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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)
What is velocity?
- a mesause of the speed of blood flowing through circulation.
- Unit of velocity: distance divided by time. (cm/s)
What is potential pressure?
Energy stored (nozzled hose)
What is Kinetic?
Energy in action (Waterfall)
What is Gravitational?
Potential energy due to gravity (elevational)
Gravitational energy is called hydrostatic pressure and is expressed in mm of mercury. (mmHg)
Etotal=Epo + Eki + Egr
The total energy at a specific location is the sum of all three energy forms.
What determines whether blood flow exists in a vessel?
There must be difference in energy at two different sites.
What determines the direction of flow within a blood vessel?
Blood flows from a region of higher energy to a region of lower energy.
Volume flow of fluid through a tube is annotated by:
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
What is viscous energy loss?
- Viscosity describes the thickness of the fluid
- Viscous energy loss is associated with blood overcoming its interneal stickness
What is Frictional Energy loss?
- Occurs when flow energy is converted to heat
- Blood sliding across vessel walls creates heat
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
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)
Resistance to Flow depends upon:
- 1. Length of vessel
- 2. Radius of vessel
- 3. Viscosity of Fluid
- -Viscosity is the thickness of blood.
- -Increase Viscosity, Increase resistance to flow
Two Factors affecting Viscosity
- 1) Polycythemia-high concentration of RBC's
- Viscosity Increases
- 2) Anemia- Low concentration of RBC's
- Viscosity Decreases
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!!
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.
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
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
Converts flow energy into other forms such as sound and vibration.
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
What is Bruit?
the audible sound associated with turbulent flow.
What is thrill?
The tissue vibration associated with turbulent flow (also called palpable murmur).
- 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)
What is Pulsatile Flow?
Blood moves with variable velocity; blood accelerates and decelerates from cardiac contraction; commonly seen in arterial circulation (in arteries)
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]
What is Steady Flow?
a fluid moves at constant velocity. (veins)
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)
What is resistance?
Measure of the impediment that must be overcome for flow to occur.
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)
What is Pressure?
measure of force per unit area
What is Potential Energy?
Energy that is stored which has ability to perform work (pressure and gravitational energy are both forms of potential energy)
What is Kinetic Energy?
Energy related to movement; directly related to velocity
What is Turbulent Flow?
Flow pattern is random and chaotic with particvles moving at different speeds in a different directions.
What is Disturbed Flow?
Flow where streamlines are not straight; particles of fluid still flow in the forward direction.
What is Plug-Flat?
at the entrance of a vessel.
What is Laminar?
Streams of different velocities.
What is Parabolic?
A Type of laminar flow downstream from the entrance of a vessel.
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.
Circulatory pressure + hydrostatic pressure
What is Continuity Principle?
To maintain volume flow across vessel and body.
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.
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).
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.