Doppler Principles

Question 1

Flow

Answer 1

to go from one place to another

Question 2

Velocity

Answer 2

is the speed and direction of flow

Question 3

Reynold’s number

Answer 3

is used to determine whether a flow will be laminar or turbulent. If Re is high (>2100), inertial forces dominate viscous forces and the flow is turbulent; if Re is low (<1100), viscous forces dominate and the flow is laminar.

Question 4

Stenosis

Answer 4

is an abnormal narrowing in a blood vessel or other tubular organ or structure

Question 5

Bruit

Answer 5

is the unusual sound that blood makes when it rushes past an obstruction (called turbulent flow)

Question 6

Thrill

Answer 6

an abnormal fine tremor or vibration in the respiratory or circulatory systems felt on palpation

Question 7

Energy Gradient

Answer 7

when energy at one location is greater than the energy at another location, an energy gradient is present. Blood flows in the body due to energy gradient.

Question 8

Plug flow

Answer 8

Speed of flow is constant across the entire tube (fluid moves like the motion of one solid object)

Question 9

Laminar flow

Answer 9

occurs when a fluid flows in parallel layers, with no disruption between the layers. At low velocities, the fluid tends to flow without lateral mixing, and adjacent layers slide past one another like playing cards.

Question 10

Parabolic flow

Answer 10

when blood flow moves fastest in the center of the vessel

Question 11

Phasic flow

Answer 11

• Occurs when blood moves through the
vessels in a variable velocity
• accelerates and decelerates as a result of
respiration.
• Occurs most often in the arterial system

Question 12

Steady flow

Answer 12

• Occurs when blood moves through the
vessels at a constant speed and velocity
• there is no acceleration and deceleration as
a result of cardiac contractions or respiration
• Is always present, is located in the venous
system

Question 13

Turbulent flow

Answer 13

• Presents as a chaotic flow pattern where the
unidirectional flow patterns are no longer
present
• often referred to as eddy currents
• associated with pathology
• converts flow energy to sound or vibrations
• sound conversion results in a murmur or bruit
• vibration conversion results in a thrill

Question 14

Pulsatile Flow

Answer 14

• Occurs when blood moves through the
vessels in a variable velocity
• accelerates and decelerates as a result of
cardiac contractions
• Occurs most often in the arterial system

Question 15

Pressure Energy

Answer 15

• A form of potential energy
• It is the ability to do work
• The major form of energy in the circulatory
system
• Provides blood to flow by over overcoming
the resistance to stand still or resist

Question 16

Gravitational Energy

Answer 16

• Much like kinetic energy this is a form of
stored energy
• All elevated objects have stored
gravitational energy that can do work

Question 17

Kinetic

Answer 17

• Associated with moving objects
• Determined by the objects mass and the
speed in which it moves
• Think of it heavy objects that are moving
fast have a lot of energy
• While light objects moving at the same
speed has less kinetic energy

Question 18

Viscous energy loss

Answer 18

• Viscosity what is it?
• The higher the viscosity the greater the energy
loss.
• It takes more energy to
overcome the stickiness or
thickness of the blood.
• It is measured in units of Poise.
• The hematocrit is the % of RBC’s in blood
– Decrease the HCT and reduce the viscosity of blood

Question 19

Friction loss

Answer 19

• This is the conversion of fluid energy to
heat.
• Occurs as blood cells rubs against each
other
• Or when they slide across the wall of the
vessels

Question 20

Inertial Energy Loss

Answer 20

• Relates to the resistance of fluid to change
in velocity
• Energy is lost anytime
there is a change in
the speed of fluid
• Occurs during 3 events
– Pulsatile flow
–Phasic flow
– Velocity changes

Question 21

Stenosis

Answer 21

• What is it?
• It can change the direction of flow as it
enters or exits the restriction.
• It can increase the velocity in the stricture
• Creates post stenotic turbulence
• Creates pressure gradients
• Can convert pulsatile flow to steady flow

Question 22

Pressure – Flow relationships

Answer 22

• Vessel elasticity cardiac pulsatility and
composition of blood contribute to the
complex nature of flow in vessels
• A more simplified way of understanding
this is
Pressure gradient = flow x resistance

Question 23

Ohm’s Law

Answer 23

• While this has nothing to do with blood
flow how electricity flows in a wire has
some similarity
Pressure gradient = flow x resistance
Voltage = current x resistance

Question 24

Hydrostatic pressure

Answer 24

• Is related to the pressure or weight of blood
pressing on a vessel
• Measured at separate heights
• Measured the same as BP in mmHg
• Is clinically related to
the patients condition
• Measurements can change depending on
where you take the measurement and the
position of the patient

Question 25

The Effects of Respirations on

Venous Pressure

Answer 25

• Has a pronounced effect because the
pressure in the venous system is low
• Respirations also alter the pressure in both
the abdominal and thoracic cavities
• Creates pressure gradient differences

Question 26

Bernoulli’s Principle

Answer 26

Explains that fluid moves against a pressure gradient from a point of low pressure to a point of high pressure

Total fluid energy remains the same

Pressure energy is converted to flow energy upon entrance to a stenosis

As flow energy increases, pressure energy decreases (velocity goes up; pressure goes down)