In The Name of Allah The Most Beneficent The Most Merciful

1. In The Name of Allah The Most Beneficent The Most Merciful

2. ECE 4552:Medical Electronics Lecture:Electro-Myo Gram (EMG) Engr. Ijlal Haider Electrical Engineering Dept. University of Lahore, Lahore

3. Types of Nerves • Sensory Nerves • Nerves that carry information from sensory parts to the brain • Motor Nerves • Nerves that carry information from brain to actuating parts

4. Types of Nerves

5. Motor Units

6. Electromyogram • Greek words • MYOS-Muscle • GRAM-Picture • Picture of Electrical Activities of Muscles

7. Stimulus • Voluntary (under willful action of brain) • Not good for diagnosis of muscle disorders which has to be diagnosed early • Impulses travel in only one direction • Evoked (on artificial stimulation) • Impulses travel in both directions

8. EMG • Using Skin Surface electrodes • Using Needle electrodes • Monopolar • Bipolar

9. Measurement of Potential 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!!

10. Measurement of Potential Difference • 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

11. 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

12. 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 • Physiotherapy or exercise (kind of mitigation or relaxing) • Another application is Bio-feedback for stroke recovery

13. 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

14. Needle Electrodes • Bipolar • In contrast to mono-polar 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

15. 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)

16. 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

17. Analysis of EMG • Signal Processing in EMG • For automated diagnosis, pattern recognition techniques are being investigated • Neural Networks, Genetic Algorithms and other AI techniques are/can be used • Old instruments used to have integrators

18. Analysis of EMG • Simple Block Diagram of EMG • EMG Amplifiers • Filter • Display • Signal processing unit/ Intelligent Systems • Audio amplifier

19. 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

20. Evoked Potential • Nothing happens under anode (+ve electrode) • Reversal of trans-membrane potential occurs under cathode (-ve electrode) • This causes generation of an action potential • Generated action potential travels along the nerves in both directions

21. Measurement of NCV • 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

22. 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

23. Sensory NCV • 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)

24. Sensory NCV • --fig. stimulation pulse • --fig. recording side, stimulation artifacts and compounded action potential • Latency of the pulse is recorded • SNVC=d/∆t

25. 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

26. Motor NCV • 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)

27. Diagnosis and Diseases • If either SNCV or MNCV is significantly less then normal values? • Is the distal latency prolonged?

28. Diagnosis and Diseases • Causes of low NCV • Demyelination • Conduction block • Axonopathy

29. Diagnosis and Diseases • Disorders • Peripheral Neurotherapy • Carpel Tunnel Syndrome (Wrist) • GB Syndrome • Cervical Spondylosis (Neck) • Lumbo-Sacral Spondylosis(Waist)

30. EMG For Prosthesis • EMG signals are used to study the electrical activities of muscles under certain movements • EMG signals are picked up from certain points and fed to the prosthetic limb or exoskeleton

31. 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 peakpower 300x50mA)

32. Commonly measured • Upper limb, Median, Ulnar, Radial, Lower Limb, Common Peroneal, Tibial • Class Activity

33. Thank You!