PHONOCARDIOGRAPHY

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PHONOCARDIOGRAPHY
Saumya Mohan Kumar T.E. Biomed-Roll No.55
7/13/2016
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Index

• 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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Pioneers

• 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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Way to heart is through ears.
Development of Stethoscopes
Early monaural stethoscope
Modern binaural stethoscope
Modern electronic stethoscope
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Working

• Acoustic stethoscopes transmit sound mechanically
  from a chest-piece 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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Advantages

• 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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Disadvantages

• 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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Phonocardiograph- an intelligent Stethoscope

• 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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Heart Sounds

• 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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• 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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Basic Heart Sounds in a Phonocardiogram Recording
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Heart murmurs

• 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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Factors involved in production of murmurs
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Heart Cycle
Name
Events
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Pressure (kPa)
10
5
0
PCG
ECG
Time 0 (sec)
0.4
0.8
0.3
0.5
0.6
0.7
0.1
0.2
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Basic Block Diagram
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Instrumentation

• 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.

• Basic transducer ?
• Amplifier ?
• Filter ?

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• Recording envelope of higher frequency over 80Hz
  along with actual signals below 80Hz.
• Increase the power of incoming signal
• Efficiency is more
• Effect of noise is lowered
• Signal is converted to digital form and stored
  permanently
• For faithful recording of heart sounds

• Integrator ?
• Power Amplifier ?
• DAC and Readout or high frequency chart recorder
  or ? oscilloscope or headphones

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Sensors

• 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 chest-wall movements
• For recording of body sounds,
• ? condenser microphones
• ? piezoelectric accelerometers
• have been recommended.

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Acquisition of Phonocardiographic Signals

• 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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Group 1 Microphones

• 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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Group 1 Microphones

• Air coupled Microphones
• shows a low-pass frequency response because of
  its air-chamber 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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Group 2 Microphones

• 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 diaphragm that is mechanically linked to the
crystal so that the sound waves are indirectly
coupled to the crystal.
a crystal is mounted so that the sound waves
strike it directly
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Group 2 Microphones

• Dynamic Microphones
• 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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Technical design of Microphone

• 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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Writing methods for phonocardiography

• 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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Ink Jet Recorders

• 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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Envelope Detection

• 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
• 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
  PC-based system that is capable to process real
  time fetal phonocardiographic signal

• Cons
• 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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Scope

• 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
• Suggested Applications
• 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
• better diagnosis of mitral valve defects
  ,evaluating the degree of its stenosis and
  characterizing the morphological changes of the
  valve.
• more informative about tricuspid valve defects
• echocardiographic data on the changes in the left
  ventricular outflow tract help to explain the
  origin of the spindle-form systolic murmur.

• Phonocardiography
• better diagnosing of mitral
• insufficiency, diagnosis of
• aortic valve defects
• more informative about state of aortic valves
• 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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Case Study
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