Blood Flow Measurements
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Transcript of Blood Flow Measurements
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MEDICAL
INSTRUMENTATION
EEE C432/INSTR C481/EEE F432/INSTR F432
Sheron Figarado
Blood flow measurement, volume
measurements
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BLOOD FLOW MEASUREMENT
� Indicator dilution methods (average
measurement)
� Continuous infusion
� Rapid injection
� Flow meters (instantaneous)
Electromagnetic� Electromagnetic
� Ultrasound
� Thermal convection velocity sensors
� Plethysmographs (volume measurements)
� Chamber Plethysmograph
� Impedance Plethysmograph
� Photoplethysmograph
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INDICATOR DILUTION METHODS THAT USES
CONTINUOUS INFUSION
� Do not measure instantaneous pulsatile
flow but, rather, flow averaged over a
number of heartbeats.
(Initial mass, m0)
(Increment , m)
•Fick technique•Dye dilution•Thermodilution
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INDICATOR DILUTION METHODS THAT USES
CONTINUOUS INFUSION (CONTD)
� Fick technique
The indicator is O2
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INDICATOR DILUTION METHODS THAT USES
RAPID-INJECTION
•A bolus of indicator is rapidly injected into the vessel, and the variation in downstream concentration of the indicator versus time is measured until the bolus has passed.•Recirculation causes peaks after the injection.•dashed curve indicates the rapid recirculation that occurs when thereis a hole between the left and right sides of the heart.
Rapid-injection indicator-dilution curve
u2
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Slide 5
u2 bolus- administration of a medication, drug or other compound that is given to raise its concentration in blood to an effective leveluser, 06-Nov-13
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DYE DILUTION
� indocyanine green (cardiogreen)
� inert, harmless, measurable,economical, always
intravascular
� Optical peak at 805nm ( at this optical absorption of
blood is independent of oxygen.)
� diluted in isotonic saline and injected directly
through a catheter.
� Blood is paased thorough the cuvette of a
colorimeter.
u1
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Slide 6
u1 Isotonic- same osmitic pressureuser, 06-Nov-13
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THERMODILUTION
� injecting a bolus of cold saline as an
indicator.
� A special four-lumen catheter is floated
through the brachial vein into place in the
pulmonary artery.
1. For balloon1. For balloon2. Injection of cold
saline3. Thermistor wires4. Blood sample (not
for thermodilution)
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SOURCES OF ERROR IN THERMODILUTION
� Inadequate mixing between the injection
site and the sampling site.
� Exchange of heat between the blood and
the walls of the heart chamber.
� Heat exchange through the catheter walls � Heat exchange through the catheter walls
before, during, and after injection.
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ELECTROMAGNETIC FLOWMETERS
� Operates with any conductive fluid.
Uniform mag. Field and uniform velocity
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RELATIVE VELOCITY CONTRIBUTION TO THE
INDUCED EMF
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CLASSIFICATION OF ELECTROMAGNETIC
FLOWMETERS
� DC flowmeter (DC magnetic field)
� AC flowmeter (AC magnetic field)- more
popular.
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DC FLOWMETER DISADVANTAGES
� The voltage across the electrode’s metal-to-
solution interface is in series with the flow
signal
� The ECG has a frequency content similar to
that of the flow signal. Near to heart, ECG
inerfere.inerfere.
� Poor SNR due to 1/f noise.
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AC FOWMETER
� Operates at 400Hz
� When the flow reverses
direction, the voltage changes
phase by 180o, so the phase-
sensitive is required.
transformer voltage!
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QUADRATURE SUPPRESSION FLOWMETER
Quadrature generator feeds back a voltage to balance out the probe-generated transformer voltage.
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ELECTRODE & MAG. FIELD ASSEMBLY
Toroidal-type cuff probe
•two oppositely wound windings on each half of the core•magnetic flux thus leaves the top of both sides
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ULTRASONIC FLOWMETERS
� Transit time flowmeter
� Continuous time Doppler flowmeter
� Pulsed Doppler flowmeter.
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TRANSDUCER
� Piezoelectric
� Thickness is half wavelength.
� Cavity between the piezo-crystal and tissue
is filled with fluid/gel.
Near fields� Near fields
� beam spread is minimum.
� Far fields
� beam diverges
� Intensity inversely proportional to (distance)2.
� Low spatial resolution.
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NEAR AND FAR FIELDS AS FUNCTION OF
TRANSDUCER DIMENSION AND FREQUENCY
Far field angle of divergence
Near field distance
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FREQUENCY?
� Absorption in tissue-
� The absorption coefficient is approximately
proportional to frequency → low freq.
� Power scattered back from moving red
blood cells is proportional to f4. → high freq.blood cells is proportional to f . → high freq.
� Usually 2-10MHz.
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TRANSIT TIME FLOWMETER
• Can be saline or blood•Requires surgical placement
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DOPPLER EFFECT
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DOPPLER ULTRASONIC BLOOD FLOWMETER
Requires particulate matter such as RBC.
•Produces a band of frequencies•Carrier intensity at the receiver end is much higher than the Doppler shifter signal intensity..
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PLACEMENT OF TRANSDUCERS
(a) Two transducers opposite (transit time)(b) Two transducers on the same side (doppler)
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THERMAL-CONVECTION VELOCITY
SENSORS
� The thermistor Ru is heated to a
temperature difference ∆T above blood
temperature by the power W dissipated
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INSTRUMENTATION FOR THERMAL
CONVECTION VELOCITY SENSOR
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CHAMBER PLETHYSMOGRAPHY
From Greek word ‘plethusmos’. (enlargement)
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CHAMBER PLETHYSMOGRAPHY
Venous-occlusion plethysmography.
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METHOD OF MEASUREMENT FOR CHAMBER
PLETHYSMOGRAPHY
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ELECTRICAL-IMPEDANCE PLETHYSMOGRAPHY
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IMPEDANCE PLETHYSMOGRAPHY
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4 ELECTRODE IMPEDANCE PLETHYSMOGRAPH
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PHOTOPLETHYSMOGRAPHY
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SIGNAL CONDITIONING FOR PHOTOPLETHYSMOGRAPH
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Thank you
Sheron Figarado