3 - Haemodynamics

Question 1

Why does the viscosity of blood increase and what happens as a result of it?

Answer 1

- Major: Increased plasma proteins, e.g polycythaemia. Dry gangrene in the peripheries

- Minor: changes to amount of things like fibrinogen as result of inflammation. Can measure inflammation by viscosity of blood

Question 2

How do you measure the level of inflammation?

Answer 2

Used to be done by viscosity of blood. Now measure amount of CRP

Question 3

What is blood made up of?

Answer 3

It moves as a fluid but made up of cells and plasma

Question 4

What is laminar and turbulent flow?

Answer 4

- Laminar flow is smooth, maintaing energy. Faster velocity in middle of vessel as friction at the edges. SILENT

- Turbulent flow is disorganised and energy is lost, pressure increase beyond what flow can match, e.g ventricles, branching vessels. NOISY

Question 5

What is flow?

Answer 5

Volume transferred per unit time (L/min)

Question 6

What is pressure?

Answer 6

Force per unit area (mmHg or Pa)

Question 7

What is conductance (k) and resistance (r)

Answer 7

• Conductance is a measure of the ease of flow
• Resistance is a measure of the difficulty of flow (reciprocal of K)

Question 8

If change in pressure is an indicator of a change in resistance, which areas of the CVS have the highest resistance?

Answer 8

• Arterioles give greatest peripheral resistance
• Resistance in systemic higher than in pulmonary circuit

Question 9

What is velocity?

Answer 9

Distance per unit time that the blood moves (cm/s)

Question 10

What is flow increased by?

Answer 10

Flow affected by diameter, length of vessel and viscosity

- Increase in pressure gradient

- Decrease in resistance

Question 11

How much resistance does the aorta/arteries have?

Answer 11

• Very little, has large diameter and relatively short
• High compliance

Question 12

What is the velocity of blood affected by?

Answer 12

• V is proportional to flow
• V is inversley proportion to r²

^{(therefore large surface area means slower velocity)}

Question 13

What does the blood pressure look like in the aorta over one cardiac cycle, draw a graph

Answer 13

Question 14

What is pulse pressure and mean arterial pressure?

Answer 14

- PP = SBP - DBP

- MAP = DBP + 1/3 PP

If MAP <70mmHg organ perfusion is impaired, usually about 90/95

Question 15

What factors is pulse pressure affected by?

Answer 15

• Compliance of arterial system
• Volume of blood ejected
  e. g haemorraghe will decrease PP and age will increase PP as higher systolic

Question 16

What is a pulse?

Answer 16

Shock wave of aortic expansion that travels down blood vessel and is amplified by tendons. Arrives slightly before the blood arrives

Question 17

What happens when you increase pulse pressure and what causes this?

Answer 17

Bounding pulse

• Bradycardia
• Vasodilation as decreased TPR
• Elite athletes (systolic increase, diastolic decrease)

Question 18

How can you work out mean arterial pressure?

Answer 18

MAP = DBP + 1/3 PP

or

MAP = CO X TPR

Question 19

What is flow affected by the most?

Answer 19

• Diameter. Small changes in radius, big changes in flow as radius is to the power of 4
• Diameter also effects resistance the most

Question 20

What is cushing’s reflex?

Answer 20

• Increased systolic BP
• Decreased HR
• Decreased respiratory rate

OCCURS DURING INCREASED INTRACRANIAL PRESSURE

Question 21

What is cardiac output?

Answer 21

CO = SV X HR

Question 22

How do you work of resistance?

Answer 22

Resistance is series is added, resistance in parallel

Question 23

What happens to MAP when exercising?

Answer 23

Maintains, systolic increases and diastolic decreases as too high MAP would harm vessels. Therefore, TPR must be decreasing as CO is increasing

Question 24

How do you measure blood pressure via auscultation?

Answer 24

• At level of heart, arm resting on table, legs uncrossed and flat on ground
• Sat down for 10-15 minutes before
• Several measurements of left and right, use the higher as reference. Take mean of two closest values
• Right size cuff

MEASURE SBP AT 1ST KOROTKOFF AND DBP WHEN NOISES DISAPPEAR

Question 25

What effect does gravity have on blood pressure?

Answer 25

- Pressure below level of heart is greater and above is lower - Pooling of blood in the venous system when you stand up **- Pooling decrease CO as less blood returned to heart so can lead to postural hypotension as lower SV.**

Question 26

Why does syncope occur when standing up?

Answer 26

Postural hypotension due to standing up so decreased SV, the heart goes into tachycardia to compensate for cardiac output so blood is not pumped to brain properly

Question 27

Why can blood pressure be measured by ausculation?

Answer 27

Laminar to turbulent to laminar flow so silent to noisy to silent

Question 28

What factors affect central venous pressure?

Answer 28

Question 29

What mechanism ensures that the right and left side of the heart pump the same amount of blood per minute?

Answer 29

- The Frank-Starling mechanism matches venous return to cardiac output - Increased cardiac output in one ventricle automatically increases the venous return to the other ventricle. - The consequent increase in myocardial fibre length in this ventricle results in an increased output which would match the other side