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EEG, ECG, EMG Mitesh Shrestha

What is Signal ?:

A signal is defined as a fluctuating quantity or impulse whose variations represent information. The amplitude or frequency of voltage, current, electric field strength, light, and sound can be varied as signals representing information. A signal can be simply defined as a function that conveys information. Signals are represented mathematically as functions of one or more independent variables. Examples: voltage, current, electric field strength, light, sound, etc. 2 What is Signal ?

Biomedical signals:

Biomedical signals means the bio-signals which are generated in biological systems only. Biomedical signals are observations of physiological activities of organisms, ranging from gene and protein sequences, to neural and cardiac rhythms, to tissue and organ images. Examples of biomedical signals: ECG (Electrocardiogram) signal, EEG (Electroencephalogram) signal, etc. Biomedical signals

How biomedical signals are generated ? :

Biomedical signals are electrical or magnetic signals generated by some biological activity in the human body. Human body is composed of living tissues that can be considered as a power station. Action of living tissues in terms of bioelectric potentials generate multiple electric signals from two internal sources-muscles and nerves system. How biomedical signals are generated ?

What are biopotentials:

What are biopotentials An electric potential that is measured between points in living cells, tissues, and organisms, and which accompanies all biochemical processes. Also describes the transfer of information between and within cells

Classification of Biomedical Signals:

Bioelectric Signal Bioacoustics Signal Biomechanical Signal Biochemical Signal Bio-magnetic Signal Bio- optical signal Classification of Biomedical Signals

Bioelectric signal:

The electrical signals which we can measure mainly on the surface of the body is known as bioelectric signal. It is generated by muscle cells and nerve cells. Basic source is the cell membrane potential. Examples: ECG, EEG, EMG, EOG Bioelectric signal

Electrocardiography (ECG):

Electrocardiography (ECG) Measures galvanically the electric activity of the heart Well known and traditional, first measurements by Augustus Waller using capillary electrometer (year 1887) Very widely used method in clinical environment Very high diagnostic value 1. Atrial depolarization 2. Ventricular depolarization 3. Ventricular repolarization


Electrocardiography The heart is an electrical organ, and its activity can be measured non-invasively Wealth of information related to: The electrical patterns proper The geometry of the heart tissue The metabolic state of the heart Standard tool used in a wide-range of medical evaluations

ECG principle:

ECG principle

Cardiac Electrical Activity:

Cardiac Electrical Activity

ECG basics:

ECG basics Amplitude: 1-5 mV Bandwidth: 0.05-100 Hz Largest measurement error sources : Motion artifacts 50/60 Hz powerline interference Typical applications: Diagnosis of ischemia Arrhythmia Conduction defects

12-Lead ECG measurement:

12-Lead ECG measurement Most widely used ECG measurement setup in clinical environment Signal is measured non-invasively with 9 electrodes Lots of measurement data and international reference databases Well-known measurement and diagnosis practices This particular method was adopted due to historical reasons, now it is already rather obsolete Einthoven leads: I, II & III Goldberger augmented leads: V R , V L & V F Precordial leads: V 1 -V 6



Why is 12-lead system obsolete?:

Why is 12-lead system obsolete? Over 90% of the heart’s electric activity can be explained with a dipole source model Only 3 orthogonal components need to be measured, which makes 9 of the leads redundant The remaining percentage, i.e. nondipolar components, may have some clinical value 12-lead system does, to some extend, enhance pattern recognition and gives the clinician a few more projections to choose from …but…. If there was no legacy problem with current systems, 12-lead system would’ve been discarded ages ago


Origination of the QRS - Signal


ECG - applications ● Diagnostics ● Functional analysis ● Implants (pace maker) ● Biofeedback ( Heartrate variability, HRV) ● Peak Performacne Training, Monitoring


Normal sinus rhythm


RATE P wave rate 60 - 100 bpm with <10% variation - Normal Rate < 60 bpm = Sinus Bradycardia - Results from: - Excessive vagal stimulation - SA nodal ischemia (Inferior MI) Rate > 100 bpm = Sinus Tachycardia - Results from: - Pain / anxiety - CHF - Volume depletion - Pericarditis - Chronotropic Drugs (Dopamine)

Electroencephalography (EEG):

Electroencephalography (EEG) An electrophysiological monitoring method to record electrical activity of the brain . Typically noninvasive , with the electrodes placed along the scalp, although invasive electrodes are sometimes used in specific applications . EEG measures voltage fluctuations resulting from ionic current within the neurons of the brain. In clinical contexts, EEG refers to the recording of the brain's spontaneous electrical activity over a period of time, as recorded from multiple electrodes placed on the scalp. Diagnostic applications generally focus on the spectral content of EEG, that is, the type of neural oscillations (popularly called "brain waves") that can be observed in EEG signals.

EEG Signal:

The Electroencephalogram (EEG) is a recording of electrical activity originating from the brain. It is recorded on the surface of the scalp using electrodes, thus the signal is retrievable non-invasively. Signal varies in terms of amplitude and frequency Normal frequency range: 0.5Hz to 50 Hz. EEG Signal Fig.: EEG signal originating from the brain


EEG Electrode – cap locations of the 10/20 system

Electroencephalogram (EEG):

Electroencephalogram (EEG) The 10-20 system of electrode placement for EEG recording.

Electroencephalogram (EEG):

Electroencephalogram (EEG) The commonly used terms for EEG frequency range: Delta (0.5-4 Hz): deep sleep Theta (4-8 Hz): beginning stages of sleep Al ph a (8-13 Hz): principal resting rhythm Beta (>13 Hz): background activity in tense and anxious subjects

Electroencephalogram (EEG):

Electroencephalogram (EEG) a: delta, b: theta, c: alpha, d: beta, e: blocking of alpha rhythm by eye opening, f: marker 50 μV, 1 sec


EEG - applications ● Diagnostics (Epilepsy, Oncology, ..) ● Cognitive Sciences ● Sleep Analysis ● Human Computer Interfaces (BCIs) ● Pharmacology ● Intensive Care, Monitoring

Electromyography (EMG) :

Electromyography (EMG) Electromyography (EMG) i s a technique for evaluating and recording the activation signal of muscles. EMG is performed by an electromyograph , which records an electromyogram . Electromyograph detects the electrical potential generated by muscle cells when these cells contract and relax.


ELECTRODE TYPES Intramuscular - Needle Electrodes Extramuscular - Surface Electrodes


EMG PROCEDURE Clean the site of application of electrode; Insert needle/place surface electrodes at muscle belly; Record muscle activity at rest; Record muscle activity upon voluntary contraction of the muscle.

EMG Contd.:

EMG Contd. Muscle Signals are Analog in nature. EMG signals are also collected over a specific period of time. Analog Signal

EMG Contd.:

EMG Contd. EMG processing: Amplification & Filtering Signal pick up Conversion of Analog signals to Digital signals Computer

Factors Influencing Signal Measured:

Factors Influencing Signal Measured Geometrical & Anatomical Factors Electrode size Electrode shape Electrode separation distance with respect to muscle tendon junctions Thickness of skin and subcutaneous fat Misalignment between electrodes and fiber alignment Physiological Factors Blood flow and temperature Type and level of contraction Muscle fiber conduction velocity Number of motor units (MU) Degree of MU synchronization

Factors That Influence the Signal Information Content of EMG:

Factors That Influence the Signal Information Content of EMG Factor Influence Neuroactivation - firing rate of motor unit AP’s - no. of motor units recruited - synchronization of motor units Muscle fiber physiology - conduction velocity of fibers Muscle anatomy - orientation & distribution of fibers - diameter of muscle fibers - total no. of motor units Electrode size/orientation - no. of fibers in pickup area

Factors That Influence the Signal Information Content of EMG:

Factors That Influence the Signal Information Content of EMG Factor Influence Electrode-electrolyte - type of material and site interface - electrode impedance decreases with increasing frequency Bipolar electrode - distance between electrodes configuration - orientation of electrodes relative to the axis of muscle fibers

EMG signal:

EMG signal

What can be learned from an EMG?:

What can be learned from an EMG? Time course of muscle contraction Contraction force Coordination of several muscles in a movement sequence These parameters are DERIVED from the amplitude, frequency, and change of these over time of the EMG signal Field of Ergonomics : from the EMG conclusions about muscle strain and the occurrence of muscular fatigue can be derived as well


APPLICATION OF EMG EMG can be used for diagnosis of Neurogenic or Myogenic Diseases. Rehabilitation Functional analysis Active Prothetics , Orthesis Biomechanics , Sports medicine


Assignment Write short notes on ECG ? [5] Write short notes on EEG ? [5] Write short notes on EMG ? [5]

Useful Links:

Useful Links https:// www.youtube.com/watch?v=RYZ4daFwMa8 https://www.youtube.com/watch?v=JSxd0UTt5gQ