Hemodynamics Flashcards
Is blood a compressible fluid?
No
What is flow?
Volume per unit of time
What is velocity?
The rate of displacement per unit of time
Ex: blood travels 1m/sec in an artery
If flow through a tube is constant, then velocity ______ as cross sectional area decreases
Increases
Ex: shooting the rapids vs entering a lake
If you decrease the cross sectional area by a factor of 5, what happens to the velocity?
Increases by a factor of 5
V=Q/A
Why is the velocity through the capillaries slower than through the aorta? They have a way smaller diameter!
Because the TOTAL cross sectional area of all of the capillaries in the body is much much bigger than the cross sectional area of the aorta
What is it:
Resistance to flow by a substance as a result of molecular cohesion
Viscosity
What are the major determinants of blood viscosity?
Proteins
RBCs
Temperature
If you double resistance, what happens to flow?
Gets cut in half
If you double the length of a tube, what happens to flow?
Gets cut in half
If you double the radius of a tube what happens to flow?
Gets increased to the 4th power
What are the assumption we make when we calculate blood flow using poiseuilles law?
- Non-pulsatile flow
- Homogenous fluid
- Rigid tubes
(NONE of these are true for blood)
What is it:
Concentric lamina sliding past one another
Laminar flow
What kind of flow has eddy currents and is noisy?
Turbulent
In laminar flow, where is the velocity fastest?
The center of the tube
Lamina at the wall of the tube are actually moving very slow
What can cause turbulence/eddies
Increased pressure and flow
Do you need larger pressure to maintain constant flow through turbulent areas?
Yes
What are examples of turbulence that we can hear?
Korotkoff sounds
Valve defects causing bruits or murmurs
Does high compliance dampen pulsatile flow?
Yes
