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BIOMEDICAL RECORDERS

R.GOWRIASSISTANT PROFESSOR/ECEKIT-KALAIGNAR KARUNANIDHI INSTITUTE OF TECHNOLOGY

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What are biopotentialsBiopotential: 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 This book focuses strictly on the measurement of potentials

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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. Ventriculardepolarization

3. Ventricular repolarization

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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

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ECG

Electrical activity of heart.Used in catheterization laboratories,

coronary care units and routine diagnostic applications in cardiology.

LEAD – Two electrodes are placed over different areas of the heart, the resulting tracing of voltage difference at any sites due to electrical activity of heart.

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EFFECTS OF ARTIFACTS

Interference from the power lineShifting of the baselineMuscle tremor

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Vectorcardiogram (VCG or EVCG) Instead of displaying the scalar amplitude

(ECG curve) the electric activation front is measured and displayed as a vector It has amplitude and direction

Diagnosis is based on the curve that the point of this vector draws in 2 or 3 dimensions

The information content of the VCG signal is roughly the same as 12-lead ECG system. The advantage comes from the way how this information is displayed

Increase in sensitivity A normal, scalar ECG curve can be formed

from this vector representation, although (for practical reasons) transformation can be quite complicated

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Display in 2 perpendicular axisLoop type patternProvides direction of depolarization and

repolarization of atria and ventricle3 loops – P wave,QRS axis(high amp –

predominate and T wave.3 images – frontal,sagittal and transverse

planes.Recognition of undetected atrial and

ventricular hypertrophy, myocardial infraction.

CONT…

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 obsoleteEinthoven leads: I, II & III Goldberger augmented leads: VR, VL & VF Precordial leads: V1-V6

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CONT..

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PCG

Graphic record heart sound - Phonogram.Recording the sounds connected with the pumping

action of heart.Sound from heart – phonocardiogramInstrument to measure this – phonocardiographBasic function – to pick up the different heart

sound,filter the required and display.Two categories – heart sound – transient characteristics with short

duration.(closing and opening of valves) murmurs – noisy characteristics with long duration.

(turbulent blood flow in heart)

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Origin of sound

Valve closureMovement of heart wallValve openingExtra cardiac sounds1. Frequency – 10 to 1000 Hz.LOW RANGE – 10 – 60 Hz(3rd and 4th)MEDIUM RANGE – 60 – 150 Hz(1st and 2nd)HIGH RANGE – 150 – 1000 Hz 2.Amplitude3.Quality

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Origin of sound

1st sound:Closure of mitral and tricuspid valves.Freq – 30 to 100 Hz and duration 50 to 100 ms2nd sound:Closure of aortic and pulmonary valves(slight

back flow of blood).Freq – 30 to 100 Hz and duration 25 to 50 ms .3rd and 4th low intensity and inaudible.(heard

among children).

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Origin of sound

3rd sound: Blood rapid movement into relaxed

ventricular chambers Freq – 10 to 100 Hz and duration 0.04 to

0.08 s.4th sound: atrial contraction. Freq – 10 to 50 Hz and duration 0.03 to 0.06

s.

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CONT..

Microphones for PCG:Crystal microphone – contains wafer of piezo-

electric material, which generates potentials when subjected to mechanical stresses due to heart sound. Smaller in size, high sensitivity.

Dynamic microphone – consists of a moving coil having a fixed magnetic core inside it. The coil moves with the heart sound and produce a voltage because of interaction with the magnetic flux.

New acoustic sensors – polymer based adherent differential-output sensors.

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Writing methods

Light beam galvanometer – expensive and require more power from amplifiers when used for high freq.

Direct writing recorders – upper freq 150 Hz.(used for only low freq).

Technique – envelope detection.Fans, Air conditioners and other noise

producing gadgets will result in artefacts on the recordings.

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Heart Sounds

S1 – onset of the ventricular contraction S2 – closure of the semilunar valves S3 – ventricular gallop S4 – atrial gallop Other – opening snap, ejection sound Murmurs

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RECORDING SET - UP

CONDENSER

MICROPHONE

ECG AMPECG

ELECTRODE

FILTERPHONO AMPLIFIER

FM TAPE RECORDER

MONITOR SCOPE

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MEDICAL APPLICATION

Rheumatic valvular lesions Allergic disease in which the heart valves are likely to be damaged. This creates

abnormal heart sound. The murmurs of aortic steonosis The blood is ejected from the left ventricles through a small opening of aortic valve.

High pressure 350 mm of Hg and causes turbulent flow of blood. The murmurs of aortic regurgitation During diastole, blood flow backward from aorta to left ventricles,causing a

blowing murmur. The murmurs of mitral regurgitation During systole, blood flow backward through mitral valve. The murmurs of mitral steonosis It produce murmurs when,Blood passes with difficulty from LA into the LV due to

pressure difference.

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SPECIAL APPLICATION OF PCG

Fetal PCGEsophageal PCGTracheal PCG - Cannula

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THANK YOU