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What is FLOW?
- The volume or amount of blood that moves through a vessel in a given time.
- It may be called volume flow rate.
- Unit of Flow: volume divded by time. (mls/sec)
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What is velocity?
- a mesause of the speed of blood flowing through circulation.
- Unit of velocity: distance divided by time. (cm/s)
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What is potential pressure?
Energy stored (nozzled hose)
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What is Kinetic?
Energy in action (Waterfall)
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What is Gravitational?
Potential energy due to gravity (elevational)
Gravitational energy is called hydrostatic pressure and is expressed in mm of mercury. (mmHg)
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Etotal=Epo + Eki + Egr
The total energy at a specific location is the sum of all three energy forms.
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What determines whether blood flow exists in a vessel?
There must be difference in energy at two different sites.
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What determines the direction of flow within a blood vessel?
Blood flows from a region of higher energy to a region of lower energy.
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Volume flow of fluid through a tube is annotated by:
Q=P(Pressure Gradient)/R(Resistance)
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Ohm's Law Comparisons to Flow
- The difference in PRESSURE bwn two points is the PRESSURE GRADIENT
- Increase the pressure gradient; flow increases
- Pressure gradient and flow are directly proportional
- Increase Resistance; Flow decreases
- Resistance and flow are indirectly proportional
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What is viscous energy loss?
- Viscosity describes the thickness of the fluid
- Viscous energy loss is associated with blood overcoming its interneal stickness
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What is Frictional Energy loss?
- Occurs when flow energy is converted to heat
- Blood sliding across vessel walls creates heat
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What is Inertial Energy Loss?
- The tendency of a fluid to resist changes in velocity
- Energy is lost when the speed of a fluid changes
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Poiseuille's Law Conclusions
- If pressure differences increases, flow rate increases
- if length of vessel increases, flow rate decreases (bc of more resistance)
- if diameter increases, flow rate increases (decrease in resistance)
- if visocity increases, flow rate decreases (bc of more resistance)
- longer vessel, more resistance (double length, double resistance)
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Resistance to Flow depends upon:
- 1. Length of vessel
- 2. Radius of vessel
- 3. Viscosity of Fluid
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Blood Viscosity
- -Viscosity is the thickness of blood.
- -Increase Viscosity, Increase resistance to flow
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Two Factors affecting Viscosity
- 1) Polycythemia-high concentration of RBC's
- Viscosity Increases
- 2) Anemia- Low concentration of RBC's
- Viscosity Decreases
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Radius of a Vessel
- The relationship between radius of a vessel and its resistance to flow is an inverse relationship.
- Resistance to Flow= 1/raidus4
- Only true if the same length and same type of liquid flowing!!
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What is Reynold's Number (Re)?
- Predicts whether flow is laminar or turbulent
- is unitless
- In a stiff tube, flow will change from laminar to disturbed/turbulent when the Re passes 2000.
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Flow disturbances can occur at lower Re values because of other factors such as:
- Body movement
- pulsatility of blood flow
- irregularities of vessel wall and plaque
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The Re Number (General Rules):
- The higher the velocity the higher the Re
- Larger vessels tends to have higher Re
- The thinner the blood the higher the Re
- The more dense the fluid the higher the Re (higher the Re, the more potential for turbulene)
- The more viscous the more laminar flow
- Lower viscosity (thinner blood) can cause higher turbulence
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Turbulent Flow
Converts flow energy into other forms such as sound and vibration.
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Turbulence is more likely to occur at:
- High velocities within large vessels
- Distal to an obstruction
- Along a rough surface
- Within a sharp turn of a vessel
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What is Bruit?
the audible sound associated with turbulent flow.
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What is thrill?
The tissue vibration associated with turbulent flow (also called palpable murmur).
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Bruit
- As severity of an obstructive lesion progresses from mild to moderate, the duration and amplitude of the bruit increases.
- Turbulence becomes more severe and more fluid energy is converted to sound energy.
- As severity of the lesion progresses from moderate to pre-occlusive, the duration and amplitude of the bruit decreases.
- Blood flow decreases, therefore the amplitude of the bruit decreases.
- (IE, ICA is the one that get stopped up the most)
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What is Pulsatile Flow?
Blood moves with variable velocity; blood accelerates and decelerates from cardiac contraction; commonly seen in arterial circulation (in arteries)
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What is Phasic Flow?
Blood moves with variable velocity; accelerates and decelerates from respiration; commonly seen in venous circulation. (IVC) [Venous pump in calf pump push blood up against gravity]
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What is Steady Flow?
a fluid moves at constant velocity. (veins)
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What is Viscosity?
resistance of a fluid to flow due to the attraction of the molecules(also can be described as thickness or stickness of fluid)
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What is resistance?
Measure of the impediment that must be overcome for flow to occur.
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What is Compliance?
- Ability of vessels walls to expand and contract; related to the ability to hold a change in volume.
- When the pressure pulse forces fluid into a complaint vessels, it expands and increases the volume within it.
- (Veins are a lot more complaint)
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What is Pressure?
measure of force per unit area
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What is Potential Energy?
Energy that is stored which has ability to perform work (pressure and gravitational energy are both forms of potential energy)
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What is Kinetic Energy?
Energy related to movement; directly related to velocity
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What is Turbulent Flow?
Flow pattern is random and chaotic with particvles moving at different speeds in a different directions.
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What is Disturbed Flow?
Flow where streamlines are not straight; particles of fluid still flow in the forward direction.
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What is Plug-Flat?
at the entrance of a vessel.
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What is Laminar?
Streams of different velocities.
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What is Parabolic?
A Type of laminar flow downstream from the entrance of a vessel.
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What is Hydrostatic pressure?
- Pressure related to the weight of blood pressing on a vessel measured at a height above or below heart level.
- *Right atrium of the heart is considered the zero pressure reference point.
- *When Pt is supine, hydrostatic pressure is Zero at all parts of the circulatory system bc every part is at the heart level.
- *When Pt is standing, hydrostatic Pressure is zero at the heart level; positive below heart level and negative above the heart level bc against gravity.
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Measure Pressure=
Circulatory pressure + hydrostatic pressure
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What is Continuity Principle?
To maintain volume flow across vessel and body.
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What is stenosis?
- Causes an increases resistance over a short distance.
- In order to maintain volume flow, velocity increases through the stenosis.
- As the stenosis gets narrower, the velocity must increase to maintain flow.
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Conclusions on changing Radius:
- Radius of Vessel is directly proportional to volume flow (changing the radius of the full length of the vessel)
- The size of the vessel is inversely proportional to the velocity of blood flow.
- As vessel radius decreases, resistance increases and velocity increases
- As vessel radius increases, velocity decreases but flow increases.
- The volume of blood flow through a stenotic vessel remains constant (continuity principle).
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What is Bernoulli Effect?
- As the vessel narrows, flow velocity increases and pressure simultaneously decreases.
- The equation shows that velocity and pressure are inversely related.
- Q=P/R
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