MEDICAL

INSTRUMENTATION

EEE C432/INSTR C481/EEE F432/INSTR F432

Sheron Figarado

Blood flow measurement, volume

measurements

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

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

INDICATOR DILUTION METHODS THAT USES

CONTINUOUS INFUSION (CONTD)

� Fick technique

The indicator is O2

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

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

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

Slide 6

u1 Isotonic- same osmitic pressureuser, 06-Nov-13

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)

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.

ELECTROMAGNETIC FLOWMETERS

� Operates with any conductive fluid.

Uniform mag. Field and uniform velocity

RELATIVE VELOCITY CONTRIBUTION TO THE

INDUCED EMF

CLASSIFICATION OF ELECTROMAGNETIC

FLOWMETERS

� DC flowmeter (DC magnetic field)

� AC flowmeter (AC magnetic field)- more

popular.

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.

AC FOWMETER

� Operates at 400Hz

� When the flow reverses

direction, the voltage changes

phase by 180o, so the phase-

sensitive is required.

transformer voltage!

QUADRATURE SUPPRESSION FLOWMETER

Quadrature generator feeds back a voltage to balance out the probe-generated transformer voltage.

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

ULTRASONIC FLOWMETERS

� Transit time flowmeter

� Continuous time Doppler flowmeter

� Pulsed Doppler flowmeter.

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.

NEAR AND FAR FIELDS AS FUNCTION OF

TRANSDUCER DIMENSION AND FREQUENCY

Far field angle of divergence

Near field distance

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.

TRANSIT TIME FLOWMETER

• Can be saline or blood•Requires surgical placement

DOPPLER EFFECT

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..

PLACEMENT OF TRANSDUCERS

(a) Two transducers opposite (transit time)(b) Two transducers on the same side (doppler)

THERMAL-CONVECTION VELOCITY

SENSORS

� The thermistor Ru is heated to a

temperature difference ∆T above blood

temperature by the power W dissipated

INSTRUMENTATION FOR THERMAL

CONVECTION VELOCITY SENSOR

CHAMBER PLETHYSMOGRAPHY

From Greek word ‘plethusmos’. (enlargement)

CHAMBER PLETHYSMOGRAPHY

Venous-occlusion plethysmography.

METHOD OF MEASUREMENT FOR CHAMBER

PLETHYSMOGRAPHY

ELECTRICAL-IMPEDANCE PLETHYSMOGRAPHY

IMPEDANCE PLETHYSMOGRAPHY

4 ELECTRODE IMPEDANCE PLETHYSMOGRAPH

PHOTOPLETHYSMOGRAPHY

SIGNAL CONDITIONING FOR PHOTOPLETHYSMOGRAPH

Thank you

Sheron Figarado