Module 2 : Arteriole Hemodynamics Flashcards
what are the two conditions for fluid to move from one point to another
- a path for the fluid
- a difference in energy (pressure) level from point to point
3 types of energy contained in moving fluids
- potential (pressure)
- kinetic
- gravitational
potential (pressure)
- the primary energy present in blood flow
kinetic energy
- energy of something already in motion
gravitational energy
- hydrostatic pressure
what is the primary pressure source in circulation
- the systolic contraction of the heart creates an energy gradient for blood to flow
what two factors dictate the volume of blood leaving the heart
- blood pressure
- peripheral resistance
stroke volume definition
- amount of blood ejected from the heart during systole
how does the arteriole system change with increased volume
- in respones to the increase volume and pressure arterial walls expand which creates POTENTIAL ENERGY within them called SYSTOLIC PRESSURE
diastole effect on volume and pressure
- blood volume decreased during diastole
- artery decreases in diameter
- pressure decreases and blood flows due to its own momentum
- DIASTOLIC PRESSURE
what is the pressure gradient between left ventricle and right atrium
- 120mmhg / 2-6mmhg
what does Bernoulli principle explain
- maintenance of energy in the movement of the fluid
Bernoulli principle describes relationships between what three things
- area
- velocity
- pressure at a stenosis
Bernoulli energy equation
total energy = potential E + kinetic E
Bernoulli and three statements on energy
- over relatively STRAIGHT partial segments, balance of kinetic (blood flow) and potential (blood pressure) energy is maintained
- if artery lumen increases kinetic energy is converted back into pressure (potential energy) when velocity is increase
- is artery lumen decreases, the potential energy is converted into kinetic energy
Bernoulli increase in kinetic energy leads to what change in velocity
- increase in kinetic energy occur in the systemic circulation where blood flow is high in stenotic lesions and luminal narrowing leads to increase in blood flow velocities and decrease pressure
laminar flow
- aka parabolic
- normal flow
- each layer travels at different velocities
- slowest flow is near the vessel wall
- fastest flow located at centre of vessel
- BLOOD MOVES IN CONCENTRIC LAYERS
blunt flow
- aka plug flow
- uniform flow across the vessel
- occurs during SYSTOLE in larger vessel
- also at some arterial branch origins
non laminar flow
- aka disturbed
- normal and abnormal
- some conditions laminar flow can be disrupted and once it is altered the velocity profile is not reestablished for
3CM
flow separation
- occurs when there is sudden WIDENING OF VESSEL
- fluid layers separate to fill the newly opened area creating MIXED BLOOD FLOW PATTERN
- this causes FLOW REVERSAL ALONG THE WALL
- considered NORMAL
transition zone
- area where the lamina reach zero-velocity is refer to as the site of the boundary layer separation
- seen at carotid bulb and distal to stenosis
flow pattern at bifurcations and branches
- layers become disrupted and will show DISTURBED flow
- flow patter may differ depending on angle and size of vessel
- A LARGER ANGLE WILL RESULT IN GREATER FLOW DISTURBANCE
- small pressure drop at bifurcation
flow patter in curved vessels
- when blood moves around a cure the fluid in the centre moves outward and is replaced by the slower flow located near the arterial wall
- called a HELICAL FLOW PATTERN
- FLUIDS FLOW FASTER ON TEH OUTSIDE AND FLOW MAY APPEAR REVERSED ON TEH INSIDE as the fluid fils the inner void from the outward shift
resistance and pressure gradient relationship
- to preserve blood flow through out the body if there is an increase in resistance the pressure gradient must increase
abbreviated poiseuilles equation
Q = (P1 - P2) / R (resistance)
flow (Q)
- the amount of fluid traveling past a point in a given amount of time (L/min)
poiseuilles law
- defines the relationship between pressure volume flow and resistance of a fluid flowing through a cylinder tube model
poiseuilles equation
Q = pi (P1 - P2)r^4 / 8Ln
Q = flow volume n = viscosity L = length of vessel r = radius P1 - P2 = pressure gradient
viscosity (n)
- resistance to flow of a fluid in motion
- how thick it is / stickiness
- frictional forces that occur as molecules of blood move against eachother
- measured in POISE
- concentration of RBC (hematocrit) and plasma protein is MOST IMPORTANT FACTOR EFFECTING VISOCISTY
length (L)
- due to increase friction a longer tube contains more resistance than a smaller tube
- RESISTANCE INCREASES AS LENGTH INCREASES
radius (r)
- artery radius has THE LARGEST EFFECT on resistance
- as vessel radius decreases resistance increases to the 4th power
- in lower extremity this is effected by ecersize and vasodilation radius increases resistance decreases
poiseuelles vs Bernoulli
- poiseuille us based in entire long tube so flow speed is less in smaller diameters
- Bernoulli is based on just the short portion of the vessel (stenosis) so flow speed is increased with smaller diameters
what is turbulent flow
chaotic flow where fluid is exiting a tight spot and entering an enlarged space
how is the fluid moving in turbulent flow
- eddies and whirls
- very disordered
what types of vessels does turbulent flow occur
- develops more easily in larger vessels with high flow volumes
spectral trace of turbulent flow
- feathered appearance
- spectral broadening
what is the Reynolds number
- the number at which turbulence occurs when it is met or exceeded
- 2000
Reynolds number equation
Re = average flow x density x tube diameter / viscosity
according to the equation what will increase turbulence
- increases flow
- increasing density
- increasing tube diameter
- decreasing velocity
why will the velocity increase at a stenosis
- velocity increases because pressure decreases (BERNOUILLI)
why will there be turbulence post stenosis
- because of increased velocity and sudden increase to vessel radius (REYNOLDS POISEUILLE)
hemodynamic effect of arterial stenosis
- according to bernouille there will be a pressure drop at the entrance to a stenosis because a higher velocity is needed to maintain flow volume
- at the exit turbulent flow may be seen due to jet entering the wider lumen
- distal to exit the velocity decreases due to increase lumen size resulting in an increase in pressure
how are velocity and pressure related in a stenosis according to Bernoulli
they are inversely related
energy can be lost within a stenosis due to what three factors
- length of stenosis
- whether there is tandem stenosis
- surface contour of plaque
7 factors within a stenosis that cause hemodynamic change
- length and diameter of narrowed segment
- surface roughness
- surface irregularity and shape of lesion
- ratio of normal vessel diameter to narrowed segment
- collateral circualtion
- pressure gradient
- peripheral resistance to stenosis
spectral tracing proximal to stenosis
- increased pulsatility
- narrow sharp peak
- low PSV dues to decreased flow
- laminar flow
- THUMPING IN SYSTOLE
spectral trace within stenosis
- increased velocities not necessarily isolated to stenotic segment
- PSV increases until 80% reduction occurs
- EDV is markedly increased with > 70% stenosis
spectral trace distal to stenosis
- flow reversal, flow separations, vortices and eddy currents seen (post stenotic turbulence)
- maximum flow disturbance is seen within 1cm with visible bruit
- ## dampened or trades parvus seen distal
tandem lesions characteristics
- greater loss of energy and volume
- first stenosis have greater incoming energy and will usually produce higher velocities than the second stenosis as it will have decreased incoming energy
low resistance flow pattern
- constant foward flow in systole and diastole with a diastolic component way above baseline
- feeding important things like brain
high resistance flow pattern
- sharp upstroke with low to absent diastolic flow
- more pulsatility
- feeding things that are less important
pulsatiility is caused by what and causes what
- due to the pulsatile pumping activity of the heart
- causes alternating phases of acceleration and deceleration
- low, moderate, high
low pulsatility
- low resistance
- broad systolic peak with forward flow in diastole
moderate pulsatility
- tall sharp peak
- little diastolic flow
high pulsatility
- high resistance
- narrow systolic peak
- flow reversal in early diastole
- little or absent late diastolic flow
pulsatility index equation
PI = PSV - EDV (lowest point) / MEAN V
resistivity index equation
RI = PSV - EDV / PSV
systolic / diastolic ratio
S/D = PSV / EDV
