Hemodynamics Flashcards
What is hemodynamics?
The physics of blood flow
What is the driving force of bulk flow in the circulatory system?
The heart
What are the 2 things that blood flow depends on?
Pressure differences across the circulatory system and vascular resistance
What is the hematocrit?
Percent of blood volume occupied by red blood cells
What happens to blood pressure as the blood progresses through the circulatory system?
Drops
You stop being able to feel a pulse once the blood reaches which type of blood vessels?
Arterioles
What are the 2 ways a liquid can flow through a tube?
Laminar and turbulent
What is laminar flow?
Smooth flow
What is turbulent flow?
Strong flow
What is the LaPlace law?
Tension on the walls of a blood vessel is proportional to the blood pressure and vessel radius
How does the LaPlace law apply to blood vessels with thin walls?
T = αPr
Shows that wall tension (T), is proportional to blood pressure (P) and vessel radius (r)
How does the LaPlace law apply to blood vessels with thick walls?
σ = Pr/w Wall stress (σ) is proportional to the blood pressure (P) and radius of the vessel (r), but inversely proportional to the wall thickness (w)
What happens to wall stress if wall thickness increases?
Decreases
What is the Law of Bulk Flow?
Fluids move from an area of higher pressure to an area of lower pressure
What creates resistance?
The friction of blood flow through blood vessels, since blood is viscous
What does Poiseuille’s Law describe?
Laminar flow of a fluid through a tube, taking into account the resistance of the tube
What 3 things affect the resistance of a tube?
Length of tube
Viscosity of the fluid
Radius of the tube
In a blood vessel with a small diameter, what happens to the resistance? Why?
High resistance. Smaller tube means increased contact surface area between the tube and the fluid, which means more friction
In a blood vessel with a large diameter, what happens to the resistance? Why?
Low resistance. Larger tube means less contact surface area and lower friction
What is the relationship between resistance and radius?
Resistance is inversely proportional to radius to the 4th power
What effect do small changes in the radius of a tube have on the resistance?
Large changes in resistance
What are the 3 assumptions of Poiseuille’s Law? How does blood flow violate them?
Tube is rigid - blood vessels are not
Flow is laminar - some blood vessels have turbulent flow
Fluid has same viscosity throughout the tube - blood viscosity changes depending on the size of the vessel it’s in
What happens to blood velocity in smaller vessels?
Slows down dramatically
How does blood pressure change across the circulatory system?
High and variable in the left ventricle, still high but more constant in the arteries, starts to drop in the arterioles and keeps becoming more constant and keeps dropping
What is the relationship between blood velocity and cross-sectional surface area?
Blood velocity is inversely proportional to cross-sectional surface area
Which blood vessels have the highest resistance in the circulatory system?
Arterioles
Why do arterioles have the highest resistance in the circulatory system?
They’re relatively narrow compared to the arteries and relatively few in number compared to the capillaries
Which blood vessels are the most important for the distribution of blood flow?
Arterioles
Why does blood flow need to be distributed?
Isn’t enough blood to fill every single capillary at all time
Which two organs will always get a constant supply of blood regardless of how blood is distributed?
Brain and heart
