3. Measurement of Blood Pressure
One of the oldest physiological measurements
Originates from the heart
Value depends on 3 factors:
Commonly refers to arterial blood pressure
Observation of blood pressure allows dynamic tracking of pathology and physiology
affecting to the cardiovascular system, which has profound effects to all other organs of
the body
Value depends on 3 factors:
cardiac output
diameter of arteries
the quantity of blood
Values should be lower than 120 / 80 mmHg
(systolic pressure (SP) / diastolic pressure (DP))
Systolic blood pressure is the pressure when
the heart beats while pumping blood. Diastolic
blood pressure is the pressure when the heart
is at rest between beats.
4. Pulse pressure (PP) = SP-DP
High value increases the risk of heart attack and strokes
Low value increases the risk of lower oxygen perfusion e.g. in brains
However, the ’normal values’ differ from person to another
MP = DP+PP/3
Mean pressure (MP)
average pressure during one cardiac cycle
driving force of the peripheral perfusion.
an estimate can be done by using an empirical formula:
SP and DP may vary significantly throughout the arterial system but MP is
quite uniform (in normal situations)
7. General Facts
Indirect measurement = non-invasive measurement(not
involving the introduction of instruments or other objects into
the body or body cavities.
Brachial artery is the most common measurement site
Close to heart
Convenient measurement
Other sites are e.g.:
forearm / radial artery
wrist (tends to give much higher SP)
The most common indirect methods are auscultation and
oscillometry
8. General Facts
An occlusive cuff is placed on arm and inflated to P > SP,then the
cuff is deflated gradually and the measurement of blood flow is
done
Cuff
The occlusive cuff should be of a correct size in order to transmit
the pressure to the artery evenly and thus to obtain accuratethe pressure to the artery evenly and thus to obtain accurate
results
A short cuff requires special attention in placement. Longer
cuff reduces this problem.
The cuff should be placed at the heart level in order to minimize
the hydrostatic effects
9. Palpatory Method (Riva-Rocci Method)
When the cuff is deflated, there is a palpable pulse
in the wrist. P = BP
Several measurements should be done as the
respiration and vasomotor waves modulate the
blood pressure levels
cuff
blood pressure levels
+) The blood pressure can be measured in noisy environment too
ADVANTAGES
-) Only the systolic pressure can be measured (not DP)
DISADVANTAGES
-) The technique does not give accurate results for infants and
hypotensive patients
+) Technique does not require much equipment
10. Auscultatory Method
Pulse waves that propagate
through the brachial artery,
generate Korotkoff sounds.
There are 5 distinct phases in the
The Korotkoff sounds are ausculted
with a stethoscope or microphone
(automatic measurement)
There are 5 distinct phases in the
Korotkoff sounds, which define SP and
DP
Also with this method, several measurements
should be done.
The frequency range is 20-300 Hz
and the accuracy is +/- 2mmHg (SP)
and +/- 4mmHg (DP)
11. Auscultatory Method (cont.)
-) Auscultatory tecnique cannot be used in noisy environment
+) Auscultatory technique is simple and does not require much
equipment
ADVANTAGES
DISADVANTAGES
-) The observations differ from observer to another
-) A mechanical error might be introduced into the system e.g. mercury
leakage, air leakage, obstruction in the cuff etc.
-) The observations do not always correspond with intra-arterial pressure
-) The technique does not give accurate results for infants and
hypotensive patients
12. Ultrasonic Method
A transcutaneous (through the skin)
Doppler sensor is applied here.
The motion of blood-vessel walls in
various states of occlusion is
measured.
The frequency difference between
transmitted (8 MHz) and received
signal is 40-500 Hz and it is
proportional to velocities of the wall motion and the blood.
The vessel opens and closes with each
heartbeat when DP < P < SPcuff
13. Ultrasonic Method (cont.)
As the cuff pressure is increased, the time between opening and closing
decreases until they coincide Systolic pressure
Again as the cuff pressure is decreased, the time between opening and closing
increases until they coincide Diastolic pressure
+) Can be also used in noisy environment
ADVANTAGES & DISADVANTAGES
+) Can be used with infants and hypotensive individuals
-) Subject’s movements change the path from sensor to vessel
increases until they coincide Diastolic pressure
14. Oscillometric Method
The intra-arterial pulsation is
transmitted via cuff to transducer (e.g.
piezo-electric)
The cuff pressure is deflated
either linearly or stepwise
http://colin-europe.com/docpdfdemos/oscillo0104.wmv
The arterial pressure oscillations
(which can be detected throughout the
measurement i.e. when P > SP and
P < DP) are superimposed on the cuff
pressure
SP and DP are estimated from the amplitudes of the oscillation by using a
(proprietary) empirical algorithm.
cuff
cuff
15. Oscillometric Method (cont.)
+) In the recent years,
oscillometric methods have
become popular for their
simplicity of use and reliability.
ADVANTAGES
DISADVANTAGE
-) Many devices use fixed
algorithms leading to
large variance in blood
pressures
+) MP can be measured
reliably even in the case of
hypotension
16. Tonometry
A sensor array is used here, because at least
one of the pressure sensors must lay directly
above the artery
Linear array of pressure sensors is pressed
against a superficial artery, which is supported
from below by a bone (radial artery).
above the artery
The pressure is increased continuously and the
measurements are made when the artery is
half collapsed
When the blood vessel is partly collapsed, the
surrounding pressure equals the artery pressure.
The hold-down pressure varies between
individuals and therefore a ’calibration’ must be
done
17. Tonometry (cont.)
ADVANTAGES
+) Can be used for non-invasive, non-painful, continuous measurement
DISADVANTAGES
-) Relatively high cost-) Relatively high cost
-) The wrist movement and tendons result
in measurement inaccuracies
19. General Facts
Direct measurement = Invasive measurement
A vessel is punctured and a catheter (a flexible tube) is guided in
The most common sites are brachial and radial arteries but
also other sites can be used e.g. femoral artery
Used only when essential to determine the blood pressure continuously and
accurately in dynamic circumstances
A division is made into extravascular and intravascular
sensor systems
This method is precise but it is
also a complex procedure
involving many risks….
20. Extravascular Sensor
The sensor is located behind the
catheter and the vascular pressure is
transmitted via this liquid-filled
catheter.
The ’normal’ measuring system
The actual pressure sensor can be e.g.
strain gage
variable inductance
variable capacitance
optoelectronic
piezoelectric, etc…
21. Extravascular Sensor (cont.)
The hydraylic link is the major source of errors. The system’s natural frequency may
be damped and degraded due (e.g.):
too narrow catheter
too long tubing
various narrow connections
.
p
R L
lichid
cateter
senzor
diafragma
V
lungime
incrementala
c sR c
R cc
Lc Lc R Ls
(a)
p
R L
lichid
cateter
senzor
diafragma
V
lungime
incrementala
c sR c
R cc
Lc Lc R Ls
(a)
air bubbles in the catheter
The catheter-sensor system must be flushed
with saline-heparine solution every few
minutes in order to prevent blood from
clotting at the tip.
R L
C
c s
d
R c
R cc
c C C
C
Lc Lc
c c
R L
C
s
s
= V
p
(b)
R L
C
c s
d
R c
R cc
c C C
C
Lc Lc
c c
R L
C
s
s
= V
p
(b)
22. Extravascular Sensor (cont.)
Normally the interesting frequency range is 0 – 100 Hz.
If only MP is measured the bandwidth is 20 Hz (harmonics > 10 are ignored)
23. Intravascular Sensor
The sensor is located in the tip of the catheter. This way the hydraulic connection is
replaced with an electrical or optical connection
+) The frequency response is not limited
The dispacement of the diaphragm is
measured
+) The frequency response is not limited
by the hydraulic properties of the
system. No time delay.
-) Breaks easily
-) More expensive
+) Electrical safety and isolation when
using fiber optics
24. Disposable Sensors
Disposable sensors decrease the risk of patient cross-contamination and reduce
the amount of handling by hospital personnel
Cheaper and more reliable than reusable pressure sensors
General on System ParametersGeneral on System Parameters
Even minute air bubbles in catheter have a dramatic effect on frequency response
The natural frequency and the length of the catheter have a
following relationship:
The catheter diameter has a linear relationship to
natural frequency
L
fn
1=
Stiffer catheters have a higher frequency response
Teflon
Polyethylene
Silicon rubber
BETTER
WORSE
25. Summary
BLOOD PRESSURE
Describes the physiology and pathology of cardiocvascular system
”Normal” values are 120 / 80 mmHg
High values may lead to heart attack and strokesHigh values may lead to heart attack and strokes
Low values may lead to low oxygen perfusion
All direct methods require skin punctuation and a use of
catheter. Methods are used only when continuous and
accurate measurements are needed.
Almost all indirect methods rely on an occlusive cuff
which is placed on the bracial artery. The actual
measurement is done when the cuff is deflated
28. Blood Flow
O and other nutrition concentration in the cells are one
of the primary measurements.
2
Blood flow helps to understand basic physiological
processes and e.g. the dissolution of a medicine into the
body.body.
Usually the blood flow measurements are more invasive
than blood pressure measurements / ECG
It also helps to understand many pathological conditions,
since many diseases alter the blood flow. Also the blood
clots in the arterial system can be detected.
30. Doppler Measurements (1) Ultrasound
Doppler
The blood cells in the fluid scatter
the Doppler signal diffusively.
In the recent years ultrasoundIn the recent years ultrasound
contrast agents have been used in
order to increase the echoes.
c
v
ff cd 2=
f = 2 – 10 MHzc
c = 1500 - 1600 m/s (1540 m/s)
f = 1,3 – 13 kHzd
The ultrasound beam is focused by a
suitable transducer geometry and a lens
31. Doppler Measurements (2) Ultrasound
Doppler
The flow velocity is obtained from the
spectral estimation of the received
Doppler signal
In order to know where along the beam the
blood flow data is colledted, a pulsed
Doppler must be used
32. Doppler Measurements (3) Ultrasound
Doppler
The ultrasound Doppler device can be either a continuous wave or a pulsed Doppler
CW DOPPLER PULSED DOPPLER
No minimum range Accuracy
Range ambiguity
Low flow cannot be
detected
Simpler hardware
Minimum range
No minimum flow
(Maximum flow) x (range)
= limited
33. Doppler Measurements (4) Ultrasound
Doppler
GENERAL PARAMETERS
the power decays exponentially because of the heating of the tissue. The
absorption coefficient ~ proportional to frequency
the far field operation should be avoided due to beam divergence.the far field operation should be avoided due to beam divergence.
λ4
2
D
dnf = D = Transducer diameter (e.g. 1 – 5 mm)
the backscattered power is proportional to f
4
the resolution and SNR are related to the pulse duration. Improving either one of
the parameters always affects inversely to the other
34. Doppler Measurements (5)
Laser Doppler Flowmetry
The principle of measurement is the
same as with ultrasound Doppler
The laser parameter may have e.g. the
following properties:
5 mW
He-Ne-laser
632,8 nm wavelength
The moving red blood cells cause
Doppler frequency 30 – 12 000 Hz.
The method is used for capillary
(microvascular) blood flow
measurements
36. Indicator Dilution Methods (1)
Dye Dilution Method
A bolus of indicator, a colored dye (indocyanine green), is rapidly injected in to the
vessel. The concentration is measured in the downstream
The blood is drawn through a colorimetric cuvette and
the concentration is measured using the principle of
absorption photometry
( )[ ]dttC
m
F t
∫ ∆
= 1
0
amount of
dye
1% peak CAvg.
flow
37. Q
Indicator Dilution Methods (2)
Thermal Dilution Method
A bolus of chilled saline solution is injected
into the blood circulation system (right
atrium). This causes decrease in the
pulmonary artery temperature.
heat content
of injectate
( )dttTc
Q
F t
bbb ∫ ∆
= 1
0
ρ
A standard technique for measuring cardiac output in critically ill patients
An artery puncture is not needed in this technique
of injectate
Several measurements can be done in relatively short time
density of blood
(e.g. 1060 kg/m3)
specific heat of blood
(e.g. 3640 J/(kg*K)
39. Plethysmography (1)
Strain Gage Method
Plethysmography means the methods for recording volume changes of an organ or
a body part (e.g. a leg)
Strain gage is made of silicone rubber
tubes, which are filled with conductive
liquid (e.g. mercury) whose impedance
changes with volume.changes with volume.
Venous occlusion cuff is inflated to 40 – 50
mmHg. In this way there will be the
arterial inflow into the limb but no venous
outflow.
If only a segment of limb is measured, there is a need for arterial occlusion cuff also.
40. Plethysmography (2)
Chamber Method
As the volume of the leg increases, the leg
squeezes some kind of bladder and decreases its
volume
Volume transducer can be e.g. water filled tube
(level) or air (pressure)
Chamber plethysmograph is the only accurate non-invasive way to measure
changes in the blood volume
The speed of the return of the
venous blood is measured
41. Plethysmography (3)
Electric-Impedance Method
Different tissues in a body have a different resistivity. Blood is one of the best conductors
in a body ( = 1,5 Ωm) ρ
A constant current is applied via skin
electrodes
I = 0,5 – 4 mA rms (SNR)
The change in the impedance is
measured
The accuracy is often poor or unknown
I = 0,5 – 4 mA rms (SNR)
f = 50 – 100 kHz
(Zskin-electrode+shock)
Z
Z
L
Vol ∆=∆ 2
0
2
ρ
42. Plethysmography (4)
Photoelectric Method
A beam of IR-light is directed to the part of
the tissue which is to be measured for
blood flow (e.g. a finger or ear lobe)
The light that is transmitted / reflected is
collected with a photodetector
The blood flow modulates the attenuated /
reflected light which is recorded.
Poor measure for changes in volume
Very sensitive to motion artefacts
Method is simple
Heart rate is clearly seen
44. Radioisotopes
A rapidly diffusing, inert radioisotope of lipid-soluble gas ( Xe or Kr) is
injected into the tissue or passively diffused
133 85
The elimination of the radioisotope from microcirculatory bed is related to the
blood flow:
( )ktCtC −= exp)( 0
2/1/2ln tk =
45. Thermal Convection Probe
The rate of heat removal from the tissue under probe is measured
The concentric rings are isolated
thermally & electrically from each
other
The central disk is heated
This is one of the earliest techniques for blood flow measurements
The central disk is heated
1 – 2 C over the temperature of
tissue
A temperature difference of
2- 3 C is established between the
disks
o
o
The method is not very common due extreme nonlinear properties and difficulties in
practical use (e.g. variable thermal characteristics of skin)
46. Summary
BLOOD FLOW
Used for understanding physiological processes (e.g. medicine
dissolution). Also used for locating clots in arteries
Usually more invasive methods are used than with blood pressure
measurements
dissolution). Also used for locating clots in arteries
Normal velocity is 0,5 - 1 m/s
Indirect measurements are done by using ultrasound or
plethysmographic method
Direct measurements are done by dilution methods (dye / thermal)
47. Measurement of heart sound
• For centuries the medical profession has been aided in its
diagnosis of certain types of heart disorders by the sounds and
vibrations associated with the beating of the heart and the
pumping of blood.
• The technique of listening to sounds produced by the organs and
vessels of the body is called auscultation, and it is still in common
use today.
• During his training the physician learns to recognize sounds or• During his training the physician learns to recognize sounds or
changes in sounds that he can associate with various types of
disorders.
• In spite of its widespread use, however, auscultation is rather
subjective, and the amount of information that can be obtained by
listening to the sounds of the heart depends largely on the skill,
experience, and hearing ability of the physician.
• Different physicians may hear the same sounds differently, and
perhaps interpret them differently.
48. • The heart sounds heard by the physician through his
stethoscope actually occur at the time of closure of
major valves in the heart.
• This timing could easily lead to the false assumption
that the sounds which are heard are primarily caused
by the snapping together of the vanes of these
valves.
• In reality, this snapping action produces almost no
sound, because of the cushioning effect of the blood.sound, because of the cushioning effect of the blood.
• The principal cause of heart sounds seems to be
vibrations set up in the blood inside the heart by the
sudden closure of the valves.
• These vibrations, together with eddy currents
induced in the blood as it is forced through the
closing valves, produce vibrations in the walls of the
heart chambers and in the adjoining blood vessels.
49. • With each heartbeat, the normal heart produces two distinct
sounds that are audible in the stethoscope—often described
as *'lub-dub.''
• The **lub'' is caused by the closure of the atrioventricular
valves, which permit flow of blood from the atria into the
ventricles but prevent flow in the reverse direction.
• Normally, this is called the first heart sound, and it occurs
approximately at the time of the QRS complex of the
electrocardiogram and just before ventricular systole.electrocardiogram and just before ventricular systole.
• The '*dub" part of the heart sounds is called the second heart
sound and is caused by the closing of the semilunar valves,
which release blood into the pulmonary and systemic
circulation systems.
• These valves close at the end of systole, just before the
atrioventricular valves reopen.
• This second heart sound occurs about the time of the end of
the T wave of the electrocardiogram.
50. • A third heart sound is sometimes heard, especially in
young adults.
• This sound, which occurs from 0.1 to 0.2 sec. after the
second heart sound, is attributed to the rush of blood
from the atria into the ventricles, which causes
turbulence and some vibration of the ventricular
walls.walls.
• This sound actually precedes atrial contraction, which
means that the inrush of blood to the ventricles
causing this sound is passive, pushed only by the
venous pressure at the inlets to the atria.
• Actually, about 70 percent of blood flow into the
ventricles occurs before atrial contraction.
51. • Figure shows the time relationships between the first, second, and third heart
sounds with respect to the electrocardiogram, and the various pressure waveforms.
52. • In abnormal hearts additional sounds, called murmurs, are
heard between the normal heart sounds.
• Murmurs are generally caused either by improper opening of
the valves (which requires the blood to be forced through a
small aperture) or by regurgitation, which results when the
valves do not close completely and allow some backward flow
of blood.
• In either case, the sound is due to high-velocity blood flow
through a small opening.
• Another cause of murmurs can be a small opening in the• Another cause of murmurs can be a small opening in the
septum, which separates the left and right sides of the heart.
• In this case, pressure differences between the two sides of
the heart force blood through the opening, usually from the
left ventricle into the right ventricle, bypassing the systemic
circulation.
• Normal heart sounds are quite short in duration,
approximately one tenth of a second for each, while murmurs
usually extend between the normal sounds.
54. • There is also a difference in frequency range between
normal and abnormal heart sounds.
• The first heart sound is composed primarily of energy in the
30- to 45-Hz range, with much of the sound below the
threshold of audibility.
• The second heart sound is usually higher in pitch than the
first, with maximum energy in the 50- to 70-Hz range.
• The third heart sound is an extremely weak vibration, with• The third heart sound is an extremely weak vibration, with
most of its energy at or below 30 Hz.
• Murmurs, on the other hand, often produce much higher
pitched sounds.
• One particular type of regurgitation, for example, causes a
murmur in the 100-to 600-Hz range.
55. • Although auscultation is still the principal method
of detecting and analyzing heart sounds, other
techniques are also often employed.
• For example, a graphic recording of heart sounds is
called a phonocardiogram.
• Even though the phonocardiogram is a graphic• Even though the phonocardiogram is a graphic
record like the electrocardiogram, it extends to a
much higher frequency range.
• The process of producing phonocardiogram is called
phonocardiography
57. Way to heart is through ears….
Development of Stethoscopes
4/4/2020 Phonocardiography 57
Early monaural
stethoscope
Modern binaural stethoscope
Modern electronic stethoscope
58. 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.
4/4/2020 Phonocardiography 58
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.
59. 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
4/4/2020 Phonocardiography 59
• 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.
60. 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
4/4/2020 Phonocardiography 60
• 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.
61. 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
4/4/2020 Phonocardiography 61
• The medical use of this knowledge is to link sounds that
diverge from normality to certain pathological conditions.
62. • Phonocardiograph:
Instrument used for
recording sounds
connected with the
pumping action of
4/4/2020 Phonocardiography 62
pumping action of
heart
63. • Phonocardiogram:
A high fedility
recording
representing the
rhythmicity and
4/4/2020 Phonocardiography 63
rhythmicity and
heart rate
4/4/2020 63
65. • 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
Heart Sounds
4/4/2020 Phonocardiography 65
• 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.
4/4/2020 65
66. First heart sound:
- occurs when the
atrioventricular (AV) valves
close at the beginning of
ventricular contraction.
- generated by the vibration of
4/4/2020 Phonocardiography 66
the blood and the ventricular
wall
- is louder, longer, more
resonant than the second heart
sound.
67. First Heart Sound
4/4/2020 Phonocardiography 67
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
Vibrations
caused by
turbulence
in ejected
blood flowing
into aorta
68. - occurs when aortic and
pulmonary semilunar valves
close at the beginning of
ventricular dilation
Second heart sound
4/4/2020 Phonocardiography 68
- generated by the vibration
of the blood and the aorta
- Aortic valve closes slightly
before pulmonary valve.
69. • 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
4/4/2020 Phonocardiography 69
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
70. 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
4/4/2020 Phonocardiography 70
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.
71. Basic Heart Sounds in a Phonocardiogram Recording
4/4/2020 Phonocardiography 71
72. 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
4/4/2020 Phonocardiography 72
• 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
73. Factors involved in production of murmurs
Heart Murmurs
4/4/2020 Phonocardiography 73
High rate of
flow through
valves
Flow through
constricted
valves
(stenosis)
Backward flow
through
incompetent
valve
Septal defects
Decreased
viscosity,
which causes
increased
turbulence
76. Instrumentation
Basic transducer
• Amplifier
• 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
4/4/2020 Phonocardiography 76
• Amplifier
• Filter
• 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.
4/4/2020 76
77. • Integrator
• Power Amplifier
• Recording envelope of higher
frequency over 80Hz along with
actual signals below 80Hz.
• Increase the power of incoming
signal
• Efficiency is more
4/4/2020 Phonocardiography 77
• DAC and Readout or high
frequency chart recorder or
oscilloscope or headphones
• Efficiency is more
• Effect of noise is lowered
• Signal is converted to digital
form and stored permanently
• For faithful recording of heart
sounds
78. 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
4/4/2020 Phonocardiography 78
• 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.
79. Acquisition of Phonocardiographic Signals
• Microphones picks up
(i). Heart sounds
(ii). Heart murmurs
(iii). Extraneous noise in the immediate vicinity of
the patient
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the patient
• Group 1-
(i) . Contact microphone
(ii). Air coupled microphone
• Group 2-
(i) Crystal microphone
(ii) Dynamic microphone
80. 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)
4/4/2020 Phonocardiography 80
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.
81. 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
4/4/2020 Phonocardiography 81
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.
82. 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
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• 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
83. 4/4/2020 Phonocardiography 83
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.
84. 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
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voltage because of its
interaction with magnetic flux
85. 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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• Hence microphones of various types cannot be interchanged.
86. 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
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(ii). Optical Galvanometric Recorders
(iii). Envelope detection
(iv). Direct recording using Ink Jet
Recorders
(v). Electrostatic Recorder
(vi). Thermal Recorder
87. 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
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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.
88. Envelope Detection
• Uses artificial frequency of
about 100 Hz in heart
sound amplifier
• Employed to oscillate
4/4/2020 Phonocardiography 88
• Employed to oscillate
stylus so that high
frequency sounds are
modulated by 100Hz
89. 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
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%.
4/4/2020 Phonocardiography 89
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
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.
90. 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
4/4/2020 Phonocardiography 90
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
91. • 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
• Phonocardiography
better diagnosing of mitral
insufficiency, diagnosis of
aortic valve defects
more informative about state of
aortic valves
The two not alternative, and the less contradictory, but mutually supplementing methods.
4/4/2020 Phonocardiography 91
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.
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.
