Haemodynamics I Flashcards
Define haemodynamics.
It is the relationship between blood flow, blood pressure and resistance to flow.
What feature of the CVS can be used to increase CO?
The low pressure venous reservoir system.
What are the 2 equations for Darcy’s Law?
Q = (P1-P2)/R - flow = pressure difference/resistance Flow = (Pa - CVP) / R
What does Bernoulli’s Law tell us?
What is the equation?
The role of pressure, kinetic and potential energies in flow
Flow = pressure (PV) + kinetic (rho x Vsquared/2) + potential (rho x g x h)
rho = fluid mass potential is effect of gravity kinetic is momentum of blood pressure is Pa-CVP
What is blood flow?
What is perfusion?
What is velocity of blood flow?
Volume of blood flowing in a given time (ml/min)
Blood flow per given mass of tissue (ml/min/g)
Blood flow divided by the cross-sectional area through which the blood flows (cm/s)
Where does laminar blood flow occur?
Where is maximum velocity?
Why is this?
Most arteries, arterioles, venules and veins
At the centre of the vessel
Concentric shells close to the walls have interactions with the wall
Where does turbulent blood flow occur?
How does blood flow in this pattern?
Why and what can be determined diagnostically from this type of blood flow?
Ventricles, aorta, atheroma
Whirlpools, eddies, vortices
Due to increased pressure, velocity increases and can cause a murmur - happens in bruit where area decreased
What type of blood flow occurs in capillaries?
Describe this type of blood flow.
Bolus
Single file of RBCs with plasma columns trapped between RBCs
What is Reynold’s number (Re)?
What is the equation associated with this number?
It describes what determines change from laminar to turbulent flow.
Re = rho x V x D / mu rho - density / V - velocity / D - diameter / mu - viscosity
How is BP maintained when the heart is not contracting?
The great arteries contain elastin which enables arteries to be compliant - under pressure they can increase their volume. The recoil of elastic fibers helps propel the blood into circulation.
How is diastolic blood pressure maintained?
Energy stored in stretched elastin. During LV diastole, energy is returned to the blood as the walls of the aorta and arteries contract.
What is the equation for pulse pressure?
Pulse pressure = SV/compliance (stretchiness)
What is significant about the elderly regarding their blood vessels?
Their arteries become stiffer (arteriosclerosis) and so compliance reduces. This means they have a large pulse pressure throughout the arterial tree when it should increase the further away you get from the aorta as vessels get less compliant.
How do you calculate mean BP?
What is a normal value?
Diastolic pressure + 1/3 pulse pressure
93.3mmHg
