Chapter 5 Part Two Blood Pressure and flow by Ibrhim AlMohimeed BMTS 353112/3/2013.
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BMTS 353 1
Chapter 5
Part Two
Blood Pressure and flowby Ibrhim AlMohimeed
12/3/2013
BMTS 353 2
Blood Pressure
12/3/2013
• Originates from the left ventricle of the heart.
• One of the oldest physiological measurements.
• Observation of blood pressure allows dynamic tracking
of pathology and physiology affecting to the
cardiovascular system.
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Blood Pressure Reading
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• Systolic: the top number, which is also the
higher of the two numbers, measures the pressure
in the arteries when the heart beats (when the
heart muscle contracts).
• Diastolic: the bottom number, which is also the
lower of the two numbers, measures the pressure
in the arteries between heartbeats (when the left
ventricle muscle is resting between beats and
refilling with blood).
Read as "117 over 76 millimeters of
mercury"
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Blood Pressure Reading
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Blood PressureCategory
Systolicmm Hg (upper #) Diastolic
mm Hg (lower #)
Normal less than 120 and less than 80
Prehypertension 120 – 139 or 80 – 89
High Blood Pressure
(Hypertension) Stage 1
140 – 159 or 90 – 99
High Blood Pressure
(Hypertension) Stage 2
160 or higher or 100 or higher
Hypertensive Crisis(Emergency care
needed)Higher than 180 or Higher than 110
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Blood Pressure Reading
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• Mean arterial pressure (MAP) is a term used in
medicine to describe an average blood pressure in an
individual.
• It is defined as the average arterial pressure during a
single cardiac cycle and given by:
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Blood Pressure Risks
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• High blood pressure (hypertension) increases the risk of: Chest pain (angina).
Heart attack.
Heart failure.
Kidney failure.
Stroke.
Blocked arteries in the legs or arms (peripheral arterial disease.
Eye damage .
Aneurysms (permanent cardiac or arterial dilatation).
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Cont. Blood Pressure Risks
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Cont. Blood Pressure Risks
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• Low blood pressure (hypotension) increases the risk of: Reduces the blood flow to the brain and other vital organs.
Dizziness or fainting.
Lack of concentration.
Blurred vision.
Fatigue.
Cold and clammy skin.
Rapid shallow breathing.
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Blood Pressure Value
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Generally, the blood pressure value
depends on two main factors:
1) Cardiac output (Blood Volume): The
more blood present in the body, the
higher the rate of blood return to the
heart and the resulting cardiac output,
potentially resulting in higher arterial
pressure.
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Cont. Blood Pressure Value
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2) Resestance of blood flow: The higher the resistance, the
higher the arterial pressure. Resistance is related to
vessel radius, blood viscosity, and the smoothness of
the blood vessel walls.
BMTS 353 11
Invasive & Non-invasive
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• In general, there are two main categories which describe
the invasiveness of a medical measurement:
Invasive: requiring the entry of a needle, catheter, or other
instrument into a part of the body.
Non-invasive: not requiring entering or penetrating the
body or disturbing body tissue.
BMTS 353 12
Blood Pressure Measurement
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Inva
sive
No
n-I
nva
sive
Blood Pressure
Palpatory Method(Riva-Rocci Method)
Auscultatory Method
Ultrasonic Method
Oscillometric Method
Extravascular Sensor
Intravascular Sensor
Automatic Method
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Blood Pressure Measurement
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Blood Pressure
Non-invasive (Indirect) Method of Blood Measurement
1
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Measurement Site
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Blood Pressure
• Brachial artery is the most common
measurement site:
Close to heart
Convenient for measuring
• Other sites are radial artery and wrist.
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Palpatory Method
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Blood Pressure
• aka Riva-Rocci Method.
1) When the cuff pressure
is higher than SBP,
artery is closed, no
pulse can be sensed.
2) When the cuff
pressure drops below
SBP, blood can pass
through the artery and
the pulse will be felt.
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Cont. Palpatory Method
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Blood Pressure
3) The pulse will continue to be felt
as the pressure in the cuff falls
down to zero.
4) The pressure indicated on the
gauge when the pulse reappears is
noted. This is the systolic
pressure.
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Cont. Palpatory Method
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Blood Pressure• The blood pressure can be measured in noisy
environment.
• It is a simple technique.
• Only the systolic blood pressure (SBP) can be measured
(not DBP).
• The technique does not give accurate results for infants
and hypotensive patients.
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Auscultatory Method
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Blood Pressure
• Auscultation: the act of listening, either directly or
through a stethoscope or other instrument, to sounds
within the body.
• This method is based on the fact that pulse waves when
first propagate through the brachial artery, generate
Korotkoff sounds.
• Video
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Korotkoff sounds
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Blood Pressure• If a stethoscope is placed over the brachial artery in a normal
person (without arterial disease), no sound should be audible.
• As the heart beats, these pulses are transmitted smoothly via
laminar (non-turbulent) blood flow throughout the arteries, and no
sound is produced.
• Similarly, if the cuff of a sphygmomanometer is placed around a
patient's upper arm and inflated to a pressure above the patient's
systolic blood pressure, there will be no sound audible because the
pressure in the cuff is high enough such that it completely blocks
the blood flow.
BMTS 353 20
Cont. Korotkoff sounds
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Blood Pressure• If the pressure is dropped to a level equal to that of the patient's
systolic blood pressure, the first Korotkoff sound will be heard.
• As the pressure in the artery rises above the pressure in the cuff and
then drops back down (because of beating), resulting in turbulence
that produces an audible sound.
• As the pressure in the cuff is allowed to fall further, thumping
sounds continue to be heard as long as the pressure in the cuff is
between the systolic and diastolic pressures, as the arterial pressure
keeps on rising above and dropping back below the pressure in the
cuff.
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Cont. Korotkoff sounds
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Blood Pressure• Eventually, as the pressure in the cuff drops further, the sounds
change in quality, then become muted, and finally disappear
altogether.
• This occurs because, as the pressure in the cuff drops below the
diastolic blood pressure, the cuff no longer provides any restriction
to blood flow allowing the blood flow to become smooth again
with no turbulence and thus produce no further audible sound.
BMTS 353 22
Auscultatory Method Procedure
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Blood Pressure
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Auscultatory Method Procedure
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Blood Pressure1) The cuff pressure is inflated quickly to a
pressure higher than the systolic pressure.
Then the air is let out of the cuff at a small
rate.
2) When the cuff pressure equal to that of the
patient's systolic blood, a korotkoff sound
will be heard with each heartbeat. This point
marks the systolic pressure.
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Auscultatory Method Procedure
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Blood Pressure
1) As the pressure is lowered further, the
character of the Korotkoff sounds change.
At some point, the sounds will disappear.
The pressure reading at this point gives the
diastolic pressure.
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Using Auscultatory Method
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Blood Pressure
• Auscultatory technique is considerd simple.
• It may be difficult to be done in a noisy environment.
• The effect of human error is large.
• It could be difficult to be used with infant.
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Oscillometric Method
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Blood Pressure• the observation of oscillations of blood flow during the
pulsation.
• It uses a sphygmomanometer cuff, like the auscultatory
method, but with pressure sensor (transducer) to observe cuff
pressure oscillations
• The pressure sensor (within the inflated cuff) detects the
pulsation of the artery wall as a pressure vibration. The
interpretation of these small vibrations amplitude provide the
blood pressure value.
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Cont. Oscillometric Method
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Blood Pressure
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Cont. Oscillometric Method
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Blood Pressure
• In the recent years, oscillometric methods have become
popular for their simplicity of use and reliability.
• It can be used with case of hypotension and infant.
• It use algorithms that may leads to large variance in
blood pressures measurement.
• Motion artifact is considered a major drawback of this
method.
BMTS 353 29
Automatic Method
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Blood Pressure• Many limitations of manual intermittent blood pressure
measurement have been overcome by automated non-
invasive blood pressure (NIBP) devices.
• There are now used widely in medical care.
• NIBP devices provide consistent, reliable values for
systolic, diastolic, and mean arterial pressure (MAP).
• Automated NIBP devices provide alarm systems to draw
attention to extreme blood pressure value.
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Cont. Automatic Method
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Blood Pressure• The greatest advantage of automated NIBP devices
compared with manual methods of blood pressure
measurement is that they don’t require an operator to
perform the measurement.
• It can easily provide a repetitive blood pressure
measurements.
• Most automated NIBP devices are based on the
oscillometry method.
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The Device Diagram
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Blood Pressure
Pressure sensor
Pressure sensor
Air pumpAir
pumpBleed valveBleed valve
Micro-processo
r
Micro-processo
r
Display
Display
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Automatic Method Errors
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Blood Pressure• Sources of error for the automatic method:
I. Cuff size: Oscillations are direct result of BP cuff application
- Cuff too small = overestimation of BP
- Cuff too large = underestimation of BP
II. Cuff position: Bladder needs to be placed over brachial
artery.
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Cont. Automatic Method Errors
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Blood PressureIII. Movement:
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Cont. Automatic Method Errors
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Blood PressureIII. Beat to beat variation: Oscillometric method requires
reasonably stable BP during cuff deflation. If BP varies due to
arrhythmia, difficult to estimate BP accurately.
BMTS 353 35
Ultrasonic Method
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Blood Pressure
• The ultrasonic Doppler technique is applied by this
method.
• The motion of blood-vessel walls of occlusion (opining
and closing) is measured by Doppler technique.
• The vessel opens and closes with each heartbeat when
DP < Pcuff < SP
BMTS 353 36
Doppler Effect
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Blood Pressure
• It is the change in frequency of the returned sound wave
(echo) from a moving object.
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Cont. Doppler Effect
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Blood Pressure
• Video
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Principle of Ultrasonic Method
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Blood Pressure
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Cont. Ultrasonic Method
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Blood Pressure
• Can be also used in noisy environment.• The device is considiered contatin compicated part.• Highly affect by motion.
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Blood Pressure Measurement
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Blood Pressure
Invasive (direct) Method of Blood Measurement
2
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The first invasive bloodpressure measurement
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Blood Pressure
• The first invasive attempt to measure blood
pressure was made by Stephen Hales in
1733.
• He inserted tubes directly into the arteries
of animals.
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Invasive Method
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Blood Pressure
• This technique involves direct measurement of arterial
pressure by inserting a catheter (thin, hollow, and
flexible tube).
• Invasive (intra-arterial) blood
pressure (IBP) monitoring is a
commonly used technique in
the Intensive Care Unit (ICU)
and in the operating theatre.
BMTS 353 43
Con.t Invasive Method
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Blood Pressure
• IBP technique also allows accurate blood pressure
readings specially the very low pressures, for example
in shocked patients.
• it allows continuous ‘beat-to-beat’ blood pressure
monitoring.
• It complex procedure involving many risks.
BMTS 353 44
Invasive Method Types
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Blood Pressure
• Generally, the Invasive technique can be divided into
two division:
Extravascular Sensor System
Intravascular Sensor System
BMTS 353 45
Extravascular Sensor System
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Blood Pressure• The sensor is located behind the catheter and the vascular
pressure is transmitted by hydraulic connection.
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Cont. Extravascular Sensor System
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Blood Pressure
• The actual pressure sensor can be:
strain gage
variable inductance
variable capacitance
optoelectronic
piezoelectric
etc…
BMTS 353 47
Intravascular Sensor System
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Blood Pressure
• The sensor is located in the tip of the catheter (inside the
body).
• The sensor connected by an electrical or optical
connection.
• The frequency response is not limited by the hydraulic
properties of the system. No time delay.
• Breaks easily.
• More expensive.
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End of the Chapter
12/3/2013
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