Principles Of Haemodynamics

Question 1

What is haemodynamics?

Answer 1

Relationship between blood flow, blood pressure and resistance to flow

Question 2

What are the key factors in haemodynamics (and how does each affect it?)?

Answer 2

• force (cardiac contraction)
• work (isovolumetric contraction/ ejection)
• pressure (difference between aorta and veins)
• compliance (arterial stretch)
• resistance (arterioles)
• flow velocity (slowing down blood flow in capillaries)

Question 3

What happens in the rest of the body if there is reduced blood flow to the other parts?

Answer 3

The blockage reduces pressure upstream which alters flow to other areas

Question 4

What is a portal system?

Answer 4

When one bit of blood goes through multiple capillary beds

Question 5

Examples of a portal vein?

Answer 5

Hepatic portal vein

Question 6

What does darcy’s law deal with?

Answer 6

Role of pressure energy in flow

Question 7

What is darcys law?

Answer 7

Flow = difference in pressure/ TPR

Question 8

What does Bernoulli’s law deal with?

Answer 8

Role of pressure, kinetic and potential energies in flow

Question 9

What is blood flow?

Answer 9

Volume of blood flowing in a given time (ml/min)

Question 10

What is perfusion?

Answer 10

Blood flow per given mass of tissue (ml/min/g)

Question 11

What is the velocity of blood flow?

Answer 11

Blood flow (cm/s) affected by the cross sectional area through which the blood flows

Question 12

What are the three patterns of blood flow?

Answer 12

Laminar, turbulent and bolus

Question 13

Where does laminar flow happen?

Answer 13

Most arteries, arterioles, venules and veins

Question 14

Where does turbulent blood flow happen?

Answer 14

Ventricles (mixing), aorta (peak flow) and atheroma (bruits)

Question 15

Where does bolus blood flow happen?

Answer 15

Capillaries

Question 16

What is laminar flow?

Answer 16

• Blood moves in concentric shells
• there is zero velocity at the walls and maximum velocity at the centre
• this speeds up blood flow through narrow vessels

Question 17

What is turbulent blood flow?

Answer 17

• blood doesnt flow linearly and in smooth layers
• forms whirlpools and vortices due to increased pressure and velocity
• high flow resistance

Question 18

What is bolus flow?

Answer 18

• RBCs have a larger diameter than the diameter of capillaries so move in single file
• plasma columns are trapped between RBC
• uniform velocity, with little internal friction and very low resistance

Question 19

What does Reynolds number describe?

Answer 19

What determines change from laminar to turbulent flow

Question 20

When does turbulence occur?

Answer 20

When Reynolds number exceeds >2000

Question 21

What is arterial pressure generated by?

Answer 21

Left ventricular contraction

Question 22

What are your systolic and diastolic pressures?

Answer 22

Systolic = Pressure when ejecting 
diastolic = pressure when relaxing

Question 23

What is pulse pressure?

Answer 23

Difference between diastolic and systolic blood pressure

Question 24

What does pulse pressure tell you about?

Answer 24

Stroke volume and arterial compliance

Question 25

What does low compliance mean about pulse pressure?

Answer 25

High pulse pressure

Question 26

What happens in arteries during exercise?

Answer 26

Greater stretch as more blood is ejected

Leads to less compliance and less recoil and the difference between systole and diastole increases (pulse pressure increases)

Question 27

What is the formula for mean BP?

Answer 27

Diastolic pressure + 1/3 (pulse pressure)

Question 28

What controls blood pressure (7)?

Answer 28

Age
Disease
Distance along arterial tree
Blood volume
Exercise
Emotion
Wake/sleep