Principles of haemodynamics

Question 1

What is haemodynamics

Answer 1

The relationship between blood flow, blood pressure and resistance to flow

Question 2

Blood flow

Answer 2

Volume of blood flowing in each time

Question 3

Perfusion

Answer 3

Blood flow per given mass of tissue

Question 4

How is Velocity of blood flow affected

Answer 4

Blood flow affected by the cross sectional area through which the blood flows.
So flow may remain the same but velocity changes if there has been a change in cross sectional area

Question 5

Relationship of blood velocity and cross sectional area

Answer 5

Greater cross sectional area = slower velocity

Question 6

Laminar blood flow

Answer 6

Most arteries, arterioles, venules, veins
0 velocity at walls (molecular interactions)
Maximum velocity at the centre
Moves RBCs towards the centre. Speeds up blood flow through narrow vessels

Question 7

Turbulent blood flow

Answer 7

Ventricles (mixing), aorta (peak flow), atheroma (bruits)
Blood does not flow linearly and smoothly in adjacent layers (whirlpools, eddies, vortices) due to increased pressure and velocity
High resistance to flow

Question 8

Bolus

Answer 8

Capillaries
RBCs have a larger diameter of capillaries so move in single file
Uniform velocity, little internal friction and very low resistance

Question 9

Reynolds number

Answer 9

Describes the change from laminar to turbulent

Turbulence occurs when Reynold’s number exceeds a value (>2000)

Question 10

Factors that affect arterial blood pressure

Answer 10

Cardiac output
Properties of arteries
Peripheral resistance
Blood viscosity

Question 11

Arterial blood pressure involves interactions between 4 key relationships

Answer 11

Systolic pressure = pressure when ejecting
Diastole pressure = pressure when relaxing
Pulse pressure = difference between diastolic and systolic pressure
Mean blood pressure = average pressure

Question 12

Describe the arterial blood pressure during LV ejection

Answer 12

60-80% of stroke volume is stored in aorta and arteries because they expand
Energy stored in stretched elastin

Question 13

Describe the arterial blood pressure during LV diastole

Answer 13

Energy returned to blood as walls of aorta and arteries contract
Sustains diastolic blood pressure and blood flow when heart is relaxed

Question 14

Pulse pressure

Answer 14

Tells you about stroke volume and arterial compliance (stretchiness)
Pulse pressure = stroke volume/compliance

Question 15

Compliance

Answer 15

Compliance = change in volume/ change in pressure
Stretchiness
If it’s low the pulse pressure will be high

Question 16

Rest vs excercise

Answer 16

Greater stroke volume
Greater stretch of arteries
Less compliant
Relatively greater systolic pressure

Question 17

During exercise what happens to pulse pressure and stroke volume

Answer 17

More blood is ejected = less compliance and less recoil and difference between systole and diastole increases
PULSE PRESSURE INCREASES
BIGGER PULSE PRESSURE - WHEN STROKE VOLUME RAISED

Question 18

Arterial compliance

Answer 18

Decreased compliance (steeper curve) stroke volume increases systolic and pulse pressure disproportionally 
stiffer arteries (ATHEROSCLEROSIS) = decreased compliance

Question 19

What happens to pulse pressure between aorta and arterial tree

Answer 19

Increases because vessels become less compliant

Question 20

What controls mean blood pressure

Answer 20

Age
Disease
Distance along arterial tree
Blood volume & excercise - SV, CO
Emotion - stress, anger, fear, apprehension, pain
Wake/sleep