Haemodynamics

Question 1

How does the heart affect flow through the vessels

Answer 1

Heart creates high pressure in the major arteries
This is much higher than the pressure in the veins, resulting in flow

Question 2

Show the equation for flow, related to pressure and resistance

Answer 2

Q = (Pa - Pv) / R

Question 3

How do vascular dimensions relate to resistance

Answer 3

Poiseuille’s equation
R = (8Lu)/pi r^4

Increases in radius of vessel results in significant drop in resistance and therefore significant reduction increase in flow

Question 4

How can Doppler assess for stenosis?

Answer 4

Increased blood velocity within and immediately downstream from the affected area
Spectral broadening in the immediate post-stenotic portion of the vessel, due to turbulent flow

Question 5

How can Doppler be used to assess the pressure drop across a stenosis?

Answer 5

Change in pressure = 4 (v^2 - v^1)

Question 6

Continuity equation

Answer 6

Blood is not created, nor destroyed. Therefore, flow must be the same at all parts in the same circulation

v1 x A1 = v2 x A2

Question 7

Resistance index

Answer 7

RI = (Systolic - Diastolic) / Systolic

Question 8

Pulsatility index

Answer 8

PI = (Systolic - Diastolic) / Mean

Question 9

Velocity profiles

Answer 9

Usually parabolic within vessels due to slower flow adjacent to vessel walls
Velocity profile can be disturbed by changes in flow due to vessel architecture

Larger sample volumes will detect spectral broadening