S1) Haemodynamics

Question 1

What is haemodynamics?

Answer 1

Haemodynamics is the study of how pressure affects blood flow in blood vessels

Question 2

Define infarction

Answer 2

Infarction is tissue death due to inadequate blood supply

Question 3

Distinguish between the blood flow to different tissues of the body:

• Brain
• Kidneys
• Heart
• Skeletal muscle
• Gut

Answer 3

• Brain needs high, constant flow
• Kidneys need high, constant flow
• Heart muscle needs high flow which can vary
• Blood flow to skeletal muscle increases during exercise
• Blood flow to gut increases after a meal

Question 4

What is perfusion rate?

Answer 4

Perfusion rate is the rate of blood flow (l.min^-1)

Question 5

Increases in metabolism are met by increases in blood flow.

Compare and contrast the perfusion rate at rest and during exercise

Answer 5

• At rest - total blood flow is about 5 l.min^-1
• During exercise - total blood flow can rise to 25 l.min^-1

Question 6

State the factors that affect the rate of diffusion

Answer 6

• Area available for exchange
• Diffusion resistance
• Concentration gradient

Question 7

Describe what determines the area available for exchange in diffusion

Answer 7

• Area available for exchange between capillaries and tissues depends on capillary density
• A tissue which is more metabolically active will have more capillaries & a higher capillary density

Question 8

Identify the 3 factors which affect diffusion resistance

Answer 8

• Nature of the molecule
• The barrier
• Distance

Question 9

Describe what determines the concentration gradient in diffusion

Answer 9

The perfusion rate determines the concentration gradient driving O₂ diffusion into the cells

Question 10

What is pericardial effusion?

Answer 10

Pericardial effusion is when excess fluid accumulates in the pericardial cavity, compressing the heart due to the inextensible fibrous pericardial layer

Question 11

What is the danger associated with pericardial effusion?

Answer 11

Compression of the heart can lead to cardiac tamponade as the heart cannot fill during diastole

Question 12

How can excess fluid be removed from the pericardial cavity?

Answer 12

Through a procedure called pericardiocentesis, excess fluid is removed for testing / to relieve compression

Question 13

What is coronary circulation?

Answer 13

Coronary circulation is the circulation of blood in the blood vessels of the heart muscle (myocardium)

Question 14

What are coronary arteries?

Answer 14

Coronary arteries are the vessels which deliver oxygen-rich blood to the myocardium

Question 15

What are cardiac veins?

Answer 15

Cardiac veins are the vessels that remove the deoxygenated blood from the myocardium

Question 16

Describe the general origins and location of the left and right coronary arteries and their branches

Answer 16

• Origins: base of the aorta from openings (coronary ostia) located behind the aortic valve leaflets
• Location: lie on the surface of the heart

Question 17

State the specific origins of the left and right coronary arteries

Answer 17

• Right coronary artery rises in the right aortic sinus
• Left coronary artery rises in the left aortic sinus

Question 18

What is the problem associated with coronary arteries?

Answer 18

Coronary arteries are vital to supply well oxygenated blood to the myocardium however, they are prone to atheroma wherein a thrombus forms and can block the artery

Question 19

Which artery is commonly blocked in an AMI and which regions does it supply?

Answer 19

• The anterior interventricular artery (LAD)
• Supplies the apex of the heart, the septum and the left ventricle and a bit of right ventricle

Question 20

Discuss the relationship between pathology in the aortic and mitral valves

Answer 20

• The aortic and mitral valves are closely associated
• Hence, if a disease affects one it will likely affect the other

Question 21

What is serum?

Answer 21

Serum is plasma minus the clotting factors

Question 22

What is the main clotting factor in the body?

Answer 22

The main clotting factor is fibrinogen

Question 23

What are the contents of buffy coat?

Answer 23

Buffy coat contains white blood cells and a few platelets

Question 24

Differentiate between the different types of fluid collected from blood

Answer 24

• The fluid collected from unclotted blood = plasma
• The fluid collected from clotted blood = serum

Question 25

Identify 4 factors which increase whole blood viscosity

Answer 25

- Increase in **plasma** viscosity - **Polycythaemia**: increase in red blood cells - **Leukaemia**: increase in white blood cells - **Thrombocythaemia**: increase in platelets

Question 26

What is the effect of increases in whole blood viscosity?

Answer 26

Increased whole blood viscosity leads to **sludging in the peripheries**

Question 27

Identify the commonest cause for increases in plasma viscosity leading to increased whole blood viscosity

Answer 27

Multiple myeloma

Question 28

In terms of plasma viscosity, how can one attempt to measure inflammation?

Answer 28

- Results from raised levels of **acute phase plasma proteins** *e.g. fibrinogen, complement factors and CRP* which increase in response to **inflammation** - Hence, minor changes in plasma viscosity can be used to ‘measure’ the inflammatory response

Question 29

Explain the difference between flow and velocity of blood

Answer 29

- **Velocity** is the distance blood has moved per unit of time (cm/sec) - **Flow** is the volume of blood that is moving per unit of time (l/min)

Question 30

Explain the difference between laminar and turbulent flow

Answer 30

- **Laminar flow:** blood usually flows in streamlines with each layer of blood remaining the same distance from the wall - **Turbulent flow:** blood flows in all directions in the vessel and continually mixing within the vessel

Question 31

Identify 5 situations wherein turbulent blood flow could happen

Answer 31

- When the **perfusion rate** becomes too great - When the blood passes by an **obstruction** in a vessel - When the blood makes a **sharp turn** - When the blood passes over a **rough surface** - Where there's **increased resistance** to blood flow

Question 32

What is peripheral resistance?

Answer 32

**Peripheral resistance** is the totality of the resistance being posed to the blood pumped from the heart

Question 33

What is the impact of low peripheral resistance?

Answer 33

**Low peripheral resistance** lowers diastolic pressure and therefore increases pulse pressure due to the vasolidation of arterioles *e.g. hot bath, exercise, pregnancy*

Question 34

What is the impact of high peripheral resistance?

Answer 34

**High peripheral resistance** raises diastolic pressure and therefore decreases pulse pressure due to the vasoconstriction of arterioles *e.g. cold, thirsty*

Question 35

What is a pulse?

Answer 35

A **pulse** is a rhythmical throbbing of the arteries as blood is propelled through them, typically as felt in the wrists or neck

Question 36

Differentiate between the terminology for weak and strong pulses

Answer 36

- A weak pulse is often described as “**thready**” - A strong pulse is often described as “**bounding**”

Question 37

Which 2 factors determine the strength (volume) of a pulse?

Answer 37

- The **force** with which the left ventricle is able to eject blood into the arterial system and thus develop a normal shock wave - The **pulse pressure**

Question 38

Identify conditions which lead to a stronger/weaker pulse

Answer 38

- **Weaker pulses** can result from left ventricular failure, aortic valve stenosis, hypovolaemia (severe dehydration, bleeding) - **Stronger pulses** can result from bradycardia seen in conditions such as heart block

Question 39

Explain what Phase I and Phase 5 are when measuring blood pressure

Answer 39

- **Phase 1** – the point at which the first sound appears - **Phase 5** – the point at which the sounds disappear

Question 40

What is pulse pressure?

Answer 40

**Pulse pressure** is peak systolic pressure – end diastolic pressure 120mm Hg – 80 mm Hg = **40mm Hg**

Question 41

Describe the impact of pulse pressure on the volume of the pulse

Answer 41

The greater the pulse pressure the stronger the pulse

Question 42

Define mean arterial pressure

Answer 42

**- Mean arterial pressure** is estimated as diastolic pressure + 1/3 of the pulse pressure - Therefore, most commonly, mean arterial pressure is 80 mmHg + 13 mmHg = 93 mm Hg