Hemodynamics Flashcards
What is the equation for simple blood flow?
change in pressure/Resistance
What is Poiseuille’s law
check
what is a way of defining resistance?
Change in pressure/ flow
What is the rearrangement of Poiseuille’s law when resistance is substituted as change in pressure/flow
check
What do flow and resistance depend on
Change in pressure, length of vessel, viscosity of fluid but huge dependence on radius of vessel
What are 5 assumptions that Ps law makes
- The blood flow is laminar
- The blood flow is consistent and not pulsatile
- The blood vessel is rigid, unbranched and with a consistent radius
- The viscosity of the fluid must be consistent
- The fluid must be incompressible
What happens if tissue pressure drops
causes the collapse of some vessels - at the critical closing pressure
What is transmural pressure? - Laplace’s law
The change in pressure between inside the vessel and just outside the vessel
P=tension/radius - tension = (P.internalradius)/wall width
What is an aneurysm
A swelling of blood - internal radius increases - wall width decreases so tension decreases (Laplace’s law) - Is the vessel can no longer produce the level of tension required a blowout (burst) may occur - positive feedback mechanism - increased tension leads to more vessel damage….
What is compliance
The change in volume/ change in pressure
What is a compliant vessel
One that can produce a large change in volume for a small change in pressure
Which are more compliant: veins or arteries
Veins - store more blood - act as capacitance vessels - post mortem blood tends to pool in veins
How is the blood flow in the aorta described
Pulsatile and discontinuous - Periods of time where there is zero flow followed by peaks and troughs
Where else is pulsatile flow seen
Renal artery - but it never hits zero
seen in arteries supplying major organs
Why is discontinuous/ pulsatile flow seen in arteries supplying the main organs
Mainly due to the elastic aorta region - Elastic tissue stretches and stores energy - once the pressure begins to drop the tissue recoils. Energy in the tissue has to go somewhere so provides an extra pumping action for the movement of blood
What is the equation for reynolds number
check
What R number dictates laminar flow of blood
<2000
What R number dictates turbulent flow of blood
> 3000
