Flashcards in Chapter 2- Physiology And Hemodynamics Deck (42):
Name the flow of blood starting from the heart
1) Left ventricle
3) Large arteries
7) Large veins
8) Vena cava
9) Right atrium
Energy: Movement of any fluid medium between two points requires two things:
1) pathway along which fluid can flow
2) pressure differential ( high pressure moves to lower pressure)
What does the amount of flow depend on?
1) energy difference
2) any resistance which tends to oppose such movement
Lower resistance = higher flow rate
Higher resistance = Lower flow rate
What is the major form of Energy for circulation of blood?
Pressure (potential/ stored energy)
What is kinetic energy?
- small for circulating blood
- expressed in terms of fluid density and velocity measurements
What is Gravitational energy?
Hydrostatic pressure (HP)
Weight of the column of blood extending from the heart to level where pressure is measured
An energy gradient is needed to move blood from one point to another. The _________ the gradient; the _________ the flow.
What is Inertia?
Related to tendency of a fluid to resist change in its velocity (example: body at rest stays in rest)
Resistance if directly proportional to what?
Viscosity (thickness of blood) and length
Resistance is inversely related to what?
What has the most dramatic effect on resistance of a blood vessel?
Elevated hematocrit does what to blood?
Increases blood viscosity ( thickness of blood)
Severe anemia: decreases blood viscosity
Increase in viscosity = decrease in velocity
Decrease in viscosity = increase in velocity
What is parabolic flow?
Higher frequency flow in center of vessel. Laminar flow considered stable flow
Where is plug flow seen?
Vessel origin as well as during initial cardiac upstroke
What causes viscous energy loss?
Increased friction between molecules and layers which ultimately cause energy loss
Where do inertial losses occur?
Deviations from laminar flow, due to direction and/or velocity changes
Example: exit of a stenosis
What does the Poiseuille’s equation show relationships of?
Pressure, volume flow, resistance
What is volume flow directly related to?
What is volume flow inversely related to?
What is the relationship between area and velocity?
- increase area ; decrease velocity
- decrease area ; increase velocity (ex: stenosis)
What is the relationship between velocity energy and pressure energy?
- increase in velocity = decrease pressure
- decrease in velocity = increase in pressure
What is boundary layer separation?
They occur because of chAnge with or without intra-luminal disease; and because of curves
In presence of flow separation, what happens with the velocity and pressure?
Decrease in velocity; increase in pressure
What is the Reynolds number when Laminar flow becomes disturbed?
> 2000 (unitless number)
AKA Turbulent flow
Looking at a triphasic waveform, what does the dicrotic notch tell us?
Related to closure of the aortic valve and the influence of peripheral resistance
What are examples of arteries that have low resistive waveforms?
** main arteries that feed organs**
What are some examples of low resistive arteries?
- extremity arteries
- fasting SMA
What can happen to a normal high resistant signal as it approaches a significant stenosis or obstruction?
What does the diastole in a waveform reflect in low and high resistance?
Low resistance: higher diastole, continuous blood flow
High resistance: little to no diastole
What is vasodilation?
Pulsatilla changes in medium/ small sized arteries of the limbs are decreased (lower resistant). When this occurs, pulsatility changes are increased in minute arteries
We inflow pressure falls due to stenosis; the usual response in periphery’s to maintain flow by vasodilation
What is vasoconstriction?
Pulsating changes in medium/small sized arteries of the limbs are increased. When this occurs, pulsatility changes are usually decreased in the minute arteries.
Know about collaterals?
1) location of the collaterals may help to determine tentative location of the stenosis/obstruction
2) arterial obstruction may alter flow in collateral channels nearby or further away from site of obstruction
Changes include: elevated velocity, increase volume flow, pulsatility changes
Know about effects of exercising?
1) causes peripheral vasodilation which lowers distal peripheral resistance, enhancing blood flow
2)Vasoconstriction and vasodilation of blood vessels within skeletal muscles are influenced by sympathetic nervous system for blood temperature
3)Exercise is a key vasodilator of resistance vessels within skeletal muscle
What is auto regulation?
Ability of most vascular beds to maintain constant level of blood flow over a wide range of perfusion pressures
When Blood pressure rises, what happens to the resistance vessels?
When blood pressure falls, what happens to resistance vessels?
Flow to a cool extremity (vasoconstriction) = pulsatile signals
Flow to a warm extremity (vasodilatation) = continuous, signals
Pulsatility changes don’t differentiate well between occlusion and severe stenosis
Waveforms may not be altered with good collateralization