The document discusses various methods for measuring blood flow and volume, which are important for understanding physiological processes. It describes electromagnetic flowmeters, ultrasonic flowmeters including Doppler and transit-time types, and indicator dilution methods using dyes or thermal changes. Electromagnetic flowmeters measure flow based on Faraday's law of induction, while ultrasonic flowmeters rely on transit time differences or the Doppler effect from blood cell movement. Indicator dilution involves injecting a substance and measuring its dispersion over time to calculate flow. Together these provide noninvasive or minimally invasive ways to obtain important blood flow information.

1. Electromagnetic Flow meters

2. Characterization of Fluid FlowCharacterization of Fluid Flow
Types of Flow
RE < 2100
RE >3000
Transitional
Turbulent ***
Laminar

3. Flowmeter PerformanceFlowmeter Performance
Accuracy
Repeatability
Linearity
Rangeability

4. Poor Repeatability Means
Poor Accuracy
Good Accuracy Means
Good Repeatability
Good Repeatability Does Not
Necessarily Mean Good Accuracy

5. Differential Pressure FlowmetersDifferential Pressure Flowmeters
Flow Measurement Principles
ORIFICE PLATE
(or FLOW TUBE)
VENA
CONTRACTA
MANOMETER
(or DP TRANSMITTER)h
Direction of Flow

6. Measurement of
Flow & Volume of Blood
 A measurement of paramount importance: concentration of O2 and other
nutrients in cells  Very difficult to measure
 Second-class measurement: blood flow and changes in blood volume 
correlate well with concentration
 Third-class measurement: blood pressure  correlates well with blood flow
 Fourth class measurement: ECG  correlates adequately with blood pressure
 How to make blood flow / volume measurements? Standard flow meters,
such as turbine flow meters, obviously cannot be used!
 Indicator-dilution method: cont./rapid injection, dye dilution, thermodilution
 Electromagnetic flowmeters
 Ultrasonic flowmeters / Doppler flowmeters
 Plethysmography: Chamber / electric impedance / photoplethysmography

7. Indicator Dilution with
Continuous Injection
 Measures flow / cardiac output averaged over several heart beats
 Fick’s technique: the amount of a substance (O2) taken up by an organ /
whole body per unit time is equal to the arterial level of O2 minus the
venous level of O2 times the blood flow 
va CC
dtdm
C
dtdm
dt
dV
F
−
=
∆
==
Blood flow, liters/min
(cardiac output)
Consumption of O2 (mL/min)
Arterial and venous
concentration of O2 (mL/L of blood)
dtdV
dtdm
C =∆
Change in [] due to
continuously added
indicator m to volume V

8. Fick’s technique
 How is dm/dt (O2 consumption) measured?
 Where and how would we measure Ca and Cv? (Exercise)
minL/5
mL/L140L/mL190
minmL/250
][O][O
min)(mL/O
22
2
=
−
=
−
=
va
nconsumptio
OutputCardiac

9. Indicator Dilution with
Rapid Injection
 A known amount of a substance, such as a dye or radioactive
isotope, is injected into the venous blood and the arterial
concentration of the indicator is measured through a serious of
measurements until the indicator has completely passed through
given volume.
 The cardiac output (blood flow) is amount of indicator injected,
divided by average concentration in arterial blood.
∫
= t
dttC
m
F
0
)(

10. Indicator – Dilution Curve
After the bolus is injected at time A, there is a transportation delay before the
concentration begins rising at time B. After the peak is passed, the curve enters an
exponential decay region between C and D, which would continue decaying alone
the dotted curve to t1 if there were no recirculation. However, recirculation causes a
second peak at E before the indicator becomes thoroughly mixed in the blood at F.
The dashed curve indicates the rapid recirculation that occurs when there is a hole
between the left and right sides of the heart.

11. An Example

12. Dye Dilution
 In dye-dilution, a commonly used dye is indocyanine green
(cardiogreen), which satisfies the following
 Inert
 Safe
 Measurable though spectrometry
 Economical
 Absorption peak is 805 nm, a wavelength at which absorption of blood is
independent of oxygenation
 50%of the dye is excreted by the kidneys in 10 minutes, so repeat
measurements is possible

13. Thermodilution
 The indicator is cold – saline, injected into the right atrium using a
catheter
 Temperature change in the blood is measured in the pulmonary
artery using a thermistor
 The temperature change is inversely proportional to the amount of
blood flowing through the pulmonary artery

14. Measuring Cardiac Output
Several methods of measuring cardiac output In the Fick method, the indicator is O2; consumption
is measured by a spirometer. The arterial-venous concentration difference is measure by drawing
simples through catheters placed in an artery and in the pulmonary artery. In the dye-dilution
method, dye is injected into the pulmonary artery and samples are taken from an artery. In the
thermodilution method, cold saline is injected into the right atrium and temperature is measured in
the pulmonary artery.

15. Electromagnetic
Flowmeters
 Based on Faraday’s law of induction that a conductor that moves
through a uniform magnetic field, or a stationary conductor placed
in a varying magnetic field generates emf on the conductor:
When blood flows in the vessel with
velocity u and passes through the magnetic
field B, the induced emf e measured at the
electrodes is.
∫ ⋅×=
L
de
0
LBu
For uniform B and uniform velocity profile u,
the induced emf is e=BLu. Flow can be obtained
by multiplying the blood velocity u with the
vessel cross section A.

16. Electromagnetic
Flowmeter Probes
• Comes in 1 mm increments for
1 ~ 24 mm diameter blood vessels
• Individual probes cost $500 each
• Made to fit snuggly to the vessel
during diastole
• Only used with arteries, not veins,
as collapsed veins during diastole
lose contact with the electrodes
• Needless to say, this is an
INVASIVE measurement!!!
• A major advantage is that it can
measure instantaneous blood
flow, not just average flow

17. Ultrasonic Flowmeters
 Based on the principle of measuring the time it takes for an acoustic
wave launched from a transducer to bounce off red blood cells and
reflect back to the receiver.
 All UT transducers, whether used for flowmeter or other
applications, invariably consists of a piezoelectric material, which
generates an acoustic (mechanical) wave when excited by an
electrical force (the converse is also true)
 UT transducers are typically used with a gel that fills the air gaps
between the transducer and the object examined

18. Near / Far Fields
 Due to finite diameters, UT transducers produce diffraction patterns,
just like an aperture does in optics.
 This creates near and far fields of the UT transducer, in which the
acoustic wave exhibit different properties
 The near field extends about dnf=D2
/4λ, where D is the transducer
diameter and λ is the wavelength. During this region, the beam is mostly
cylindrical (with little spreading), however with nonuniform intensity.
 In the far field, the beam diverges with an angle sinθ=1.2 λ/D, but the
intensity uniformly attenuates proportional to the square of the distance
from the transducer
Higher frequencies and larger
transducers should be used for near
field operation. Typical operating
frequency is 2 ~ 10 MHz.

19. UT Flowmeters
Zero-crossing
detector / LPF
Determine
direction
High acoustic
impedance material

20. Transit time flowmeters
Effective velocity of sound in blood: velocity of sound (c) +
velocity of flow of blood averaged along the path of the ultrasound (û)
û=1.33ū for laminar flow, û=1.07ū for turbulent flow
ū: velocity of blood averaged over the cross sectional area, this is different
than û because the UT path is along a single line not over an averaged of
cross sectional area
Transit time in up/down stream direction:
Difference between upstream and downstream directions
θcosˆvelocityconduction
distance
uc
D
t
±
==
2222
cosˆ2
)cosˆ(
cosˆ2
c
uD
uc
uD
t
θ
θ
θ
≅
−
=∆

21. Transit Time
Flowmeters
The quantity ∆T is typically very small
and very difficult to measure,
particularly in the presence of noise.
Therefore phase detection techniques
are usually employed rather then
measuring actual timing.

22. Doppler
Flowmeters
 The Doppler effect describes the change in the frequency of a
received signal , with respect to that of the transmitted signal, when
it is bounced off of a moving object.
 Doppler frequency shift
c
uf
f o
d
θcos2
=
Speed of sound in blood
(~1500 m/s)
Angle between UT beam
and flow of blood
Speed of blood flow
(~150 cm/s)
Source signal
frequency

23. Doppler
Flowmeters
c
u
fF s )cos(cos φθ +±=∆

24. Problems Associated with
Doppler Flowmeters
 There are two major issues with Doppler flowmeters
 Unlike what the equations may suggest, obtaining direction information is not
easy due to very small changes in frequency shift that when not in baseband,
removing the carrier signal without affecting the shift frequency becomes very
difficult
 Also unlike what the equation may suggest, the Doppler shift is not a single
frequency, but rather a band of frequencies because
• Not all cells are moving at the same velocity (velocity profile is not
uniform)
• A cell remains within the UT beam for a very short period of time; the
obtained signal needs to be gated, creating side lobes in the frequency shift
• Acoustic energy traveling within the beam, but at an angle from the bam
axis create an effective ∆θ, causing variations in Doppler shift
• Tumbling and collision of cells cause various Doppler shifts

25. Directional Doppler
 Directional Doppler borrows the quadrature phase detector
technique from radar in determining the speed and direction of an
aircraft.
 Two carrier signals at 90º phase shift are used instead of a single
carrier. The +/- phase difference between these carriers after the
signal is bounced off of the blood cells indicate the direction,
whereas the change in frequency indicate the flowrate

26. Directional Doppler
(a) Quadrature-phase detector. Sine and cosine signals at the carrier frequency are summed with the
RF output before detection. The output C from the cosine channel then leads (or lags) the output S
from the sine channel if the flow is away from (or toward) the transducer. (b) Logic circuits route
one-shot pulses through the top (or bottom) AND gate when the flow is away from (or toward) the
transducer. The differential amplifier provides bi-directional output pulses that are then filtered.

27. Electromagnetic Flowmeters
• Magnetic flowmeters have been widely used in industry for many
years.
• Unlike many other types of flowmeters, they offer true
noninvasive measurements.
• They are easy to install and use to the extent that existing pipes
in a process can be turned into meters simply by adding external
electrodes and suitable magnets.
• They can measure reverse flows and are insensitive to viscosity,
density, and flow disturbances.
• Electromagnetic flowmeters can rapidly respond to flow changes
and they are linear devices for a wide range of measurements.
• As in the case of many electric devices, the underlying principle
of the electromagnetic flowmeter is Faraday’s law of
electromagnetic induction.
• The induced voltages in an electromagnetic flowmeter are
linearly proportional to the mean velocity of liquids or to the
volumetric flow rates.

28. • As is the case in many applications, if the pipe walls are made
from nonconducting elements, then the induced voltage is
independent of the properties of the fluid.
• The accuracy of these meters can be as low as 0.25% and, in most
applications, an accuracy of 1% is used.
• At worst, 5% accuracy is obtained in some difficult applications
where impurities of liquids and the contact resistances of the
electrodes are inferior as in the case of low-purity sodium liquid
solutions.
• Faraday’s Law of Induction
• This law states that if a conductor of length l (m) is moving with a
velocity v (m/s–1
), perpendicular to a magnetic field of flux density
B (Tesla), then the induced voltage e across the ends of conductor
can be expressed by:
Blve =

29. The velocity of the conductor is
proportional to the mean flow velocity
of the liquid.
Hence, the induced voltage becomes:
BDve =

30. BDve =
vDAvQ 2
4
π
==
D
BQ
e
π
4
=

32. Ultrasonic Flowmeters
• There are various types of ultrasonic flowmeters in use for
discharge measurement:
• (1) Transit time: This is today’s state-of-the-art technology and
most widely used type.
• This type of ultrasonic flowmeter makes use of the difference
in the time for a sonic pulse to travel a fixed distance.
• First against the flow and then in the direction of flow.
• Transmit time flowmeters are sensitive to suspended solids or
air bubbles in the fluid.
• (2) Doppler: This type is more popular and less expensive, but
is not considered as accurate as the transit time flowmeter.
• It makes use of the Doppler frequency shift caused by sound
reflected or scattered from suspensions in the flow path and is
therefore more complementary than competitive to transit time
flowmeters.

33. Principle of transit time flowmeters.

34. Transit Time Flowmeter
• Principle of Operation
• The acoustic method of discharge measurement is based on the
fact that the propagation velocity of an acoustic wave and the
flow velocity are summed vectorially.
• This type of flowmeter measures the difference in transit times
between two ultrasonic pulses transmitted upstream t21 and
downstream t12 across the flow.
• If there are no transverse flow components in the conduit, these
two transmit times of acoustic pulses are given by:

35. Since the transducers are generally used both as transmitters and
receivers, the difference in travel time can be determined with the
same pair of transducers.
Thus, the mean axial velocity along the path is given by:

36. Example
• The following example shows the demands on the time
measurement technique:
• Assume a closed conduit with diameter D = 150 mm, angle φ =
60°, flow velocity = 1 m/s, and water temperature =20°C.
• This results in transmit times of about 116 s and a time
difference
∀ ∆t =t12 – t21 on the order of 78 ns.
• To achieve an accuracy of 1% of the corresponding full-scale
range, ∆t has to be measured with a resolution of at least 100 ps
(1X10–10
s).
• Standard time measurement techniques are not able to meet such
requirements so that special techniques must be applied.
• Digital timers with the state-of-the –art Micro computers will
make it possible to measure these time difference.

38. Point Velocity Measurement
• Pitot Probe Anemometry : Potential Flow Theory &
Bernoulli’s Theory .
• Thermal Anemometry : Newton’s Law of Cooling.
• Laser Anemometry: Doppler Theory.

39. Blood Pressure and flow
39

40. BMTS 353 40
Blood Flow
12/3/2013
• 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.

41. 41
Cont. Blood Flow
Normal blood flow velocity 0,5 m/s 1 m/s (Systolic, large vessel)

42. 42
Blood Flow Measurement
Blood Pressure

43. 43
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.
c
v
ff cd 2=
f = 2 – 10 MHzc
c = 1500 - 1600 m/s (1540 m/s)
f = 1,3 – 13 kHzd

44. 44
Cont. Ultrasonic Doppler Method
Blood Pressure
CW DOPPLER PULSED DOPPLER
Range ambiguity
Low flow cannot be
detected
No minimum range
Simpler hardware
Minimum range
Accuracy
No minimum flow
(Maximum flow) x (range)
= limited
The ultrasound Doppler device can be either a continuous wave
or a pulsed Doppler

45. 45
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.

46. 46
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.

47. 47
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.

48. 48
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.
Poor measure for changes in volume
Very sensitive to motion artefacts
Method is simple
Heart rate is clearly seen

49. 49
Blood Flow Measurement
Blood Pressure

50. 50
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.

51. 51
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.