EE 4BD4 Lecture 10

Electromyography

Goals of Electromyography

• Diagnosis (Identify Neuromuscular Disease, e.g. ALS, muscular dystrophy)

• Determine extent of disease and monitor progress

• Study control of muscles during movement• Measure dysfunction and propose solutions• Study normal anatomy and physiology

Surface Diagnostic Techniques(Motor and Sensory Conduction)

Patient Instrumentation(Sensory and Motor Conduction Velocity)

Stimulation at Wrist

Stimulation at the Elbow

Pathological Findings

Some Lossof AxonsDemyelinatingConditionComplete Loss of Axons

Motor Unit Electrical and Mechanical Responses

Invasive Techniques

• Measure motor unit action potentials (MUAPs)• Recorded from voluntary contractions• Information is in shape, duration and

amplitude of MUAPs• Considered “gold standard” by physicians• Pattern recognition is subjective except for

fibrillation and fasiculation potentials• MUAPs from low threshold units only

Selectivity of Recording

Needle Recorded EMG

Extracting Motor Unit Action Potentialsfrom Higher Level Recordings

Needle Recorded Signal – InterferencePattern (20 Hz – 5 KHz)

High Pass Filtered400 Hz – 5 KHz

Extracted MUAPs by“Spike Triggered Averaging”

Central Nervous System Identification

• Diagnose and monitor diseases of the central nervous system (Parkinsonism)

• Assess dysfunction following trauma

• Assess effects of intervention (drugs, physiotherapy, surgery)

• Study normal muscle control

• Prosthesis Control

Modeling the Electromyographic Signal

Measuring Control of Individual Motor UnitsRecorded with Single Fibre 25 micron Needle

Compressed Single Fibre MUAPs(one to several contributing fibres)

Motor Unit Firing Rates

Surface Recorded EMG

RAW EMG DURING GAIT

LEFT FOOT

RIGHT QUAD

RIGHTHAM

RIGHTTIB ANT

Right GAST.

RIGHT FOOT

0 TIME 5 SEC

LEFT HEMIPLGIC GAIT NO AIDS WALKING SPEED .87 m/sec

50 μvolt Div

EMG PROCESSINGFull –Wave Rectification plus LPF

EFFECTS OF INCREASING SMOOTHING

LEFTFOOT

LEFTTIB ANTFULL WAVERECTIFIED

10 HZ

5 HZ

2 HZ

0 TIME 4.5 sec

50 μvolt Div

EMG Profiles for Light HemiplegiaMean Profile plus 1 Std Dev

0% 100%

EMG Profiles for Severe HemiplegiaMean Profile plus 1 Std Dev

EMG Profiles for Severe HemiplegiaMean Profile plus 1 Std Dev