Doppler Principles Flashcards
Flow
to go from one place to another
Velocity
is the speed and direction of flow
Reynold’s number
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.
Stenosis
is an abnormal narrowing in a blood vessel or other tubular organ or structure
Bruit
is the unusual sound that blood makes when it rushes past an obstruction (called turbulent flow)
Thrill
an abnormal fine tremor or vibration in the respiratory or circulatory systems felt on palpation
Energy Gradient
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.
Plug flow
Speed of flow is constant across the entire tube (fluid moves like the motion of one solid object)
Laminar flow
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.
Parabolic flow
when blood flow moves fastest in the center of the vessel
Phasic flow
• 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
Steady flow
• 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
Turbulent flow
• 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
Pulsatile Flow
• 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
Pressure Energy
• 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
Gravitational Energy
• Much like kinetic energy this is a form of
stored energy
• All elevated objects have stored
gravitational energy that can do work
Kinetic
• 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
Viscous energy loss
• 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
Friction loss
• 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
Inertial Energy Loss
• 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
Stenosis
• 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
Pressure – Flow relationships
• 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
Ohm’s Law
• 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
Hydrostatic pressure
• 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
The Effects of Respirations on
Venous Pressure
• 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
Bernoulli’s Principle
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)
