Chapter 2- Arterial Hemodynamics Flashcards
Where in the body is pressure the greatest?
At the heart ;
it decreases as it moves further away from the heart
movement of any fluid medium between two points requires what two things?
1) a PATHWAY along the fluid can flow
2) Difference in energy levels (pressure/energy differential )
The amount of flow moving through the circulatory system depends on
Important
energy difference and resistance
Blood leaves the heart with a mean pressure of
85-95 mmHG
Think about how hot that is if that was the weather outside. It would make my heart beat fast.
Arterioles are also known as “_____” vessels
Resistance
The pressure in an arteriole drops down to
25-30 mmHg
Once the blood comes back to the heart in the right atrium the pressure measures
0 mmhg
REMEMER:
Blood moves from an area of (high or low?) pressure to areas of (high or low) pressure?
Remember heart is has the highest amount of pressure :)
High to low pressure
Heart is always the highest
What causes blood to move?
Energy
What are the three types of energy?
Potential Energy, Kinenetic energy and gravitational energy
Also known as pressure, motion, and hydrostatic energy
In this analogy, identify which energy sources are used in which part.
The water tower
Water coming out of a faucet
Turning on the water faucet
The water tower is the potential energy. Its being stored (potential energy). When you turn on the water in a faucet, that is the hydrostatic pressure being released. The water coming out of the faucet is the motion/kinetic energy :)
The ejection of blood from the heart into the arteries distends the elastic artery wall and this becomes ________. What kind of energy is this describing?
Stored energy/potential energy
During potential energy, how is the energy released?
when the walls recoil.
What is kinetic energy?
it comes from the movement of blood as it ejects from the heart.
The weight of the column of blood from the heart to the level where the pressure is measured. THIS IS VERY IMPORTANT IN VENOUS CIRCULATION. what kind of energy is this?
Hydrostatic / Gravitational energy
When a patient is laying down The arteries and veins are about the same level as the heart. What is the hydrostatic pressure at that point?
0 mmhg
everything is equal. 0 difference
When the patient stands up the hydrostatic pressure increases at the ankles, making the pressure ____ mmHg?
100 mmhg
Understanding the concept then when a patient stands, this adds 100 mmhg of hydrostatic pressure to the ankles, complete this equation,
If the hydrostatic pressure at the brachials is 110 standing up, what would the ankle pressure be?
210
Adding 100 to this.
What word describes the “thickness” of the blood?
Viscosity.
The thicker the fluid the “_____” ( greater, lesser) the friction and the “___” (greater/lesser) the energy loss
Thicker fluid=greater friction=greater energy loss
When a patient has severe anemia, meaning less blood in the body, would this decrease or increase the viscosity or thickness of blood?
Decreases the viscosity. There is less of it therefore it isn’t as thick. The more blood the thicker it’ll be.
What are the three main types of energy loss?
Friction, viscosity ( thickness of fluid), and intertia.
How does friction loss occur? What happens as a result?
when one object rubs against another. This creates friction when the cells rub against each other; this converts energy to heat.
Objects in motion stay in motion and objects at rest tend to stay at rest.
True False?
True.
Once flowing, blood cells like to travel in a straight line unless an external force messes that up. How does this affect energy loss?
Where can you sometimes see this at?
it creates energy loss when the speed or direction changes.
At a vessel bifurication or stenosis.
What is laminar flow?
Fluids flowing smoothly in an organized manner; evenly layered.
What is the boundary layer in pertains to laminar flow (flow moving in a straight even line)
The layer of fluid along the vessel wall.
Is the blood flow at the boundary layer usually faster or slower than the flow in the middle of the vessel?
Slow because its interacting with the wall creating friction (a form of energy loss)
What are the two types of laminar flow?
Parabolic and plug flow.
What is plug flow? What part of a vessel do you often seen this?
When the speed of blood in the middle of the vessel and the speed on the boundaries are almost similar in speed.
Happens as bifurications and branches.
What is parabolic fluid **most often seen)
Blood flow is faster in the middle of the vessel due to the drag of the wall on the blood (aka boundary layer)
What are Eddys currents in relation to the boundary layer of a vessel?
Often blood flow wants to keep going in a straight line so when it gets to a biffurication it often continues this way creating a separation, that’s when Eddy’s currents come in and fill in the separation.
Where is disturbed flow often seen in a vessel?
A stenosis or carotid bulb
Disturbed flow ALWAYS means there is some sort of disease
TRUE FALSE
False! Not always.
What is turbulent flow?
flow that has varying directions and speeds. seen with disease
What does the Reynolds number describe?
Predicts the point at which laminar flow becomes turbulent
What is the Reynolds number?
> 2000
<1500 is laminar
>2000 is turbulent
What are the two factors that affect resistance of flow?
The size of the vessel and the properties such as speed/thickness of blood
If a vessel is long and contains thick blood , would there be more resistance or less and why?
MORE resistance, They are directly related.
Resistance is_____ proportional to the vessel radius?
inversely
When the radius diameter decreases, the resistance increases.
What is Pouiselle’s Law in relation to pressure and resistance?
- Will come back with more info on this*
- very important*
The resistance of flow through a vessel.
Flow=pressure/resistance
Of all the factors of Pouiselle’s Law, which is the most important?
A)Thickeness of the blood
B) Diameter change/Radius
C)length of the vessel
RADIUS.
Think of this analogy
Honey moving through a very long straw…will there be a lot of resistance or no?
yes. Honey is THICK, and if it has a long way to travel and is thick, it’ll have a lot of resistance coming out
Water through a large/wide diameter pipe will have more resistance or less?
Less. Water isn’t think and it has wide pipe to go through. Easy.
What does the Dicrotic notch represent?
When does it occur? in the end diastole, early systole or early diastole?
The aortic valve closing. (temporary reversed flow)
Happens in the early diastole
In the early systole, the aortic valve is opening or close?
Opening
What kind of arteries have low resistance flow?
IMPORTANT ONES such as the carotid ICA and renal veins.
What type of arteries have high resistance flow?
Carotid ICA/Legs/Arms
Not as important ones
Low resistive flow means it needs constant flow where as high resistive doesn’t need as constant of flow. Low resistive is more important
True/False
True
Little to no diastole is seen in ___ resistive vessels
High resistive
Area and velocity are _____ proportional
Inversely.
Smaller diameter vessel means faster speed. True or False?
True
Within the area of a stenosis, what kind of waveform should you expect?
In a stenosis the vessel is getting narrower therefore it speeds up ( higher velocity) and spectral broadening.
Proximal to a stenosis, what kind of waveform should you expect?
Often dampened
Distal to a stenosis what kind of waveform should you expect?
Flow reversel, turbulence, eddy currents.
If there is a HEMODYNAMICALLY SIGNIFICANT stenosis seen, ( such as 50% diameter reduction), what kind of pressure will you see? Decreased or increased?
decreased pressure.
**50 % diameter reduction = 75% area reduction
Explain Bernoulli’s principle?
It is the relationship between ____ and _____.
Relationship between pressure and speed (velocity).
Higher pressure lower speed
Low pressure- higher speed.
Is velocity and pressure directly or inversely proportional?
Inversely
As speed/velocity increases the pressure decreases
As velocity decreases, pressure increases.
Which one of these will have a higher velocity and why?
an ICA stenosis or aortic aneurysm?
The ICA will have higher velocity because the vessel is narrower and speed goes faster through a narrower vessel.
** as area decreases, velocity increases***
Which one of these will have the lowest pressure and why?
an ICA stenosis or aortic aneurysm?
The ICA stenosis will have the lowest pressure because speed and pressure are inversely related.
An arterial occlusion or stenosis may result in ______ (decreased/increased) pressure distally
Decreased. ** remember bernoullis rule of speed being inversely related to pressure.
Stenosis has higher speed, therefore pressure is decreased.
What does the vessel do anytime blood flow is reduced to the point it cannot accommodate the demand?
*Think about bernoullis again. If the pressure gets low, the vessel will do this to increase the pressure **
Vasodilatation
- page 25 in book**
What is autoregulation?
the ability for most vascular beds to maintain a constant flow
What are vasoconstriction and vasodilation controlled by? which part in brain
Sympathetic nervous system
What is the difference in waveform if a complete artery occlusion has collateralization versus if it doesn’t?
With collateralization- this allows adequate blood flow, no dilatation, minimally altered
Without collateralization- inadequate blood flow, decreased pressure therefore vasodiliataion will occur.
During exercise does vasoconstriction or vasodilatation occur?
vasodilatation.
More blood is needed for exercise, so the arterial bed will dilate to allow blood flow.
If the blood pressure drops, the arteries will _______ (dilate/constrict) allowing for constant blood flow volume.
Vasodilation.
If the blood pressure drops, the arteries will (dilate/constrict) allowing a steady blood flow volume.
Vasoconstriction.
An increased heart rate delivers what?
an increase in blood volume
What is the heart pump?
it generates the pressure to move to the blood
Explain the process of how cardiac contraction works?
1) pressure in the left ventricle arises rapidly
2) Left ventricle pressure exceeds that than in the aorta
3) aortic valve opens, blood is ejected, BP rises
What does the cardiac contraction do?
it distends the arteries, which serve as a reservoir and source of potential energy
How is flow rate and resisitance related?
Inversely or directly/
Inversely
What is the HP is the ankle when a patient is standing?
100
What is the HP in the ankle when a patient is supine?
0
internal friction within a fluid is measured by what/
viscosity ( thickness of the blood)
What is the relationship between velocity and viscosity?
inversely
What is laminar flow?
layers of fluid particles moving against one another
What is low resistance flow?
Flow of continuous steady nature feeding a dilated vascular bed…needs CONSTANT flow
What vessels are low resistive?
ICA, vertebrals, renal, celiac, splenic, hepatic, non-fasting SMA
What is high resistance flow?
flow of pulsatile nature.
- between indident pulses, hydraulic reflections travel back up the vessel from the periphery producing flow reversals in the vascular compartment
- doesn’t need constant flow*
What vessels are high resisitive
ECA , subclavian, aorta, iliac, extremity arteries, fasting SMA
What can happen to the reversal component of a high resistant signal distal to a stenosis?
It may disappear due to decreased peripheral resistance, secondary to ischemia
What does the doppler flow distal to a stenosis look like?
Low resistant, more rounded in appearance, and weaker in strength, tardus parvus!
What happens when a high resistance wave form approaches a stenosis?
it can go from triphasic to monophasic
as the inflow pressure falls as a result of a stenosis, what is the peripheries natural response?
Vasodilate or vasoconstrict?
vasodilate
True or False
The location of collaterals help provide tenative location of the obstruction
true
What changes when BP rises?
constriction of vessels
What happens when BP falls?
dilation of vessels
What happens when cross sectional area reduction of 75%
Diameter reduction by 50%
Where are the lower frequencies distributed?
The walls/boundary layer
What happens pre-stenosis?
flow frequencies are dampened
What happens at stenosis?
increase in frequencies, spectral broadening and elevated velocity
