3 - Haemodynamics

Question 1

What is the difference between plasma and serum?

Answer 1

Serum is plasma without the clotting factors

Question 2

What is polycythaemia?

Answer 2

Excess red blood cells leading to increased blood viscosity

Question 3

What is thrombocythaemia?

Answer 3

Excess platelets leading to increased blood viscosity

Question 4

What is leukaemia?

Answer 4

A cancer which starts in blood-forming tissue, usually the bone marrow. It leads to the over-production of abnormal white blood cells

Question 5

Whole blood viscosity changes are uncommon (e.g. polycythaemia), minor changes to viscosity of the plasma are more typical. What plasma proteins typically change?

Answer 5

• Fibrinogen
• Compliment
• C-reactive protein (CRP)

Question 6

What vessel has the largest diameter lumen?

Answer 6

Vena cava

Question 7

What vessel has the highest thickness wall?

Answer 7

Aorta

Question 8

What type of liquid flow is found in the majority of blood vessels? Describe this type of flow?

Answer 8

Laminar flow

Smooth, fast flow (fastest in the centre due to more resistance around the edges of the vessel). Most energy efficient.

Question 9

What causes turbulent flow?

Answer 9

An obstruction/constriction in the vessel, leading to disorganised flow after the obstruction. Energy is lost.

E.g. stenosed arteries, changing direction of vessels (branching)

Question 10

In laminar flow, flow is …….. ……………. to perfusion pressure.

Answer 10

Directly proportional

Question 11

The point at which laminar flow becomes turbulent flow as pressure increases is called the critical ………….. number.

Answer 11

Reynolds

Question 12

What is the SI unit of pressure?

Answer 12

Pascal

Question 13

What is conductance?

Answer 13

Measure of the ease of flow

Question 14

What is resistance?

Answer 14

Measure of the difficulty of flow, reciprocal of conductance.

Question 15

What is the relationship between flow, pressure and resistance (Darcy’s Law)?

Answer 15

Flow = ΔP / R

ΔP = pressure gradient

Question 16

When blood supply to an organ needs to be changed how is flow altered?

Answer 16

• By changing the vascular resistance.

- Blood pressure does not change

Question 17

What factors affect vascular resistance?

Which is most important physiologically?

Answer 17

• Diameter of vessel
• Length of vessel
• Viscosity of blood

Vessel length and viscosity don’t change so diameter is the most important.

Question 18

The radius of a vessel has a large impact on flow. Flow is proportional to radius to what power?

Answer 18

4

Flow α r^4

Question 19

In which artery is resistance the lowest?

Answer 19

The aorta - large diameter and relatively short

Question 20

Which vessels contribute the most to total peripheral resistance?

Answer 20

The arterioles

• Play the biggest role in resistance of the systemic circulation
• Biggest drop in pressure

Question 21

Resistance in the pulmonary circulation is ………. than in the systemic system. Why is this?

Answer 21

Lower - due to shorter and wider vessels

Question 22

How is flow related to the velocity of the blood in the vessel?

Answer 22

F = V x A

• A is the cross-sectional area of the vessel
• In constant flow, V is inversely proportional to r^2

Question 23

Velocity of blood flow depends on the total ………………… ……….

Answer 23

Cross-sectional area

Question 24

In what type of vessel is blood flow the slowest?

Answer 24

The capillaries

• Very large cross-sectional area
• Velocity is reduced and increases again as they merge into veins

Question 25

What is the pulse pressure?

Answer 25

Systolic BP - diastolic BP

Question 26

How is mean arterial pressure calculated?

Answer 26

Mean arterial pressure = diastolic BP - (pulse pressure / 3) - Time-weighted mean

Question 27

How is mean arterial pressure related to cardiac output and total peripheral resistance?

Answer 27

MAP = CO x TPR

Question 28

How is cardiac output calculated?

Answer 28

Heart rate x Stroke volume

Question 29

What factors affect the pulse pressure?

Answer 29

- Volume of blood ejected (stroke volume) | - Compliance (stretch) of the arterial system

Question 30

During exercise, what changes to increase the pulse pressure?

Answer 30

Stroke volume increases

Question 31

What is the effect on pulse pressure of: a) Haemorrhage? b) Age?

Answer 31

a) blood volume loss = decreased PP | b) atherosclerosis reduces compliance of vessels - less stretch to account for the pressure change = increase PP

Question 32

What is the pulse?

Answer 32

The shock wave that arrives slightly before the blood in a vessel

Question 33

An increased pulse pressure is described as having a ............... pulse

Answer 33

Bounding

Question 34

What can cause a bounding pulse?

Answer 34

- Heart block (reduced electrical transmission between atria and ventricles) - bradycardia - Vasodilation - decreases peripheral resistance (occurs in pregnancy) - Elite athletes - systolic BP increases and diastolic BP decreases (large PP)

Question 35

In pathological turbulent flow, what is the effect on: a) velocity? b) flow?

Answer 35

a) Velocity increases | b) Flow decreases

Question 36

In terms of turbulent flow is vessels, what is: a) Thrill? b) Bruit?

Answer 36

Thrill - the feeling of turbulent flow Bruit - the sound in the vessel of turbulent flow

Question 37

When measuring blood pressure, turbulent flow is created intentionally by compressing a vessel. What type of sounds can be heard?

Answer 37

Korotkoff sounds

Question 38

What is the name for a blood pressure cuff?

Answer 38

Sphygmomanometer

Question 39

Which artery is used to auscultate for blood pressure?

Answer 39

Brachial artery

Question 40

If the blood pressure cuff is too small, what will happen to the estimate of blood pressure?

Answer 40

Will overestimate the blood pressure (too high)

Question 41

If the blood pressure cuff is too big, what will happen to the estimate of blood pressure?

Answer 41

Will underestimate the blood pressure (too low)

Question 42

How should a patient be positioned for blood pressure measurement?

Answer 42

- Taken at rest - Sat comfortably upright, legs uncrossed and feet flat on the floor - Arm supported - Measurement taken at level of the heart

Question 43

What effect does gravity have on blood pressure?

Answer 43

- Pressure below the level of the heart is greater than above - Gravity maintains a pressure gradient that allows blood to flow from the heart to the feet - Pooling of blood occurs in the venous system when standing

Question 44

What is postural hypotension?

Answer 44

- Dizziness upon standing due to transient arterial hypotension - When standing there is a delay in constriction of resistance vessels in the lower body, blood pools in the lower limbs - Less blood returns to the heart causing a transient reduction in cardiac output (Starling's Law) - Less blood is pumped to the brain (dizziness, nausea, fainting)