Biomedical Engineering Module -2 PPT as per KTU syllabus

1. BIOMEDICAL
ENGINEERING
By,
Shilpa Das
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2. Heart
• The human heart has four chambers
1. Right Atrium
2. Left Atrium
3. Right Ventricle
4. Left Ventricle
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3. • The arteries of the heart carry blood away from the
heart.
• The veins of the heart carry blood to the heart.
• The largest artery in the body is the aorta.
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4. • The Tricuspid valve or right atrio-ventricular valve—between right
atrium and ventricle. It consists of three flaps or cusps. It prevents
backward flow of blood from right ventricle to right atrium.
• Bicuspid Mitral or left atrio-ventricular valve—between left atrium and
left ventricle. The valve has two flaps or cusps. It prevents backward
flow of blood from left ventricle to atrium.
• Pulmonary valve—at the right ventricle. It consists of three half moon
shaped cusps. This does not allow blood to come back to the right
ventricle.
• Aortic valve—between left ventricle and aorta. Its construction is like
pulmonary valve. This valve prevents the return of blood back to the left
ventricle from aorta.
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5. The heart wall consists of three layers:
(i) The pericardium, which is the outer layer of the heart. It keeps
the outer surface moist and prevents friction as the heart beats.
(ii) The myocardium is the middle layer of the heart. It is the
main muscle of the heart, which is made up of short cylindrical
fibres. This muscle is automatic in action, contracting and
relaxing rythmically throughout life.
(iii) The endocardiumis the inner layer of the heart. It provides
smooth lining for the blood to flow.
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6. Four Chambers of the heart
Right Atrium Left Atrium
Right Ventricle
Left Ventricle
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7. Arteries and Veins
Superior Vena Cava
Pulmonary Veins
Inferior Vena Cava
Aorta
Left Pulmonary
Artery
Pulmonary Veins
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8. RightAtrium
• Receives de-oxygenated blood from the superior vena
cava and pumps it into the right ventricle.
Right Atrium
Right Ventricle
(Heart)
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9. Right Ventricle
• Receives de-oxygenated blood from the right atrium
and pumps it into the pulmonary artery.
Right Ventricle
Pulmonary
artery
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10. PulmonaryArtery
• Receives de-oxygenated blood from the right ventricle
and moves it into the lungs to pick up oxygen.
• Fact: arteries carry blood away from the heart.
Pulmonary Artery
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11. LeftAtrium
• Is larger than the right atrium, it receives oxygenated
blood from the pulmonary veins, and pumps it into the
left ventricle.
Left Atrium
Left Ventricle
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12. Left Ventricle
• Is larger then the right ventricle, it receives oxygenated
blood from the left atrium, and pumps it into the aorta.
Left Ventricle
Aorta
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13. Aorta
• Is the largest artery in the human body, it receives
oxygenated blood from the left ventricle of the heart
and moves it to all parts of the body.
Aorta
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14. Pulmonary Veins
• Carry oxygenated blood from the lungs to the left
atrium of the heart.
• Fact: They are the only veins that carry oxygenated
blood.
Pulmonary Veins
Pulmonary Veins
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15. Inferior Vena Cava
• Is the large vein that carries de-oxygenated blood from
the lower half of the body into the heart.
Inferior Vena Cava
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16. Superior Vena Cava
• Is a large but short vein that carries de-oxygenated
blood from the upper half of the body to the hearts
right atrium.
Superior Vena
Cava
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19. Electro conduction system of the heart
The conduction system of the heart consist of the
• Sinoatrial Node (SA Node)
• Bundle of His
• Atrioventricular node (AV Node)
• The bundle branches
• Purkinje fibers
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20. • Cardiac conduction is the rate at which the heart conducts
electrical impulses. These impulses cause the heart to contract
and then relax.
• The constant cycle of heart muscle contraction followed by
relaxation causes blood to be pumped throughout the body.
• Systole – Contraction of atria and ventricles
• Diastole – Relaxation and filling of atria and ventricles
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21. STEP1: PACEMAKER IMPULSE GENERATION
• The first step of cardiac conduction is impulse generation.
The sinoatrial (SA) node (also referred to as the pacemaker of
the heart) contracts, generating nerve impulses that travel
throughout the heart wall.
• This causes both atria to contract.
• The SA node is located in the upper wall of the right atrium. It
is composed of nodal tissue that has characteristics of
both muscle and nervous tissue.
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23. STEP2:AV NODE IMPULSE CONDUCTION
• The atrioventricular (AV) node lies on the right side of the
partition that divides the atria, near the bottom of the right
atrium.
• When the impulses from the SA node reach the AV node, they
are delayed for about a tenth of a second.
• This delay allows atria to contract and empty their contents into
the ventricles prior to ventricle contraction.
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24. STEP3:AV BUNDLE IMPULSE CONDUCTION
• The impulses are then sent down the atrioventricular bundle.
This bundle of fibers branches off into two bundles and the
impulses are carried down the center of the heart to the left and
right ventricles.
STEP 4: PURKINJE FIBERS IMPULSE CONDUCTION
• At the base of the heart the atrioventricular bundles start to
divide further into Purkinje fibers.
• When the impulses reach these fibers they trigger the muscle
fibers in the ventricles to contract. The right ventricle sends
blood to the lungs via the pulmonary artery. The left ventricle
pumps blood to the aorta.
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26. CARDIAC CONDUCTIONAND THE CARDIAC CYCLE
• Cardiac conduction is the driving force behind the cardiac cycle.
This cycle is the sequence of events that occur when the
heart beats.
• During the diastole phase of the cardiac cycle, the atria and
ventricles are relaxed and blood flows into the atria and
ventricles.
• In the systole phase, the ventricles contract sending blood to the
rest of the body.
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27. ELECTROCARDIOGRAPHY
• The electrocardiograph (ECG) is an instrument, which
records the electrical activity of the heart.
• ECG provides valuable information about a wide range of
cardiac disorders such as the presence of an inactive part
(infarction) or an enlargement (cardiac hypertrophy) of the heart
muscle.
• The diagnostically useful frequency range is usually accepted as
0.05 to 150 Hz. CMRR of the order of 100–120 dB with 5 kW
unbalance in the leads is a desirable feature of ECG machines
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28. Electrocardiogram
• Graphic representation of heart’s electrical activity
• Often referred to as an ECG or EKG
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29. • Electrocardiograms are almost invariably recorded on graph
paper with horizontal and vertical lines at 1 mm intervals with a
thicker line at 5 mm intervals.
• Time measurements and heart rate measurements are made
horizontally on the electrocardiogram. For routine work, the
paper recording speed is 25 mm/s. Amplitude measurements are
made vertically in millivolts. The sensitivity of an
electrocardiograph is typically set at 10 mm/mV.
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30. ECG MACHINE BLOCK DIAGRAM
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31. The ECG Paper
• Horizontally
• One small box - 0.04 s
• One large box - 0.20 s
• Vertically
• One large box - 0.5 mV
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32. ECG Waveform
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33. • P wave: the sequential activation (depolarization) of the right and
left atria or contraction
• QRS complex: right and left ventricular depolarization (normally
the ventricles are activated simultaneously)
• ST-T wave: ventricular repolarization or Relaxation of
Myocardium
• U wave: Slow repolarisation of the intraventricular system.
• PR interval: time interval from onset of atrial depolarization (P
wave) to onset of ventricular depolarization (QRS complex)
• QRS duration: duration of ventricular muscle depolarization
• QT interval: duration of ventricular depolarization and
repolarization
• RR interval: duration of ventricular cardiac cycle (an indicator of
ventricular rate)
• PP interval: duration of atrial cycle (an indicator of atrial rate)
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35. ECG LEADS
• Which measure the difference in electrical potential between
two points
There are 3 types of electrode system
1) Bipolar limb leads or standard leads
2) Augumented unipolar limb leads
3) Chest Leads or precordial leads
4) Frank lead system or corrected orthogonal leads.
Among these four systems, first three are widely used.
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36. Bipolar Leads:
• In bipolar leads, ECG is recorded by using two electrodes such that
the final trace corresponds to the difference of electrical potentials
existing between them. They are called standard leads and have
been universally adopted. They are sometimes also referred to as
Einthoven leads
Bipolar limb Lead positions
• Lead I: RA (-) to LA (+)
• Lead II: RA (-) to LL (+)
• Lead III: LA (-) to LL (+)
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38. Einthoven’s Triangle
• Einthoven postulated that at any given instant of the cardiac cycle,
the electrical axis of the heart can be represented as a two
dimensional vector.
• He proposed that the electric field of the heart could be
represented diagrammatically as a triangle, with the heart ideally
located at the centre. The triangle, known as the “Einthoven
triangle”.
• The sides of the triangle represent the lines along which the three
projections of the ECG vector are measured. It was shown that the
instantaneous voltage measured from any one of the three limb
lead positions is approximately equal to the algebraic sum of the
other two or that the vector sum of the projections on all three
lines is equal to zero.
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41. Unipolar Leads (V Leads):
• In this arrangement, the electrocardiogram is recorded between
a single exploratory electrode and the central terminal, which
has a potential corresponding to the centre of the body.
• In practice, the reference electrode or central terminal is
obtained by a combination of several electrodes tied together at
one point.
• Two types of unipolar leads are employed which are:
(i) limb leads, and (ii) precordial leads.
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42. Limb leads
• In unipolar limb leads , two of the limb leads are tied together and
recorded with respect to the third limb.
• In the lead identified as AVR, the right arm is recorded with
respect to a reference established by joining the left arm and left
leg electrodes.
• In the AVL lead, the left arm is recorded with respect to the
common junction of the right arm and left leg.
• In the AVF lead, the left leg is recorded with respect to the two
arm electrodes tied together.
• They are also called augmented leads or ‘averaging leads’. The
resistances inserted between the electrodes-machine connections
are known as ‘averaging resistances’.
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43. • Lead aVR: RA (+) to [LA & LL] (-)
• Lead aVL: LA (+) to [RA & LL] (-)
• Lead aVF: LL (+) to [RA & LA] (-)
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44. Precordial leads
• The second type of unipolar lead is a precordial lead. It employs
an exploring electrode to record the potential of the heart action
on the chest at six different positions.
• These leads are designated by the capital letter ‘V’ followed by a
subscript numeral, which represents the position of the electrode
on the pericardium.
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45. V1 - Fourth intercostal space at the left border of the sternum
V2 - Fourth intercostal space at the right border of the sternum
V3 - Midway between placement of V2 and V4
V4 - Fifth intercostal space at the midclavicular line
V5 - Anterior axillary line on the same horizontal level as V4
V6 - Mid-axillary line on the same horizontal level as V4 and V5
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46. ECG potentials are measured with colour coded leads according
to the convention.
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47. ECG Recording System
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48. Analysis of ECG Signals
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52. Therapeutic Equipments : Pacemakers
• A device capable of generating artificial pacing impulses and
delivering them to the heart is known as a pacemaker system
(commonly called a pacemaker).
• Consists of a pulse generator and appropriate electrodes.
• Pacemakers are available in a variety of forms.
• Internal pacemakers may be permanently implanted in patients
whose SA nodes have failed to function properly or who suffer from
permanent heart block because of a heart attack. An internal
pacemaker is defined as one in which the entire system is inside the
body.
• An External pacemaker usually consists of an externally worn
pulse generator connected to electrodes located on or within the
myocardium.
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53. • External pacemakers are used on patients with temporary heart
irregularities, such as those encountered in the coronary patient,
including heart blocks.
• They are also used for temporary management of certain
arrhythmias that may occur in patients during critical
postoperative periods and in patients during cardiac surgery,
especially if the surgery involves the valves or septum.
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57. Pacemaker Components
• Pulse Generator
• Electronic Circuitry
• Lead system
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58. Pulse Generator
• Lithium-iodine cell is the current standard battery
Advantages:
• Long life – 4 to 10 years
• Output voltage decreases gradually with time making sudden
battery failure unlikely
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59. Electronic Circuitry
• Determines the function of the pacemaker itself
• Utilizes a standard nomenclature for describing pacemakers
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60. Lead Systems
• Endocardial leads which are inserted using a subclavian vein
approach
• Actively fixed to the endocardium using screws or tines
• Unipolar or bipolar leads
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61. Types of Pacing Modes
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62. Block Diagram of Pacemaker
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63. DEFIBRILLATORS
• A condition in which this necessary synchronism is lost is known as
fibrillation.
• During fibrillation the normal rhythmic contractions of either the
atria or the ventricles are replaced by rapid irregular switching of
the muscular wall.
• Fibrillation of atrial muscles is called atrial fibrillation; fibrillation
of the ventricles is known as ventricular fibrillation.
• Ventricular fibrillation is far more dangerous, for under this
condition the ventricles are unable to pump blood; and if the
fibrillation is not corrected, death will usually occur within a few
minutes. known as ventricular fibrillation.
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64. • The most successful method of defibrillation is the application
of an electric shock to the area of the heart.
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65. 65
External Defibrillator
power
supply
energy
storage
patient
ECG
monitor
timing
circuitry
gate
charge discharge
standby
switch is under
operator control
applies shock about 20 ms after
QRS complex, avoids T-wave
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66. DC DEFIBRILLATOR CIRCUIT
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67. Measurement of heart sounds-Phonocardiography
• The stethoscope (from the Greek word, stethos, meaning “chest”,
and skopein, meaning “to examine") is simply a device that carries
sound energy from the chest of the patient to the ear of the
physician via a column of air.
• A graphic record of heart sounds is called a phonocardiogram.
• The instrument for producing this recording is called a
phonocardiograph.
.
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68. Phonocardiograph(PCG)
• The phonocardiograph is an instrument used for recording the
sounds connected with the pumping action of the heart. These
sounds provide an indication of the heart rate and its rhythmicity.
They also give useful information regarding effectiveness of
blood pumping and valve action
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69. Origin of Heart sounds
• The first sound, which corresponds to the R wave of the ECG, is
longer in duration, lower in frequency, and greater in intensity than
the second sound.
• The sound is produced principally by closure of the valves between
the upper and lower chambers of the heart, i.e. it occurs at the
termination of the atrial contraction and at the onset of the ventricular
contraction. The closure of the mitral and tricuspid valve contributes
largely to the first sound.
• The frequencies of these sounds are generally in the range of 30 to
100 Hz and the duration is between 50 to 100 ms.
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70. • The second sound is higher in pitch than the first, with frequencies above
100 Hz and the duration between 25 to 50 ms.
• This sound is produced by the slight back flow of blood into the heart before
the valves close and then by the closure of the valves in the arteries leading
out of the ventricles. This means that it occurs at the closure of aortic and the
pulmonic valves.
• The heart also produces third and fourth sounds but they are much lower in
intensity and are normally inaudible.
• The third sound is produced by the inflow of blood to the ventricles and the
fourth sound is produced by the contraction of the atria. These sounds are
called diastolic sounds and are generally inaudible in the normal adult but are
commonly heard among children.
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72. Microphones for PCG
• Two types of microphones are commonly in use for recording
phonocardiograms. They are the contact microphone and the air
coupled microphone. They are further categorized into crystal
type or dynamic type based on their principle of operation.
• The crystal microphone contains a wafer of piezo-electric
material, which generates potentials when subjected to
mechanical stresses due to heart sounds. They are smaller in size
and more sensitive than the dynamic microphone.
• The dynamic type microphone consists of a moving coil having a
fixed magnetic core inside it.
• The coil moves with the heart sounds and produces a voltage
because of its interaction with the magnetic flux.
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73. Amplifiers for PCG
• The amplifier used for a phonocardiograph has wide bandwidth with
a frequency range of about 20 to 2000 Hz. Filters permit selection of
suitable frequency bands, so that particular heart sound frequencies
can be recorded. In general, the high frequency components of
cardiovascular sound have a much smaller intensity than the low
frequency components and that much information of medical interest
is contained in the relatively high frequency part of this spectrum.
Therefore, high-pass filters are used to separate the louder low
frequency components from the soft and interesting high frequency
murmurs.
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74. • The basic transducer for the phonocardiogram is a microphone
having the necessary frequency response, generally ranging
from below 5 Hz to above 1000 Hz. An amplifier with similar
response characteristics is required, which may offer a selective
low pass filter to allow the high frequency cutoff to be adjusted
for noise and other considerations. In one instance, where the
associated pen recorder is inadequate to reproduce higher
frequencies, an integrator is employed and the envelope of
frequencies over 80 Hz is recorded along with actual signals
below 80 Hz.
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75. Writing Methods for PCG
• The readout of a phonocardiograph is either a high-frequency
chart recorder or an oscilloscope. Because most pen
galvanometer recorders have an upper-frequency limitation of
around 100 or 200 Hz, photographic or light-galvanometer
recorders are required for faithful recording of heart sounds.
Although normal heart sounds fall well within the frequency
range of pen recorders, the high-frequency murmurs that are
often important in diagnosis require the greater response of the
photographic device.
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76. Measurement of Blood Pressure
• Direct Method
• Indirect Method
• Korotkoff Method
• Ausculatory Method
• Oscillometric Method
• Ultra sonic Doppler Shift Method
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77. INDIRECT MEASUREMENTS
• The familiar indirect method of measuring blood pressure
involves the use of a sphygmomanometer and a stethoscope.
• The sphygmomanometer consists of an inflatable pressure cuff
and a mercury or aneroid manometer to measure the pressure in
the cuff.
• The cuff consists of a rubber bladder inside an inelastic fabric
covering that can be wrapped around the upper arm and
fastened with either hooks or a Velcro fastener.
• The cuff is normally inflated manually with a rubber bulb and
deflated slowly through a needle valve.
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78. • To obtain a blood pressure measurement with a
sphygmomanometer and a stethoscope, the pressure cuff on the
upper arm is first inflated to a pressure well above systolic
pressure.
• At this point no sounds can be heard through the stethoscope,
which is placed over the brachial artery, for that artery has been
collapsed by the pressure of the cuff.
• The pressure in the cuff is then gradually reduced. As soon as
cuff pressure falls below systolic pressure, small amounts of
blood spurt past the cuff and Korotkoff sounds begin to be
heard through the stethoscope.
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79. • The pressure of the cuff that is indicated on the manometer
when the first Korotkoff sound is heard is recorded as the
systolic blood pressure.
• As the pressure in the cuff continues to drop, the Korotkoff
sounds continue until the cuff pressure is no longer sufficient to
occlude the vessel during any part of the cycle.
• Below this pressure the Korotkoff sounds disappear, marking
the value of the diastolic pressure.
• This familiar method of locating the systolic and diastolic
pressure values by listening to the Korotkoff sounds is called
the auscultatory method of sphygmomanometry.
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80. Figure: Principle of blood pressure
measurement based on Korotkoff sounds
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81. Oscillometric Method
• Oscillometric method of non-invasive blood pressure
measurement has distinct advantages over the auscultatory
method
• Since sound is not used to measure blood pressure in the
oscillometric technique, high environmental noise levels such as
those found in a busy clinical or emergency room do not hamper
the measurement.
• In addition, because this technique does not require a microphone
or transducer in the cuff.
• Placement of cuff is not critical.
• Excessive movement or vibration during the measurement can
cause inaccurate readings or failure to obtain any reading at all.
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82. • The oscillometric technique operates on the principle that as an
occluding cuff deflates from a level above the systolic pressure, the
artery walls begin to vibrate or oscillate as the blood flows
turbulently through the partially occluded artery and these
vibrations will be sensed in the transducer system monitoring cuff
pressure.
• As the pressure in the cuff further decrease, the oscillations increase
to a maximum amplitude and then decrease until the cuff fully
deflates and blood flow returns to normal.
• The cuff pressure at the point of maximum oscillations usually
corresponds to the mean arterial pressure.
• The point above the mean pressure at which the oscillations begin
to rapidly increase in amplitude correlates with the diastolic
pressure
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