Week 7 Flashcards
What is the Womersley flow equation used for?
To model time-dependent blood flow in arteries
Important for understanding pulsatile flow.
What is the Windkessel model?
A model used to describe the elastic properties of arterial walls and the storage of blood volume
It helps in understanding the compliance of blood vessels.
What types of blood vessels are there?
- Arteries
- Veins
- Capillaries
Each type has distinct structural and functional characteristics.
What is blood primarily composed of?
A suspension of cells (35-55% cells) in an aqueous fluid (plasma)
Major blood cells include erythrocytes, leucocytes, and platelets.
Define blood viscosity in the context of large arteries.
Blood can be simulated as a Newtonian fluid with a viscosity of approximately 4 mPa s
This simplification is useful for modeling blood flow.
What factors contribute to the complexity of modeling blood flow?
- Highly unsteady and pulsatile flow
- Non-Newtonian properties of blood
*Haemodynamic properties vary with time and space - Vessels with changing diameter and shape
- Deformation of vessel walls
- Wide ranges of scales in blood vessel diameters
These factors complicate accurate simulations.
What does the Reynolds number’s indicate turbulent blood flow?
Transition to turbulent flow starts at Re > 2000
Reynolds numbers vary from approximately 4500 in large arteries to 0.001 in capillaries.
What does the equation of continuity describe in Womersley flow?
It simplifies to show that the only flow component is axial flow
Assumes axial symmetry and neglects gravity.
What are the assumptions made in the derivation of Womersley flow?
- Neglect gravity
- Assume axial symmetry
- Fully developed flow
These assumptions simplify the analysis of blood flow.
What are the components of stress acting on blood vessels?
- Internal pressure (blood pressure)
- External pressure (tissue pressure)
- Circumferential stress
- Longitudinal stress (axial direction)
- Shear stress
Each type of stress affects vessel function.
What are haemodynamic properties?
- Blood pressure
- Blood flow rate
- Blood flow velocity
- Luminal cross-sectional area
- Viscosity
- Resistance
- Compliance
- Blood volume
What is the significance of compliance in the cardiovascular system?
Refers to the ability of blood vessels to expand and contract with changes in pressure
Important for maintaining blood pressure and flow.
What are the main components of the cardiovascular system?
The Heart, The Blood, Blood Vessels
What is Poiseuille Flow?
Highly idealised: does not account for
time and space variations in blood flow
and pressure; assumes blood vessels to
be rigid
What does Womersley Flow describe?
Time-dependent blood flow
What is the Windkessel Model?
A model that describes the compliance and resistance in blood flow
What does ‘Qin’ represent in the Windkessel Model?
Inflow of blood
What does ‘Qout’ represent in the Windkessel Model?
Outflow of blood
What is the equation for compliance (C) in the Windkessel Model?
C = dV/dP
What is the relationship between pressure and compliance (C)?
Increases in compliance (C) lower pulse pressure (PP)
What is the effect of resistance (R) on mean arterial pressure (MAP)?
Increases in resistance (R) raise mean arterial pressure (MAP)
What does the Windkessel equation describe?
The relationship between pressure, volume, and flow in the arterial system
What happens to pressure during diastole according to the Windkessel Model?
Pressure decays exponentially
True or False: The Windkessel Model accounts for the space-variation of haemodynamic quantities.
False
