Bioelectric Signals Monitoring PDF

Chapter 2 Bioelectric Signals Monitoring Learning Objective I. ECG II. EMG III. EEG IV. Sleep Study Bioelectric Signals Monitoring OCTOBER SEMESTER Electrical Activities in the Muscles Neuromuscular...

Chapter 2 Bioelectric Signals Monitoring Learning Objective I. ECG II. EMG III. EEG IV. Sleep Study Bioelectric Signals Monitoring OCTOBER SEMESTER Electrical Activities in the Muscles Neuromuscular Muscle Fibers Junctions Motor Spinal Cord Unit 1 Motor Unit 2 Motor Unit 3 Motor Neurons Motor Unit = Muscle Fibers + Neuromuscular Junctions + Motor Neurons Bioelectric Signals Monitoring OCTOBER SEMESTER Presentation title Electrical Activities in the Muscles Bioelectric Signals Monitoring OCTOBER SEMESTER Presentation title Electrical Activities in the Muscles Muscle Fibers Motor Unit Spinal Cord Action Potentials (MUAP) Motor Neurons Neuromuscular Junctions Motor Unit = Muscle Fibers + Neuromuscular Junctions + Motor Neurons Bioelectric Signals Monitoring OCTOBER SEMESTER Presentation title Electrical Activities in the Muscles EMG Recording : Combined waveform of many individual signals from each motor unit Individual signal trains from each individual motor unit (MUAP) Bioelectric Signals Monitoring OCTOBER SEMESTER Presentation title Electrical Activities in the Muscles Electromyogram (EMG) The graphical recording of electrical activity in a skeletal muscle. There is normally very little electrical activity in a muscle while at rest. Flexing a muscle causes some electrical activity to appear. Further contraction of muscle increases the electrical activity, creating a pattern. This pattern helps doctor determine if the muscle is responding as it should. Inserting the needles into the muscle also cause some electrical activity, but once the muscles quiet down, there should be little electrical activity detected. Bioelectric Signals Monitoring OCTOBER SEMESTER Presentation title Electrical Activities in the Muscles Electromyogram (EMG) Raw EMG signal is the difference in electrical potential measured between two recording electrodes. The signal's origins include electrical activity from various tissues Motor neuron action potential produces an end plate potential in motor units of muscle fibers End plate potential directly depolarizes muscle membrane near muscle fiber's center Depolarization wave travels from muscle's surface along transverse tubules into fiber's interior Depolarization travels simultaneously along membrane's surface by local current flow, creating a train of bipoles +/- Bioelectric Signals Monitoring OCTOBER SEMESTER  https://www.youtube.com/watch?v=3KTFJOi-SGk EMG signal Bioelectric Signals Monitoring OCTOBER SEMESTER Electrical Activities in the Muscles Electromyogram (EMG) The characteristics of EMG: The frequency response of the EMG signal is between 20Hz to 200Hz; The EMG signal has maximum amplitude of 10mV. EMG provides information regarding Kinesiological EMG (scientific study of movements of body parts) which includes functional anatomy, force development, reflexes of muscles, etc. Diagnostic EMG. Bioelectric Signals Monitoring OCTOBER SEMESTER Presentation title Electrical Activities in the Muscles Electromyogram (EMG) Diagnostic and clinical applications of EMG: Test nerve and muscle integrity through strength-duration curves Distinguish nerve disease from muscle disease Differentiate weakness and abnormalities of sensation due to peripheral nerve and muscle Determine nerve compression or injury through nerve conduction velocity test Detect nerve root injury Detect firing characteristics of motor neurons and motor units to determine fibrillation Detect partial paralysis, etc. Bioelectric Signals Monitoring OCTOBER SEMESTER Presentation title Electrical Activities in the Muscles Electromyogram (EMG) Factors affecting the amplitude of EMG recording : Type and placement of electrodes Degree of muscular exertion The needle electrode is in contact with single muscle fibre and picks up spike of voltages A surface electrode picks up many overlapping spikes and therefore produces an average voltage effect. Bioelectric Signals Monitoring OCTOBER SEMESTER Electrical Activities in the Muscles Electromyograph The machine/instrument to record the electrical activity in a skeletal muscle. Detects the electrical potential generated by muscle cells when these cells are electrically or neurologically activated Signal ADC Processor Filtering & Conditioning Amplifier EMG Recording Unit Bioelectric Signals Monitoring OCTOBER SEMESTER Presentation title Electrical Activities in the Muscles Electrodes Used in EMG Surface electrodes (Ag-AgCl) – small metal disc on the skin overlaying the muscle. 0.5 cm to 1.5 cm long. Record EMG superficial muscles. Surface EMG recording – a pair of small self-adhesive sensors is placed on the skin over the muscle site. The sensors then read electrical impulses from the muscle. Records information regarding overall muscle function and condition. Non-invasive, painless and perfectly safe to the patient. Bioelectric Signals Monitoring OCTOBER SEMESTER Electrical Activities in the Muscles Electrodes Used in EMG Hypodermic-needle/Inserted/Concentric electrode – inserted through the skin into muscle. 25mm by 25+ gauge. Used to record EMG signal of deep muscles. Needle EMG recording – a needle electrode is penetrated into the skin directly into the muscle. Provides information about a single muscle fibre rather than information on the overall condition of a muscle. Bioelectric Signals Monitoring OCTOBER SEMESTER Electrical Activities in the Muscles Electromyography Method of recording the electrical activity in a skeletal muscle. Most commonly involves testing and recording neuromuscular activity by the electrical stimulation of nerves. The presence, size, and shape of the EMG waveform provides information about the ability of the muscle to respond to nervous stimulation. Due to the high impedance of the electrode/skin or electrode/muscle interfaces, amplifiers used for EMG must have very high input impedance for proper impedance matching to amplify the raw EMG signal acquired by the electrodes. Bioelectric Signals Monitoring OCTOBER SEMESTER Presentation title Electrical Activities in the Muscles Electromyography Evoked EMG Measurements/ENG The termination/distal point of the nerve under study is identified. Two EMG electrodes are placed at the termination point to observe the signal of the muscle innervated by the nerve. A stimulator is attached to the muscle just above the nerve, which is the origin of the neural pathway (near the site of injury). The stimulator sends a sharp pulse down the neural pathway and muscle. Bioelectric Signals Monitoring OCTOBER SEMESTER Presentation title Electrical Activities in the Muscles Electromyography Evoked EMG Measurements/ENG Time taken for the pulse to reach the distal point is measured. A normal nerve will respond in less than 10 ms, giving rise to a healthy single wave In pathological conditions, the waveform contains multiple waves and the response duration is always more than 10 ms. Bioelectric Signals Monitoring OCTOBER SEMESTER Presentation title Electrical Activities in the Muscles Electromyography Evoked EMG Measurements/ENG Normal/Healthy Vo + _ Recording EMG Pathological + Stimulating pulse - 10 ms Bioelectric Signals Monitoring OCTOBER SEMESTER Presentation title Electrical Activities in the Muscles Electromyography Nerve conduction velocity test (NCV) Diagnose nerve damage/destruction and diseases of nerve/muscle. Test how fast electrical signals move through a nerve. Surface electrodes are placed over nerves at various locations. Each electrodes gives off a very mild electrical impulse to stimulates the nerve. The nerve's resulting electrical activity is recorded by the other electrodes. The distance between electrodes and the time it takes for electrical impulses to travel between electrodes are used to determine the speed of the nerve signals. Bioelectric Signals Monitoring OCTOBER SEMESTER Presentation title  https://www.youtube.com/watch?v=H80009Cxtcc What to expect at your electromyography (EMG) and nerve conduction velocity (NCV) test Bioelectric Signals Monitoring OCTOBER SEMESTER Electrical Activities in the Muscles Electromyography EMG signal processing Preferred manner for processing EMG signal: 1) Rectify the EMG signal: Rectification “flips” the negative content across the zero axis, making the whole signal positive. 2) Filtering: Uses high pass filter (fc = 10 Hz) – eliminates unwanted and meaningless electrical noise like movement artifact. 3) Digital smoothing: Applying algorithms to outline the mean trend of the signal. Steep amplitude spikes are removed, resulting in a “linear envelope”. Bioelectric Signals Monitoring OCTOBER SEMESTER Presentation title Electrical Activities in the Muscles Electromyography EMG signal processing Preferred manner for processing EMG signal: 4) Integration: Calculates the area under the linear envelope. Integrating signal over specified time interval, forming a time series of the integrated values. 5) Resulting output: Integrated rectified EMG signal 6) Alternatively, the root mean squared (rms) value of the EMG signal may be calculated. The rms value corresponds to an equivalent average power measure of the signal, thus it is preferred for most application. Bioelectric Signals Monitoring OCTOBER SEMESTER Presentation title Electrical Activities in the Muscles Electromyography Raw EMG EMG signal processing Rectified EMG Linear Enveloped Integrated Bioelectric Signals Monitoring OCTOBER SEMESTER Presentation title Electrical Activities in the Muscles Major points of Consideration for surface EMG Recording Signal to noise ratio of acquired signal Methods for reducing the noise include Using large surface areas for the detection surfaces, Using conductive electrolytes to improve skin contact Removing dead (less conductive) dermis level of the skin. Bioelectric Signals Monitoring OCTOBER SEMESTER Presentation title Electrical Activities in the Muscles Major points of Consideration for surface EMG Recording Bandwidth Affected by inter-detection surface spacing and nerve conduction velocity of the action potentials along muscle fibers. For an conduction velocity of 4 mm/ms and a spacing of 1.0 cm, the pass frequency is 200 Hz. Filter cut-off frequency should be 200 Hz. This bandwidth captures the full frequency spectrum of the EMG signal and suppresses noise at higher frequencies. Bioelectric Signals Monitoring OCTOBER SEMESTER Presentation title Electrical Activities in the Muscles Major points of Consideration for surface EMG Recording Muscle sample size The muscle sample size need not be large because the muscle fibers of motor units are distributed throughout most of the muscle cross- section. It is not necessary to cover a large portion of the muscle with the detection surface of the electrode to obtain a representative sample of the EMG signal for a particular set of active motor units. Bioelectric Signals Monitoring OCTOBER SEMESTER Presentation title Electrical Activities in the Muscles Major points of Consideration for surface EMG Recording Cross-talk susceptibility Often overlooked. The greater the width and length of the detection surfaces and the greater the inter detection surface distance the closer the electrode will be to adjacent muscles. Thus, larger electrodes are more susceptible to detect signals from adjacent (lateral and below) muscles. It is advisable to reduce the size of the electrode. Bioelectric Signals Monitoring OCTOBER SEMESTER Presentation title Electrical Activities in the Muscles Major points of Consideration for surface EMG Recording Cross-talk susceptibility Bioelectric Signals Monitoring OCTOBER SEMESTER Presentation title