Haemodynamics Flashcards
(30 cards)
Describe normal blood flow
Laminar and predictable
What causes turbulent blood flow
Occlusive disease
Equation for volume flow
Q = vA
Volume of blood p/second = velocity x area
Q volume/time
v velocity
A area
What happens to RBC velocity at a narrowing?
Increases
What happens to velocity if area decreases
Velocity increases
What happens to velocity if are increases
Velocity decreases
What % stenosis leads to a drop in pressure?
50%
What happens to perfusion if flow is reduced
Reduced perfusion of flow is reduced
How to calculate % stenosis with Doppler ultrasound
Measure changes in velocity
Why might ABPI <1
Proximal disease such as stenosis
Describe the normal flow in arteries
High pressure
Pulsatile and determined by heart rate and Q
Elastic walls help propel blood volume
How do veins accommodate large volumes of blood
Collapse and distend
Use of elastic walls in arteries
Aid pulse propagation, and flow
This modifies waveforms
How to determine vein from artery on US
Veins are compressible unless thrombus is present
Describe blood flow in veins
One way
Valves
Affected by gravity
Effects of impaired venous return
Cause dilation of veins or transfer of fluid to interstitial spaces (oedema)
What aids venous return
Calf pump
Valves open when calf contracts
What causes varicose veins
If veins are incompetent, valves don’t work correctly and cause reflux
What do Doppler waveforms plot
Velocity not flow
What is on the axis of the waveforms
X time
Y velocity of RBC
What is a triphasic waveform
One up followed by a negative and another small positive deflection
Common in young people due to reflections from distal branches and elasticity of vessel walls
What does a damped waveform suggest
Poor flow
Systolic component of waveform is very sensitive to proximal disease
What does a proximal pulsatile waveform and distal damped waveform suggest
Disease somewhere between to areas scanned
