Transcript
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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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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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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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