I N T HE N AME OF A LLAH T HE M OST B ENEFICENT T HE M OST M ERCIFUL 1

ECE 4552: M EDICAL E LECTRONICS L ECTURE : E LECTRO -M YO G RAM (EMG) Engr. Ijlal Haider Electrical Engineering Dept. University of Lahore, Lahore 2

T YPES OF N ERVES Sensory Nerves Nerves that carry information from sensory parts to the brain Motor Nerves Nerves that carry information from brain to actuating parts 3

T YPES OF N ERVES 4

M OTOR U NITS 5

E LECTROMYOGRAM Greek words MYOS-Muscle GRAM-Picture Picture of Electrical Activities of Muscles

S TIMULUS 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

EMG Using Skin Surface electrodes Using Needle electrodes Monopolar Bipolar

M EASUREMENT OF P OTENTIAL D IFFERENCE 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!!

M EASUREMENT OF P OTENTIAL D IFFERENCE 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

S KIN S URFACE E LECTRODES 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

S KIN S URFACE E LECTRODES 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

N EEDLE E LECTRODES Monopolar Similar to a coaxial We use instrumentation (differential) amplifiers Requires 3 probes Active, Reference, Common Common is taken from a skin surface electrode

N EEDLE E LECTRODES 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

N EEDLE 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)

A NALYSIS 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

A NALYSIS 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

A NALYSIS OF EMG Simple Block Diagram of EMG EMG Amplifiers Filter Display Signal processing unit/ Intelligent Systems Audio amplifier

M EASUREMENT 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

E VOKED P OTENTIAL 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

M EASUREMENT 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

S ENSORY 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

S ENSORY 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)

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

M OTOR 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

M OTOR 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)

D IAGNOSIS AND D ISEASES If either SNCV or MNCV is significantly less then normal values? Is the distal latency prolonged?

D IAGNOSIS AND D ISEASES Causes of low NCV Demyelination Conduction block Axonopathy

D IAGNOSIS AND D ISEASES Disorders Peripheral Neurotherapy Carpel Tunnel Syndrome (Wrist) GB Syndrome Cervical Spondylosis (Neck) Lumbo-Sacral Spondylosis (Waist)

EMG F OR P ROSTHESIS 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 30

N ERVE S TIMULATOR For a single pulse: Monostable Multi-vibrator For repetitive pulses: Astable Multi-vibrator Amplitude required: volts Pulse duration: less then 2msec Peak current requirement near to 20 mA (max 50 mA) Power requirement (for peak power 300x50mA)

C OMMONLY MEASURED Upper limb, Median, Ulnar, Radial, Lower Limb, Common Peroneal, Tibial Class Activity 32

T HANK Y OU ! 33