Hemodynamics Flashcards
What is flow?
The movement of fluid from a location to another
It measures how much fluid moves per unit of time
What is another term used to describe flow?
Volume flow rate
How are flow and velocity different?
Flow measures volume of fluid that moves per unit of time (liters/min)
Velocity measures speed of that fluid (distance/time)
What is pulsatile flow?
It occurs when blood moves with variable velocity
Has high variability because of cardiac contraction and is often associated with high pressure and higher flow rate
What vessels show pulsatile flow?
Arteries
What is phasic flow?
It occurs when blood moves with variable velocity
It has variability when the vessel is compressed due to respiration, and is associated with lower pressure and lower flow rate
What vessels show phasic flow?
Veins
What is steady flow?
Flow that moves at a constant velocity or speed
When is steady flow seen?
When patient holds their breath
What is laminar flow?
When the flow streamlines are parallel and aligned
Can be plug or parabolic
What is plug flow?
When all layers and blood vessels travel at an equal velocity
What is parabolic flow?
When the flow is in the shape of a bullet
The center of the vessel holds the highest velocity
What is the Reynolds number?
Unitless number that predicts whether flow will be turbulent or laminar
What is turbulent flow?
When flow is chaotic and goes in many directions and speeds
Streamlines are obliterated and results in spectral broadening
Energy is lost when converted to sound or vibration
What is turbulent flow associated with?
Cardiac and vascular pathologies and spectral broadening
For Reynolds number, what is the threshold for predicting turbulent flow?
2000
What is viscosity?
Thickness of a fluid
Comes from a fluid sticking to itself with internal friction
Increased viscosity - increased hematocrit and hemoglobin
Reduced viscosity - anemia
What is stenosis?
Irregularity or narrowing of the lumen in a blood vessel
It can cause a change in flow direction, increased velocity in the narrowed area, turbulent flow after the stenosis, a pressure gradient, and loss of arterial flow pulsatility
What happens to velocity of blood within a stenosis?
The velocity of flow increases within the stenosis, with the highest velocity occurring at the greatest narrowing
What type of turbulence may be seen downstream from a stenosis?
Downstream from a stenosis, the turbulence is post-stenotic turbulence
The lumen extends more dramatically than it can be filled by streamlines of blood flow
What is Bernoulli’s principle?
It describes the relationship between the pressure and velocity in a moving fluid
The sum of kinetic and pressure energy remains constant
Velocity increases as vessel narrows, while pressure decreases when vessel narrows
What is Ohm’s law?
It states that movements of fluid through a tube and electrical current through a wire are similar
Voltage = current x resistance
Q = (change in P)/R
How does the cross sectional shape of a vein change in high or low pressure situations?
The cross-sectional shape of a vein during higher pressure is large and round and during lower pressure (normal) is flattened in an hourglass shape
What is Hydrostatic Pressure?
The weight of blood pressing on a vessel measured either above or below the level of the heart
What is hydrostatic pressure in a supine patient?
It is 0 at all locations when the patient is supine
What is the hydrostatic pressure at certain levels?
Head = -30 mmHg Heart = 0 mmHg Hands = 50 mmHg Knees = 75 mmHg Feet = 100 mmHg
During inspiration what happens to venous flow from the legs?
During inspiration, venous flow from the legs decreases.
During inspiration what happens to venous flow from the arms and abdomen to the heart?
During inspiration, venous return from the arms and abdomen to the heart increases.
During expiration what happens to venous flow from the legs?
During expiration, venous flow from the legs increases.
During expiration what happens to venous flow from the arms and abdomen to the heart?
During expiration, venous return from the arms and abdomen to the heart decreases
What is a pressure gradient?
The difference or change in pressure from one location to another
How is pressure gradient related to flow?
Pressure gradient = flow x resistance
It is directly related to flow because pressure gradient increasing will cause a flow increase
