Hemodynamics Flashcards
hemodynamics is the study of
blood flow in the circulatory system and refers to both power and blood
blood composition
plasma 55%
erythrocytes 45%
leukocytes/platelets <1%
hematocrit
makes up 45% of blood volume and is made up of RBCs
density (in reference to hemodynamics)
the mass per unit volume or the resistance of an object to accelerate
viscosity
the resistance to flow (more viscous=slower velocity)
veins accounts for ____ of blood
65%
there is relatively ___ volume and velocity in the capillaries
low
the capillaries have an area of _____ that of the other vessels
600-1000x
ASK SHANE AS IT SAYS 600-100
what is required for any fluid to flow
a pressure difference
the pressure difference can be created by the ____ or ____
heart
gravity
an increase in pressure results in an _____ flow rate
increased
Ohm’s law (actual vs for blood)
current= voltage/resistance
for blood
volume flow rate (Q)= ΔP/R
pressure gradient formula
P Gradient = (P1-P2)/L
L= distance
the total adult blood flow rate is approximately ______ and is called the
5000mL/min
cardiac output
what happens to the volume flow rate if the pressure gradient increases
flow increases
what happens to the volume flow rate if the resistance to flow increase
flow decreases
Poiseuille’s Law for Resistance
R= (8 x length x viscosity) / (π x radius^4)
what has biggest influence on resistance
radius as it is to the power of 4
viscosity increase = resistance ____
increases
increase tube length = ____ flow resistance
increases
a decrease in the radius or diameter = ____ in flow resistance
increase
Poiseuille’s Law for volume flow rate
Q= (ΔP x π x diameter^4) / (128 x length x viscosity)
increase in pressure difference and/or diameter will ___ the volume flow rate
increase
a decrease in the length of the tube and/or the viscosity of the fluid will ____ the volume flow rate
increase
5 flow patterns
plug
laminar (parabolic)
jet
disturbed
turbulent
plug flow (what/appearance on spectral tracing)
is seen at the opening of a large vessel (ex aorta) and has almost all RBCs travelling at the same v (thin envelope)
laminar parabolic flow (what/appearance on spectral tracing)
most common flow pattern in normal arteries
RBC’s move in concentric layers with the ones in center moving faster than ones near wall (envelope slightly thicker + clear window)
jet flow (what/appearance on spectral tracing)
is seen when there is a significant reduction in the diameter of a vessel
velocities within narrow opening are much faster than the rest (thick envelope/no window/ high v)
75% reduction in diameter= velocity ____, 95% reduction = velocity _____
quadruples
slows
disturbed flow (what/appearance on spectral tracing)
can occur naturally in the presence of vessel tapering, curvatures, bifurcations, etc
not all layers of blood move in a laminar fashion
ex. at carotid blub
may have some backwards flow
turbulent flow (what/appearance on spectral tracing)
seen just past a stenosis
flow velocities are varied as are flow directions (chaotic)
unusual in the body except near the heart
super thick (no window) and some backwards flow
if the Reynolds number (RN) is above 2000 then ____ results
turbulence
if the Reynolds number (RN) is above ______ then turbulence results
2000
in the presence of a stenosis, the volume of flow must _____ proximal to, at, and distal to the stenosis. To achieve this, the ____ of blood flow increases in a stenosis
remain constant
velocity
if the diameter of the stenosis is 1/2 of the normal vessel, then the velocity is ____ through the stenosis to maintain the volume flow rate
doubled
Bernoulli’s Principle
established relationship between kinetic energy, gravitiational potential energy, and pressure in a frictionless fluid system
total fluid energy (E) is compromised of both ____ energy and ____ energy
potential
kinetic
potential energy is the _______ plus the _____
intravascular pressure
gravitational potential energy
pressure is produced by the ____ of the heart, the ______, and the ______
contraction
hydrostatic pressure
static filling pressure
at the stenosis there is a pressure ____ which is necessary for the fluid to ______ through the stenosis and ____ past the stenosis
drop
accelerate
decelerate
pressure or potential energy is converted to ______ on entry and back to pressure energy on exit (of stenosis)
kinetic energy (flow)
the drop in pressure, in a stenosis, can be calculated using what formula
ΔP=4(V2)^2
tardus parvus
after a stenosis, there is a drop in the acceleration time and peak systolic velocity of arterial flow
the stenosis detracts from the pressure gradient that was created by the heart
Windkessel effect
the continued forward flow in the aorta during diastole as a result of the elasticity of the vessel walls contracting back to their original diameter
the flow cant reverse back into the heart because the aortic valve has closed
the pressure wave along the walls of the vessel travels _____ than the blood flowing within
faster
when the wave reaches the end of the arterial system there is a ______ wave that causes the vessel wall to _____ and _____ against the flow of ____
reflected
expand
contract
blood
Blood is reversed back towards the heart because of the ______ pressure _____ and the heart is in diastole
increased
down stream
arteries get _____ further away from the heart = wave gets ____ than blood/gets to door = ______
stiffer
faster
reverses
A reduction in the diameter of a blood vessel
stenosis
The amount of blood passing a point per unit of time
volume flow rate
An significant increase in the blood velocity as a result of a reduction in diameter of the blood vessel
jet
Non-laminar flow pattern with subtle variations in velocity and direction
disturbed flow
Great variations in blood velocity and direction found distal to a significant stenosis
turbulence
The difference in pressure divided by the distance between two points
pressure gradient
A flow pattern seen distal to a significant stenosis with a reduction in velocity and acceleration time
tardus parvus
Continued forward flow in a vessel as a result of the elasticity in the vessel wall
Windkessel effect
blood traveling in concentric layers with the fastest at the center
laminar parabolic
The resistance of a fluid to flow
viscosity
Most red blood cells traveling at the same velocity
plug flow
When referring to Ohm’s law, what part of the equation is synonymous with the pressure gradient in blood flow?
A) Current
B) Voltage
C) Amperage
D) Resistance
B
Poiseuille’s Law states there will be a reduction in flow when the diameter of a tube is reduced but we know this to be the opposite in a stenosis of a blood vessel. What other factor accounts for this?
A) Ohm’s law
B) Continuity rule
C) Reynold’s number
D) Bernoulli’s principle
b
The pressure wave velocity and blood flow velocity are inversely related.
A) True
B) False
a
The majority of energy contained within the vascular system is of what type?
A) Heat
B) Kinetic
C) Potential
D) Gravitational
c
What does the Bernoulli equation relate?
A) Flow and energy
B) Flow and resistance
C) Pressure and radius
D) Pressure and velocity
d
What part of the body is referred to as the venous heart?
A) Valves
B) Venules
C) Calf muscles
D) Right ventricle
c
List the types of vessels of the circulatory system, in order, from the left ventricle to the right atrium and state which one controls the resistance to blood flow.
Arteries - Arterioles - Capillaries - Venules - Veins
Arterioles help regulate the resistance to flow as they contain sphincters that can open and close to control the amount of flow that enters the peripheral vessels.
What is the role of the heart in the circulatory system?
The heart is responsible for creating the pressure gradient that allows blood to flow.
What two things can be done to increase the volume flow rate?
Increasing the pressure gradient or lowering the resistance to flow would increase the volume flow rate.
What are the resistive factors that are considered when assessing flow in a tube?
The resistive factors are the length of the tube, the viscosity of the fluid and the radius of the tube.
If the radius of a tube is halved, how many times is the flow in that tube reduced?
Flow would be reduced 16 times due to the fact that the radius is to the power of 4 in the equation.
How does the length of the tube and viscosity of the fluid relate to flow in Poiseuille’s equation?
If either the length of the tube or the viscosity of the fluid is increased, then the flow will be decreased.
Can you provide examples of where you might find the following flow profiles:
Plug flow
Laminar flow
Disturbed flow
Turbulent flow
Plug flow - origin of large vessels like the aorta
Laminar flow - In all straight normal vessels like the CCA
Disturbed flow - At bifurcations, anastomoses or tortuous vessels
Turbulent flow - After a hemodymically significant stenosis or in and near the heart
Explain how the body maintains a constant flow rate in the presence of disease.
The continuity rule describes how flow the flow rate remains constant in the presence of a stenosis. IF the area of the lumen is reduced, the flow rate increases to maintain the 5 L of blood through the heart in one minute.
What is responsible for the increased velocity of the blood through a stenosis?
There is a drop in pressure at the stenosis that increases the pressure gradient related to the pre-stenotic blood flow. The increased pressure gradient will result in the increased blood flow velocity.
Explain the different types of energy found in the circulatory system and state the one that is most prevalent.
There is potential energy and kinetic energy. Kinetic energy is the energy contained within the moving red blood cells and the potential energy is the energy stored in the vessel walls and the gravitational energy from the weight of the blood in the vessels. Potential energy is the most prevalent type in the circulatory system.
Explain how the Windkessel effect maintains forward flow in a normal proximal artery.
Elasticity of the vessel walls and the closed aortic valve result in an expansion of the vessel when a bolus of blood passes through in systole. The recoil of the wall in late systole/early diastole forces the blood in a forward direction since the closed aortic valve prohibits the blood from reversing.
Explain why flow reversal is seen in the normal peripheral artery.
The pressure wave, created with the heart’s contraction, travels along the vessel walls faster then the bolus of blood. When the pressure wave in the wall reaches the arterioles, it is reflected back towards the heart resulting in a reversal of flow.
