Topic: The Vascular
system and the
medical physics of
pressure, flow and
resistance.
Course: 317
Study Unit 5
,Questions Notes
Blood flow mans the quantity of blood that passes a given point in the
circulation in a given period of time. Expressed in milliliters per
What is blood flow? minute/ litres per minute. The overall blood flow in an adult is 5000
ml/min- also known as the cardiac output.
5L/min = CO
How is blood flow Many mechanical and mechanoelectrical devices can be inserted in
measured? series
with a blood vessel or, in some instances, applied to the
outside of the vessel to measure flow. These devices are
called flowmeters.
Electromagnetic Flowmeter.
A device for measuring blood flow experimentally without opening
the vessel is
the electromagnetic flowmeter, the principles of which shows the
generation of electromotive force (electrical voltage) in a wire that is
moved rapidly in a cross-wise direction through a magnetic field. This
is the well-known principle for production of electricity by the electric
generator. In this case, a blood vessel is placed between the poles of a
strong magnet, and electrodes are placed on the two sides of the
vessel perpendicular to the magnetic lines of force. When blood flows
through the vessel, an electrical voltage proportional to the rate of
blood flow is generated between the two electrodes, and this voltage
is recorded using an appropriate voltmeter or electronic recording
apparatus. an actual “probe” that is placed on a large blood vessel to
record its blood flow. The probe contains both the strong magnet and
the electrodes.
A special advantage of the electromagnetic flowmeter is that it can
record changes in flow in less than 1/100 of a second, allowing
accurate recoding of pulsatile changes in flow, as well as steady flow.
Ultrasonic Doppler Flowmeter.
Another type of flowmeter that can be applied to the outside of the
vessel and
that has many of the same advantages as the electromagnetic
flowmeter is the ultrasonic Doppler flowmeter. A minute piezoelectric
crystal is mounted
at one end in the wall of the device. This crystal, when energized with
an appropriate electronic apparatus, transmits ultrasound at a
, frequency of several hundred thousand cycles per second
downstream along the flowing
blood. A portion of the sound is reflected by the red blood cells in the
flowing blood. The reflected ultrasound waves then travel backward
from the blood cells toward the crystal. These reflected waves have a
lower frequency than the transmitted wave because the red blood
cells are moving away from the transmitter crystal. This effect is
called the Doppler effect. (It is the same effect that one experiences
when a train approaches and passes by while blowing its whistle.
Once the whistle has passed by the person, the pitch of the sound
from the whistle suddenly becomes much lower than when the train
is
approaching.) high frequency ultrasound wave is intermittently cut
off, and the
reflected wave is received back onto the crystal and amplified greatly
by the electronic apparatus. Another portion of the electronic
apparatus determines the frequency difference between the
transmitted wave and the reflected wave,
thus determining the velocity of blood flow. As long as the diameter
of a blood vessel does not change, changes in blood flow in the vessel
are directly related to changes in flow velocity. Like the
electromagnetic flowmeter, the ultrasonic
Doppler flowmeter is capable of recording rapid, pulsatile changes in
flow, as well as steady flow.
What types of flow Laminar Flow of Blood in Vessels.
are found in the o When blood is flowing at a steady rate through a long,
circulatory system? smooth blood vessel- streamlines.Blood remaining the
same distance away from the wall Central most portion
of blood remains in the center. This type of flow is
called laminar flow or streamline flow.
Parabolic Velocity Profile During Laminar Flow.
o with laminar flow, velocity of the flow in the center is
greater than at the edges
o Parabolic interface: The parabolic profile for velocity of
blood flow
fluid adjacent to vessel wall hardly moves
fluid slightly away from the wall, moves a small
distance
fluid in the center, moves a long distance.
The cause of the parabolic profile is the following:
o The fluid molecules touching the wall move slowly
because of
system and the
medical physics of
pressure, flow and
resistance.
Course: 317
Study Unit 5
,Questions Notes
Blood flow mans the quantity of blood that passes a given point in the
circulation in a given period of time. Expressed in milliliters per
What is blood flow? minute/ litres per minute. The overall blood flow in an adult is 5000
ml/min- also known as the cardiac output.
5L/min = CO
How is blood flow Many mechanical and mechanoelectrical devices can be inserted in
measured? series
with a blood vessel or, in some instances, applied to the
outside of the vessel to measure flow. These devices are
called flowmeters.
Electromagnetic Flowmeter.
A device for measuring blood flow experimentally without opening
the vessel is
the electromagnetic flowmeter, the principles of which shows the
generation of electromotive force (electrical voltage) in a wire that is
moved rapidly in a cross-wise direction through a magnetic field. This
is the well-known principle for production of electricity by the electric
generator. In this case, a blood vessel is placed between the poles of a
strong magnet, and electrodes are placed on the two sides of the
vessel perpendicular to the magnetic lines of force. When blood flows
through the vessel, an electrical voltage proportional to the rate of
blood flow is generated between the two electrodes, and this voltage
is recorded using an appropriate voltmeter or electronic recording
apparatus. an actual “probe” that is placed on a large blood vessel to
record its blood flow. The probe contains both the strong magnet and
the electrodes.
A special advantage of the electromagnetic flowmeter is that it can
record changes in flow in less than 1/100 of a second, allowing
accurate recoding of pulsatile changes in flow, as well as steady flow.
Ultrasonic Doppler Flowmeter.
Another type of flowmeter that can be applied to the outside of the
vessel and
that has many of the same advantages as the electromagnetic
flowmeter is the ultrasonic Doppler flowmeter. A minute piezoelectric
crystal is mounted
at one end in the wall of the device. This crystal, when energized with
an appropriate electronic apparatus, transmits ultrasound at a
, frequency of several hundred thousand cycles per second
downstream along the flowing
blood. A portion of the sound is reflected by the red blood cells in the
flowing blood. The reflected ultrasound waves then travel backward
from the blood cells toward the crystal. These reflected waves have a
lower frequency than the transmitted wave because the red blood
cells are moving away from the transmitter crystal. This effect is
called the Doppler effect. (It is the same effect that one experiences
when a train approaches and passes by while blowing its whistle.
Once the whistle has passed by the person, the pitch of the sound
from the whistle suddenly becomes much lower than when the train
is
approaching.) high frequency ultrasound wave is intermittently cut
off, and the
reflected wave is received back onto the crystal and amplified greatly
by the electronic apparatus. Another portion of the electronic
apparatus determines the frequency difference between the
transmitted wave and the reflected wave,
thus determining the velocity of blood flow. As long as the diameter
of a blood vessel does not change, changes in blood flow in the vessel
are directly related to changes in flow velocity. Like the
electromagnetic flowmeter, the ultrasonic
Doppler flowmeter is capable of recording rapid, pulsatile changes in
flow, as well as steady flow.
What types of flow Laminar Flow of Blood in Vessels.
are found in the o When blood is flowing at a steady rate through a long,
circulatory system? smooth blood vessel- streamlines.Blood remaining the
same distance away from the wall Central most portion
of blood remains in the center. This type of flow is
called laminar flow or streamline flow.
Parabolic Velocity Profile During Laminar Flow.
o with laminar flow, velocity of the flow in the center is
greater than at the edges
o Parabolic interface: The parabolic profile for velocity of
blood flow
fluid adjacent to vessel wall hardly moves
fluid slightly away from the wall, moves a small
distance
fluid in the center, moves a long distance.
The cause of the parabolic profile is the following:
o The fluid molecules touching the wall move slowly
because of
