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
