Hemodynamics Flashcards
Does a damped waveform always indicate a proximal obstruction?
No, this could also result from heart condition.
When there is adequate blood flow at rest, but exercise creates a painful lack of blood to the working muscles, this is called:
Claudication
What does the spectral display indicate proximal to, within, and distal to a stenosis?
Proximal: Increased resistance if no significant collateral, no diastolic flow, increased pulsatility, low velocity.
Stenotic Zone: High velocity, PSV, EDV, and systolic ratios. Spectral broadening, then increased PSV, then increased EDV. May reduce to trickle flow.
Distal: Dampened, slow acceleration time, rounded peak, tardus parvus.
What are the secondary effects of stenosis? (4)
Increased velocity (compensatory flow)
Increased volume flow
Reversed flow direction (steals)
Pulsatility changes - i.e. delayed accel. time
What measurements are used to assess a stenosis? (5)
PSV EDV Systolic Velocity Ratio Diastolic Velocity Ratio Post Stenotic Turbulence
What steps occur in the development of a stenosis, including the effect on the vessel and collaterals?
Dilation
Collateral development
Possible steal development
Peripheral dilation of run off bed to reduce resistance
How is a hemodynamically significant stenosis defined?
As a drop in both pressure and flow.
Peripheral resistance is primarily controlled by what structures?
Pre-capillary sphincter muscles.
What are the three main sources of energy loss in blood vessels?
Friction
Inertia
Viscosity
Phasic venous flow results from what action in the body?
Respiration
Steady flow may be found in these two parts of the circulatory system:
Capillaries (normal steady flow)
Veins (abnormal, indicates partial blockage)
Layered, non-turbulent flow is called:
Laminar flow
Laminar flow which has the highest velocity in the center and lower velocity near the wall is called:
Parabolic flow
Laminar flow in which the velocity in the center is similar to the velocity near the wall is called:
Plug flow
Name two areas where Plug Flow can be found.
Aorta
Entrance to stenosis
What is the Reynolds number for turbulent flow?
> 2000
What is the cause of phenomena such as murmurs, thrills, and bruits?
Turbulent flow
Changes in the direction of flow would result in what kind of energy loss?
Inertial energy loss
An increase in hematocrit or a decrease in temperature would increase what kind of energy loss?
Viscous energy loss
Energy conversion to heat is due to which type of energy loss?
Frictional energy loss
Poiseuille’s Law calculates flow volume based on pressure gradient, vessel radius, vessel length, and fluid viscosity. Which of these variables has the greatest effect on the flow volume?
Radius (radius to the fourth power)
In what structures in the cardiovascular system is atherosclerosis most likely to occur?
Branch points and bifurcations such as the carotid and aortic bifurcations; and renal, celiac, and other branch points.
Name three areas with a high incidence of atherosclerosis which are not branch points or bifurcations.
Hunter’s Canal
Proximal ATA
Distal PTA
The increase in pulse pressure as the pressure wave moves from the heart to the extremities is called:
Systolic Amplification
Normal systolic ankle pressure is 10% greater than brachial systolic pressure. What phenomena accounts for this increase?
Systolic Amplification
A critical stenosis causes what sort of change to pressure and flow?
A hemodynamically significant drop in pressure and flow.
A 50% diameter reduction equates to what percent of area reduction?
75%
What is the most important factor influencing the severity of an obstruction?
The change in diameter.
What may develop over time to prevent a loss of total flow to an extremity due to an obstruction?
Collaterals
Which entrance to a stenosis causes more energy loss, an irregular (asymmetrical) entrance, or a symmetrical entrance?
An irregular entrance causes more losses, due to greater friction.
Where are energy losses are greater, at the entrance to a stenosis, or at its exit?
Exit losses are greater than entrance losses, due to turbulence on the exit side.
Which condition would cause greater energy loss, two stenoses in series, or one stenosis as long as the other two combined (assuming all stenoses have the same diameters).
Stenoses in series have greater energy losses due to the additive effect of entrance and exit losses.
What factors act to compensate for lost flow when plaque is mild to moderate?
Vessels expand from increased sheer stress which releases a muscle relaxing factor from the endothelium, leading to vessel expansion.
When plaques become severe, what two compensatory mechanisms occur to increase flow to downstream tissues?
Development of collaterals
Dilation of capillary beds
Collaterals consist of three vessel segments:
Stem arteries (ex. ECA) Midzone collaterals (ex. facial) Re-entry vessels (ex. opthalmic)
What waveform is seen in a resting patient with PAD/claudication?
Monophasic - resistance is low from dilated capillary beds to provide adequate flow at rest.
Are patients with rest pain subjected to exercise tests?
No need - it would be positive.
In a stenosis, Bernoulli’s principle predicts what changes to pressure and velocity?
Pressure will decrease while velocity increases. This maintains an equilibrium between kinetic and potential (pressure) energy.
List three conditions resulting in distal venous pulsatility.
CHF
Fluid Overload
Tricuspid regurgitation
Inspiration has what effect on venous return from the lower extremities?
Inspiration slows venous return from lower extremities.
Inspiration has what effect on venous return from the upper extremities?
Inspiration increases venous return from upper extremities.
Roughly two-thirds of the total blood volume is found in which vessels: arteries; veins; capillaries?
Veins
The weight of the uninterrupted column of blood due to gravity is termed ___ pressure.
Hydrostatic
What structures in the veins prevent retrograde flow and interrupt the column of blood to reduce hydrostatic pressure?
Valves
List four trophic changes which occur with chronic venous incompetence.
Edema
Fibrous deposits
Brawny appearance in gaiter area
Ulceration
What must be present for an effective calf veno-motor pump?
Working calf muscles
Competent valves
Patent outflow veins
Formula for Resistive Index?
RI = [1 - (EDV/PSV)] * 100
Normal Resistive Index for renal arteries?
< 80
What problem with cardiac function will be shown in the waveform as a delayed upstroke?
Slowed ventricular emptying
What problem with cardiac function will be shown in the waveform as reversed diastolic flow?
Aortic valve reflux
What problem with cardiac function will be shown in the waveform as damping of the pulse?
Aortic stenosis
What is the effect on resistance, pulsatility and velocity PROXIMAL to a stenosis?
Greater resistance and pulsatility, lower velocity.
As a vessel narrows over time due to stenosis, what is the effect on the spectral signal, the PSV, and the EDV within the stenotic area?
First spectral broadening occurs, followed by increased PSV, and finally increased EDV.
Which is the better indicator of severe (70-90%) stenosis, PSV or EDV?
EDV.
List the five measurements used to assess stenosis.
PSV EDV Systolic velocity ratio Diastolic velocity ratio Post stenotic turbulance
What is the effect on the waveform DISTAL to a stenosis?
Damped appearance: slow acceleration time, rounded peak, decreased systolic and increased diastolic velocity. Tardus parvus.
List three problems which may trigger a visual bruit.
A/V Fistula
Pseudoaneurysm
Significant stenosis
When using a headset, which earphone (right or left) provides the forward (antegrade) signals?
Right
Formula for Pulsatility Index?
Peak-to-peak frequency / Mean frequency
Which quantitative measure can help differentiate inflow from outflow disease? (Pulsatility index; Inverse damping factor; Acceleration time)
Acceleration time
How much wider should the pneumatic cuff be than the diameter of the limb on which it is used?
At least 20%.
For segmental limb pressures, a drop of at least how many mmHg between two consecutive levels is considered significant?
> 30mmHg for legs, > 20mmHg arms.
A horizontal difference between same segments of legs of how many mmHg suggests obstructive disease in the leg with the lower pressure?
20 - 30 mmHg
A thigh pressure index of at least what is normal?
1.2
For healing of foot ulcers, what is the minimum toe pressure needed?
At least 30mmHg
