Haemodynamics Flashcards
What is haemodynamics? [1 mark]
The relationship between blood flow, blood pressure and resistance to flow.
What is Darcy’s law? [2 marks]
- It describes the rate at which a fluid flows through a permeable medium
- Considers the role of pressure energy in flow
What is the formula for Darcy’s law? [3 marks]
Flow (Q) = (Pressure difference between arteries and veins)/Resistance to flow
What is Bernoulli’s law? [2 marks]
- States that an increase in the speed of a fluid occurs simultaneously with a decrease in pressure/potential energy
- Considers the role of pressure, kinetic and potential energy in flow
What can explain blood moving against the pressure gradient? [1 mark
Bernoulli’s law
What is the formula for Bernoulli’s law? [4 marks[
Flow = Pressure (PV) +Kinetic ((ρV^2)/2) + Potential (ρgh)
What is blood flow? [1 mark]
The volume of blood flowing in a given time (ml/min).
What is perfusion? [1 ark]
The blood flow per given mass of tissue (ml/min/g).
What is velocity of blood flow affected by? [2 marks]
- Cross sectional area
- Smaller CS = faster velocity
(and vice versa)
What is the formula for volume flow [3 marks]
Volume flow (Q) = Velocity (V) x Cross sectional area (A)
What happens in laminar blood flow? [5 marks]
- Smooth flow
- Friction between H2O molecules and blood vessels
- Concentric shells
- Zero velocity at walls
- Max. velocity at the centre
What does laminar blood flow do to RBCs and blood? [2 marks]
- Moves RBCs to the centre
- Speeds up blood flow
Where does laminar blood flow occur? [2 mars]
- Arteries and arterioles
- Veins and venules
What happens in turbulent blood flow? [2 marks]
- Blood does not flow linearly and smoothly in adjacent layers.
- There are whirlpools, eddies, vortices.
What causes turbulent blood flow? [2 marks]
- Increased pressure
- Increased velocity
(due to obstruction)
Where can you get turbulent blood flow? [3 marks]
- Ventricles at mixing
- Aorta at its peak flow
- Atheroma (plaque that cause bruits)
What happens in bolus blood flow? [3 marks]
- Uniform velocity
- Little internal friction
- Very low resistance
What happens to RBCs in bolus blood flow? [3 marks]
- RBC are larger than capillaries
- So they move in single file
- Plasma columns are trapped between RBC
Where does bolus blood flow occur? [1 mark]
Capillaries
What does Reynold’s number tell us? [2 marks]
- When flow changes from lumbar to turbulent
- At around 1000-2000
What is the formula for Reynold’s number? [3 marks]
Re=ρVD/μ
Re = (density x velocity x diameter)/viscosity
Why is the systolic pressure not 0? [1 marks]
Arteries keep expanding and contracting
What factors affect arterial blood pressure? [4 marks]
- Cardiac output (SV, HR) – increases it
- Properties of arteries
- Peripheral resistance
- Blood viscosity
What is pulse pressure? [2 marks]
- The difference between diastolic and systolic pressures.
- Tells you about the stroke volume and arterial compliance
What is the dicrotic notch? [1 mark]
Closure of aortic valves
What is the formula for pulse pressure? [3 marks]
Pulse pressure = (Stroke volume)/compliance
What is compliance? [1 mark]
A measure of how easily the heart can be distended
What happens in decreased compliance? [3 marks]
- Systolic and pulse pressure increase disproportionally
- Because aorta can’t stretch anymore
- Afterload increases
What diseases can arise from decreased arterial compliance? [2 marks]
- Strokes
- Aneurysms
What is the formula for compliance? [3 marks]
Compliance = (Change in volume)/(Change in pressure)
OR
Pulse pressure = (Stroke volume)/compliance
What can cause decreased arterial compliance? [2 marks]
- Old age (stiff arteries)
- Obesity
How do you find the mean blood pressure? [3 marks]
Diastolic pressure + 1/3(pulse pressure)
What controls mean blood pressure? [9 marks]
- Age
- Disease
- Distance along arterial tree
- Blood volume - SV, CO
- Exercise - SV, CO
- Emotion - stress, anger, fear, apprehension, pain
- Wake/sleep - low BP 80/50 mmHg
What is the pulse pressure like at the aorta? [1 mark]
Small
What happens to pulse pressure as you go down the arterial tree? [2 marks]
- Increases slightly
- Vessels become less compliant
