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BIO-SIGNALS

*The bio-signals potentials are generate atcellular level and the source of thesepotentials is ionic in nature.

* cell consists of an ionic conductor

separated from the outside environment bya semi permeable membrane which acts as aselective ionic filter to the ions. This means

that some ions can pass through themembrane freely where as other cannot doso.

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*All living matters are composed of cellsdifferent types.

* The bio-signals are EMG, EOG, ECG, orEEG this signals can be analyzed andsensors.

*This signal can monitoring ,rehabilitation ,feedback functions and control gain .

* EMG is electro mayo graph its detect

contraction of the skeletal muscles result ingeneration of action potentials in theindividual muscle fibers.

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*EOG is electro oculo graph its detect thepotentials that generated by the movement

of the eye ball.

The EEG electro cardio gram its detect thebrain waves which indicate the function of

the brain.

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ELECTRICAL SYSTEM OF HEART

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THE ECG WAVEFORM

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ECG BASICS

*P wave: represents the depolarizationimpulse across the atria

*Q, R and S waves: all these three wavesrepresent the ventricular depolarization

*T wave: represents the repolarization of

the ventricles

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ECG Basics

*P wave : 0.25 mv

*R wave : 1.60 mv

*Q wave : 25% of R-wave

*T wave : 0.1 to 0.5 mv

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ECG Basics

*P-R Interval : 0.12 to 0.20 s

*Q-T Interval : 0.35 to 0.44 s

*S-T Segment : 0.05 to 0.15 s

*P wave : 0.11 s

*QRS Interval : 0.09 s

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Electro cardio graph

*ECG is an instrument which records the electrical

activity of the heart.

Electrical signals from the heart characteristicallyprecede the normal mechanical function and

monitoring of these signals has greatsignificance.

*ECG provides valuable information about widerange of cardiac disorders such as the presence

of an inactive part (infarctions) or anenlargement (cardiac hypertrophy) of the heartmuscle.

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Block diagram

*The potentials pick up by electrodes are taken to

the lead selector switch. In the lead selector theelectrodes are selected two by two according tothe lead program.

*The signal is connected symmetrically to the pairdeferential amplifier. The pre amplifier is usually athree or four stages the output signal pick topower amplifier.

*Direct writing recorder is usually adequate sincethe ESG signal of the interested has limited hasbandwidth.

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Frequency selective network is an R-C network.Which provides necessary damping of the penmotor and is preset by the manufacture.

*The auxiliary circuit provide a 1mV calibrationsignal and automatic blocking of the amplifierduring a change in the position of the lead switch.

*It may include a speed control circuit for thechart drive motor.

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*Isolated preamplifier :

It had traditional for all ECG to have the right leg(RL) electrode connected to the chassis . And fromthere to the ground.

*this provided a ready path for any groundseeking current through the patient and presentedan electrical hazard.

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ECG LEADS

*Two electrodes placed over different areas of theheart and connected to the galvanometer willpicket up the electrical current resulting from thepotentials difference between them.

*So that any two sides due to electrical activity ofthe heart is called (LEAD)

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Bipolar lead:

ECG recording by using two electrodes such

that the final trace corresponds to the difference ofelectrical potentials existing between them. Theyare called standard leads

* I lead the electrodes are placed on theright and the left arm (RA&LA).

* II lead the electrodes are placed on theright arm and left leg (RA&LL).

* III lead the electrodes are placed on theleft arm and left leg (LA & LL).

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Unipolar limb leads:

*Also know as augmented limb leads, examine the

composite potentials from all three limbssimultaneously.

*in all three augmented leads, the signals from

two limbs are summed in resistor network andthen applied to the amplifiers inverting input.

*the signal from the remaining limb electrode isapplied to the noninverting input.

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*Lead aVR: RA is connected to the no invertinginput while LA and LL are summed at the invertinginput

*Lead aVL: LA is connected to the no invertinginput, while RA and LL are summed at the

inverting input.

*Lead aVF: LL is connected to the no inverting

input while RA and LA are summed at theinverting input.

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Unipolar chest leads:

V1 through V6 are measured with the signalsfrom certain specified location on the chestapplied to the amplifier no inverting input.

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Leads Combination

* LEAD I :LA+RA

* LEAD II :LL+RA

* LEAD III :LL+LA

* AVR :RA & LA+LF

* AVF :LF & RA+LA

* AVL :LA & RA+LF

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Electrode Placement

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Electrode Placement

* v1 - the fourth intercostals space on theright side of the sternum

* v2 - the fourth intercostals space on theleft edge of the sternum

* v3 half way between C2 and C4

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Electrode Placement

* v4 - the fifth intercostals space in the leftcentral clavicular line

* v5 - straight line from the C4 pointperpendicularly to the left front auxiliaryline in the intersection point with this line.

* v6 - at the same level as C5, but in leftcentral auxiliary line

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ELECTRODES:

*Bioelectric events have to be picked up

from the surface of the body before theycan be put into the amplifier forsubsequent record or display.

*This done by using electrodes.*Electrodes make a transfer from theionic conduction in the tissue to the

electronic conduction which is necessaryfor making measurements.

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*They are two types of the electrodes areused in practice surface electrodes and thedeep seated electrodes.

*The surface electrodes pick up the potentialdifference from the tissue surface when placedover it without damping the live tissue.

*Whereas the deep-seated electrodes indicatethe electric potential difference arising inside

the live tissue or cell.

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Electrode-Tissue Interface:

*used electrodes in patient monitoring and

related studies are surface electrodes.

*The notable examples are when they are

used for recording ECG, EEG and respiratoryactivity by impedance pneumography.

*The characteristics of a surface electrodes ofa metal electrode and attached to the surfacebody through electrolyte jell depend on thecondition of metal-electrolyte interface .

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Metal electrolyte interface :

*They are tendency for each electrodes todischarge ions to the solution and for ionsin the electrolyte to combine with eachelectrode.

*That creations a charge gradient(difference- potentials)

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Electrodes tissue interface

Tissue Electrolyteskininterface

Electrolyte MetalElectrolyte

Interface

ToInstruments

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ECG electrodes:

1- Limb electrodes

* rectangular surface* German silver

* impedance is 2 to 5 K

* using in surgery

2- Floating electrodes:

* used without jell

* contact impedance 50K

3- Pregelled Disposable Electrodes:* stress testing ,long term monitoring

* reducing possibility of artifacts and drift

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Limb Electrode for ECG

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Floating Electrode

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ECG Machine Block Diagram

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Leads Selector

A multiplexer is a logic circuit which accepts

several data inputs and outputs, but only one ofthem at a time. In essence, it behaves as multi-position switch which operates under the controlof select or address inputs, the figure show

Inputs output

Select input

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Preamplifier

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Operation Amplifier

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Galvanometer:* A galvanometer is a permanent magnet movingcoil (PMMC).

* The pen will at rest in the centre of its travelwhen no current flows in the coil. The movementof the pin is depend on the current supply to thecoils.

they are also other types of writing:

* hot-tip (styles) heated by resistor wire.

* the thermal paper its turn black when its heat

* writing knife edge in the thermal recorder.

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* Dot matrix printer used with the computer its 27pin printer make good quality recording waveformand numerical number like blood pressure,temperature etc.

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Motors:

*The motor is connected to the drive rollerthrough either a drive a chain or a gear train.

*Most machines use ac motors, with tappedwindings to select drive speed.

*Some ac motors provide very accurate drivespeeds that are synchronized to the ac power

mains frequency 60 Hz in the united states.

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*Only few models use dc motors, and thoseregulated speed by using a regulated dc powersupply.

* in some cases an alternator /tachometer onthe motor shaft to provide negative feedback.

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Figure 239 small

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ECG FAULTS AND TROUBLESHOOTING:-

Most common problem that occur in an ECG are:

PROBLEM 1:-

SYMPTOM: machine runs but the thermal tip stylus doesnot writes or writes very lightly.

POSSIBLE CAUSE:(1) Too little heat on the stylus tip .

(2) Insufficient stylus pressure.

TROUBLESHOOTING: Use a screw driver or anyisolated tool to gently press the stylus if a dark line appearson the paper the problem is pressure , but if no dark lineappears the problem is heat.

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SOLUTION:

(1) For no heat check the heater voltage at the stylus

,if voltage is correct change the stylus ,if voltage is

not correct refer the service manual for details on

stylus power drive.(2) Adjust the stylus pressure , use a pressure gage

and refer to the service manual for the correct

value.on some models pressure must be made at a

specific heater voltage.

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PROBLEM 2:-SYMPTOM: Smeared trace.

POSSIBLE CAUSE:

Worn stylus or incorrectly loaded paper.

TROUBLESHOOTING:

Check paper loading and if proper ,check stylus for wear

,pitting and other irregularities.

Incorrect loading is one of the most common fault and

often results from bypassing the paper brake or tension

bar.

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PROBLEM 3:-

SYMPTOMS: Poor recording.

POSSIBLE CAUSE: Electronic or mechanicalproblem , bad switch or patient cable.

TROUBLESHOOTING:(1) Place lead selector switch in STD ,short allelectrodes together and press 1- mv cal button.

(2) If normal calibration pulse appears then problem

is connection to the patient.(3) If problem persists then repeat step 1 using knowngood patient cable .


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60 Hz INTERFERENCE:-

CAUSES: 60 Hz interference appears due to power

mains,another cause of 60 Hz interference if a broken

or loose cable or broken power main ground on the

ECG machine, additionally some dc supply alsocause these artifacts.

SOLUTION:

The problem can be isolated by shorting together all

electrodes of the patient cable and checking eachposition of the lead selector switch.

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(1) If the interference ceases , then the problem is a badelectrode or no electrolytic gel.

(2)If the interference exists on all positions of the lead

selector switch then the problem is internal of the

machine.

(3) If the problem occurs in certain lead position of the

selector switch then suspect an open wire, useohmmeter for continuity.

St ECG

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Stress ECG

*Some potentials dangerous cardiac arrhythmiaand other anomalies shown up only under stressconditions.

*Physicians examine the stress condition by placing

the patient on the treadmill or stair stepper whilemonitoring the patient's ECG waveform on both anoscilloscope monitor and a paper chart.

*Modern stress ECG machines are usually equippedwith a microcomputer that analyzes the waveform .

* h d f h

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*A common method is to perform the stress test,recording the ECG waveform, and then follow thestress test with a thallium scan.

*The radioactive thallium is taken up by healthycardiac cells, so areas of the heart where blood

flow is sufficient appear darker on a gammacamera display then healthy areas.

*These two tests allow the physician to evaluatethe existence, location and extent of cardiacdisease.

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Manual Controller

The optional manual controller

Allows personal treadmill operation, whilegiving the user control of speed and

elevation functions without interferingwith

medical usage.

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Drive Assembly

The low profile design and simplified layout of

drive assembly components provide easyaccessibility for maintenance and provides ahigh level of performance.

di l

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displaysBody weight, Time, Distance ,Elevation

Total calories, Calories per minutePace (minutes/mile), Heart rate.

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ECG PARAMETER

ECG leads 12 standard Record speed 5/25/50

Sensitivity 2.5/5/10/20

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Operations and Controls

INST: No signal gets recorded when this ispressed

ADV: Pressing this forward the leadposition by one lead.

REV: Pressing this takes the lead position

by one lead.

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TECHNICAL SPECIFICATIONS

GENERAL Dimensions 297 x 210 x 80mm Weight

4.8 kg with battery POWER SUPPLYAC Mains 180 - 260 VAC

Battery Back-up 100 m

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TECHNICAL SPECIFICATIONS

RECORDING Power Thermo-sensitivePaper with Recording Consumption :

50 mm (Recording 40 mm) 25 and 50mm/sec. (switch selection)

LEAD SELECTION 12 lead selection

Selector Positions Test, I, II, III, aVR, aVL,aVF, V

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