haaemodynamics Flashcards
what does Haemodynamics mean?
the physical laws governing the pressure relationships in blood vessels
what is the equation between flow, pressure and resistance?
flow=difference in pressure (between arteries and veins) / resistance
which blood vessels have the highest velocity?
the aorta have the highest velocity, the capillaries have the lowest velocity.
order the different blood vessels from smallest to largest cross sectional area?
aorta < arteries< arterioles< veins< venules< capillaries
why does the capillaries have the largest collective cross sectional area, when the aorta has the largest individual cross sectional area?
as there are a lot more capillaries whereas one aorta. so all the cross sectional areas of the capillaries added together is larger than the aorta.
what is the equation for velocity?
velocity=flow/total cross sectional area.
or
velocity=distance/unit time
what equation does Darcy’s law of flow produce?
flow is directly proportional to pressure difference between arteries and veins.
flow is inversely proportional to resistance.
so:
flow = difference in pressure / resistance.
how is flow related to length of tube.
flow is inversely proportional to length of tube.
how is flow related to viscosity of fluid?
flow is inversely proportional to viscosity of fluid
how is flow related to radius?
flow is inversely proportional to radius^4
is the pressure difference between arteries and veins increases, what happens to the flow speed?
there is greater flow, if there is a greater pressure gradient
if there is a longer blood vessel, what happens to the speed of flow?
the Flow is lower/slower as the length of the blood vessel increases.
if the fluid has increased viscosity, what happens to the flow speed?
the flow is lower if the fluid is more viscose.
if the radius of the vessel if greater, what happens to the speed of flow?
there is a greater flow speed if the radius is greater.
what is the resistance of the blood vessel mostly determined by?
by radius, as in human blood Vessels the length of blood vessels, and viscosity of blood remain mostly constant.
so the resistance is largely determined by radius.
which vessels has the most potential to change radius and why?
small arteries and arterioles as they have a lot of smooth muscle to carry out vasodilation or vasoconstriction.
small arteries and arterioles are resistance vessels.
between which vessels is the biggest drop in pressure?
between small arteries and arterioles as they are resistance vessels.
what are resistance vessels?
small arteries and arterioles as they have the role of slowing down blood flow due to their smaller lumen.
what’s the difference between laminar flow and turbulent flow?
the laminar flow is flowing uniformly through the blood vessel, so the velocity is at max. through the centre of the vessel.
turbulent flow is flowing non-uniformly and need a higher pressure to achieve the same flow.
how do you define compliance?
the change in volume for a give change in pressure.
what is the function of arterial compliance vs. venous compliance?
arterial compliance has the purpose fo smoothing out the blood flow. the venous compliance has the purpose of providing a larger human or capacity to carry more blood.
why do some veins need to be constricted?
by reducing the venous capacity, it encourages blood return to the heart. so it improves the circulating blood volume
how does the skeletal muscles in legs help venous blood return?
it uses the skeletal-muscle pump.
this is when the skeletal muscles compress the underling veins to encourage blood flow back to the heart.
how does inspiration encourage venous blood return to heart?
intra-thoracic pressure- decreases during inspiration and volume increases.
intra-abdominal pressure- increases during inspiration. so creates a pressure gradient so blood is encourages to travel upward.
