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119 Cards in this Set
- Front
- Back
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What are the 2 systems of the Circulatory system?
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2 systems
1. High pressure, high energy arterial reservoir and 2. A venous pool of low pressure energy These 2 systems are connected by microcirculation |
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what does microcirculation consist of
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arterioles, capillaries, and venules
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what are arterioles?
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Arteries progressively decrease in size from Aorta (largest) to the arterioles (smallest)
Considered resistance vessels help regulate blood flow by contracting (vasoconstriction) and relaxing (vasodilatation) Measure 30 microns in diameter Cannot see!! |
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What is vasoconstriction and vasodilation?
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Vasoconstriction
Increased state of contraction Vasodilation Decreased state of contraction This mechanism is most important for the arterial side of the circuit.  |
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Arterial system information....
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Multi-branched elastic conduit set into oscillation by each beat of the heart
Each beat pumps about 70 milliliters of blood into the aorta causing a blood pressure pulse Cardiac contraction begins: Pressure in the left ventricle rises rapidly Pressure in left ventricle exceeds that of the aorta Aortic valve opens, blood is ejected, BP rises |
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what plays an important role in movement of blood through the Arterial system?
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PATIENT'S CARDIAC STATUS plays an important role in the movement of blood throughout the vascular system
Increased heart rate delivers an increased blood volume |
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what kind of energy is created when the Heart pumps
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Every time the heart beats:
Pressure (potential) energy is generated and moves the blood !! Producing an arterial pressure wave, that travels rapidly throughout the arterial system, demonstrating a gradual transformation as it travels distally |
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What results in pumping of the Heart?
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The pumping action of the heart results in HIGH VOLUME of blood in arteries to maintain a high pressure gradient between the arterial and venous circulation
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What is Cardiac output and peripheral resistance
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The amount of blood that enters the arteries is the cardiac output
 The amount that leaves depends on the arterial pressure and on the total peripheral resistance, which is controlled in turn by the amount of vasoconstriction in the arterioles (microcirculation) |
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Why do our arteries distend?
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Each cardiac contraction distends the arteries
During this instant in time, the arteries serve as reservoirs to store some blood volume and potential energy supplied to the system |
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Where is pressure the greatest?,
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Pressure is greatest at the heart, gradually decreasing as the blood moves further away
This pressure difference is necessary to maintain blood flow |
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circulation of blood is the basic principle of?
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fluid dynamics
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Physiologic factors governing blood flow and its characteristics?
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Energy and pressure
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What determines whether blood flow exists in a vessel?
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‘Energy’ gradient – a difference in energy of the fluid at 2 locations
the Greater the energy gradient the Greater the volume flow  |
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‘What is Volume’ Flow?
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The volume or amount of blood that moves through a vessel in a time period
Units of volume divided by time 7 liters per minute |
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what does velocity measure?
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The measure of swiftness or speed of blood flowing through the circulation
Direction Units of distance divided by time 100 cm per second  |
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What determines the direction of flow within a vessel?
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Blood will flow from the region of higher energy to the region of lower energy
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The reason why we say energy gradient is because.....
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The total energy contained in moving fluid is the sum of pressure (potential), kinetic, and gravitation energies
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What are the difference in energy levels due to?
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Typically, the difference in energy levels are due to pressure level differences
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What is the main form of energy in blood
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PRESSURE (POTENTIAL) ENERGY
It is the pressure distending the vessels |
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What is Pressure energy in blood?
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Typically, the difference in energy levels are due to pressure level differences
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What is kinetic energy in circulatory system?
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A small component of the energy in blood is kinetic, when compared to potential energy
Blood is moving – kinetic energy It is defined as the ability of flowing blood to do work as a result of its velocity |
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Forms of energy in blood
Kinetic Energy |
In normal circumstances:
Equivalent to a few mmHg Proportional to the blood’s density (stable) Squared to the velocity of blood Therefore, significant increases of kinetic energy occur when flow is high (ex: exercise, stenotic lesions with an increase in blood velocity) |
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What happens to kinetic energy when velocity has normalized after exercise?
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Kinetic energy is converted back into pressure (potential) energy when velocity has normalized or decreased
ex: normal segment of the |
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What is Gravitation Energy?
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Due to the gravitational pull:
variation in the energy of blood is associated with differences in the levels of body parts |
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A column of blood has weight known as....?
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Hydrostatic pressure equals the weight of blood pressing on the vessels from heart level to the point of measurement (standing)
transmural pressure and distension of the vessels increases |
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3 forms of ENERGY in blood?
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Kinetic
Pressure Gravitational |
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How can one eliminate hydrostatic pressure?
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Supine, supine, supine....
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Peripheral resistance flow patterns?
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Low and high resistance flow
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LOW Peripheral resistance =
HIGH peripheral resistance = |
Low peripheral resistance = high flow rate
High peripheral resistance = low flow rate |
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Low resistance flow characteristics?
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flow that is continuous and ‘steady’ throughout systole and diastole
Always flowing forward Feeding a dilated vascular bed Ex: ICA, vert, renal, celiac, splenic, and hepatic (post-prandial SMA) |
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High resistance flow characteristics?
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Pulsatile in nature
Flow reversals are produced from the peripheral resistance A normal high resistance flow pattern is called tri-phasic flow Forward, reversal, and forward flow again |
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What is the trademark of diastolic flow?
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Diastolic flow reversal is a trademark of vessels that supply high resistance peripheral vascular beds
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High resistance flow examples?
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Ex: ECA, subclavian, Aorta, iliacs extremity arteries and fasting (pre- prandial) superior mesenteric arteries
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Low pulsatility wave form characteristics?
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Low resistance flow
Broad systolic peak Sharp upstroke Delayed downstroke High diastolic component |
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moderate pulsatility wave form characteristics?
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Narrow and sharp systolic peak
Sharp upstroke sharp downstroke low diastolic component High resistance flow ECA |
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high pulsatility wave form characteristics?
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high resistance flow
narrow systolic peak Sharp upstroke sharp downstroke Reversal component in early diastole absent diastolic component in late diastole Peripheral arteries |
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exercise affects on flow
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Induces peripheral vasodilation in the microcirculation
Thus, decreasing peripheral resistance Increasing blood flow 5-7 times more!! Peripheral resistance can also be altered in response to heat, cold, tobacco and emotional stress!! |
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Does flow reversal increase or decrease with Vasoconstriction?
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Flow reversal increases with vasoconstriction (cooling)
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Does flow reversal increase or decrease with vasodilation?
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Flow reversal decreases with vasodilatation (heating)
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sympathetic innervation fibers are influenced by?
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Sympathetic nervous system and vasodilatation of the blood vessels within the skeletal muscles are also influenced by sympathetic innervation fibers that function primarily to regulate body temperature
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Laminar flow characteristics..
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Characterized by individual layers of blood that travel at individual speeds
These layers of blood are aligned and parallel Layers at the wall are at “zero” speed This type of flow pattern is associated with normal physiologic states |
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When is PLUG FLOW seen?
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Plug flow –occurs when ALL the layers and
blood cells travel at the same velocity - typically seen at vessel origins |
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When is PARABOLIC FLOW SEEN?
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Parabolic flow – occurs when velocity is higher in the center of the lumen and
slower at the periphery (bullet shaped profile) - typically seen downstream |
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What are the 2 types of Laminar flow?
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Plug
Parabolic |
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Do both plug and parabolic flow patterns are laminar and associated with normal physiology?
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Yes
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When is energy loss in blood known as?
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energy is lost in the blood, known as viscous energy loss
due to friction between its lamina and particles, causing a decrease in pressure and energy levels from both systems  |
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Why is energy lost in blood?
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energy is lost due to FRICTION
amount of friction and energy loss is determined mostly by the dimensions of the vessels |
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Friction in small vessels increased?
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Small vessels ex: microcirculation
Friction is increased due the lamina rubbing against the walls resulting in resistance to flow increased energy loss |
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What happens to Friction loss in large vessels?
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Large vessels
Less rubbing of layers against the walls of the vessel Frictional energy losses are minimal Resistance is minimal |
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Why does Inertial energy loss occur?
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This occurs due to deviations from laminar flow due to changes in:
Direction Bifurcations, curves, etc. |
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What happens to the flow of blood when Inertial energy loss occurs?
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Velocity changes
Results: • The parabolic flow profile becomes flattened • Flow moves in a disorganized fashion • This type of energy loss occurs at the EXIT of a stenosis |
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Why does Inertial energy loss occur?
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Direction
Velocity |
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What Other Factors affect
resistance to flow? |
Movement of fluid is dependent upon the physical properties of the fluid and what its moving through..
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R = 8Lη / π r4
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R = resistance
L = length of vessel η = viscosity r = radius of vessel |
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What do viscosity and length have an effect on?
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Viscosity and length have an effect on resistance, however, a change in vessel diameter has a more profound effect on resistance!
L, η are typically constant |
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What is the interaction between the vessel and the fluid
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The longer the vessel, the longer the fluid is in contact with the vessel, thus increasing friction, producing energy losses, increasing resistance!
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What is friction generated by?
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by the viscous properties of fluid
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What happens with thicker fluids?
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The thicker the fluid, the greater molecular attraction and the more energy required to move the fluid, increased energy
High viscosity situation in the circulatory system: Elevated hematocrit - erythrocytosis, polycythemia Low viscosity low hematocrit - anemialosses and increase of resistance |
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What is the relationship between Viscosity and velocity?
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When viscosity is high
Velocity is low |
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When does Resistance increase?
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Resistance increases with High Viscous properties and Longer Vessels
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What is the relationship between friction and resistance?
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Direct
High Friction High resistance |
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What is Poiseuille’s Law and Equation?
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Q = π (P1 – P2) r4
8Lη |
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What does Poiseuille's Law calculate?
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Calculates how much fluid is moving through a vessel
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Poiseuille’s Law states?
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Volume Flow is directly proportional to the difference between the inflow and outflow pressures.
Volume Flow is directly proportional to the fourth power of the radius. Volume Flow is inversely proportional to the length of the tube and viscosity. Q = π (P1 – P2) r4 8Lη  |
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Why is Poiseuille’s Law useful?
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Helps define the relationship between: pressure, volume flow, and resistance
Resistance is inversely related to r4, therefore, when there is a narrowing, resistance will increase! Pressure difference and blood flow can be measured, therefore resistance can be calculated Therefore, Poiseuille’s law can be re- writen or simplified: Q = P/R |
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What is Ohm's Law?
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Movement of fluid through a tube and the movement of electricity through a wire are somewhat similar
Please be aware of the similar relationship between Ohm’s Law and the way movement of fluid is described |
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Ohm's Law vs Poiseuille's Law?
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Fluid
Q-flow P - pressure R - resistance Electricity(Ohm’s) I -current V - voltage R - resistance Q= P / R I= V / R |
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When is Poiseuille’s Law used?
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Only used with laminar flow
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Poiseuille’s Law in changes of radius of vessels and pressure?
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Realistically, alterations in blood flow occur mainly as a result of changes in the radius of the vessels and the pressure energy available for flow
Q = π (P1 – P2) r4 8Lη  |
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How are Velocity and CSA related?
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Inversely
In a closed system, Q (volume flow) is constant. v (velocity) is inversely proportional to A (area) E.g. area reduction from a stenosis |
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How are Area and velocity related
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Inversely
When area is small Velocity is high |
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velocity vs. area
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Diameter of vessel decreases:
 Velocity goes up! Vice-versa |
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Bernoulli equation states:?
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Velocity and pressure are inversely related
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What is the sum of total energy?
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the total energy contained in moving fluid is the sum of potential (pressure), kinetic (velocity), and gravitational energies
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Kinetic (velocity) and potential (pressure) energy
What happens if one of these variables changes? |
If one of these variables changes, the others also must change to maintain total fluid energy at the same level...law of conservation of matter
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What happens if potential every decreases?
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If potential (pressure) energy decreases, kinetic energy must increase in order to maintain the same total fluid energy
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What happens to energy within the narrowing?
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Some of the pressure energy converts to kinetic energy, reducing pressure energy
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What happens within a normal segment?
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Within the normal segment, the velocity decreases, kinetic energy decreases, and pressure energy goes back up
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What happens when a cross sectional area decreases?
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Velocity increases
⤴ Kinetic energy increases ⤵ Pressure energy decreases |
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What happens in the pre-stenoitc segment?
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Increase in resistance
⤵ Slight decrease in velocity |
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What happens in the Region of post-stenotic turbulence.......
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velocity slows down
⤵ kinetic energy decreases ⤴ Pressure energy goes back up |
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What is non-laminar flow?
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disturbed flow
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What happens with Disturbed or turbulent flow?
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Occurs when the parallel streamlines of laminar flow are altered from their straight form
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Can non-laminar flow occur within normal conditions?
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Yes
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Disturbances in flow occur due to:?
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Flow velocity changes due to the cardiac cycle:
systole = velocities accelerate Diastole = velocities decelerate changes of the lines of flow Vessel dimension alterations Distortion of lines of flow Curves, bifurcations, and branches that take off at various angles |
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Flow velocity changes due to the cardiac cycle: changes of the lines of flow Distortion of lines of flow...what happens to laminar flow?
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Because of these and other factors, laminar flow may be disturbed or fully turbulent, even in a disease ‘free’ vessel
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What occurs with Disturbed or turbulent flow
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Fluid elements are not confined to definite layers but mixing occurs
Irregular motions of fluid elements |
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Turbulence can be found clinically through....?
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Bruits and thrills
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Bruits and thrills =
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turbulent flow
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Does turbulence happen in large or small vessels?
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Turbulence develops more readily in LARGE VESSELS under conditions of HIGH flow and may cause vessel walls to VIBRATE
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What do bruits produce?
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The harmonics of this vibration produce vascular bruits and can be heard by auscultation
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What do thrills produce?
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Thrills can be felt or palpated as one feels the vibration of the vessel caused by high flow rate within the vessel
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Can turbulence be detected clinically?
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YES... by the finding of bruits and thrills (ex: ao, fem. A, carotid bif.
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Turbulent flow =
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Vortex and eddy currents – swirling patterns of rotational flow
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What is also seen in turbulent flow?
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Cross currents
Boundary layer separation occurs Flow near the vessel edges become stagnant or retrograde Multiple velocity components Disturbances in direction of flow Flow profile elongates and eventually re- establishes as parabolic  |
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Can we diagnose turbulent flow sonographically??
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Turbulent flow can be assessed and detected with sonographic equipment and such assessments can be applied for diagnostic purposes
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What is Spectral broadening proportional to?
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The degree of spectral broadening is proportionate to the severity of flow disturbance
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What can a large/ wide sample volume mimic?
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A large/wide sample volume can mimic SPECTRAL BROADENING because it is encompassing both the higher center velocities and the slower outer velocities
1.5-2 mm sample volume size |
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Why is the detection of turbulence important?
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Manifestations of turbulence is a diagnostic feature observed in the post stenotic zone of arteries with severe stenosis, hence post- stenotic turbulence
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What happens in the Region of post-stenotic turbulence.......
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velocity slows down
⥥ kinetic energy decreases ⥣Pressure energy goes back up |
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What causes Arterial stenosis?
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Arterial stenosis, caused by atheroslerotic plaque, can result in reduced pressure and flow levels distal to an obstruction
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When do hemodynamic occur before hemodynamic changes occur
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arterial stenosis has to be relatively extensive before hemodynamic changes can occur
Hemodynamic changes = reduction of flow and pressure |
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Hemodynamic significant stenosis aka.....
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“critical stenosis”
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When is hemodynamic stenosis significant?
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With 70-90% decrease in cross- sectional area will cause hemodynamic changes in small vessels such as the iliac, carotid, renal, and femoral arteries
Pressure drops distally! Carotid – neuorologic defecits |
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Diameter vs cross- sectional area reduction
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When atheroslerotic plaque or thrombus is present, arterial lumen diameter and area are reduced
It is important to differentiate between percentage decrease in cross-sectional area and diameter |
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How many ways to measure reduction in wall size of lumen?
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2 ways to measure the reduction with our system!
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When do flow separations occur?
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occur due to changes in vessel geometry: curves, bifurcations, anastomosis
Results of little movement or sluggish flow within the flow separation The main thing you need to know for the exam is the pressure/velocity energy relationship in the flow separation  |
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Pressure/velocity relationship within flow separations
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Flow separation =
increase Pressure ⤴ decrease Velocity⤵ |
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Where are flow separations seen?
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seen when there is a curve in the vessel
usually seen towards the inside of the curve; while the higher velocity energy is along the outside of the curve Please know the pressure/velocity energy relationship in the flow separation  |
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Flow separation in a curved / turtuous vesse
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flow separation =
⤴ increase pressure ⤵decrease velocity |
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Effects of stenosis on flow during entrance
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During entrance
Flow will change direction in order to travel within the narrowing |
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Effects of stenosis on flow at the stenosis
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Velocity will increase
Heat energy is created Thus increasing energy losses!!  |
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What are the effects of stenosis on flow
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energy losses are mostly due to inertia!!
 as blood flows through a stenosis, speed is increased. This acceleration causes an additional energy loss known as inertial loss or inertia, due to the friction between adjacent RB |
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When exiting stenosis, what happens to flow?
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When exiting the stenosis:
vortices, eddy currents and turbulence are produced  |
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What happens with 2 or more stenotic lesions?
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2 or more stenotic lesions that occur in series have a more pronounced effect on distal pressure and flow than does a single lesion of equal total length
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What factors are considered for the occurrence and degree of hemodynamic changes produced by a stenosis
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Length, shape, diameter, and degree of narrowing
Roughness of endothelial surface Arterio-venous pressure gradient Rate of flow Collateral circulation |
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What is an occlusion?
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Complete obstruction of a vessel due to atherosclerotic plaque or thrombosis
No blood flow passes through No Doppler signal is usually present in both color or PW  |
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What doppler techniques must be performed when considering occlusion?
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Appropriate Doppler techniques is a must, when an occlusion is in question!
Minimize color scale Increase Doppler gain Increase sample volume size Identification of vessel Are you on the vessel? Doppler technique Steering, angle correct |
