Session 1: Haemodynamics

Question 1

What does blood contain? (4)

Answer 1

1. Plasma
2. WBCs
3. Platelets
4. RBCs

Question 2

What does an increase in plasma viscosity lead to and why?

Answer 2

Increased whole blood viscosity and sludging of blood in peripheries - colder in the peripheries

Question 3

What is the comments cause of increased plasma viscosity?

Answer 3

Multiple myeloma (cancer of plasma cells)

Question 4

What leads to whole blood viscosity? (4)

Answer 4

1. Increase in plasma viscosity - caused by multiple myeloma
2. Polycythaemia (increase in RBCs)
3. Thrombocythaemia (increase in platelets)
4. Leukaemia (increase in WBCs)

Question 5

What is peripheral resistance?

Answer 5

Determined by the state of contraction of resistant arterioles

Question 6

What can minor changes in plasma viscosity measure?

Answer 6

Inflammatory response

Question 7

What can minor changes in plasma viscosity result from?

Answer 7

Raised levels of acute phase plasma proteins eg fibrinogen, complement factors, C-reactive protein

Question 8

What is characteristic of blood flow in vessels? (Type of flow)

Answer 8

Laminar flow

Question 9

What is laminar flow?

Answer 9

Blood flows in streamlines layer of blood remaining the same distance from the wall

Question 10

Describe the velocity of blood when in laminar flow?

Answer 10

Velocity of blood is greater in the centre of the vessel than that toward the outer edge (parabolic profile)

Question 11

When does turbulent flow of blood occur? (5)

Answer 11

1. When the rate of blood flow becomes too great
2. Occlusion/stenosis
3. Sharp turn in the vessel
4. Blood passes a rough surface
5. Increased resistance to blood flow

Question 12

What units are used to measure flow?

Answer 12

Volume per unit time

Question 13

What is characteristic of a compliant vessel?

Answer 13

Its blood volume will change in response to a change in pressure

Question 14

What happens to flow when there is narrowing (stenosis) in a vessel?

Answer 14

Decreases (remember volume per unit time)

Question 15

What happens to the velocity of blood in a stenotic vessel?

Answer 15

Increases

Question 16

What happens in a vessel when there are consecutive stenoses?

Answer 16

Pressure decreases after every stenosis - two consecutive stenosis could stop flow altogether

Question 17

What is critical limb ischaemia?

Answer 17

Consecutive stenoses in arteries in the limb resulting in reduced or no blood flow

Question 18

What happens to an artery following a stenosis?

Answer 18

Post-stenotic dilatation (aneurysm)- increased velocity and therefore energy of blood causes walls to stretch

Question 19

What is clinically relevant about calcified arteries in the elderly?

Answer 19

Pulse cannot be felt

Question 20

What is an aortic thrill?

Answer 20

Vibration felt near stenotic aorta

Question 21

On a descending aorta pressure tracing graph, what does the dicrotic notch denote? (3)

Answer 21

1. Aortic valve shuts
2. Systole ends
3. Diastole begins (ventricles start to relax - pressure drops)

Question 22

What is pulse pressure?

Answer 22

Difference between peak systolic pressure and end diastolic pressure (120-80=40mmHg)

Question 23

How can mean arterial pressure be estimated?

Answer 23

Diastolic pressure + 1/3 pulse pressure (usually 93 mmHg)

Question 24

A patient’s mean arterial pressure was measured - <70 mmHg. What does this value signify?

Answer 24

Organ perfusion will impaired

Question 25

When is retrograde flow in the arterial system greatest?

Answer 25

When peripheral resistance is high - blood ‘bounces’ back

Question 26

What determines the strength of the pulse? (2)

Answer 26

1. Pulse pressure (main determinant)

2. Force with which the left ventricle ejects blood into arterial system

Question 27

What are the possible causes of a weak/’thready’ pulse? (3)

Answer 27

1. Left-ventricular failure
2. Aortic valve stenosis
3. Hypervolaemia (severe dehydration, bleeding)

Question 28

What is the principle behind a stronger pulse?

Answer 28

Increase in pulse pressure as a result of a decrease in end-diastolic pressure

Question 29

What are the possible causes of a strong/’bounding’ pulse? (2)

Answer 29

1. Bradycardia

2. Low peripheral resistance - hot bath, exercise, pregnancy

Question 30

How does bradycardia result in a bounding pulse?

Answer 30

Each systole starts later, which gives diastole more time to occur - end-diastolic pressure goes down (seen on pressure trace)
Pulse pressure widens

Question 31

How does low peripheral resistance result in a bounding pulse? (Hint: think of pressure trace)

Answer 31

Vasodilatation of arterioles - less resistance means blood flows out to peripheral circulation more quickly
Pressure trace - diastolic decline becomes steeper; before the next pulse comes in, diastolic pressure has gotten lower

Question 32

What is the significance of using the right-sized cuff while measuring someone’s BP?

Answer 32

Wrong cuff can give a falsely hypertensive reading

Question 33

How does gravity affect arterial and venous pressure when standing?

Answer 33

1. Arterial pressure - if BP measured on arm placed above the heart, pressure decreases (below the heart, increased pressure)
2. Venous pressure - the further away from the heart, the higher the pressure