Chapter 5
Part Three
Blood Pressure and flow
by Ibrhim AlMohimeed
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Blood Flow
• Blood flow helps to understand basic physiological
processes and e.g. the dissolution of a medicine into the
body.
• Blood flow and changes in blood volume, are usually
correlated with concentration of nutrients and other
substance in the blood.
• Also, Blood Flow measurement reflects the
concentration of O2.
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Cont. Blood Flow
Normal blood flow velocity 0,5 m/s
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1 m/s (Systolic, large vessel)
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Blood Flow Measurement
Blood Pressure
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Ultrasonic Doppler Method
Blood Pressure
• The blood cells in the fluid
reflects the ultrasound signal
with a shift in the ultrasonic
frequency due to its movement.
• In the recent years ultrasound contrast agents have been used in
order to increase the echoes.
v
fd  2 fc
c
f c = 2 – 10 MHz
c = 1500 - 1600 m/s (1540 m/s)
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f d = 1,3 – 13 kHz
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Cont. Ultrasonic Doppler Method
Blood Pressure
The ultrasound Doppler device can be either a continuous wave
or a pulsed Doppler
CW DOPPLER
PULSED DOPPLER
No minimum range
Accuracy
Simpler hardware
No minimum flow
Range ambiguity
Low flow cannot be
detected
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Minimum range
(Maximum flow) x (range)
= limited
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Laser Doppler Flowmetry
Blood Pressure
• 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 method is used for capillary
(microvascular) blood flow
measurements.
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Plethysmography Method
(Strain Gage)
Blood Pressure
Plethysmography means the methods
for recording volume changes of an
organ or a body part.
• Strain gage is made of silicone rubber tubes, which are filled with
conductive liquid (e.g. mercury) whose impedance 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.
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Plethysmography Method
(Electric-Impedance)
Blood Pressure
• Different tissues in a body have a different resistivity. Blood is one
of the best conductors in a body.
• A constant current is applied
via skin electrodes.
• The change in the impedance
is measured.
• The accuracy is often poor.
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Plethysmography Method
(Photoelectric)
Blood Pressure
• 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 blood flow modulates the attenuated / reflected light which is
recorded.
• The light that is transmitted / reflected is collected with a photo
detector.
Method is simple
Heart rate is clearly seen
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Poor measure for changes in volume
Very sensitive to motion artefacts
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Blood Flow Measurement
Blood Pressure
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Indicator Dilution Methods
(Dye Dilution)
Blood Pressure
• 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.
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Indicator Dilution Methods
(Thermal Dilution)
Blood Pressure
• A bolus of chilled saline solution is injected into the
blood circulation system (right atrium).
• This causes decrease in the artery temperature.
• Catheter-tip probes are used to measure the change in
tempreture.
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End of the Chapter
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