BSP Lecture 01 Ch01 Kntu

1- Introduction to Biological Signals

Biological Signal Processingg g g

Introduction to Biological Signals

Dr. R. JafariElectrical Engineering Department

K.N. Toosi University of Technologyy gy

BSP- R. Jafari K. N. Toosi University of Technology1


The Nature of Biological Signals

Living organisms are made up of some levels:

g g

Chemical levelsCellular levelsTissue levelsOrgan levelsSystem levelsOrganization levelsg

The human body includes several systems.For example: the nervous system, the cardiovascular system, the musculoskeletalFor example: the nervous system, the cardiovascular system, the musculoskeletal system.

Each system is made of subsystems (organs, tissues, etc.) that are responsible for


y y ( g , , ) pcertain physiological processes.


1-1 The Nature of Biological Signals

Physiological processes are complex phenomena, including

1. nervous or hormonal stimulation and control;2. inputs and outputs that could be in the form of physical material, m neurotransmitters, or information; and3. action that could be mechanical, electrical, or biochemical.

Most physiological processes are accompanied by signals of several types that reflect their nature and activities:

1. biochemical, in the form of hormones and neurotransmitters,2. electrical, in the form of potential or current, and3. physical, in the form of pressure or temperature.



Di d f t i bi l i l t lt ti i it l


Diseases or defects in a biological system cause alterations in its normal physiological processes, leading to pathological (organic) processes that affect the performance, health, and well-being of the system.Pathological process: an organic process occurring as a consequence ofPathological process: an organic process occurring as a consequence of disease.

Any deviation of these signals from their normal parameters typically represents a disease / disorders and leads to a pathological condition.Observing these signals and comparing them to their known norms, we canoften detect the pathological conditions.

For example:• Most infections an increase in body-core temperature

C di l di d h th i i l t di (ECG)• Cardiovascular disorders arrhythmias in electrocardiogram (ECG), or changes in blood pressure

• Certain neurological disorders (such as epilepsy) electroencephalogram


(EEG)



Each quantity may also be measured quantitatively or qualitatively• Increase in body temperature- The palm of one’s hand (qualitatively)- Mercury based thermometer under arm (quantitatively )- Termistor based thermometer in the artery using a catheter (quantitatively )y g (q y )

When such measurements are observed over a period of time, a one dimensional time-series is obtained this is a physiological signal

A single measurement x of temperature is a scalar:represents the thermal state of the body at a particular or single instant of time t p y p gand a particular position.

If we record the temperature continuously, we obtain a signal as a function of


time: expressed in continuous time or analog form as x(t).



it may be expressed in discrete time form as x(nT) or x(n),n: index or measurement sample number of the array of values,T: uniform interval between the time instants of measurement.

A discrete time signal that can take amplitude values only from a limited list g p yof quantized levels is called a digital signal.




Figure 1.1: Measurements of the temperature of a patient presented as (a) a scalar with one temperature measurement x at a time instant t; (b) an array x(n) made up of several measurements t diff t i t t f ti d ) i l (t) ( ) Th h i t l i f th l t t


at different instants of time; and c) a signal x(t) or x(n). The horizontal axis of the plot represents time in hours; the vertical axis gives temperature in degrees Celsius. Data courtesy of Foothills Hospital, Calgary.



Another basic measurement in health care and monitoring:blood pressure (BP).Each measurement consists of two values —the systolic pressure and the diastolic pressure.

Units: millimeters of mercury (mm of Hg) in clinical practice,although the international standard unit for pressure is the Pascal.

A single BP measurement:a vector x = [x1, x2]T with two components:x1 indicating the systolic pressure andx1 indicating the systolic pressure andx2 indicating the diastolic pressure.

When BP is measured at a few instants of time:


When BP is measured at a few instants of time:an array of vectorial values x(n) or a function of time x(t).



Figure 1.2: Measurements of the blood pressure of a patient presented as (a) a single pair or vector of systolic andsingle pair or vector of systolic and diastolic measurements x in mm of Hg at a time instant t; (b) an array x(n) made up of several measurements at different instants of time; and (c) a i l ( ) ( ) N h fsignal x(t) or x(n). Note the use of

boldface x to indicate that each measurement is a vector with two components. The horizontal axis of the plot represents time in hours; theplot represents time in hours; the vertical axis gives the systolic pressure (upper trace) and the diastolic pressure (lower trace) in mm of Hg. Data courtesy of Foothills Hospital, Calgary.



Examples of Biological SignalsExamples of Biological Signals• The action potential – mother of all biological signals• The electroneurogram (ENG) – propagation of nerve action potential

( G) i i i f• The electromyogram (EMG) – electrical activity of the muscle cells• The electrocardiogram (ECG) – electrical activity of the heart / cardiac cells• The electroencephalogram (EEG) – electrical activity of the brain• The electrogastogram (EGG) – electrical activity of the stomachg g ( ) y• The phonocardiogram (PCG) – audio recording of the heart’s mechanical activity• The carotid pulse (CP) – pressure of the carotid artery• The electoretinogram (ERG) – electrical activity of the retinal cells

Th l t l (EOG) l t i l ti it f th l• The electrooculogram (EOG) – electrical activity of the eye muscles

The action potential is the origin of all biopotentials The action potential is the origin of all biopotentials.

All biological signals of electrical origin are made up from integration of many action potentials.


1- Introduction to Biological Signals1-2 Examples of Biological Signals

Action potential :

The action potential (AP) is the origin of all biopotentials. All biological signals of electrical origin are made up from integration of many action potentials.g y p

The AP is the electrical signal that is generated by a single cell when it is mechanically, electrically or chemically stimulated.


1- Introduction to Biological Signals1-2 Examples of Biological Signals Action potential

• Resting State - Steady electrical potential of difference between internal and y p

external environments

-Typically between -70 to -90mV, relative to the external medium

• Active State- Electrical response to adequate stimulation

- Consists of “all-or-none” action potential after the cell threshold

potential has been reached


1- Introduction to Biological Signals1-2 Examples of Biological Signals Action potential

• Polarized cell membrane

Ad i l i• Adequate stimulation

• Depolarization

• Repolarization• Repolarization

• Hyperpolarization

• “all-or-none” propertyall or none property

Recording of action potential of an invertebrate nerve axon (a) An electronic stimulator supplies a brief pulse of current to the axon, strong enough to excite the axon. A recording of this activity is made at a downstream site via a penetrating micropipet. (b) The movement artifact is recorded as the tip of the micropipet drives through the membrane to record resting potential. A short time later, an electrical stimulus is delivered to the axon; its field effect is


precorded instantaneously at downstream measurement site as the stimulus artifact. The action potential proceeds along the axon at a constant propagation velocity. The time period L is the latent period or transmission time from stimulus to recording site. Taken from Webster, John G., Medical Instrumentation: Application and Design, 2nd ed., 1995


A ti C t

1-2 Examples of Biological Signals Action potential

Action Current:

Figure 4.1* Clarification of the terminology used in connection with the action impulse: A) The source of the action impulse may be nerve or muscle cell. Correspondingly it is called a nerve impulse or a muscle impulse. B) The electric quantity measured from the action impulse may be potential or current


electric quantity measured from the action impulse may be potential or current. Correspondingly the recording is called an action potential or an action current.

Taken from Malvimuo, R. Polensey, “ Bioelectromagnetism”.


ENG is the response of a (peripheral) nerve when it is stimulated

The Electroneurogram (ENG):

p (p p )with an electrical shock.

• Used to determine the conduction velocity of the nerve.If the nerve does not respond quickly enough, or does not respond at all, it signifies a nerve injury.

• Stimulation of neural field potential:

By applying stimuli to motor nerveBy applying stimuli to motor nerve

• Measurement: by needle or surface electrodes


1- Introduction to Biological Signals1-2 Examples of Biological Signals Electroneurogram (ENG)

V°(t)

Measurement of neural conduction velocity:By stimulating a motor nerve

Reference

S2S1

Muscle+ +

D

R

S2

L t DV°(t)

Velocity = u =

2 ms

S1

L2

L1 L2

L1

t D

V°(t)1

mV

2 msFigure 4.7 Measurement of neural conduction velocity via measurement of latency of evoked electrical response in muscle. The nerve was stimulated at two different sites a known distance D apart.Taken from Webster John G Medical Instrumentation: Application and Design 2nd ed 1995


Taken from Webster, John G., Medical Instrumentation: Application and Design, 2nd ed., 1995


Fi ld t ti l fField potential responses from sensory nerves

Sensory nerve action potentials evoked from median nerve of a healthy subject t elb d i t fte ti l ti f i de fi e ith i ele t de The te ti l t theat elbow and wrist after stimulation of index finger with ring electrodes. The potential at the

wrist is triphasic and of much larger magnitude than the delayed potential recorded at the elbow. Considering the median nerve to be of the same size and shape at the elbow as at the wrist, we find that the difference in magnitude and waveshape of the potentials is due to the size of the


volume conductor at each location and the radial distance of the measurement point from the neural source. (From J. A. R. Lenman and A. E. Ritchie, Clinical Electromyography, 2nd ed., Philadelphia: Lippencott, 1977; reproduced by permission of the authors.)


BSP- R. Jafari K. N. Toosi University of Technology18Taken from: www.hughston.com

10-sural nerve

Taken from: http://www.qen.ru/n_spinnomozgovye_nervy.html


The action potential (AP), associated with the muscle activity in individual

Electromyogram (EMG):p ( ) y

muscle fiber, is a record known as electromyogram (EMG). Unlike AP which is measured on the cellular level, the EMG is a surface signalobtained through surface and/or needle electrodes. It is the collection / i t ti f illi f l AP d f th ki fintegration of millions of muscle APs as measured from the skin surface.

EMG measurements indicates amount of muscles’ activity.Th EMG i d d i h h ’ i d lThe EMG is used to determine whether a person’s perceived muscle weakness is caused by a disease within the muscle or by a problem in a nerve supplying the muscle.


1- Introduction to Biological Signals1-2 Examples of Biological Signals Electromyogram (EMG)

Skeletal muscle fibers are considered to be twitch fibers because they produce a mechanical twitch response for a single stimulus and generate a propagated action potential. Skeletal muscles are made up of collections of motor units (MUs), each of which consists of an anterior horn cell (motor neuron), its axon, and all muscle fibers innervated by that axon. A motor unit is the smallest muscle unit that can be activated by volitional effort. The constituent fibers of a motor unit are activated synchronously Component fibers of afibers of a motor unit are activated synchronously. Component fibers of a motor unit extend lengthwise in loose bundles along the muscle.

When stimulated by a neural signal, each motor unit contracts and causes anelectrical signal that is the summation of the action potentials of all of its constituent cells. This is known as the single-motor-unit (SMU) action potential (SMUAP), and may be recorded using needle electrodes inserted into the muscle region of interestA SMU consists of a single motor neuron and the group of skeletal muscle fibers. The evoked extracellular field potential from the active fibers of an SMU has a biphasic or triphasc form of brief duration (3-15 ms) and an

into the muscle region of interest.


p p ( )amplitude of 20–2000 micrometer. In a relaxed muscle, there are normally no action potentials.


Si l t it (SMU)

1-2 Examples of Biological Signals Electromyogram (EMG)

Single motor unit (SMU)

Figure 4 10 Diagram of a single motor unit (SMU) which consists of a single motor neuronFigure 4.10 Diagram of a single motor unit (SMU), which consists of a single motor neuronand the group of skeletal muscle fibers that it innervates. Length transducers [muscle spindles] in the muscle activate sensory nerve fibers whose cell bodies are located in the dorsal root ganglion. These bipolar neurons send axonal projections to the spinal cord that divide into a descending and an ascending branch. The descending branch enters into a simple reflex arc with the motor neuron,


g g p ,while the ascending branch conveys information regarding current muscle length to higher centers in the CNS via ascending nerve fiber tracts in the spinal cord and brain stem. Taken from Webster, John G., Medical Instrumentation: Application and Design, 2nd ed., 1995.



Taken from G.A. Thibodeau and K. T. Patton, “Anatomy & Physiology”, Mosby, 5th edition, 2003.


Schematic representation of a motor unit

3-3 Bioelectrical signals Electromyogram (EMG)

Schematic representation of a motor unitand model for the generation of EMGsignals.

T l A t it i l d t i h llTop panel: A motor unit includes an anterior horn cellor motor neuron (illustrated in a cross-section of thespinal cord), an axon, and several connected musclefibers. The hatched fibers belong to one motor unit; the

h t h d fib b l t th t it A dlnon-hatched fibers belong to other motor units. A needleelectrode is also illustrated.

Middl lMiddle panel: The firing pattern of each motor neuronis represented by an impulse train. Each system hi(t)shown represents a motor unit that is activated andgenerates a train of SMUAPs. The net EMG is the sumof several SMUAP trains.

Bottom panel: Effects of instrumentation on the EMG

BSP- R. Jafari K. N. Toosi University of Technology23Taken from Rangaraj M. Rangayyan“Biomedical Signal Analysis: A Case-Study Approach”

signal acquired. The observed EMG is a function of timet and muscular force produced F.



Taken from Rangaraj M. Rangayyan“Biomedical Signal Analysis: A Case-Study Approach”


Electrocardiogram (ECG)Electrocardiogram (ECG)ECG is the graphical recording of the electrical activity of the heart. The existence of ECG (hence the existence of the

l ) i di t th f lifpulse) indicates the presence of life.

ECG can be obtained easily using surface electrodes. ECG waveshape is altered by cardiovascular diseases and

abnormalities: myocardial ischemia and infarction, ventricular hypertrophy and conduction problems

It is the combination of many APs from different regions of the heart that makes up the ECG.

hypertrophy, and conduction problems.

p• Its characteristic shape is widely recognized.• It consists of a large peak (QRS) indicating the main contraction of the ventricular muscles, along with


, gseveral other peaks representing the contraction and relaxation of different cardiac muscle groups.

1- Introduction to Biological Signals1-2 Examples of Biological Signals Electrocardiogram (ECG)

Anatomy and Function of the HeartA four chambered pump with two atria for collection of blood and two ventricles for pumping out of blood.

Anatomy and Function of the Heart

BSP- R. Jafari K. N. Toosi University of Technology26Taken from G.A. Thibodeau and K. T. Patton, “Anatomy & Physiology, Mosby, 5th edition, 2003.


A t f th H t

3-3 Bioelectrical signals Electrocardiogram (ECG)

Anatomy of the Heart …

Taken from hrsbstaff.ednet.ns.ca/pellers/pages/HBI/blood/heart.ppt




Resting or filling phase of a cardiac chamber: diastole;contracting or pumping phase: systole.g p p g p y

Right atrium (or auricle, RA): collects impure blood from the i d i f isuperior and inferior vena cavae.

Atrial contraction: blood is passed from the right atrium to the right ventricle (RV) through the tricuspid valve. g ( ) g p

Ventricular systole: impure blood in the right ventricle pumped out through the pulmonary valve to the lungs for purificationout through the pulmonary valve to the lungs for purification (oxygenation).



Left atrium (LA) receives purified blood from the lungs.Atrial contraction: blood passed to the left ventricle (LV) via theAtrial contraction: blood passed to the left ventricle (LV) via the mitral valve.Left ventricle: largest and most important cardiac chamber.

LV contracts the strongest among the cardiac chambers:to pump oxygenated blood through the aortic valve and the aorta

i t th f th t f th l t f th b dagainst the pressure of the rest of the vascular system of the body.The terms systole and diastole are applied to the ventricles by default.

Heart rate (HR) or cardiac rhythm controlled by specialized pacemaker cells in the sinoatrial (SA) node.


pacemaker cells in the sinoatrial (SA) node.


Electrical Behavior of Cardiac Cells

Figure 4.13 Representative electric activity from various regions of the heart. The bottom trace is a scalar ECG, which has a typical QRS amplitude of 1-3 mV.


, yp Q p(© Copyright 1969 CIBA Pharmaceutical Company, Division of CIBAGEIGY Corp. Reproduced, with permission, from The Ciba Collection of Medical Illustrations, by Frank H. Netter, M. D. All rights reserved.)


Sequence of events and waves in a cardiac cycle:1. The SA node fires. 2 El t i l ti it t d th h t i l l t t2. Electrical activity propagated through atrial musculature at

comparatively low rates, causing slow moving depolarization or contraction of the atria: P wave in the ECG D l i d ll i f h iECG. Due to slow contraction and small size of the atria, the P wave is a slow, low amplitude wave: 0.1 − 0.2 mV , 60 − 80 ms.

3. Propagation delay at the atrioventricular (AV) node. Normally isoelectric segment of 60 − 80 ms after the P wave in the ECG—PQ segment. Transfer of blood from the atria Q gto the ventricles.

4. The AV node fires.



5. The His bundle, the bundle branches, and the Purkinje system of specialized conduction fibers propagate the stimulus to the ventricles at a high rate.

6. The wave of stimulus spreads rapidly from the apex of the heart upwards, causing rapid depolarization or contraction of the ventricles: QRS wave —sharp biphasic or triphasic wave Q p p p1 mV amplitude and 80 ms duration.

7. Ventricular muscle cells possess a relatively long action potential duration of 300 − 350 ms The plateau portion ofpotential duration of 300 350 ms. The plateau portion of the action potential causes a normally iso-electric segment of about 100 − 120 ms after the QRS: the ST segment.

8 Repolari ation or rela ation of the entricles ca ses the8. Repolarization or relaxation of the ventricles causes the slow T wave, with amplitude of 0.1 − 0.3 mV and duration of 120 − 160 ms.



Heart Valves:

1-2 Examples of Biological Signals Electrocardiogram (ECG)

Heart Valves:The tricuspid valve is between the right atrium and right ventricle. The pulmonary valve is between the right ventricle and the pulmonary artery. The mitral valve is between the left atrium and left ventricle. The aortic valve is between the left ventricle and the aorta.



http://training.seer.cancer.gov/module_anatomy/images/illu_pulmonary_circuit.jpg



Blood circulatory systems1-2 Examples of Biological Signals Electrocardiogram (ECG)

Blood circulatory systems

Figure 7 1 The left ventricle ejects blood into the systemic circulatory


Figure 7.1 The left ventricle ejects blood into the systemic circulatory system. The right ventricle ejects blood into the pulmonary circulatory system.


Concurrent processes:1-2 Examples of Biological Signals Electrocardiogram (ECG)

Changes in left atrial pressure, left ventricular pressure, aortic pressure, ventricular volume, the electrocardiogram, and the phonocardiogram.

Concurrent processes:


From: Medical Physiology, Arthur C. Guyton and John E. Hall


A typical ECG signal (male subject of age 24 years). (Note: Signal values are not calibrated, that is, specified in physical units, in many applications. Signal values in this plot is in

bi li d i )


arbitrary or normalized units.)



ECG signal acquisition:

1-2 Examples of Biological Signals Electrocardiogram (ECG)

ECG signal acquisition:Clinical practice: standard 12channel ECG obtained using four limb leads and chest leads in six positions.

Right leg: reference electrode.Left arm right arm left leg: leads I II and IIILeft arm, right arm, left leg: leads I, II, and III.



Wilson’s central terminal:

formed by combining left arm, right arm, and left leg leads:used as the reference for chest leads.

The augmented limb leads known as aVR, aVL, and aVF(aV for augmented lead, R for right arm, L for left arm, and F for left foot) obtained by using the exploring electrode on the limbleft foot) obtained by using the exploring electrode on the limbindicated by the lead name, with the reference beingWilson’s central terminal without the exploring limb lead.



Hypothetical equilateral triangle formed byleads I, II, and III: Einthoven’s triangle.C t f th t i l Wil ’ t l t i lCenter of the triangle: Wilson’s central terminal.Schematically, the heart is at the center of the triangle.

The six leads measure projections of the 3D cardiacelectrical vector onto the axes of the leads.Six axes: sample the 0◦ − 180 ◦ range in steps of 30 ◦.Facilitate viewing and analysis of the electrical activityFacilitate viewing and analysis of the electrical activityof the heart from different perspectives in the frontal plane.



Figure 1.16: Einthoven’s triangle and the axes of the six ECG leads formed by i f li b l d


using four limb leads.



Figure 1.17: Positions for placement of the precordial (chest) leads V1 – V6 for ECG, auscultation areas for heart sounds, and pulse transducer positions for the carotid and jugular pulse signals. ICS: intercostal space.


Six chest leads (V1 – V6) obtained from six standardized positions on the chest with Wilson’s central terminal as the referencereference.

V1 and V2 leads placed at the fourth intercostal space just to h i h d l f f h i lthe right and left of the sternum, respectively.

V4: fifth intercostal space at the left midclavicular line, etc.V4: fifth intercostal space at the left midclavicular line, etc.



The six chest leads permit viewing the cardiac electrical vector from different orientations in a cross-sectional plane:

V5 and V6 most sensitive to left ventricular activity;V3 and V4 depict septal activity best;V3 and V4 depict septal activity best;V1 and V2 reflect activity in the right half of the heart.




Figure 1.18: Standard 12-lead ECG of a normal male adult. Courtesy of E. Gedamu and L.B. Mitchell, Foothills Hospital, Calgary.


N l d Ab l C di Rh th1-2 Examples of Biological Signals Electrocardiogram (ECG)

Normal and Abnormal Cardiac RhythmsThe rhythm of the heart in terms of beats per minute (bpm)may be estimated by counting the readily identifiable waves

Normal, resting heart rate: 70 bpm.Ab ll l H t t (HR) < 60 b d i ti it

may be estimated by counting the readily identifiable waves.

Abnormally low Heart rate (HR) < 60 bpm during activity: bradycardia.

High resting HR due to illness or cardiac abnormalities:tachycardia.

QRS waveshape affected by conduction disorders:

B dl b h bl k id d d j d QRS


Bundle-branch block causes a widened and jagged QRS.

Ventricular hypertrophy or enlargement: wide QRS.


ECG signal of a patient with right bundle-branch block and hypertrophy (male patient of age 3 months). The QRS complex is wider than normal, and displays an abnormal, jagged waveform due to desynchronized


p y , j gg ycontraction of the ventricles. (The signal also has a base-line drift, which has not been corrected for.)



Arrh thmias1-2 Examples of Biological Signals Electrocardiogram (ECG)

Arrhythmias

Disturbance in the regular rhythmic activity of the heart: arrhythmia.Cardiac arrhythmia may be caused by:irregular firing patterns from the SA node abnormal and

M t f th h t i h t h th i it d k

irregular firing patterns from the SA node, abnormal and additional pacing activity from other parts of the heart.

Many parts of the heart possess inherent rhythmicity and pacemaker properties:SA node, AV node, Purkinje fibers, atrial tissue, and ventricular tissue.

If the SA node is depressed or inactive, any one of the abovemay take over the role of the pacemaker or introduce ectopic beats


may take over the role of the pacemaker or introduce ectopic beats.


A h th i1-2 Examples of Biological Signals Electrocardiogram (ECG)

Arrhythmias …

Figure 4.18 Normal ECG followed by an ectopic beat An irritable focus, or ectopic pacemaker, g y p p pwithin the ventricle or specialized conduction system may discharge, producing an extra beat, or extra systole, that interrupts the normal rhythm. This extra systole is also referred to as a premature ventricular contraction (PVC). (Adapted from Brendan Phibbs, The Human Heart, 3rd ed., St. Louis: The C. V. Mosby Company, 1975.)


Premature ventricular contraction (PVC): انقباض زودرس بطنی


ECG signal with PVCs. The third and sixth beats are PVCs. The first PVC has blocked the normal beat that would have appeared at about the same time instant, but the second PVC has not blocked any normal beat triggered


, y ggby the SA node.



Arrhythmias …ST segment: normally isoelectric flat and in line with the PQ g y Qsegment.May be elevated or depressed due to myocardial ischemiareduced blood supply to a part of the heart muscles due to areduced blood supply to a part of the heart muscles due to a block in the coronary arteries



ST elevation: Ischemic Heart Disease: Acute transmural injury, acute anterior MI.http://library.med.utah.edu/kw/ecg/ecg outline/Lesson10/index.html



Electroencephalogram (EEG)Electroencephalogram (EEG)EEG or brain waves: electrical activity of the brain.

V l d t di t i l i l• Very commonly used to diagnose certain neurological disorders, such as epilepsy

• More recently, also investigated whether it can detect various o e ece y, so ves g ed w e e c de ec v ousforms of dementia

EEG is the specific recording obtained using the scalp electrodes from the surface of the skull.

Just like ECG, EEG is also obtained using several different electrodes places on different regions of the head / brain.



Anatomy of Brain

1-2 Examples of Biological Signals Electroencephalogram (EEG)

Anatomy of BrainMain parts of the brain: cerebrum, cerebellum, brain stem (midbrain, pons medulla, reticular formation), thalamus (between the midbrain and the hemispheres).p )



1- Introduction to Biological Signals1-2 Examples of Biological Signals Electroencephalogram (EEG)

C b di id d i t t h i h t d b

Anatomy of Brain

Cerebrum divided into two hemispheres, separated by a longitudinal fissure with a large connective band of fibers: corpus callosum.

Outer surface of the cerebral hemispheres (cerebral cortex)composed of neurons (grey matter) in convoluted patternscomposed of neurons (grey matter) in convoluted patterns,separated into regions by fissures (sulci).

Beneath the cortex lie nerve fibers that lead to other parts of the brain and the body (white matter).



Anatomy of Brain1-2 Examples of Biological Signals Electroencephalogram (EEG)

Anatomy of Brain

Figure 4.25 The cerebrum, showing the four lobes (frontal, parietal, temporal, and


occipital), the lateral and longitudinal fissures, and the central sulcus. (From A. B. McNaught and R. Callander, Illustrated Physiology, 3rd ed., 1975. Edinburgh: Churchill Livingstone. Used with permission of Churchill Livingstone.)


f C C


Ultrastructure of the Cerebral CortexExcitatorysynaptic input

Lines of current flow

EEG waveactivity

Lines of current flow

Apical dendritic treepCell body (soma)

dipole

Figure 4.26 Electrogenesis of cortical field potentials for a net excitatory input to the apical

+ Basilar dendritesAxon


g g p y p pdendritic tree of a typical pyramidal cell. For the case of a net inhibitory input, polarity is reversed and the apical region becomes a source (+). Current flow to and from active fluctuating synaptic knobs on the dendrites produces wave-like activity. See text.


Cortical potentials generated due to excitatory and inhibitory postsynaptic potentials developed by cell bodies and dendrites of pyramidal neuronspyramidal neurons.

Physiological control processes, thought processes, and external stimuli generate signals in the corresponding parts of the brain:recorded at the scalp using surface electrodes.

Scalp EEG: average of multifarious activities of manysmall zones of the cortical surface beneath the electrode.



Resting Rhythms of the Brain1-2 Examples of Biological Signals Electroencephalogram (EEG)

Resting Rhythms of the Brain

Figure 4 27 (a) Different types of normal EEG waves (b) Replacement of alpha rhythm by


Figure 4.27 (a) Different types of normal EEG waves. (b) Replacement of alpha rhythm by an asynchronous discharge when patient opens eyes. (c) Representative abnormal EEG waveforms in different types of epilepsy. (From A. C. Guyton, Structure and Function of the Nervous System, 2nd ed., Philadelphia: W.B. Saunders, 1972; used with permission.)


EEG rhythms or frequency bands:1-2 Examples of Biological Signals Electroencephalogram (EEG)

EEG rhythms or frequency bands:associated with physiological and mental processes.EEG rhythms:

Al h i i l ti h th f th b iAlpha: principal resting rhythm of the brain:common in wakeful, resting adults.Auditory and mental arithmetic tasks with the eyes closed lead to strong alpha

waves: suppressed when the eyes are opened.waves: suppressed when the eyes are opened.Alpha wave replaced by slower rhythms at various stages of sleep.Beta waves: High frequency waves. background activity in tense and anxious subjects.Theta waves: beginning stages of sleep.Delta waves: deep sleep stages.Spikes and sharp waves: epileptogenic regions.

Frequency bands:Delta ( ): 0.5 ≤ f < 4 Hz;Th t ( ) 4 ≤ f < 8 H


Theta ( ): 4 ≤ f < 8 Hz;Alpha ( ): 8 ≤ f ≤ 13 Hz; andBeta (): f > 13 Hz.


From top to bottom: (a) delta rhythm; (b) theta rhythm; (c) alpha rhythm; (d) beta rhythm; (e) blocking of the alpha rhythm by eye opening; (f) 1 s time markers and 50 µV marker. Reproduced with permission from R. Cooper, J.W. Osselton, and J.C. Shaw, EEG Technology, 3rd Edition, 1980. cButterworthHeinemann Publishers a division of Reed Educational & Professional



Heinemann Publishers, a division of Reed Educational & Professional Publishing Ltd., Oxford, UK.


Cli i l EEG


In 1958, a 10-20 electrode placement

Clinical EEG

In 1958, a 10 20 electrode placement system was recommended by International Federation of EEG Societies .

The 10 − 20 system of electrode placement for EEG recording. Notes regarding channel labels: pg– naso-pharyngeal, a– auricular (ear lobes), fp– pre-frontal, f–frontal, p– pareital, c– central, o– occipital, t– temporal, cb– cerebellar, z– midline,


frontal, p pareital, c central, o occipital, t temporal, cb cerebellar, z midline, odd numbers on the left, even numbers on the right of the subject.



Labels for points according to 10-20 electrode placement system.


Taken from M. Teplan, "Fundamentals of EEG Measurement", Measurement Science Review, Vol. 2, Section 2, 2002.



Figure 4.28 The 10-20 electrode system (From H. H. Jasper, "The Ten-Twenty Electrode System of the International Federation in Electroencephalography and Clinical Neurophysiology," EEG Journal, 1958, 10 (Appendix), 371-375.)


Oth EEG t1-2 Examples of Biological Signals Electroencephalogram (EEG)

Other EEG systemsElectrode-caps allowed additional (64-128) electrodes to be usedused.

The GES 120 is designed for efficiency and speed in routine clinical use.

http://www.egi.com/c_120.html



Eight channels of the EEG of a subject displaying alpha rhythm. See Figure 1.20 for details regarding channel labels. Data courtesy of Y.



Mizuno-Matsumoto, Osaka University Medical School, Osaka, Japan.


Event-related potentials (ERPs)

Th t t l t d t ti l i l th dپتانسيل هاي مرتبط با رخداد

The term event-related potential is more general than and preferred to the term evoked potential (پتانسيل هاي برانگيخته).

ERPs are really EEGs obtained under a specific protocol that requires the patient to response to certain stimuli such as light, sound stimuli – hence event related potentials.sound stimuli hence event related potentials.

These signals can be used to diagnose certain neurological disorders s ch as dementia and the can also be sed as a liedisorders such as dementia, and they can also be used as a lie detector.



Event-related potentials (ERPs)

A wave showing several ERP components.In neuroscience, N1 is a large, negative-going evoked potential measured by electroencephalography


electroencephalography


Somatosensory evoked potentials (SEPs)

S t k d t ti l t d b ti l tiSomatosensory evoked potentials are generated by stimulation of afferent peripheral nerve fibers by either physiological or electrical means.

SEPs are useful for noninvasive evaluation of the nervous system from a peripheral recepotor to the cerebral cortex.system from a peripheral recepotor to the cerebral cortex. Median nerve short-latency SEPs are obtained by placing stimulating electrodes about 2-3 cm apart over the median

t th i t ith l t i l ti l ti t 5 10 lnerve at the wrist with electrical stimulation at 5-10 pulse per second (pps), each stimulus pulse being of duration of 0.5 ms with an amplitude of about 100 V (producing a visible thumb


twitch)..


Electrogastogram ( EGG)Electrogastogram ( EGG)

The EGG is the graphical representation of the electricalThe EGG is the graphical representation of the electrical activity of the stomach

- Created by the rhythmic depolarization and repolarization of the underlying smooth muscle cells of the stomach

J t lik th EEG th EGG ti it i l t d it i t i- Just like the EEG, the EGG activity is always present and it is not in response to specific contractions of the stomach muscle.

EGG i l bt i d i f l t d• EGG is also obtained using surface electrodes.



Electrogastogram ( EGG)1-2 Examples of Biological Signals Electrogastogram (EGG)

Electrogastogram ( EGG)

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Electroretinogram (ERG)The ERG is the record of the retinal action currents produced pby the retina in response to a light stimulus.

• It measures the electrical responses of the light-sensitive cells (such as rods and cones)cells (such as rods and cones).The stimuli are often a series of light flashes or rotating patternsp

• The ERG is recorded using contact lens electrode that the subject wears while watching the stimuli.


1- Introduction to Biological Signals1-2 Examples of Biological Signals Electroretinogram (ERG)

Recording ERG

http://www.metrovision.fr/mv-electrodes-im01.gif

The transparent contact lens contains one electrode, shown here on horizontal section of the right eye.


Reference electrode is placed on the right temple.


Fig re 4 23 Vertebrate electroretinogram a eform in response to a 2 s light flashFigure 4.23 Vertebrate electroretinogram waveform in response to a 2-s light flash



The cells of retina and the standard ERG waveform (courtesy: Jaakko


The cells of retina and the standard ERG waveform (courtesy: JaakkoMalmimo and Robert Plonsey, “Bioelectro-magnetism Principles andApplications of Bioelectric and Biomagnetic fields”).



http://www.neuroscience.cam.ac.uk/directory/profile.php?oarm2


The Electro-Oculogram (EOG)g ( )The EOG measures the resting potential of the retina. Unlike ERG it is not recorded in response to a stimulusrecorded in response to a stimulus.

The EOG is often used in recording the eye-movementseye movements.EOG is also used in diagnosing certain sleep disorders.


Taken from S. K. Venkata Ram, “Bio-Medical Electronics & Instrumentation


Phonocardiogram (PCG)The PCG is the graphic record of the heart sounds and murmurs. It is thus a mechanical / audio signal, rather than an electrical signal

Can be easily heard using a stethoscope- Can be easily heard using a stethoscope- Or can be converted into an electrical signal using a transducer- Typically used to determine the disorders related to the heart valve, since

their routine opening and closing create the well-known soundstheir routine opening and closing create the well known sounds.

• S1 sounds: First heart sounds – Closure of the AV (mitral and tricuspid) valves, then opening of semilunar (aortic and pulmonary) valves and blood ejected out of ventricles – immediately follows the QRS complexp

• S2 sounds: Second heart sounds – Closure of semilunar (aortic and pulmonary )valves• Any unexpected sound may indicate a malfunctioning valve that causes the blood flow

into / out of a chamber when it should not. Also called heart murmurs.



Carotid Pulse (CP)Carotid Pulse (CP)CP is a mechanical signal measured using pressure transducer over the carotid arteryover the carotid artery

- Provides the pulse signal indicating the changes in arterial blood pressure / volume with each heart beat – usually measured together with p y gPCG and ECG.

-While it closely resembles the actual pressure, it does not measure the pressure itself directly.

-Its components:P P i Ej i f bl d f h l f i l• P: Percussion wave; Ejection of blood from the left ventricle

• T: Tidal wave; Pulse returning from upper body• D: Dicrotic notch; Closure of the aortic valve• DW: Dicrotic wave ; Pulse reflected from lower body


• DW: Dicrotic wave ; Pulse reflected from lower body


Carotid Pulse (CP)


Figure 1.24: Three-channel simultaneous record of the PCG, ECG, and carotid pulse signals of a normal male adult.


Vibromyogram (VMG)Vibromyogram (VMG)

VMG: mechanical manifestation of contraction of skeletal muscle;ib ti i l th t i th EMGvibration signal that accompanies the EMG.

Muscle sounds or vibrations related to the change in dimensions (contraction) of the constituent muscle fibers(contraction) of the constituent muscle fibers.

Recorded using contact microphones or accelerometers.VMG frequency and intensity vary in proportion to contraction q y y y p plevel.

VMG and EMG useful in studies on neuromuscular controlVMG and EMG useful in studies on neuromuscular control, muscle contraction, athletic training, and biofeedback.



Properties of Biological SignalsProperties of Biological SignalsBiological signals, in general are extremely difficult to process:

First they are difficult to acquire- First, they are difficult to acquire

- The signal amplitudes are very small, which require large amplification

- They are very prone to noise• due to large amplification• due to their small original amplitude (and hence masked by external, stronger

signals)signals)• due to the presence of so many other biological signals in the near vicinity, e.g. one

often sees EMG noise on ECG, EOG noise on EEG, etc.

Th i h i f h i h i- They are non-stationary: their frequency content changes with time.It leads that Fourier based techniques are often not adequate

- The noise spectrum often coincides with that of the signal spectrum, and


p g p ,hence standard filtering approaches fail. Therefore, they need more advances filtering techniques.

BSP Lecture 01 Ch01 Kntu

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