Haemodynamics

Question 1

What is haemodynamics?

Answer 1

Physical factors that control blood flow

Question 2

What is serum?

Answer 2

Plasma without the clotting factors

Question 3

When can whole blood viscosity change?

Answer 3

• Polycytheamia
• Thrombocytopenia
• Leukaemia

Leads to thick ‘sludgy’ blood and dry gangrene in peripheries

Question 4

When do minor changes to plasma viscosity occur?

Answer 4

Typically from acute phase proteins (fibrinogen, compliment, c-reactive protein)
- Used to measure plasma viscocity as indicator of imflammation

Question 5

What is flow?

Answer 5

• Volume transferred per unit time (L/min, but for blood usually ml/min)

Question 6

What is pressure?

Answer 6

Force per unit area (mmHg used for BP)

Question 7

What is resistance in blood vessels known as?

Answer 7

Vascular resistance

Question 8

How are flow and resistance related in the circulation?

Answer 8

Reciprocally related

Flow and pressure in the circulation pulsate

Question 9

What is laminar flow?

Answer 9

• The smooth, silent, maintaining energy and typical of most arteries, arterioles, venules and veins
• Moves in stream lines

Question 10

What is turbulent flow?

Answer 10

• Disorganised, noisy flow where energy is lost
• Pressure increases in the vessel beyond which flow can match it linearly (called Reynold’s number)
• eg. after stenosis

Question 11

Where does turbulent flow occur?

Answer 11

• Changing directions of vessels (branching)
• In stenosed arteries
• Stenotic heart valves

Question 12

What is stenosis?

Answer 12

Abnormal discrete narrowing of an artery or open area of a heart valve

Question 13

What are the primary factors for resistance to flow?

Answer 13

• Diameter
• Length of vessel
• Viscosity

Physiologically diameter is most important quantitatively as is Poiseuille’s law the radius is to the 4th power so it has a large impact on flow and/or resistance

Question 14

What does a drop in vessel pressure indicate?

Answer 14

• Drop in pressure indicative of a change in resistance across the vessel class
• Resistance in the aorta is low (as they have a large diameter but are really short)
• Smallest arteries and arterioles contribute greatest component if total peripheral resistance

Question 15

What is the formula for pulse pressure?

Answer 15

Pulse pressure = Systolic Blood Pressure - Diastolic Blood Pressure

Question 16

What is the formula for total peripheral pressure?

Answer 16

TPR = mean aortic pressure / cardiac output

Question 17

What is the formula for mean arterial pressure?

Answer 17

Mean arterial pressure = Cardiac output x total peripheral resistance

Question 18

What is the formula for cardiac output?

Answer 18

Cardiac output = Stroke volume x Heart rate

Question 19

What affects pulse pressure?

Answer 19

• Volume of blood ejected and the compliance of the arterial system govern pulse pressure
  INCREASE:
• Increase in stroke volume during exercise with the relative compliance of vessels will cause an increase
  DECREASE:
• Haemorrhage causes a reduction due to reduction in blood return
• Age, atherosclerosis leads to reduced compliance

Question 20

What is the pulse?

Answer 20

Shock wave that arrives slightly before the blood itself

Question 21

What increases pulse pressure and what is it called?

Answer 21

• Described as a ‘bounding’ pulse
• Bradycardia
• Vasodilation causes a decrease in peripheral resistance (eg. hot bath, pregnancy)
• Elite athletes; systolic increased and diastolic decreased

Question 22

How is blood pressure measured?

Answer 22

• Indirect measurement used in modern times
• Convenient, non-invasive, can be carried out with minimal training
• Rely on changes in type of flow from laminar to turbulent to laminar

Question 23

How is blood flow affected by stenosis?

Answer 23

• “Pathological turbulence”
• • Caused by atheroma or stenosed vessel
• Velocity increases though the stenosis and turbulence occurs beyond the stenosis

Question 24

What can be detected in blood pressure readings (felt/heard)

Answer 24

Thrill = felt
Bruit = heard

Question 25

What are the sounds heard in blood pressure readings?

Answer 25

Korotkoff sounds - Changes in laminar to turbulent flow create sounds which can be heard and used to estimate blood pressure - First tapping sounds --> Auscultatory systolic sound - Then Korotkoff sounds (turbulent flow) - Then sound disappears as pressure decreases --> auscultatory diastolic

Question 26

What factors can affect blood pressure estimations by auscultation?

Answer 26

- Cuff size (too small = overestimate blood pressure, too big = underestimate blood pressure) - Positioning of the cuff - Measure in both arms as there is often a difference (higher reference should be used) - Sat comfortably, upright with legs uncrossed and flat on the ground - Arm should be supported Assume the measurement will be taken at the level of the heart and resting

Question 27

What are the effects of gravity on blood pressure?

Answer 27

- Maintains a pressure gradient allowing blood flow from heart to the foot when standing - Pooling of blood occurs below the level of the heart upon standing in the venous system

Question 28

What happens to blood pressure when it is taken above/below the level of the heart?

Answer 28

Below the heart --> Pressure greater | Above the heart --> Pressure reduced

Question 29

What clinical condition is associated with pooling of blood when standing?

Answer 29

Postural hypotension - Dizziness upon standing - Due to reduced stroke volume causing transient arterial hypotension

Question 30

What is the formula for mean arterial pressure?

Answer 30

MAP = Diastolic Blood Pressure + ((Systolic Blood Pressure-Diastolic Blood Pressure)/3) = DBP + 1/3PP