Vascular Lecture Unit 2: Arteriole Hemodynamic and Physiology
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135 Terms
What is the arterial system known as?
Resistance system
Why is understanding resistance important?
It affects blood flow.
What does Ohm's Law describe?
The relationship between voltage, current, and resistance.
What is the formula for Ohm's Law?
E or V = I × R
In blood flow, voltage is similar to what?
Pressure.
In blood flow, current is similar to what?
Blood flow.
What is the hemodynamic form of Ohm's Law?
ΔP = Q × R
What does ΔP represent?
Change in pressure.
What does Q represent?
Blood flow.
What does R represent?
Resistance.
What is velocity?
Rate of flow.
What is blood flow?
Volume of flow.
What happens to velocity when volume decreases in a stenosis?
Velocity increases.
What is the source of pressure in the circulatory system?
The heart.
What is the flow equation?
Q = Velocity × Area
What is the velocity equation?
Velocity = Flow ÷ Area
What is power?
The rate at which work is performed.
What provides power for blood flow?
The heart.
What is work?
The amount of energy transferred or total energy expended.
What is the formula for work?
Work = Average power × Total time
What happens when blood meets resistance from a stenosis?
The artery must work harder to maintain flow.
What makes up total fluid energy?
Potential energy + kinetic energy.
What is potential energy in blood flow?
Stored pressure energy.
What percentage of circulatory energy is potential energy?
98%.
What supplies potential energy?
Contraction of the heart.
What is gravitational potential energy?
Energy related to the force of gravity.
What is hydrostatic pressure?
Pressure caused by the weight of a column of blood due to gravity.
What is kinetic energy?
Energy of work or motion.
What represents kinetic energy in moving blood?
Velocity.
Blood moves from what pressure to what pressure?
High pressure to low pressure.
What is a pressure gradient?
The difference in pressure from one point to another.
What is the pressure gradient equation?
Q = (P1 − P2) ÷ R
What does the Bernoulli principle state about total fluid energy?
Total fluid energy remains constant if there is no frictional loss.
What happens to pressure when velocity increases?
Pressure decreases.
What is the relationship between velocity and pressure?
Inverse relationship.
What is the Bernoulli pressure equation?
Pressure = 4v²
What happens to pressure within a stenosis?
It decreases.
What is viscosity?
A fluid's resistance to flow.
What happens to resistance when viscosity increases?
Resistance increases.
How does blood viscosity relate to hematocrit?
They are directly proportional.
Does water have higher or lower viscosity than blood?
Lower viscosity.
What is inertia?
The tendency of an object at rest to stay at rest or an object in motion to stay in motion.
When do inertial energy losses occur?
When blood changes direction or velocity.
What factors affect inertial losses?
Blood density and velocity.
What is volume flow?
Volume moved per unit of time.
What happens to velocity when vessel area decreases?
Velocity increases.
Where is total cross-sectional area highest?
Capillaries.
Where is blood velocity lowest?
Capillaries.
Why is velocity low in the capillaries?
To allow proper nutrient exchange.
What is the formula for area?
Area = πr²
What happens to volumetric flow when area increases at a fixed velocity?
Flow increases.
What happens to flow when mean velocity increases?
Flow increases.
What is the continuity equation?
Q = Mean velocity × Area
What does Poiseuille's Law describe?
Steady laminar flow and pressure-flow relationships.
Which factor has a major effect on flow in Poiseuille's Law?
Radius.
Why does radius greatly affect flow?
It is raised to the fourth power.
What are assumptions of Poiseuille's Law?
Rigid tube, steady laminar flow, and Newtonian fluid.
What is the problem with applying Poiseuille's Law to blood vessels?
Blood vessels stretch when pressure increases.
What is hemodynamic resistance?
Resistance to blood flow.
How can resistance be calculated?
Pressure drop ÷ flow.
What mainly causes changes in resistance in the circulatory system?
Changes in vessel radius.
What happens to resistance when viscosity increases?
Resistance increases.
What happens to resistance when radius decreases?
Resistance increases.
What happens to resistance when vessel length increases?
Resistance increases.
What is the simplified Poiseuille relationship?
ΔP = Q × R
What happens to total resistance with multiple stenoses in series?
Total resistance increases.
What happens to overall resistance when more parallel pathways are added?
Overall resistance decreases.
What is peripheral resistance?
The resistance created mainly by small arteries and arterioles.
What factors affect total peripheral resistance?
Arteriole diameter, blood viscosity, and vessel length.
What is the MAP equation?
MAP = Cardiac Output × Total Peripheral Resistance
What does low peripheral resistance mean?
High flow.
What does a low-resistance vascular bed do?
It allows more blood flow.
Where are low-resistance waveforms commonly seen?
Brain, organs, or areas with high demand.
What does high peripheral resistance mean?
Lower flow.
What causes high-resistance flow?
Slight vasoconstriction of distal arterioles.
Where are high-resistance waveforms commonly found?
Vessels that perfuse muscles.
What type of flow occurs in high-resistance states?
Pulsatile flow.
What happens to resistance during exercise?
It decreases.
Why does resistance decrease during exercise?
Vasodilation occurs.
What happens to blood flow during exercise?
It increases to meet metabolic needs.
What is compliance?
The ability to hold a change in volume per pressure.
What is high compliance?
Large increase in volume with a small increase in pressure.
What is low compliance?
Small increase in volume with a large increase in pressure.
What is steady flow?
Constant volumetric flow.
What is pulsatile flow?
Volumetric flow that changes over time.
Steady flow is associated with what resistance?
Low resistance.
Pulsatile flow is associated with what resistance?
High resistance.
What is laminar flow?
Streamlined flow in a cylindrical tube.
What is plug flow?
Blood cells moving at approximately the same velocity.
What is parabolic flow?
Flow where the center moves faster than the edges.
Why does blood move slower near vessel walls?
Friction against the vessel walls.
What is friction?
Resistance between layers of blood or between blood and the vessel wall.
What happens to friction when vessel radius decreases?
Friction increases.
Where should the PW Doppler sample gate be placed?
In the center of the vessel.
What does a large sample volume produce?
A wide spectrum with spectral broadening.
What does a small sample volume produce?
A narrow spectrum with minimal spectral broadening.
When does plug flow occur?
During flow acceleration in systole and at the vessel origin.
What is non-laminar flow?
Flow that deviates from laminar flow.
What are examples of non-laminar flow?
Helical flow, flow separation, and vortices.
What can cause disturbed flow?
High flow rate, branching, turning, or an obstruction.