Transcript Document

Saumya Mohan Kumar
Phonocardiography
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T.E. Biomed-Roll No.55
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Pioneers in auscultation
Development of Stethoscope
Development of Phonocardiograph
Heart sounds
Heart Murmurs
Basic Block Diagram and Instrumentation
Acquisition of phonocardiographic signals
Writing methods for phonocardiography
Pros and Cons
Scope
Echocardiography vs. Phonocardiography
Case Study
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Hippocrates laid the foundation for auscultation
Robert Hook realized diagnostic use of cardiac
auscultation
Biggest breakthrough in auscultation:
Rene Laennec invented stethoscope
Dr. Jean Bennett Maguire devised a method of
real-time spectral phonocardiography for the
detection and classification of heart murmurs.
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Development of Stethoscopes
Early monaural stethoscope Modern binaural stethoscope Modern electronic stethoscope
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Acoustic stethoscopes transmit sound mechanically from a chestpiece via air filled hollow tubes to the listener's ears.
The diaphragm and the bell work as two filters, transmitting
higher frequency sounds and lower frequency sounds,
respectively.
Electronic stethoscopes function in a similar way, but the sound
is converted to an electronic signal which is transmitted to the
listener by wire.
Functionalities often included in electronic stethoscopes are
amplification of the signal, filters imitating the function of the
diaphragm and the bell and in some cases recording abilities to
allow storage of data.
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Allow volume control of heart and lung sounds heard more
easily without amplifying other sounds.
Even subtle changes in breath sounds can be picked up and
magnified
Aid health-care professionals in hearing heart murmurs
Electronic stethoscopes also allow the user to distinguish
between body sounds of high and low frequency.
They now have wireless capabilities, which allow data to be
transferred to a computer or handheld device for storage and
retrieval at a later time.
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Patients undergoing surgery have the sterile field
invaded thereby risking infection
Patients are frequently awakened and disturbed
Serious developmental abnormalities in newborn
infants who are frequently disturbed
In the absence of airtight seal between stethoscope and
skin, which determines the quality of sound wave
transmission, background noise is detected and
physiologic sound transmission is impaired.
They are not capable of generating constructive
interference of physiologic sound waves.
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Bioacoustic research
Establish a relationship between mechanical event- conduction
of heart- within the body and the sounds these events give rise
to.
The medical use of this knowledge is to link sounds that
diverge from normality to certain pathological conditions.
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Phonocardiograph:
Instrument used for
recording sounds
connected with the
pumping action of
heart
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Phonocardiogram:
A high fedility
recording
representing the
rhythmicity and
heart rate
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Phonocardiography:
the process of
graphical recording of
heart sounds or
murmurs
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Mechanical working processes of the heart produce sound
which indicate health status of the individual.
The relationship between blood volumes, pressures and flows
within the heart determines the opening and closing of the
heart valves.
Normal heart sounds- lub and dub- occur during the closure
of the valves.
The valvular theory states that heart sounds emanate from a
point sources located near the valves.
In the cardiohemic theory the heart and the blood represent
an interdependent system that vibrates as a whole and
propagates sound as waves of alternate pressure.
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First heart sound:
- occurs when the
atrioventricular (AV) valves
close at the beginning of
ventricular contraction.
- generated by the vibration of
the blood and the ventricular
wall
- is louder, longer, more
resonant than the second heart
sound.
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First Heart Sound
Initial vibrations
occur when first
contraction of
ventricle move
blood towards
atria, closing
AV valves
Abrupt tension
of closed AV
valves,
decelerating
the blood
Oscillation of
blood between
root of aorta
and
ventricular walls
Phonocardiography
Vibrations
caused by
turbulence
in ejected
blood flowing
into aorta
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Second heart sound
- occurs when aortic and
pulmonary semilunar
valves close at the
beginning of ventricular
dilation
- generated by the vibration
of the blood and the aorta
- Aortic valve closes slightly
before pulmonary valve.
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The second sound (S2) signals the end of systole and
the beginning of diastole
It is heard at the time of the closing of the aortic and
pulmonary valves
S2 is probably the result of oscillations in the
cardiohemic system caused by deceleration and
reversal of flow into the aorta and the pulmonary artery
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A third heart sound (S3)
 connected with the diastolic filling period. The rapid
filling phase starts with the opening of the semilunar
valves.
 attributes energy released with the sudden deceleration
of blood that enters the ventricle throughout this period
A fourth heart sound (S4)
 connected with the late diastolic filling period
 occur during atrial systole where blood is forced into
the ventricles.
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Murmurs are extra heart sounds that are produced as a result of
turbulent blood flow which is sufficient to produce audible noise.
Innocent murmurs are present in normal hearts without any heart
disease.
Pathologic Murmurs are as a result of various problems, such as
narrowing or leaking of valves, or the presence of abnormal
passages through which blood flows in or near the heart.
Heart murmurs occur when the blood flow is accelerated above the
Reynolds number, which induces non-stationary random vibrations,
that are transmitted through the cardiac and thoracic tissues up to
the surface of the thorax
They are graded by intensity from I to VI.
Grade I is very faint and heard only with special effort
Grade VI is extremely loud and accompanied by a palpable thrill
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Heart Murmurs
High rate of
flow through
valves
Flow through
constricted
valves
(stenosis)
Backward flow
through
incompetent
valve
Septal defects
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Decreased
viscosity,
which causes
increased
turbulence
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Events
Name
Pressure (kPa)
20
15
10
5
0
PCG
ECG
Time 0
0.4
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Basic transducer
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Amplifier
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Filter
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Piezoelectric sensor to convert sound or
vibrations to electricity
Crystal or moving coil microphone
having frequency response between 5Hz
and 1000Hz
Similar response characteristics
Offer selective high pass filter to allow
frequency cutoff
Bandwidth : 20- 2000Hz
Amplify signal
Permit selection of suitable frequency
bands
Avoid aliasing
Separate louder low frequency signals
from lower intensity, much informative
high frequency murmurs.
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Integrator
Power Amplifier
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Recording envelope of higher
frequency over 80Hz along with
actual signals below 80Hz.
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Increase the power of incoming
signal
Efficiency is more
Effect of noise is lowered
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DAC and Readout or high
frequency chart recorder or 
oscilloscope or headphones
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Signal is converted to digital
form and stored permanently
For faithful recording of heart
sounds
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Sensors used when recording sound:
 Microphones
 Accelerometers
 These sensors have a high-frequency response that is quite adequate for
body sounds.
 The microphone is an air coupled sensor that measure pressure waves
induced by chest-wall movements
 The accelerometers are contact sensors which directly measures chestwall movements
 For recording of body sounds,
 condenser microphones
 piezoelectric accelerometers
have been recommended.
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Microphones picks up
(i). Heart sounds
(ii). Heart murmurs
(iii). Extraneous noise in the immediate vicinity of
the patient
Group 1(i) . Contact microphone
(ii). Air coupled microphone
Group 2(i) Crystal microphone
(ii) Dynamic microphone
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Contact Microphone
also known as a pickup or a piezo
microphone
made of a thin piezoelectric
ceramic round disc (+ve) glued to
a thin brass or alloy metal disc (ve)
designed to transmit audio
vibrations through solid objects.
contact mics act as transducers
which pick up vibrations and
convert them into a voltage which
can then be made audible.
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Air coupled Microphones
shows a low-pass frequency response because of its airchamber compliance.
In the pass band, it is considered that the microphone
has a flat response, where the mechanical impedance of
air chamber is much higher than that of chest wall, the
vibration of the measured chest-wall surface is stopped
by both the air chamber and the coupler surface in
contact with the chest wall.
The sound pressure, or normal stress exerted on the
chamber should be constant to keep a flat response.
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Crystal Microphones
uses the piezoelectric effect of Rochelle salt, quartz, or
other crystalline materials.
This means that when mechanical stress, due to heart
sounds, is placed upon the material, a voltage
electromagnetic force is generated.
Since Rochelle salt has the largest voltage output for a
given mechanical stress, it is the most commonly used
crystal in microphones.
smaller in size, more sensitive than dynamic ones
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a crystal is mounted so
that the sound waves strike
it directly
a diaphragm that is mechanically
linked to the crystal so that the sound
waves are indirectly coupled to the
crystal.
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Dynamic Microphones
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consists of a moving coil with
fixed magnetic core inside.
This moving coil moves with
heart sounds, and produces
voltage because of its
interaction with magnetic flux
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It does not transform acoustic oscillations into electrical
potentials uniformly for all frequencies.
Hence heart sound recording done with microphone is valid for
a particular type of frequency only..
Hence microphones of various types cannot be interchanged.
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Requires a writing system capable of responding to
2000 Hz.
Types of writing methods:
(i). Mechanical Recorders
(ii). Optical Galvanometric Recorders
(iii). Envelope detection
(iv). Direct recording using Ink Jet
Recorders
(v). Electrostatic Recorder
(vi). Thermal Recorder
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Merits
very little loss of diagnostically important
information
 eliminates the effort and delay of
photographic processing
 immediacy of the results affords a means
for continuously monitoring the records
for quality and special content at the time
of registration.
Demerits
 writing recorders with an upper frequency
response of 150 Hz cannot be used to write
frequencies that lie beyond their working
range.
 can only record heart sound intensity
picked up every 10 msec.
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Uses artificial frequency of
about 100 Hz in heart
sound amplifier
Employed to oscillate
stylus so that high
frequency sounds are
modulated by 100Hz
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Pros
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Can provide real-time traces of
heart beats, movement and
breathing.
Taken together this can provide a
unique view of cardiac condition.
Passive, therefore inherently safe
and can be used for long periods.
Inherently cheap, (low data rates),
and ideal for screening of large
populations and home
monitoring.
simple, low cost, houses the
necessary opto-electronic
elements. and non-invasive PCbased system that is capable to
process real time fetal
phonocardiographic signal
Cons
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Existing microphones are bulky
and obtrusive
Signal to noise ratio influenced
motion artifacts
Inherently 1 dimensional
Extended instruments are
intended for a pass band from 0.2
to100 Hz with nonlinear
distortions to 10%.
Recording of frequency
components above this limit is
related with an appreciable drop
in amplitude of recording and an
increase in distortions.
The use of contacting transducers
to sense the vibrations is
inappropriate.
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Further Work
1. Design of clinical prototype
2. Improvements to signal conditioning and control electronics
3. Investigate wireless links for cordless monitoring
4. Remote measurement of small displacements at compliant surfaces
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Suggested Applications
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Remote sensing of sub 50 micron displacements
Adult and fetal phonocardiography and phonography
Remote measurements of compliant materials in wind-tunnels
Infrasound intensity measurement
Biomedical instrumentation
Low-cost and low power confocal microscopy
Cell culture measurement
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The two not alternative, and the less contradictory, but mutually supplementing methods.
Echocardiography
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Phonocardiography
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better diagnosis of mitral valve
defects ,evaluating the degree of
its stenosis and characterizing
the morphological changes of the
valve.
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better diagnosing of mitral
insufficiency, diagnosis of
aortic valve defects
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more informative about tricuspid
valve defects
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echocardiographic data on the
changes in the left ventricular
outflow tract help to explain the
origin of the spindle-form
systolic murmur.
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more informative about state of
aortic valves
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interpretation of systolic murmur
was rather complicated, although
they are often seen on
phonocardiographic data of
normal individuals and patients
with heart diseases.
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