Most Merciful ECE 4550: Biomedical Instrumentation Lecture: Electro Myo Gram (EMG) Engr. Ijlal Haider University of Lahore, Lahore 2 3 Electrical Activities of Muscles Similar to that of nerve fibers Except that magnitude of potentials and time duration are different Conduction velocities are less (muscle fibers are smaller in length, so not a big issue) Nerve fibers opens in muscles fibers through a junction 5 Muscle Potential is generated in almost the same way as a Nerve Potential is generated (l.e. due to change in ionic concentrations) Visit following link to know more about generation of muscle potential http://highered.mcgrawhill.com/sites/0072495855/student_view0/cha pter10/animation__action_potentials_and_mu scle_contraction.html 6 A wave of excitation along a muscle fiber initiated at the neuromuscular endplate; accompanied by chemical and electrical changes at the surface of the muscle fiber and by activation of the contractile elements of the muscle fiber; detectable electronically (electromyographically); and followed by a transient refractory period. 7 Sensory Nerves Motor Nerves 8 9 Voluntary Muscle System (Normal Muscles-under our conscious control) Automatic Muscle System (Smooth Muscles-not under our conscious control) Electromyogram Greek words MYOS-Muscle GRAM-Picture Picture of Electrical Activities of Muscles Voluntary (under willful action of brain) Not good for diagnosis of muscle disorders which has to be diagnosed early Evoked (on artificial stimulation) Measurement of Potetial Difference How do we get a potential difference between two points outside a muscle fiber (or a nerve fiber??) When Fully Polarized!! Partially Depolarized!! Fully Depolarized!! When there is partially depolarization, ionic current start flowing which gives rise to voltage In case of fully polarized or fully depolarized, no current flows and hence we don’t get any voltage out Voluntary EMG Measurement Using Skin Surface electrodes Using Needle electrodes Monopolar Bipolar Skin Surface Electrodes Compound or composite of Muscle Action Potential from individual muscle fibers is recorded Sometime called Interference Pattern Contribution from muscle fibers will depend on the closeness and proximity to the electrodes We cannot make out much on the origin of these signals We can only use it to find gross muscular disorders Which can already be felt by muscle weakness and can be visually seen as wasted muscle Skin Surface Electrodes Surface electrodes are not very much used for the diagnosis of muscle disorders They are used majorly for evoked potential study in Nerve Conduction Velocity (NCV) measurement Bio feedback study or exercise (kind of mitigation or relaxing) Another application is Bio-feedback for stroke recovery Needle Electrodes Monopolar Similar to a coaxial We use instrumentation (differential) amplifiers Requires 3 probes Active, Reference, Common Common is taken from a skin surface electrode Needle Electrodes Bipolar In contrast to monopolar electrodes, bipolar have two electrodes inside and one outside Instrument amplifiers are used All three probes are taken from the bipolar needle electrode itself Mostly used for research purpose Needle EMG Used for diagnosis of muscle disorders Helps in localizing a focus of disorder As injecting a pin (needle) inside skin is painful and to diagnose properly multiple points are needed, the whole process becomes very painful To reduce pain, insertion points are reduced and in each points the angle of pin is changed without bringing needle outside the skin (mostly 3 angles) Analysis of EMG Analysis is done empirically by doctors (clinical experiences) Looks for EMG patterns when the needle is being inserted Listens to the sound produced by feeding the muscle signal into a loud speaker Also looks at the pattern and listens to the sound on mild voluntary contraction Analysis of EMG Signal Processing in EMG For automated diagnosis, pattern recognition techniques are being investigated Old instruments used to have integrators Analysis of EMG Simple EMG Block Diagram of EMG Amplifiers Filter Display Integrator (signal processing unit) Audio amplifier Measurement of NCV Using evoked potential Through artificial stimulation of nerve For example by giving a voltage of 100 volts for very short time approximately 2 msec, hand movements must be observed --fig. evoking an action potential using surface electrodes Nothing happens under anode (+ve electrode) Reversal of transmembrane potential occurs under cathode (-ve electrode) This causes generation of an action potential Generated action potential travels along the nerves Similar to a sprint race where a stopwatch is pressed on when runner starts and time is recorded untill he reaches the finish line and velocity is calculated from the distance travelled and time, NCV is recoded by measuring the time for nerve action potential to travel a distance “d” from stimulation point to recording point Sensory NCV Nerve stimulator applies stimulation through ring electrodes at fingers Median Nerve contains both sensory and motor nerves Recording site is selected near middle of arm Conventions Cathode of the stimulation electrodes is kept near the recording side, so that action potential is not perturbed by anode) Recording electrode which is towards the stimulation side is connected to the inverting input of the amplifier Common electrode is placed ideally at an equidistant point from both electrodes (to have min common mode voltage) --fig. stimulation pulse --fig. recording side, stimulation artifacts and compounded action potential Latency of the pulse is recorded SNVC=d/∆t Motor NCV In contrast to SNCV measurement, MNCV measurement involves stimulating at two sites and recording at one For median nerve Stimulation sites Wrist Elbow Recording site Thenar Muscle Why we stimulate on two sites? Neuromuscular junction has unknown delay Record latencies of proximal and distal stimulation sites individually (let t1 and t2 be the latencies of both respectively) Distance between both stimulation sites is taken --fig. MNVC signals MNCV=d/(t2-t1) Diagnosis and Diseases If either SNCV or MNCV is significantly less then normal values? Is the distal latency prolonged? Causes of low NCV Demyelination Conduction block Axonopathy Disorders Peripheral Neurotherapy Carpel Tunnel Syndrome GB Syndrome Nerve Stimulator For a single pulse: Monostable Multi-vibrator For repetitive pulses: Astable Multi-vibrator Amplitude required: 100-200 volts Pulse duration: less then 2msec Peak current requirement near to 20 mA (max 50 mA) Power requirement (for peak power 300x50mA) 36 Commonly measured Upper limb, Median, Ulnar, Radial, Lower Limb, Common Peroneal, Tibial Class Activity 37 Thank You!
